Foreword

TCVN 4085:2011 replaces TCVN 4085:1985.

TCVN 4085:2011 was compiled by the Institute of Construction Science and Technology, proposed by the Ministry of Construction, appraised by the General Department of Standards, Metrology and Quality, and announced by the Ministry of Science and Technology.

1. Scope of application

This standard is applied for the construction and acceptance of masonry structures made of clay bricks, ceramics, silicate bricks, unbaked bricks, dressed stones, rubble stones and rubble concrete in new construction, renovation of buildings and works.

2. References

The following reference documents are essential for the application of this standard. For dated references, only the cited edition applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

TCVN 2231:1989, Building lime.

TCVN 4453:1995, Cast-in-place reinforced concrete structures – Construction and acceptance standards.

TCVN 4459:1987, Guidance for mixing and using construction mortar.

TCVN 7570:2006, Aggregates for concrete and mortar – Technical requirements.

3. General provisions

3.1. When constructing masonry structures, in addition to the provisions of this standard, it is necessary to comply with the current relevant state standards and regulations.

3.2. The base benchmark elevation at the construction site must be determined according to the fixed benchmark. It is allowed to determine the base benchmark elevation according to the available benchmarks in adjacent buildings and works or other special benchmarks if these benchmarks have sufficient reliability.

3.3. Materials and products used for constructing masonry structures must comply with the provisions in the current national standards, technical documents and construction drawings.

It is not allowed to move masonry structures by wire.

3.4. The construction of masonry structures must be carried out in accordance with the design.

3.5. Whole ceramic bricks must be used for building basement walls with bricks. It is not allowed to use silicate bricks for this purpose.

3.6. It is not allowed to create openings, niches, construction holes that weaken the masonry structure without complying with the design.

3.7. Frame infill walls must be carried out in accordance with the requirements for constructing load-bearing masonry structures.

4. Preparation works

4.1. Site and foundation

4.1.1. After the site has been prepared, it is necessary to determine the axes of the building and works, determine the foundation centerline and edges of the foundation pit according to the construction drawings.

On the site, the allowable deviations of dimensions in length and width of the building and works are specified as follows:

• Not exceeding 10 mm when these dimensions are up to 10 m;
• Not exceeding 30 mm when these dimensions are 100 m or more;
• For other intermediate dimensions, the allowable deviation is taken by interpolation.

4.1.2. The work of determining benchmarks, building and works axes must be checked, accepted and recorded in a minutes. After being handed over and during construction, the contractor is responsible for protecting the benchmarks and centerline stakes according to the correct dimensions and positions.

4.1.3. Before laying the foundation, the bottom and sides of the foundation pit must be checked and protected. Water and debris must be cleaned. When the foundation soil is soft and flowing or has other unusual phenomena, it must be reported to the designer for handling.

4.1.4. After completing the foundation, foundation walls and basement columns, the axes of the first floor structures must be checked. The deviation due to the displacement of the structural axes must not exceed the allowable values in the standard for assessing the quality of works and in Table 1 of this standard.

4.1.5. New foundations placed adjacent to or near old building foundations, settlement joints and expansion joints must be constructed according to separate instructions from the design.

4.1.6. When adjacent foundation pits have different foundation depths, steps must be excavated to transition from one depth to another. The ratio between the height and width of the steps must comply with the following provisions:

• For clay or loamy soil: not exceeding 1:1, step height not exceeding 1 m;
• For sandy or silty soil: not exceeding 1:2, height not exceeding 0.6 m.

If the foundation pit has a depth of 1 m or more, it is necessary to have measures to protect the foundation pit according to the design instructions.

4.1.7. The construction of foundation pits must comply with the provisions of this standard and the regulations on construction and acceptance of “earthworks”.

Table 1 – Allowable deviations due to structural axis displacement

Unit: millimeters

4.2. Materials

4.2.1. The types of sand used for masonry mortar and plastering mortar must meet the requirements specified in TCVN 7570:2006.

The maximum grain size of sand must not exceed:

• For masonry with bricks and dressed stones: 2.5 mm;
• For rubble stone masonry: 5.0 mm.

4.2.2. Black sand is only used for low-grade mortar. Do not use black sand for masonry below the groundwater level and in corrosive water.

4.2.3. Sea sand and sand taken from brackish water areas must absolutely not be used in masonry containing reinforcement.

4.2.4. Lime used to produce masonry mortar and plastering mortar must meet the requirements specified in TCVN 2231:1989. The storage and slaking of lime must comply with the regulations on technical safety in construction.

4.2.5. Cement supplied to the construction site must ensure the quality specified by the manufacturer and have a quality certificate from the product quality inspection organization.

4.2.6. Cement used for masonry mortar must meet the requirements specified in the current national standards on cement.

4.2.7. Special types of cement such as sulfate-resistant cement, acid-resistant cement, etc. shall only be used when required by the design.

4.2.8. Different types of cement, or of the same grade but produced by many different manufacturers, should not be mixed together.

4.2.9. The types of masonry bricks must ensure the requirements on strength, specifications and technical standards as specified in the current national standards on masonry bricks.

The types of paving and cladding stones and bricks must ensure the color according to the design requirements and must meet the technical standards (strength, water absorption, abrasion resistance, etc.).

If not meeting the requirements, they must be rejected.

4.2.10. The types of bricks supplied to the construction site must have a certificate of specifications and quality issued by the manufacturer.

4.2.11. The material storage yard at the construction site must be arranged appropriately, with drainage ditches made. If there is debris, it must be cleaned or a layer of bricks must be laid, or the ground must be compacted. Around the sand pile, wooden boards or bricks must be set up as a barrier to prevent the sand from being washed away by rain, with a height of at least 0.3 m. Do not pile loose materials mixed with each other.

Stacked bricks and stones must ensure technical safety, and must not be allowed to grow moss, mold, or become dirty.

