How to plaster walls from foam blocks, retaining their ability to "breathe"

Gusevsky Andrey Anatolyevich

Internal stucco walls of foam blocks in a residential building

Foam blocks belong to modern building materials from the group of cellular concrete. Their advantages include low weight, ease of processing, good thermal insulation properties, high vapor permeability.

The latter property allows you to put them on a par with a tree, since vapor permeability is essentially the ability to "breathe", removing water vapor and carbon dioxide. But you need to know how to plaster walls from foam blocks correctly so as not to deprive them of this useful quality.

Features of the material and its finishes

Raw materials for the manufacture of foam blocks are ordinary cement and sand. But due to the addition of a foaming agent to the mixture during solidification, it gets a porous structure.

In each closed hollow cell there is air, which is an excellent heat insulator, and the material itself has the ability to pass gases and water vapor through itself.

Methods of manufacturing foam blocks

Foam concrete blocks are made in two ways: injection and sawing. If you chose plastering walls from foam blocks as the decoration and protection of the building from moisture, then for construction it is better to choose the material produced by the sawing method.

Explain why:

• The casting technology consists in the fact that the finished solution is poured into collapsible metal cassettes with bulkheads, from which, after solidification, ready-made blocks are removed. Due to the imperfection of the cassettes, they can have an unstable geometry, at least one uneven face, which turned out to be on top, and surface defects resulting from the removal of formwork. But the most unpleasant for the quality of the material and its subsequent finishing are the remains of the oil lubricant used to process the cassettes from the inside. It worsens the adhesion of the foam blocks and the stucco on them does not hold well. Therefore, before finishing, such walls have to be cleaned and sanded.

Photo blocks at the time of removal of formwork

• The sawing method consists in casting foam concrete in one large form and its subsequent cutting into blocks of the right size. This technology is more advanced, because it allows you to get products with clearly defined parameters and perfectly even edges and angles, which allows you to make high-quality masonry with a minimum thickness of joints. And the absence of lubricants has a positive effect on the adhesion properties of the surface. All this simplifies and facilitates the subsequent DIY home decoration from foam blocks.

For reference. The price of foam blocks made using sawing technology is higher than molding. But their use allows to reduce the cost of glue and stucco, as well as time and labor for construction and decoration.

What you need to know about foam concrete plaster

In addition to the advantages described at the beginning of the article, foam concrete also has significant disadvantages. These include insufficiently presentable appearance and instability to moisture.

However, they are easy to eliminate if you know how to plaster the walls of the foam blocks inside and out.

Such decoration should perform the following functions:

• Protection of the building from moisture. If it accumulates in the material, this will negatively affect the microclimate in the room, and after several cycles of freezing and thawing, it will begin to collapse;
• Preservation and improvement of thermal insulation properties;
• Protection against dust and dirt, giving an aesthetic appearance;
• Increased structural strength.

But the most important thing: wall plaster from foam blocks should not prevent the outflow of wet steam from the room to the outside, to reduce their vapor permeability.

The ability to "breathe" is one of the main advantages of this material.

To ensure that this requirement is met, two conditions must be met:

• Use only special vapor-permeable formulations intended for cellular concrete;
• Adhere to the ratio of the thickness of the inner layer of the plaster to the outer 2: 1. Ideally, it is advisable to perform special calculations in order to determine the optimal thickness of the internal and facade plaster in each case. But these proportions are in principle applicable to any conditions.

Note. Porous materials do not need thick plaster, on the contrary, it will only reduce their quality indicators. Therefore, the plastering of walls from foam blocks is performed with a thin layer: not more than 1.5-2 cm inside and 0.7-1 cm outside.

Which plaster to choose

If the choice of the mixture is not difficult for professionals, then plastering the walls from foam blocks with your own hands should be preceded by a serious study of the market. Of course, there can be no talk of any home-made mortars made of sand and cement, and the desire to save money will cause the coating to either fall off the surface or negate all the positive properties of cellular concrete.

When choosing the right composition, look for one that fully meets the following requirements:

• Compatibility with foam concrete, high adhesion with it;
• Good vapor permeability;
• Water repellent properties;
• Strength;
• Durability.

For facade plaster, it is also important such a property as frost resistance, resistance to temperature changes.

We’ll hasten to reassure you: you don’t have to look for and compare all the mixtures available on the construction market for a long time, choosing how to plaster the walls from foam blocks. Those that you need are specially marked or indicated for the possibility of using foam concrete or other cellular structures for finishing.

The most popular brands recommended by experienced finishers:

• Atlas KB-Tink - the lightest of all known plasters;
• Ceresit ST 24 - a mixture based on cement with special binders;

This plaster has good ductility, easy to apply and smooth.

• Mask mix - polymer-cement mixture with the addition of quartzite;
• Profit Kontakt MN - mixture for machine plaster;
• Sh-36 Decor - cement plaster with reinforcing synthetic fibers.

Foam concrete plaster

It will help you better understand the information on how to plaster the walls from the foam block video taken during the production process. But the main points will not be amiss to repeat.

We remember that the layer of plaster should not be thick, therefore, before starting work, you need to knock down all the gushes in the joints and clean the surface of dust. Walls from injection foam blocks must also be carefully sanded.

This is followed by surface treatment with a deep penetration primer with hydrophobic properties. One layer is not enough, it is better to apply two to provide better adhesion.

Primer walls before finishing

Before plastering a wall of foam blocks, it is necessary to fix a reinforcing fiberglass mesh on it that is resistant to alkaline conditions. It will provide the best contact of the plaster with the base, strengthen the formed finish layer, and prevent its cracking and detachment.

Grid plaster

Note. It is not necessary to mount the grid on the entire surface, it is enough to strengthen only the areas experiencing increased load: the internal and external corners of the building, door and window openings.

After that, you can proceed directly to the application and leveling of the solution, having prepared it according to the instructions on the package from the selected dry mixture. Plastering can be done manually using a spatula or by machine. The main thing is to comply with the specified thickness.

You can evenly distribute the solution on the surface using a grater when it grabs slightly

Conclusion

The very process of plastering walls made of foam blocks is no different from similar work on brick or concrete. You could see this by watching the video in this article.

A feature of this work is only the correct choice of the mixture and compliance with the proportionality of the thickness of the internal and external plasters.