Aerated concrete laying on glue-foam

Recommendation points

• Development history and technology features
• Production and technical base
• Laying the starter row
• Wall erection process

Much has been said about the high performance properties of autoclaved aerated concrete, but the technology of its seamless laying on glue-foam has been undeservedly deprived of the attention of domestic builders. At the same time, this is a fairly technologically advanced way of building walls, which we will tell you about in detail..

Development history and technology features

Seamless gas silicate masonry implies a complete rejection of the cement-sand-based adhesive. Instead, a special polyurethane based adhesive foam is used to tie the blocks. It has the same form of delivery as the polyurethane foam, but differs in almost complete absence of residual expansion. The result of this method of masonry is the observance of the required ultimate compressive strength, as well as a number of additional advantages that are unattainable when using mineral glue..

The building regulatory framework positions gas silicate blocks primarily as a material for laying interior partitions and filling cells of monolithic and precast-monolithic buildings on a reinforced concrete frame. The use of cellular concrete for the construction of load-bearing walls was previously possible only with the use of thin-seam technology, however, since 2015, the first successful attempts to certify masonry for glue-foam have been carried out through tests by individual manufacturers. As a result, it was found that the seamless masonry technology provides the required physical and mechanical properties and is suitable for the construction of load-bearing enclosing structures up to three storeys high in regions where there are no factors of increased seismic hazard. The designers were able, relying on the provisions of SNiP 11-22-81, to calculate the compressive strength according to the standard methodology and to establish a sufficient block thickness in accordance with the predicted combined loads, as well as to ensure high durability of structures, guided by the requirements for frost resistance of monolithic aerated concrete masonry.

Subsequent tests, initiated mainly by the manufacturers of autoclaved aerated concrete and adhesive foam, made it possible to clarify the strength characteristics of such walls. It turned out that they have a slightly higher fracture limit in compression, but are characterized by a slight increase in the accompanying deformation and an increased modulus of elasticity. This is due to the fact that as the wall accepts the load from its own weight, floors and roof, the foam seams finally crumple, while the entire masonry acquires non-zero elasticity and does not require reinforcement to prevent the formation of temperature and sedimentary cracks. Additional advantages of the technology were declared the absence of time-consuming preparation of the adhesive mixture, the continuity and homogeneity of the thermal circuit, the unnecessary residual drying of the building before the installation of the thermal protection belt and the ability to almost completely eliminate the blow-through of the walls.

Production and technical base

The technology of aerated concrete seamless masonry is not without its drawbacks. To ensure the required compressive strength, direct contact of the blocks with each other is necessary, because the adhesive foam works mainly as a factor in counteracting the lateral displacement of the masonry elements. Because of this, there are increased requirements for the geometry of aerated concrete, therefore, for seamless masonry, only blocks of the first category with a tolerance of a deviation in height of no more than 1 mm can be used. This error is established by GOST 31360-2007, however, when choosing materials, it will not be superfluous to make sure that the tolerances provided for by the TU, which are guided by the manufacturer.

And even a block deviation of 1 mm can make the work of glue-foam ineffective: the slightest difference at the vertical joints leads to a loose fit and the formation of a cumulative error. This forces the masons to carry out an intermediate roughing of the surface of each row before laying the previous one. For these purposes, use special graters or self-made devices from mounting nail plates for wooden trusses.

Some special tools are also required, first of all – a gun for glue-foam, preferably of the highest quality with precise adjustment of the pressure. Additionally, you will need equipment and devices for cleaning open surface pores from dust, as a rule, this is done by blowing with compressed air. It is possible to additionally increase adhesion and shorten the setting time by pretreating the blocks with acrylic primers with mineral fillers. Intermediate alignment of blocks is not required, the total height difference at the end of the masonry belt is, as a rule, no more than 10–12 mm, which is easily compensated for when pouring a reinforced crown in full compliance with the norms for eccentricity of loads.

Laying the starter row

In general, the method of laying on glue-foam differs little from the technology using glue mixtures on a mineral basis. The procedure for carrying out and monitoring work, as well as the design solutions used are described in sufficient detail in STO NOSTROY 2.9.136–2013.

The first row of aerated concrete blocks is laid on the foundation after waterproofing from 1–2 layers of basic bituminous materials. To ensure a high flatness of the surface of the row, it is installed on a correction layer of cement-sand mortar of grade 100, the maximum thickness of which can be up to 20 mm or up to 40 mm with reinforcement with a masonry mesh. First, set the corner stones, the position of which in the plane of the row is determined by the rangefinder, and the height – by a level or laser axle builder with a tolerance of no more than 3 mm per 10 m of length.

After the adjustment layer has set, the mooring line is pulled under the corner elements and the linear sections are filled in such a way that the additional elements have a length of at least 50 mm and are placed either at the corners or after 3-4 solid stones from the corner. The starting row end pieces as a whole determine the entire ligation scheme, their size should be chosen so that a displacement of at least 1/5 of the block height is provided when building on incompressible soils and at least 1/2 of the block height when erecting walls on a MLF, based on weakened soil. When the starter row is laid out, it is left for a period from 10 hours to a day for the preliminary setting of the cement mortar.

Wall erection process

Aerated concrete laying is performed strictly sequentially in rows without removing corner peaks. Work on each subsequent row begins with wiping down the upper plane of the laid blocks until the slightest height differences at the vertical joints cease to be tactilely felt. Due to the increased creep of the masonry, due to the presence of a waterproofing layer, it is necessary to cut a groove in the central section of the wall to lay out the reinforcement. Reinforcing rods with a periodic profile are placed in a groove after being bundled into a single contour and filling the groove with a mineral-based adhesive composition, protruding excess glue is rubbed into the surface with a spatula. After wiping, the surface is dedusted with compressed air, then one of the corner stones is placed first. In this case, the alternation of pokes and spoons in adjacent rows must be observed.

The block is installed in place after the application of two parallel foam flagella with a diameter of up to 15–20 mm with a distance of at least 50 mm from each edge of the masonry. The foam must be applied in a continuous contour, first on a horizontal plane, and then on a poke of a neighboring stone. After applying the foam, there is about a minute to install and position the next block. It is tried on to the installation site, achieving an initial displacement of no more than 5 mm, and then finally aligned along the general plane of the wall. The curing time of the glue-foam before the temporary fixation gains strength is 3 minutes, the final drying of the binder occurs no later than 15–20 minutes after application, which must be taken into account for the timely correction of masonry errors.

Particular attention must be paid when installing additional elements. The adjoining planes of the blocks must be carefully adjusted to form a minimum gap. In this case, the glue-foam is applied on the horizontal plane in a standard way, and on the butt surfaces – with an excess that increases as it approaches the top of the blocks. The same rule applies to the manufacture of overhangs at the junction of the inner bearing walls with the outer ones. When connecting load-bearing walls with self-supporting partitions, it is not necessary to tie them up. When using glue-foam, it is most reasonable to make quarters in openings not by trimming, but by gluing flanges.