4.2.12. The specifications and quality of other types of materials used in the construction of masonry structures must comply with the provisions of relevant current national standards and regulations.

4.3. Construction mortar

4.3.1. Mortar used in masonry must have a grade and technical indicators that meet the design requirements and the requirements of this standard as well as the provisions in TCVN 4459:1987.

4.3.2. In mortar factories and mixing stations, the quality of mortar must be checked for each batch, and a record must be made when receiving and handing over. Each batch of mortar handed over must have a written instruction indicating: mortar type, grade and plasticity of mortar, date, time, month of production, grade and type of cement used.

4.3.3. Construction mortar produced with inorganic binders used for masonry structures includes the following types: Lime mortar, cement mortar, cement-lime mortar, mortar used for regular plastering, special plastering (decorative, waterproof, fireproof, acid-resistant), paving mortar, cladding mortar.

4.3.4. Materials for producing mortar (binders, aggregates) must ensure the requirements and technical standards, and must also comply with the provisions in 4.2.5 of this standard.

Water used for mixing mortar must not contain harmful impurities that hinder the hardening process of the binder. When using groundwater on-site or water from the technical water supply system to mix mortar, it must be analyzed by experiment; if taking water from the domestic water supply system – no need to check.

4.3.5. The types of binders for producing masonry mortar for structures under the ground with aggressive water must comply with the design instructions.

When building masonry below the groundwater level or in water-saturated moist soil, mortar that hardens in water must be used.

4.3.6. The dry mortar mixture produced by the factory must have an instruction sheet of the composition and grade of mortar achieved after mixing the mortar. When transporting the dry mortar mixture, it is necessary to preserve it from getting wet, spilling, and getting dirty.

4.3.7. When producing construction mortar, it is necessary to ensure:

• The deviation when measuring the ingredients compared to the mortar composition is not greater than 1% for water and cement; for sand not greater than 5%;
• Mortar grade according to design requirements;
• The plasticity of the mortar (according to the slump of the standard cone) must comply with the design regulations;
• Uniformity in composition and color;
• High water retention capacity.

To increase the plasticity and water retention capacity of the mortar, plasticizing additives are added to the mortar composition according to the instructions from experiments and design instructions.

4.3.8. The mixing time of mortar by machine from the time the aggregates are completely poured into the mixer must not be less than 2 minutes.

The time for mixing mortar by hand from the start of mixing must not be less than 3 minutes. During mixing by machine or by hand, no additional materials may be added to the mortar trough.

4.3.9. Mixed mortar must be used up before it starts to harden, do not use mortar that has hardened or dried out. If the mortar has been layered, it must be carefully re-mixed on-site before use.

4.3.10. When constructing in summer or dry season, it is necessary to ensure sufficient moisture for the mortar to harden by: soaking bricks and stones in water before building and using mortar with high plasticity. Do not pour mortar in the sun, avoid rapid water loss. When it rains, the mortar must be carefully covered.

4.3.11. Slaked lime used for producing mortar must not have unslaked lumps. When slaking lime, do not let the lime become hard and get dirty. Slaked lime can only be used after at least 7 days. Machine-slaked lime can be used immediately.

4.3.12. Mechanical transportation equipment, mortar pumps, and modified vehicles for transporting mortar should be utilized to avoid mortar layering and contamination by other impurities.

4.3.13. The quality of mortar must be checked by testing samples taken right at the mortar production site. The plasticity of the mortar must be checked during production and right at the construction site. The data and test results must be recorded in the construction diary.

4.3.14. The determination of the mixing ratio of mortar to ensure the mortar grade must be carried out before starting the masonry and during the construction of the masonry.

When changing materials (binders, aggregates, additives), changing the composition and grade of mortar, the mortar must be tested. When the materials, composition and grade of mortar are not changed, the mortar is checked according to the regulations of the standard “Mortars and mortar mixes for construction – Methods of mechanical tests”.

4.4. Scaffolding, formwork

4.4.1. The work of formwork and scaffolding during the construction of masonry structures must be carried out according to the provisions of the current national standards on formwork and scaffolding.

4.4.2. The types of scaffolding must ensure stability, durability, withstand the effects of people, the placement of masonry materials and the movement of mortar buckets on the scaffolding during construction. Scaffolding must not obstruct the construction process, dismantling and assembling must be easy, moving must not be cumbersome and difficult.

4.4.3. It is not allowed to use types of scaffolding that lean against the wall being built, do not place boards on the newly built wall, the scaffolding must be at least 0.05 m away from the wall being built. When choosing scaffolding types, it is necessary to consider economics and technical aspects.

4.4.4. The erection of scaffolding and formwork must be carried out according to the instructions of the construction design.

During use, the durability and stability must be regularly checked to meet technical safety requirements.

5. Construction

5.1. Requirements during construction

5.1.1. When transporting bricks and stones, they must be neatly stacked and not piled up. Do not dump them directly on the ground. When transporting mortar to the construction site, do not pour it on the ground, there must be a mat to contain the mortar.

5.1.2. Lime pits must be arranged near the transportation route, near a water source, near the mortar mixing area, and avoid obstructing construction. The bottom of the pit must be lined with a layer of bricks, the walls of the pit must be lined with bricks or boards at least 0.1 m higher than the ground surface. Around the pit, there must be drainage ditches and safety fences.

The surface of the slaked lime layer must have a layer of water 0.2 m thick or greater, or be covered with a layer of sand that is always moist with a thickness of at least 0.2 m.

5.1.3. The difference in height between adjacent parts of the foundation masonry must not exceed 1.2 m.

5.1.4. Masonry structures must be constructed in accordance with the design.

During construction, holes, pipe trenches for water, ventilation ducts, decorative places, and places for future installation work must be reserved.

