MOULDED BLOCK INSTALLATION
MASONRY LAYING AND CONCRETING
1. General recommendations
1.1. Stacking
The moulded blocks must be stacked so that their cavities are over one another. It is not recommended to spread the mortar completely under the first layer (row) of the blocks because the infill concrete must have contact with the foundation. The masonry comprising the moulded blocks is concreted completely. Prior to concreting you must install the pipes that you need for cables and service lines. Each moulded block is designed so that during compacting the concrete enters the voids between the blocks and interconnects the blocks horizontally, too. Thus connections are created between the adjacent concrete pillars. This serves to achieve the best inner structural result from concreting.
1.2. Reinforcing
Vertical armature can be installed before or after laying of the concrete masonry. Vertical and horizontal armature rods must be inserted and attached properly. The distance between the armature and the block wall must be at least 0.5-1.2 cm, depending on the chosen concrete filler materials.
Concreting
2. Low concreting
2.1. General part
Low concreting is easier and more widespread. For low concreting the masonry height cannot exceed 1.6 m (8 block rows). After that the cavities are concreted and the next masonry part is added (not exceeding 1.6 m in height) and the process is repeated.
2.2. Armature continuation
The vertical armature rods can be relatively short because they should extend over the concrete layer just enough to ensure sufficient overlapping with the armature rods in the next concrete layer. The overlapping length for the armature rods in the pressure zone must be at least 20 Ø + 150 mm; in the tension zone – 25 Ø + 150 mm. The overlapping length cannot be less than 300 mm.
2.3. Concreting and compacting
In most cases a special concrete pump is used in concreting work. In small-scale projects apertures are filled in manually. You should avoid covering the top surface of the block row with infill concrete because the moulded blocks are stacked without any mortar. When concreting work was suspended for at least one hour, the final structural horizontal layer must be finished at least 2.5 cm below the upper edge of the block. This will ensure bonding between the new concrete layer and the block row. The infill concrete must be compacted in the course of the concreting work. Due to the liquid consistence of the infill concrete it can be compacted without great effort.
3. High concreting
3.1. General part
High concreting is for such structures where the armature, the apertures and the masonry elements are arranged in a manner that enables free flowing of the infill concrete. Concreting commences when the masonry has been raised to the project height. Concreting is performed by layers with a maximum height of 1.6 m (see point 3.2).
3.2. Concreting and compacting
Select the concreting sections so that by the end of the working day concreting reaches the final height of the masonry (concrete is poured simultaneously on a layer not exceeding 1.6 m in height). By no later than within 10 minutes after installation of the concrete layer the workers must begin compacting by vibration. Each subsequent layer of concrete is pumped and compacted periodically, after 30 minutes at the least and after 60 minutes at the most (precise timing depends on the weather conditions and concrete absorption). This time is necessary for the installed infill concrete to finish shrinking and for the excessive water to become absorbed by the surrounding concrete element. The aforementioned waiting period also lowers the hydrostatic pressure of the infill concrete and it serves to reduce the threat of blocks shifting. Each next layer should in the course of stacking be bound with the previous layer to the extent of 30-35 cm by applying vibration. With the masonry concreting work completed, the façade should be washed with pressurised water to remove all foam and stains caused by the concrete seeping out of the joints. After cleaning with pressurised water the masonry can undergo the necessary “cosmetic treatment”.
USER MANUAL: MASONRY FROM MOULDED BLOCKS
After completion of the structure its masonry made from moulded blocks does not require special maintenance. You should take into account the surface porosity and the fact that this is a “breathing” construction material. We advise that you follow these recommendations:
1. Prior to treating the stone surface with chemicals make sure that they are suitable for this purpose.
2. Use detergents while maintaining the proper detergent/solvent (often water) ratio.
3. Prior to washing the surface layer with water-soluble substances you should moisturise the porous surface with clean water to prevent deeper absorption of the chemicals.
4. Avoid damage to the stone surface from power-washing and mechanical cleaning. (For instance, when the pressure washer is too close to the surface, the wall will have traces of the water jet; the wall will be scratched after cleaning with a hard metal tool).
