Foam concrete house in Batumi: where it fits and how to build it

People usually choose a foam concrete house in Batumi to save on the walls: the blocks are cheaper than aerated concrete. But foam concrete hardens without an autoclave, shrinks more and varies more from batch to batch. It needs more reinforcement, more mesh and more time before finishing, and by the time the wall is finished, the saving is small. How the two blocks differ in shrinkage, accuracy of size and strength is covered in the comparison of aerated concrete and foam concrete.

Where foam concrete fits and where we'll suggest something else

Foam concrete blocks are good where a hairline crack in the plaster won't spoil anything and the walls don't carry a heavy floor slab. Usually these are single-storey buildings on the plot:

• a utility shed or workshop, or a plant room for the pumps and water heater;
• a detached garage, if the door is held by a concrete or steel frame;
• an outdoor kitchen or a canopy with a solid wall that doesn't need a finished surface;
• a boundary wall along the plot, to be rendered later;
• a small single-storey country house that you come to in summer.

For a two-storey home, a guest house to rent out with a good finish, and walls under heavy cladding, we suggest autoclaved aerated concrete. A shell built with it costs only a few per cent more, and there is noticeably less to fix after the first winter. If foam concrete is still chosen for the house, we build by the rules below and show in the estimate what each of these measures costs.

How we choose the manufacturer and the batch

Foam concrete blocks are made on simple equipment without an autoclave, so there are many manufacturers, and their quality varies. Before ordering we ask for strength and density test reports and find out how the blocks are made: cast in individual moulds or cut from a large block of foam concrete. Cut blocks are more even, and they can be laid on adhesive.

The second question is the production date. A fresh block is still gaining strength and goes on shrinking in the wall, so we don't use batches less than four weeks old. We order the whole quantity for the building at once, from a single batch: blocks made on different days vary in strength more noticeably than those from an autoclave plant.

Frame, ring beams and reinforcement

We offer a foam concrete house of two storeys or more only with a cast-in-place concrete frame: the columns and slabs carry the load, and the blocks fill the walls. A single-storey building can stand on load-bearing masonry if a reinforced concrete ring beam runs along the top of the walls and concrete cores stand at the corners and by the openings. The structural engineer chooses the scheme and takes the strength of the foam blocks from the lower limit in the test reports, not from the average.

We reinforce foam concrete more often than aerated concrete: usually the first course and the courses below and above the windows, then as the design specifies. The bars go in chases, and with mortar joints, mesh can be laid in the joint. Lintels over windows are cast in place. Whether to lay on adhesive or on mortar depends on the geometry of the batch, and so does whether the whole wall will need insulation.

Moisture and the facade for foam concrete

As with aerated concrete, we never leave foam concrete by the sea without a facade on the outside. From the inside, vapour from the kitchen, the bathroom and laundry dried indoors moves into the wall, and it needs a way out. So inside we don't cover the walls with dense finishes, we put extraction in the bathrooms and kitchen, and on the outside we use something that doesn't hold vapour back: mineral wool with a render for porous substrates, or a ventilated facade. We don't glue polystyrene onto foam concrete: the vapour runs into it, and the moisture stays in the masonry.

Because of shrinkage, we embed reinforcing mesh in the render over the whole surface of the wall, not just at the corners of openings, and before rendering we let the masonry stand under the roof for a while. For walls exposed to the sea we more often choose a ventilated facade. The pros and cons of both options are set out in our look at ventilated facades and ETICS.

Fixings in foam concrete

Blocks of the same density grade from different mixes hold an anchor differently. Before hanging a facade or heavy equipment, we pull-test several anchors on blocks from that batch. The water heater, tool racks in a workshop and the garage door motor are fixed through concrete inserts that we build into the masonry in advance, or with threaded rods passing right through the wall, with wide washers.

We don't fix garage doors or wide doors to foam concrete at all. The opening is framed in concrete or steel, and the door with its motor hangs on that frame. The same goes for a boundary wall: the posts and the gate are held by concrete or steel, and the foam blocks fill the spans.

Where to buy foam concrete blocks in Georgia

We usually order foam concrete blocks straight from the manufacturer rather than off a shop shelf: that makes it easier to get the whole quantity from one batch, with its test reports. On building sites almost any lightweight block gets called a foam block, so the supply contract states the material, the density and strength grades and the requirement to provide test reports.

If there are no test reports and the manufacturer isn't willing to show you the workshop, we advise aerated concrete. Autoclaved aerated concrete is made in Georgia itself, the manufacturer has a certificate for every batch, and the difference in the price of the shell is small.

How much a foam concrete house costs in Batumi

The shell of a foam concrete house costs from 720 ₾ per m². It covers the foundations, floor slabs, roof and foam concrete blockwork in a concrete frame or with seismic ring beams, while windows, building services, the facade and finishing are separate lines. A turnkey foam concrete house costs the same as an aerated concrete one, economy level from 1,200 ₾ per m² and mid-range from 1,680 ₾, because the finishing and services don't depend on the block.

Laying a 30 cm wall with materials starts from 130 ₾ per m², against 145 ₾ for aerated concrete, and an aerated concrete shell starts from 750 ₾ per m². A single-storey foam concrete building without a frame needs a seismic ring beam on the masonry, from 100 ₾ per linear metre, and under an ETICS facade, which costs from 205 ₾ per m², we lay mesh over the whole wall. We price both options side by side, and you decide on the final figure.

We send a preliminary estimate from the building plan and photos of the plot within 24 hours on business days. The final cost is set on the basis of the design, after a visit to the plot and once the estimate is agreed.