In places not specified, holes that weaken the masonry structure are not allowed.

5.1.5. To connect window and door frames to the walls, during construction, pre-treated wooden inserts resistant to termites or other connection methods must be placed according to the design instructions.

5.1.6. During the construction of masonry structures, the design must not be arbitrarily changed. If errors are found in the design or abnormal phenomena such as sand flow, strong groundwater, etc. are encountered, it must be immediately reported to the governing body and the design unit for timely resolution. If the soil foundation at the construction site does not match the design soil foundation, the design agency must re-specify the foundation depth and dimensions.

5.1.7. When constructing masonry with large blocks, the following procedures must be ensured:

• Mark the foundation axes, mark the foundation edges, position the corners and connection points;
• Place corner blocks and reference blocks;
• Mark the position of blocks in each row;
• Build blocks according to the alignment.

5.1.8. When each row of blocks is completed, the levelness must be checked by measuring the height of the constructed rows.

5.1.9. When building the base of walls and columns, only solid clay bricks must be used, silicate bricks are not allowed.

5.1.10. The levelness of the rows, the verticality of the sides and internal corners of the masonry must be checked at least 2 times in a section with a height of 0.5 m to 0.6 m, if a slope is detected, it must be corrected immediately.

5.1.11. The intersections and joints of wall masonry must be built simultaneously, when temporarily stopping construction, toothed joints must be made, sawtooth joints are not allowed.

5.1.12. In adjacent or intersecting construction sections between exterior and interior walls, the height difference must not exceed the height of 1 floor.

5.1.13. In masonry with prefabricated or cast-in-place lintels, it is necessary to wait until the concrete has sufficient strength and the masonry above the lintel has sufficient counterweight height and strength before removing the formwork and support members.

5.1.14. Only after completing the load-bearing structures of the lower floor can the structures on the next upper floor be built.

5.1.15. After completing each floor, the levelness and verticality of the masonry must be checked (not including intermediate checks).

5.1.16. It is not allowed to strongly impact, transport, place materials, lean tools, and walk directly on the masonry being constructed or on newly built masonry.

If building on old masonry, all moss must be scraped off, the old masonry must be washed clean and sprinkled with water, then mortar is spread to build the new masonry.

5.1.17. During construction, if cracks are detected, it must be immediately reported to the governing body and the designer to find the cause and remedial measures, and markers must be made to monitor the development of the cracks.

5.1.18. When completing chimneys and ventilation ducts, the joints must be filled with mortar, the inner surface of the chimney must be carefully scraped of mortar, smoothed and flattened.

5.2. Rubble stone and rubble concrete masonry

5.2.1. Before construction, the bottom of the foundation pit must be cleaned, leveled, and large, flat-bottomed stones must be selected for the first row and the corners and transitions of the foundation. Broken stones should be used inside the rubble masonry, but small stones must be wedged into the broken areas.

5.2.2. When building foundations, rubble stones must be laid in rows with a height of 0.3 m, when building walls – each row with a height of 0.25 m.

In each row of stone masonry, there must be bonding stones, creating a tie system according to the following requirements:

• For every square meter on the vertical surface of the wall, there must be at least one bonding stone 0.40 m long;
• When building stone walls with a thickness not exceeding 0.40 m, 3 bonding stones must be placed per square meter throughout the wall base.

5.2.3. When building columns and pillars, rubble must be laid in rows with a height of 0.25 m. Long, thick stones should be selected; stones with beveled edges and thin stones should not be used. The face stones must be arranged with legs deeply embedded into the masonry.

When building intersecting walls, in each row, bonding stones must be arranged to tie the wall ends together. Do not build in a stele-like manner in foundation, wall, column, and pillar masonry. The empty joints inside the masonry must be tightly filled with mortar and small stones. Do not build with coinciding joints on the outer face as well as inside the masonry. Stones must not be placed in direct contact with each other without mortar bedding.

5.2.4. When building uncoursed rubble masonry (rough rubble), in addition to the requirements for coursed rubble masonry, the following provisions must be followed:

• The thickness of the mortar joints must not exceed 20 mm and must be uniform; the horizontal and vertical joints must not be concentrated into a knot point, there must be no intersecting joints, parallel vertical joints, cross-shaped diagonal joints, or uneven mortar joints;
• Large and small stones must be evenly distributed within the masonry. Do not wedge stone fragments into the mortar joints on the outer face of the masonry.

5.2.5. When building with dressed stones, the thickness of the mortar joint must not exceed 15 mm, the outer face must be flat and smooth, at the corners, it must be built in a stack bond pattern with stones at least 0.30 m long and wide. When placing the stones, attention must be paid to ensure that the longitudinal grain of the stone is relatively perpendicular to the force direction.

Vertical mortar joints need to be tightly filled with mortar using a trowel or a Ø10 steel rod. The masonry joints must follow the design scheme.

5.2.6. Do not build rubble stone foundations in subsiding soil. Coconut stones (round, smooth pebbles) are only used for building foundations of houses not exceeding 2 floors.

The exposed wall surface is required to be flat and smooth.

5.2.7. The brick (or stone) cladding layer of the rubble masonry must be done simultaneously with the masonry. Every 4 to 6 rows of vertical bricks, but not exceeding 0.6 m, must be tied with a row of horizontal bricks; this horizontal brick row must coincide with the horizontal joint of the rubble stone masonry.

5.2.8. During construction, the height difference between adjacent wall sections must not exceed 12 m. The height of the wall (rubble stone or rubble concrete) when temporarily stopping during the construction phase must not exceed 1.2 m.

In special cases (due to construction conditions), the stopping height can be increased to 4 m, but measures must be taken to ensure the stability and monolithic bonding of the masonry.

5.2.9. Before stopping the construction, the voids inside the top masonry row must be filled with mortar and wedged with small stones. When continuing construction, mortar must be spread on the surface of this row.

