Aerated concrete vs foam concrete: what to choose for a house in Batumi

At the builders' yard, aerated concrete and foam concrete blocks (also called foamed concrete) look alike: light, porous blocks that are easy to saw. The difference is in how they are made. Factory aerated concrete hardens in an autoclave under steam and pressure, while foam concrete gains strength in the open air. This decides the shrinkage, how accurate the sizes are and how much the strength varies. So for a house in Batumi, aerated concrete vs foam concrete comes down to how many cracks and repairs a block will cause a year later. The price per cubic metre comes second.

Shrinkage and cracks

After production, foam concrete keeps drying and shrinking, noticeably more than aerated concrete. In the wall this does not show at once. A few months later hairline cracks run along the joints and above the openings, and the plaster cracks along the same lines. An autoclaved block shrinks little, so finishing can start sooner.

A humid climate adds movement. A block that soaks up water over the winter and gives it up in summer changes size slightly again, and a weak foam block reacts more strongly. Reinforcement in the courses and mesh in the plaster help, but they will not fix a weak block.

Accuracy, joints and cold lines

Factory aerated concrete is cut with wires, so the blocks are almost identical in size. They are laid on adhesive with thin joints. Foam blocks cast in moulds often vary in size, so they are laid on mortar with thick joints, and every thick joint becomes a cold bridge.

In Batumi you see this in winter. Moisture from the room air settles on the cold joints, and a dark grid shows through on the wall, especially in a house that is heated in winter and where laundry is dried indoors. External insulation removes the problem, but then the main argument for a cheap block disappears too.

The low price of foam blocks at the yard melts away on the way to a finished wall. Thick joints eat up mortar, uneven faces need an extra coat of plaster, and cracks have to be opened up and filled after the first winter. Add the reinforcement and mesh that foam blocks need more than aerated concrete does, and the difference in the estimate becomes small.

Aerated concrete vs foam concrete in a humid climate

Both blocks are porous, and by the sea neither should be left without a facade. The pores in foam concrete are mostly closed, so it takes up water from the surface more slowly, and it is often praised for this. The advantage is lost if the block is made in a backyard workshop: uneven foam, voids and shrinkage cracks let water in just as well as open pores do.

Aerated concrete absorbs water more readily, so a vapour-permeable facade and a damp-proof course under the first row are part of the plan for it. That is standard practice wherever it is damp, and in Batumi these items simply go into the estimate from the start.

Strength and seismic load

In a seismic area we do not use either block for the load-bearing walls of a house with several storeys. A cast-in-place concrete frame carries the load, and the blocks fill it in. For infill, consistent strength and weight matter. Factory aerated concrete has one strength grade across the whole batch, while the strength of foam blocks can vary even within one delivery.

A weak block is dangerous wherever something is fixed to it, such as a tie to a column or the anchor of a window frame. In a tremor, or simply under load, it is the first thing to crumble. So for foam blocks we require the batch test reports, and if there are none, we suggest aerated concrete.

How to check a batch from abroad

Blocks can be checked from documents and photos. We ask the supplier for the batch certificate with the strength grade and density, and on site we measure blocks from different pallets with a tape measure. For foam blocks we add a photo of a fresh break: the pores should be small and even, with no large voids.

These photos go into the weekly report, and the documents for the materials later go into the handover file. A batch that fails the check goes back to the supplier before laying starts, because rebuilding a wall costs more than waiting for another delivery.