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Foam block or gas block – choose a material for construction

We will find out what is the difference between some of the most popular building materials in private housing construction.

What is better to use during construction – a foam block or a gas block? The correct answer to this question is not as simple as it seems, because, other things being equal, the technical characteristics of both materials are approximately similar. This is confirmed by the fact that there is only one regulatory document for them – an interstate standard in force in seven CIS countries – GOST 31359-2007.

Which is better – a foam block or a gas block?

  • What’s the difference?
  • What is the confusion between sales managers and garage producers?
  • Which is cheaper to use – a foam block or a gas block?

If the production processes are built according to the current regulatory documents and the products are manufactured in compliance with them, then the difference between the autoclave types of foam and gas blocks will be insignificant.

Foam block or gas block - choose a material for construction

The difference is significant only between autoclaved and non-autoclaved concrete

What’s the difference?

The high demand for honeycomb blocks that has appeared in the last decade in the construction industry has led to the fact that only the lazy do not produce it. Simplicity of technology, inexpensive equipment for non-autoclave production, relatively inexpensive foaming agents, low capital investments in the beginning of production, the ability to produce in small rooms, even in a garage, etc. the name of “foam blocks”. The porous structure of the foam block and gas block with an increase

To choose the right one, you need to know about the difference between autoclaved foam blocks and aerated blocks. It is as follows.

Foam blocks are made by mechanical mixing of ready-made foam and a slurry of concrete mix – cement and / or lime, sand, additives and water. Foam is formed in a separate container when the foaming agent and water are mixed.

The finished mixture is poured into individual or group forms. Withstands from 4 to 8 hours to gain initial strength. Blocks are removed from individual molds and sent for aging to gain tempering strength – 70% of the nominal. The large block from the group shape is cut with strings into blocks of nominal size. This method of forming a block is better, as it gives a much higher manufacturing accuracy.

Gas blocks are made by thorough mixing of concrete solution with aluminum powder or paste based on it. Up to 400 gr is used per cubic meter of mixture. powder.

After mixing, grains of aluminum begin a chemical reaction with negatively charged OH-ions of the mixture. As a result, high-strength aluminum oxide and hydrogen are formed in the form of a gas, which “gasses” the solution. From 1 cubic meter of solution I get about 2 cubic meters of aerated concrete. In the reactions, aluminum is completely consumed, and it is not in the form of powder in the finished aerated concrete.

The foamed mass gains initial strength in a few hours and, like foam concrete, is cut into blocks of the desired size. The blocks are gaining strength in an autoclave at high pressure and temperature. There, a variety of hydrosilicates are formed from a mechanical mixture of Portland cement, quartz sand, lime and the remains of aluminum powder in the ongoing chemical reaction – very chemically resistant and durable.

What is the confusion between sales managers and garage producers?

It is believed that aerated concrete has a white tint, and dark gray is foam concrete. But here they confuse the silicate base of one material produced on a lime binder and the Portland cement component of another cellular concrete.

Foam block or gas block - choose a material for construction

The color of the foam block and the gas block can either be the same or different.

It is believed that autoclave gas blocks have smaller deviations from the nominal dimensions. Here, too, two different technologies for obtaining a block are “piled up”:

  • cutting a large monoblock of aerated concrete into blocks of nominal size with a tightly stretched steel string, giving high manufacturing accuracy – ± 1 – 2 mm;
  • casting blocks into individual molds gives a range of sizes up to ± 10 mm, non-parallelism of the sides is possible, there may be different density and porosity along the height of the cast block.

Incompetent “experts” claim that one material picks up water like a sponge and sinks quickly, while the other floats like a float for hours or even days. However, this is a myth.

All cellular concrete absorbs water. This is due to the fact that during their manufacture, water not only provides the chemical processes of hydration – the transformation of cement, sand, lime and additives into an artificial monolith stone – but also liquefies the mixture, allowing it to mix easily, envelop all filler particles with cement, and not form large voids and fill in all the corners of the form. When “drying”, or rather gaining strength, excess water, often up to 65 – 70% of the initial amount, will inevitably make capillary passages outside the block and a structure is formed that subsequently passes steam and even water.

The release moisture content of ready-made autoclave cellular blocks of factory production can be much higher than the equilibrium moisture obtained during operation in the wall. After laying in the wall, they dry up to 2 – 3 years before reaching an equilibrium moisture content. It can be in the range of 3 – 4 and even 6 – 8%.

Drying of blocks in an autoclave lasts only 5 hours, and in the open air for almost a month
Drying of blocks in an autoclave lasts only 5 hours, and in the open air for almost a month

It is also claimed that non-autoclave foam blocks will “gain” their strength in the wall for many months. In fact, a finished non-autoclave block can be used for construction only with a tempering strength that is not less than 70% of the standard strength. In the process of “drying”, the block gains more than half of the standard strength in 5-6 days. And the autoclave block takes a day (which is much better), but for this it needs to be heated to 180-210 ° C under a pressure of 11-14 atmospheres, or about 1-1.4 MPa.

Foam blocks made without autoclaving in the garage may not have time to gain strength.

Which is cheaper to use – a foam block or a gas block?


Even autoclave foam blocks and gas blocks have different prices. At the same time, the foam block is slightly cheaper than gas blocks.

When choosing foam concrete or aerated concrete, only one parameter can be physically checked – the accuracy of block manufacturing. It is necessary to measure several blocks on different pallets with a metal ruler or tape measure – for construction it is better to use blocks with the most accurate geometry.

The rest of the parameters for a layman by eye to distinguish, if not impossible, then very difficult, and it is better to check the accompanying document:

  • density (kg / cubic meter) is different for blocks for various purposes – for insulation – from 200 to 400, for structural and insulation – up to 700, for construction – from 600-700 to 1200;
  • strength class – determined by the purpose of the block as an element of load-bearing walls;
  • shrinkage resulting from drying, mm / m – from 0.1 to 0.7;
  • frost resistance – characterizes the duration of operation, it can be from F15 to F 50, F75 and above.

Autoclaved aerated concrete in the understanding of a construction specialist will be slightly better than the same foam concrete. The difference is determined by different sources of raw materials and the quality of the blowing agents.

Foam block or gas block - choose a material for construction

For most amateur builders, the concepts of “aerated concrete” and “foam concrete” have a significant preponderance in favor of aerated concrete. And it is determined by the fact that the overwhelming majority of aerated concrete is produced at serious enterprises and using autoclave technology, therefore it is better, and foam concrete – most often without heating in an autoclave. published by econet.ru

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If you have any questions on this topic, ask the specialists and readers of our project here.

PS And remember, just by changing your consumption – together we are changing the world! © econet


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