In summer and dry season, when temporarily stopping, rubble stone and rubble concrete masonry must be sprinkled with water to keep it constantly moist. Before continuing construction, the surface of the rubble stone and rubble concrete row must be cleaned of debris and sprinkled with water.

5.2.10. When constructing rubble concrete masonry, the preparation of the concrete mixture, the erection and removal of formwork, the quality control of concrete must satisfy the requirements of the construction and acceptance standard TCVN 4453:1995.

5.2.11. Rubble concrete masonry is a mixture of concrete and rubble stones. The volume of rubble stones in the concrete accounts for about 1/2 of the masonry volume.

In rubble concrete masonry, the concrete mixture is spread in horizontal layers with a thickness not exceeding 0.2 m. Rubble stones are continuously embedded in rows into that concrete layer, submerged more than half the thickness of the stone, and the distance between the rows is from 4 mm to 6 mm. The size of the stone must not exceed 1/3 of the thickness of the structure. Stones must not be thrown into the concrete mixture that has begun to set.

5.2.12. Rubble concrete masonry is vibrated in layers, the concrete mixture must have a slump of 5 mm to 7 mm.

When the work volume is small, it is allowed not to use vibration but to use hand tamping, but the concrete must have a slump of 8 mm to 12 mm.

5.2.13. When the foundation pit walls are vertical and stable, it is allowed to use the foundation pit walls instead of formwork to construct rubble concrete.

5.2.14. Construction can only be stopped after the rubble stones have been fully embedded into the concrete layer and compacted. If continuing construction, debris must be cleaned and water must be sprinkled on the surface of the old rubble concrete layer before starting to spread the concrete mixture.

5.2.15. The curing of rubble stone and rubble concrete masonry in hot and dry climates must also be carried out similarly to the curing of solid concrete structures.

5.3. Brick masonry

5.3.1. General section

5.3.1.1. Brick masonry must ensure the following technical construction principles: Level – flat; vertical – straight; corners – square; non-coinciding joints; forming a solid monolithic block.

5.3.1.2. Construction mortar must have a strength meeting the design requirements and have a plasticity according to the slump of the standard cone as follows:

• For brick walls and columns: from 9 cm to 13 cm;
• For masonry lintels and aprons: from 5 cm to 6 cm;
• For other brick masonry: from 9 cm to 13 cm.
• When constructing in hot and dry summer, as well as when constructing brick column and wall structures that must bear large loads, the mortar joints are required to be full and have a slump of 14 cm. The newly built wall section must be carefully covered, avoid rain and sun, and must be regularly sprinkled with water.

5.3.1.3. The bonding pattern and tie courses in the masonry must be made according to the design requirements. The commonly used bonding patterns in masonry are stretcher bond or English bond.

5.3.1.4. In brick masonry, the average thickness of the horizontal mortar joint is 12 mm. The thickness of each horizontal mortar joint must not be less than 8 mm and not greater than 15 mm. The average thickness of the vertical mortar joint is 10 mm, the thickness of each vertical mortar joint must not be less than 8 mm and not greater than 15 mm. The vertical mortar joints must be staggered by at least 50 mm.

5.3.1.5. All horizontal, longitudinal, and vertical mortar joints in lintels, wall sections near doors, and columns must be fully filled with mortar (except for recessed joint masonry).

In recessed joint masonry, the depth of the unfilled mortar on the outer face joints is specified as follows:

• Not greater than 15 mm – for walls.
• Not greater than 10 mm – for columns.

5.3.1.6. Selected whole bricks must be used to build load-bearing walls, wall sections near doors, and columns. Half-broken bricks can only be used in areas with small loads such as enclosure walls, partition walls, and walls below windows.

Broken bricks and brick rubble must not be used for filling or bedding in load-bearing masonry.

5.3.1.7. It is allowed to use pre-placed reinforcement in main walls and columns to tie walls and foundations (1/2 and one brick) with main walls and columns, when these structures are not built simultaneously.

5.3.1.8. In the masonry, the horizontal brick courses must be whole bricks. Regardless of the bonding pattern, these horizontal brick courses must be ensured:

• Built in the first (bottom) course and the last (top) course;
• Built at the top level of columns, walls, etc.
• Built in the protruding parts of the masonry structure (cornices, bands, ties).

In addition, whole horizontal bricks must be placed under the ends of beams, trusses, joists, floor slabs, balconies, and other installed structures.

5.3.1.9. The outer vertical face of unplastered and unclad walls must be built with selected whole solid bricks with uniform color and edges. The thickness of the mortar joints must follow the design.

5.3.1.10. The error in the cross-section of the supports under joists, rafters, crane beams, and other load-bearing structures in any direction compared to the design position must be less than or equal to 10 mm.

5.3.1.11. When stopping construction due to storms, the masonry must be covered to avoid getting wet.

5.3.2. Lintel masonry

5.3.2.1. All types of lintels must be built with selected whole bricks.

Lintels built flat must use mortar with a grade specified in the design but not less than 25. The height of flat-built lintels must be equivalent to the height of 5 or 6 brick courses, the two ends must be embedded into the wall sections on both sides of the opening at least 0.2 m from the edge. Under the last brick course of the lintel, a layer of reinforced mortar must be placed. The number of steel bars is placed according to the design but not less than three bars. The plain round steel bars used for lintels must have a diameter of not less than 6 mm, the two ends of the steel must be embedded into the two sides of the opening at least 0.25 m and have bent hooks. Ribbed (deformed) steel bars do not need bent hooks.

5.3.2.2. Wedge-shaped lintels must have dense wedge-shaped mortar joints, the bottom end of the joint must have a thickness of at least 5 mm, the top end must not be thicker than 25 mm. The lintels must be built simultaneously from both ends converging to the middle, the keystone must be located exactly in the middle of the lintel (the centerline of the lintel divides the keystone in half). Flat lintels are only allowed when the opening is 1.2 m and wedge-shaped lintels when the span is over 2 m if the building and works are not subject to vibration or uneven settlement.