5. To remove paint, oil, etc., it is best to have a specialist help you choose the right technology. If you intend to use a strong chemical, you must first try it on a smaller testing surface.
6. To preserve the fresh appearance of the masonry we recommend maintaining in good condition all the rainpipes and gutters that were installed to prevent water from flowing uncontrollably down the stone surfaces. A constant flow of water down the wall surface results in a washout of the salts (efflorescence) and growth of lichens and algae on the surface. It also reduces the useful lifetime of the structure (carbonisation, increased quantity of freezing cycles).
7. To reduce water absorption by the surface you can use waterproofing agents (they make the surface pores narrower but leave them open enough for steam to escape) that also make it easy to wash a surface that often becomes dirty or wet or make such a surface completely water-repellent.
8. To paint the surfaces you can only use special paints and whitewashes designed for stone and plastered surfaces.
As long as you follow the above recommendations the structure will retain a satisfactory appearance and good technical properties for several generations and your investment will remain valuable.
Primary requirements for concrete block usage in masonry work
2. Stacking
2.1. We recommend performing plastering of the wall prior to hydroinsulating it in those structural elements that can become water-saturated (cellar walls, foundations). Plastering and/or hydroinsulation are also necessary for other structural elements where water can damage the masonry.
3. Façade anchoring
3.1. At least 5 ties per square metre are necessary.
3.2. We recommend using Ø4…6 mm wire anchors from stainless or galvanised steel.
4. Settlement joints
4.1. Settlement joints are necessary for all masonry materials, including moulded blocks, as they serve to alleviate tension derived from masonry volume changes.
4.2. The intervals between the settlement joints in masonry without armature is 6…7.5 metres, with the precise interval depending on the particular structure (placement and dimensions of the apertures, posts, pilasters, wall cross-section change spots, etc.).
5. Protection from moisture
5.1. For multi-layered walls you should install a sheet-metal apron under the bottom row in the wall for removal of condensation and rainwater seeping through the joints.
5.2. In the lower row in the wall on the façade side at approximately 80 cm intervals a vertical joint is left empty to ensure airing and drainage. The same is done in the upper part of the façade if there are no other airing possibilities.
5.3. A sheet-metal apron must also be installed on the lintel of each window and door, with airing apertures left there.
5.4. When using concrete stones and blocks you should take into account their relatively large pores and, accordingly, the higher water absorption and release speeds.
6. Masonry reinforcing and concreting
6.1. In masonry comprising moulded blocks the height of a wall without armature can be up to 20 block widths, with reinforced moulded blocks – up to 30 block widths.
6.2. You should definitely reinforce the bottom horizontal row and the top horizontal row (under the panels) in a wall comprising hollow blocks.
6.3. Such hollow-blocks walls that have eccentric pressure, long lintels or other complicated structural solutions must have a solution implemented on the basis of design engineer’s consultation and calculations.
6.4. The moulded block must have all cavities filled with concrete.
6.5. When filling vertical cavities with concrete, you should take into account both the pressure that will be created in the cavity by the concrete column and the complicated nature of the infill concrete compacting process. It is recommended to apply the infill concrete at one storey height in several parts.
6.6. When performing concreting work in cold environments the infill concrete cannot freeze through during the first 48 hours. It is not recommended to perform concreting work at temperatures below -15°C. See also CK-7-3:02 “Armeeritud müüritise ladumine ja betoneerimine“ (“Stacking and concreting of reinforced masonry”).
7. Maintenance
• Remove any concrete from the façade after it has begun drying up.
• Make sure that the airing apertures in the façade do not become clogged up.
• Having completed all construction work, you should wash the whole façade with a pressure washer. If necessary, for removal of salts you can use an up to 10% water solution of hydrochloric acid, and only up to 3% when treating coloured stones. Prior to washing with the acid you must moisturise the wall with clean water. You should not treat more than one square metre at a time. Be careful when working with acids!