5.3.2.3. Construction stop joints for arch lintels with large spans are allowed to be arranged one arch-blocking from the two ends of the lintel at an angle of about 30°. The remaining blocking arch section must be fully built in the following stages.

The mortar for building arch lintels must comply with the design requirements.

5.3.2.4. The bricks and mortar joints in wedge-shaped and arch lintels must be oriented towards the center of the arch. It is forbidden to place bricks in a stack bond pattern.

If the width of the wall section between the lintels is less than 1 m, the wall must be built with mortar of the same grade as the lintel mortar and not less than 25.

5.3.2.5. The time period for keeping lintels on formwork must not be less than the values shown in Table 2.

Table 2 – Time period for keeping lintels on formwork

5.3.3. Cornice, frame infill, and facade masonry

5.3.3.1. Cornice masonry must be carried out according to the design. The projecting portion of each brick course in cornice masonry must not exceed 1/3 of the brick length, and the total projecting portion of the unreinforced brick cornice must not exceed 1/2 of the wall thickness.

Cornices projecting more than 1/2 of the wall thickness must be built with reinforced brickwork or reinforced concrete or prefabricated elements and must be firmly anchored to the masonry.

5.3.3.2. Cornice masonry with a projecting portion greater than 1/2 of the building wall thickness, gable wall masonry with a height greater than 3 times the building wall thickness and greater than 3 times its own thickness, must all be built with mortar of grade not less than 2.5.

5.3.3.3. Cornices anchored to the wall can only be built after the wall has reached the design strength. If it needs to be done earlier, temporary reinforcement must be provided to ensure the stability of the cornice and wall masonry. In all cases, temporary support must be provided until the cornice and wall reach the required strength.

5.3.3.4. Infill walls in building frames must be tied to the frame columns with steel ties according to the design instructions and tied to the longitudinal beams of the frame. Infill walls with a thickness not exceeding 22 cm can be built with perforated bricks.

5.3.3.5. In perforated brick wall masonry, the bands, cornices, gables, fire walls, and wall sections requiring external joint pointing must be built with solid bricks.

5.3.3.6. The decoration of the main facade of the building with a cladding layer can be done simultaneously with the wall construction. The cladding panels and details need to be pre-sorted and selected according to the sizes and colors specified in the design.

5.3.3.7. Ventilation openings in walls must be built with solid bricks of grade not less than 75 or silicate bricks of grade 100 for elevations below the attic floor level, and at higher elevations – with fired clay bricks of grade 100.

5.3.4. Reinforced brick masonry

5.3.4.1. In brick masonry with horizontal reinforcement meshes, the thickness of the mortar joint must be at least 4 mm greater than the total diameter of the intersecting steel bars and at the same time still ensure the specified average thickness in the masonry. Column and door jamb masonry must use rectangular or chi-shaped horizontal reinforcement meshes, tightly tied or fastened. The spacing between the bars in the mesh must not be less than 3 mm and not greater than 12 mm. The diameter of the reinforcement in the mesh must not be less than 3 mm and not greater than 8 mm. When the reinforcement has a diameter greater than 5 mm, chi-shaped meshes can be made.

5.3.4.2. It is not allowed to place loose steel bars to replace tied or welded reinforcement meshes in the masonry.

During fabrication and construction, attention must be paid to ensure that the ends of the reinforcing bars protrude 2 mm to 3 mm from the outer face of the masonry for easy inspection.

5.3.4.3. Rectangular or chi-shaped horizontal reinforcement meshes are placed into the masonry according to the design instructions and not spaced more than 5 brick courses apart. Chi-shaped meshes must be placed so that the steel bars of two meshes in two consecutive masonry courses are perpendicular to each other.

5.3.4.4. The diameter of the longitudinal reinforcing bars must not be less than 8 mm, the ties from 3 mm to 6 mm. The maximum spacing between the centers of the ties must not exceed 5 mm.

Longitudinal reinforcement must be connected to each other by welded joints. If not welded, the bars must be bent with hooks and tied with steel wire, the overlap length is 20 d (d is the bar diameter). The ends of the tensile reinforcing bars must be bent with hooks and welded to the bars to anchor into the concrete or mortar layer.

5.3.4.5. The thickness of the protective layer (measured from the outer edge of the tensile reinforcement) of cement mortar in reinforced brick structures must not be less than the values shown in Table 3.

Table 3 – Protective layer thickness for reinforcement

Unit: millimeters

5.3.5. Vault and thin shell masonry

5.3.5.1. Vault masonry (including arch lintels) and shells must use bricks and stones of standard dimensions. Cement mortar or mixed mortar can be used to build vaults, shells, etc.

5.3.5.2. For cylindrical vaults, thin shells, double-curved thin shells, the formwork must have a structure so that it can support evenly. The columns supporting the formwork must be placed on wooden bases or dry sand boxes or steel pipe columns with adjustable support legs.

5.3.5.3. The dimensional deviations of the formwork for double-curved thin shells compared to the design must not exceed the following specified values: for the deflection value at any point: 1/200 of the shell deflection value; for the displacement of the formwork at the mid-section compared to the vertical plane: 1/200 of the shell deflection value; for the shell span width: 10 mm. These values do not apply to the movable formwork of wavy shells.

5.3.5.4. Before building, based on the existing brick and stone sizes, the formwork must be pre-divided (from top to bottom) and adjusted to whole bricks.

The bricks and stones used for vault and thin shell masonry must be thoroughly soaked in water before building. Cracked, broken, or warped bricks must all be replaced.

5.3.5.5. Building materials can only be evenly arranged on the top of the arch formwork. If they cannot be arranged, a separate scaffolding must be made to place the materials. Strong impacts that deform or displace the formwork must be avoided. Bricks should only be evenly placed on four sides of the double-curved thin shell formwork.

5.3.5.6. In vault and thin shell masonry, only Portland cement mortar should be used, not slag Portland cement mortar and pozzolanic Portland cement as well as other types of cement that harden slowly at low temperatures.

5.3.5.7. After completing the supporting wall section at the base of the vault or thin shell, if the air temperature is above 10 °C, the vault and thin shell construction can only begin after at least 7 days. If the temperature is from 5 °C to 10 °C, the above period is extended by 1.5 times, if from 1 °C to 5 °C – then extended by 2 times.

If the vault base is prefabricated reinforced concrete with tensioning wires, the vault masonry construction can begin immediately after completing the vault base supporting section and even before removing the formwork.

5.3.5.8. The tensioning of wires in cylindrical vaults and thin shells, double-curved thin shells must be done immediately after completing that masonry and before removing the formwork.

5.3.5.9. The removal of formwork must be done gently in a symmetrical sequence across the entire vault or thin shell. First, the wedges or adjustment sand boxes at the support legs are removed to lower the entire formwork by 0.1 m to 0.15 m. After checking that there are no cracking, collapsing phenomena, the formwork can be completely removed.

5.3.5.10. For double-curved thin shells with an opening area up to 1/4 of the shell width, the sequence of removing the formwork must follow the design instructions.

5.3.5.11. After removing the formwork of double-curved thin shells and cylindrical thin shells, only then is it allowed to build the gable walls.

5.3.5.12. After completing cylindrical thin shells, double-curved thin shells, and the junctions between spans of wavy shells, the time period for keeping the formwork must be ensured:

• When the air temperature is above 10 °C: not less than 7 days;
• At lower temperatures: the period is increased as specified in 5.3.5.7 of this standard.

5.3.5.13. When building cylindrical thin shells, double-curved thin shells, and vaults, construction must be carried out simultaneously from both bases converging to the middle. The mortar joints must be uniform in thickness and density. If the masonry uses cement mortar, it must be cured (sprinkled with moisture and shaded from the sun) for the first three days after completion. Vault masonry with a span greater than 2 m must follow the provisions in 5.3.2.2, 5.3.2.3, 5.3.2.4, 5.3.2.5 of this standard.

5.3.5.14. The upper surface of thin shell masonry must be plastered with cement mortar. Before plastering, the masonry surface needs to be regularly sprinkled with water.

5.3.5.15. The time period allowed to begin loading on the surface of cylindrical thin shells and double-curved thin shells is specified as follows:

• When the air temperature is greater than 10 °C: 7 days;
• When the air temperature is less than 10 °C: the above period is increased according to the provisions in 5.3.5.7 of this standard.

When loading on the surface of thin shells and vaults earlier than the allowed time period, the formwork and supporting scaffolding must be kept. The insulation and roofing layers that cause instantaneous one-sided loading on the thin shells and vaults must not be built.

5.3.6. Additional requirements for the construction of masonry structures in earthquake zones

5.3.6.1. When constructing brick and stone masonry in earthquake zones, special attention must be paid to ensuring the adhesion between bricks, stones, and mortar.

Before laying bricks and stones, dust and mud must be washed clean. After stopping, if construction is continued, water must be sprinkled on the top brick and stone course of the masonry.

Fired clay bricks and natural lightweight porous stones with high water absorption must be soaked in water for at least 1 minute before laying.

5.3.6.2. Masonry mortar must use plastic mortar (with additives), the slump of the mortar must be ensured as follows:

• From 6 cm to 8 cm – for heavy stone masonry (volumetric weight greater than 1800 kg/cm³);
• From 12 cm to 14 cm – for brick and lightweight stone masonry. The vertical and horizontal mortar joints must be fully filled with mortar.

When the daytime air temperature at the construction site is 25 °C and higher, the mortar must be mixed indoors or in a shaded place.

Newly completed masonry must be cured by sprinkling water 3 times a day for a period of 3 days and nights.

5.3.6.3. After an earthquake or strong storm, the masonry being constructed must be carefully examined, if there are bad cracking phenomena (cracks, tilting, etc.), it must be immediately reported to the designer for timely handling.

5.3.6.4. When building with polymer cement mortar, before placing bricks and masonry, they should not be wetted during the time when the masonry is gaining strength.

5.3.6.5. It is not allowed to reduce the width of the seismic ties clearly specified in the design.

The seismic ties must be free from formwork and construction debris. It is not allowed to make seismic ties with bricks, mortar, materials made from sawdust, etc.

5.3.7. Plastering, paving, cladding

5.3.7.1. General provisions

The provisions of this section only apply to regular plastering, paving, and cladding work in civil and industrial construction. Special plastering, paving, and cladding (waterproofing, corrosion-resistant, etc.) must be carried out according to separate standards.

5.3.7.2. Plastering

5.3.7.2.1. Before plastering, the surface of the structure must be cleaned (scrubbing off moss, oil stains, bitumen, dirt) and sprinkled with water to moisten. If the surface is metal, rust must be completely removed.

When the plaster thickness is greater than 8 mm, plastering is done in multiple layers. The thickness of each layer must not be less than 5 mm and not greater than 8 mm. The thickness of the plaster surface must not exceed 20 mm. The plaster layers must all be leveled when the previous layer has set before applying the next layer, if the previous layer has dried too much, it must be sprinkled with water to moisten.

5.3.7.2.2. The adhesion of the mortar must be checked by lightly tapping on the plastered surface, all hollow areas must be re-plastered by breaking open that area, pressing the surrounding mortar edges tightly, and allowing the surface to set before re-plastering.

5.3.7.2.3. The wall surface after plastering must not have cracks, roughness, chipping, or mortar dripping. Attention must be paid to plastering under window sills, door jambs, wall bases, stove bases, kitchens, places where sanitary equipment is installed, and places that are easily missed.

5.3.7.2.4. The edges of columns, door jambs, and walls must be flat and sharp; right angles must be checked with a square. The window sill bands must be aligned with each other. The top surface of window sills must have a slope according to the design and the plaster layer must extend at least 10 mm under the window frame.

5.3.7.2.5. For panel ceilings or prefabricated structural elements, before plastering, a steel brush must be used to clean the form lining paper, lubricating oil, and dirt.

If the concrete surface is too smooth, it must be roughened and sprinkled with water to moisten.

The thickness of the plaster layer must be ensured from 10 mm to 15 mm, if thicker, steel mesh or measures to prevent mortar from falling must be provided.

5.3.7.2.6. For surfaces lacking roughness such as concrete surfaces (cast in steel formwork), metal surfaces, planed wood, plywood, before plastering, they must be prepared by notching or sand blasting to ensure the mortar adheres firmly to the structural surface. Plastering must be tested in a few places to determine the adhesion. Before plastering the joints between wooden components and masonry structures, a layer of steel mesh or a coil of steel wire must be wrapped or the wood surface must be roughened for easy mortar adhesion.

5.3.7.2.7. When creating a spiked plaster surface, a sprayer can be used to spray liquid mortar onto the wall surface or a brush can be used to splatter. For coarse-grained rough (stippled) surfaces, spraying is done multiple times, the next layer is splattered only after the previous layer has set. The grains must adhere evenly to the wall.

5.3.7.2.8. Pebble-dashed surfaces are plastered with mortar mixed with pebbles or crushed stone with a grain size of 6 mm to 12 mm. After plastering the mortar for 12 hours, the outer mortar layer is beaten to expose the stone surface.

5.3.7.2.9. Terrazzo plastering (polished plaster) must be carried out as follows: 24 hours after plastering the stone surface, polishing begins (rough polishing, fine polishing). Fine polishing can begin no earlier than 2 days after rough polishing. When polishing, the plastered surface must be soaked with water, polishing from top to bottom until the surface is smooth and shiny. The polished surface must be washed clean, evenly coated with turpentine oil, and waxed to a shine.

5.3.7.2.10. For terrazzo plastering (washed plaster), 1 hour after plastering the stone surface, washing is carried out. The plastered surface needs to be carefully preserved until completely dry.

5.3.7.2.11. For terrazzo plastering (bush-hammered plaster), 6 days after plastering the stone surface, a bush hammer is used to chip. The hammer must be evenly struck perpendicular to the plastered surface, chipping off the colored cement layer until the stone surface protrudes evenly.

5.3.7.3. Paving

5.3.7.3.1. Paving work can only begin after the surface to be paved has been completed and cleaned.

Paving tiles must be thoroughly soaked in water before paving, arranged according to the correct type, color, and pattern. Paving tiles must not be cracked, warped, have broken corners, or have other defects on the surface. The cut edges of trimmed tiles must be straight, broken tiles should be used for random paving.

5.3.7.3.2. The paved surface must be flat, not rough, and regularly checked with a level and a 2 m long ruler. The gap between the paved surface and the inspection ruler must not exceed 3 m. The slope and slope direction of the paved surface must follow the design. The drainage slope must be checked by pouring test water or letting a 10 mm diameter steel ball roll. If there are puddles, it must be re-paved.

5.3.7.3.3. The density and bond between the paving tiles and the underlying floor structure must be checked by tapping on all the paving tiles, if any area sounds hollow, it must be removed and re-paved.

5.3.7.3.4. The thickness of the bedding cement mortar layer must not exceed 15 mm. The thickness of the waterproofing bitumen layer (if any) must not exceed 3 mm. The joints between the tiles must not exceed 1 mm. The joints are filled with thin cement slurry. Before filling the joints, walking or impacts that peel off the paving layer are not allowed.

The spacing between paved surfaces and between the paved surface and the wall base must be paved with random tiles. Open joints between the paved surface and the wall base bands must be filled with cement mortar.

5.3.7.3.5. The paved surface must meet the requirements for flatness, slope, adhesion to the paved base surface. The thickness of the bedding mortar layer, the thickness of the mortar joints, colors, decorative shapes must all be made according to the design.

5.3.7.4. Cladding

5.3.7.4.1. Cladding materials must not be warped, cracked, chipped at corners and edges, have no scratches, stains, or holes, the edges must be straight and sharp, the corners must be square.

The steel structural details in contact with the cladding surface and the steel details between the cladding surface must be rust-proofed. The anchoring details (nails, pins, hooks) must be galvanized or made of stainless steel. To hold natural stone cladding panels (marble, granite), brass, copper-plated, or stainless steel connection details should be used.

During construction, staining on the cladding surface must not be caused, impacts and damage to the cladding surface must be avoided as much as possible.

5.3.7.4.2. The cement mortar used for pointing tiles between the cladding panels must match the color specified in the design or the same color as the cladding panels.

5.3.7.5. Natural stone cladding

5.3.7.5.1. Special tools must be used to lift the cladding panels, steel wire rope must not be used for tying. Before cladding, the back of the cladding panel must be washed for good mortar adhesion. The gap between the structural surface and the cladding panel must be filled with mortar and poured in multiple layers to avoid displacing the cladding panel.

5.3.7.5.2. For cladding panels with a non-glossy surface, the width of the cladding mortar joint must not exceed 2 mm. For cladding panels with a glossy surface, the steel joints must be very tight and polished to recess the joints or aligned with thin lead sheets or other materials specified by the design.

The walls in the room must be clad before paving the floor. After cladding, the cladding surface must be washed and wiped clean. For walls clad with glossy stone, hot water must be used to thoroughly wash, then a dry cloth is used to wipe clean.

The deviation of the edges between the cladding panels, or between the edge of the cladding panel and the edge of the architectural detail, must not exceed 0.5 mm.

5.3.7.6. Ceramic tile, glazed tile cladding

5.3.7.6.1. Before cladding, the concealed electrical system and wiring must be installed. The structure to be clad must be firm, before cladding, adhered mortar stains, oil stains, dirt on the surface must be cleaned off. If the cladding surface has areas protruding more than 15 mm and deviating from the vertical direction by more than 15 mm, it must be repaired with cement mortar. Plastered wall surfaces and concrete surfaces before cladding must be roughened, the plastered surface where cladding is applied must not exceed 5 cm and not exceed the width of the cladding tile.

5.3.7.6.2. Cladding tiles must not be warped, bent, dirty, stained, or have dull glaze. The cladding corners and edges must be even, the edges must be straight and sharp. Before cladding, the cladding tiles must be washed clean.

The mortar used for cladding must use washed clean sand and Portland cement with a grade not less than 300, the mortar grade must meet the design requirements. The thickness of the bedding mortar layer is from 6 mm to 10 mm, the thickness of the cladding joints must not exceed 2 mm and filled with thin cement.

5.3.7.6.3. After cladding, the cladding surface must meet the following requirements:

• The cladding tiles must have the correct pattern, size, color, the cladding surfaces must be level, vertical, with deviations according to the design requirements;
• The mortar layer under the cladding tiles must be dense (checked by tapping on the cladding tiles, hollow tiles must be removed and re-clad);
• After pointing the joints, the cladding surface must be scrubbed clean, leaving no mortar stains;
• Chipped edges on cladding tiles according to the design requirements;
• When checked with a 1 m long ruler, the gap between the ruler and the cladding surface must not exceed 2 mm.

5.3.7.7. Inspection and acceptance

When inspecting and accepting plastering, paving, and cladding work, it is necessary to base on the provisions of this standard, and at the same time comply with the provisions of the standard for acceptance of construction works and the standard for assessing the quality of works.

6. Acceptance of masonry structures

6.1. The acceptance of masonry structure construction work must be carried out before plastering the surface.

The acceptance work must be based on the following documents and standards:

• Building and works design;
• Construction drawings of buildings and works;
• Construction diary;
• Documents on foundation soil geology;
• Test reports of mortar and materials;
• Standard for assessing the quality of works;
• Standard for construction and acceptance of masonry structures;
• Acceptance of construction works.

6.2. The acceptance work must be carried out:

• Checking the level of completion of the construction work according to the requirements of the design and other related documents;
• Preparing a record clearly stating the errors discovered during the acceptance process, clearly specifying the repair time and assessing the quality of the work.

6.3. When accepting the construction work of masonry structures, the following must be checked:

• Ensuring the masonry principles on vertical surfaces, horizontal surfaces, corners of the masonry (non-coinciding joints, thickness, density of joints, verticality and horizontality, flatness and perpendicularity, etc.);
• The thickness and density of the bond mortar joints, the position of the tie brick courses;
• The correct and sufficient placement of bond and anchor components;
• The accurate construction of settlement joints and expansion joints;
• The correct construction of ventilation ducts, flues, the location of pre-made holes for installing pipes and wires later;
• The quality of the wall surface clad with cladding stones or other types of cladding tiles;
• The dimensions of the masonry;
• The placement and fabrication of reinforcement;
• The documents determining the grade of materials, semi-finished products, and products used;

For unplastered brick walls, it must be ensured: the outer faces of the walls must have a uniform color, the requirements for masonry joints and joint pointing, the decorative lines must follow the design.

6.4. The structures and parts of the works that will be concealed by the structures and parts of the works built later must be inspected and accepted before constructing the structures and parts of the works built later.

6.5. The construction of the following concealed parts requires an acceptance record:

• The quality and condition of the foundation soil, foundation depth, foundation dimensions, quality of foundation masonry, waterproofing work in foundations and basement walls;
• Settlement joints and expansion joints;
• Insulation layers in the masonry;
• The placement of reinforcement, steel details in the masonry, and rust-proofing measures;
• Embedded details, anchors for fixing lintels, balconies, corbels;
• Supports for beams, slabs on walls, columns, and bearing pads under beam ends, anchoring between steel structures, and termite protection for wooden structures placed on walls and columns;
• Erection work and allowable deviations;
• Other concealed parts.

6.6. The quality of materials, semi-finished products, and finished products manufactured in factories, when accepted, must be based on the production history of the factory. The quality of mortar and concrete produced at the construction site is based on the test results of samples taken at the site.

The acceptance of materials must be recorded, unsuitable materials must be rejected and handled immediately.

6.7. The acceptance of special parts of structures, tanks, basement walls, vaults or thin shells must be recorded in separate documents.

6.8. When accepting masonry structures built in earthquake zones, the following must also be checked:

• Reinforcement bands at the foundation level;
• Seismic ties on each floor;
• The connection of thin walls and thin partitions with load-bearing walls, with frames, and with floors;
• The reinforcement of brick walls with prefabricated and cast-in-place reinforced concrete elements;
• Anchoring of elements protruding from the attic floor, as well as the adhesive strength of mortar with brick wall materials.

6.9. The deviation from the design in terms of: dimensions, placement position, and displacement in masonry structures must not exceed the values shown in Table 4 and the limit indicators for assessing the quality of works.

The deviation of the structural axis and the elevation deviation along the height of the floor must be adjusted on the next floor.

If the actual deviation in the masonry structures is greater than the provisions in Table 4, the continuation of construction must be determined by the design agency.

The deviation of the position of the supports under beams and crane beams in the plan compared to the design position must not exceed 5 mm.

Table 4 – Allowable deviation values

Unit: millimeters