Clay block house in Batumi: warm masonry for a seismic zone

We build clay block houses in Batumi when the owner wants a warm masonry wall without a multi-layer build-up. The block is fired from clay, like brick, but by volume it replaces about ten bricks and is riddled with tiny pores, so the wall comes out lighter and warmer than a brick one. The price for this is brittleness, and almost everything particular about building with it comes down to that.

How a porous clay block works, and a wall built from it

Before firing, sawdust or other particles that burn away are mixed into the clay. In the kiln they burn out and leave tiny pores in the fired body, and inside the block there are also rows of vertical voids with thin webs between them. It is the air in the pores and voids that keeps the heat in the wall.

The block is made as wide as the finished wall, so an external wall is laid as a single leaf and usually needs no separate insulation. The ends of the block are tongue-and-groove, and in most systems the vertical joint isn't filled with mortar. Whether it needs filling in your house is for the structural engineer to decide: in a seismic zone, it affects how the wall resists shear.

We choose the width of the block by thermal calculation. For a house lived in all year round the external wall is thicker, while a summer house and partitions can make do with a narrow block.

Adhesive or thermal mortar

Precision-ground blocks with flat bed faces are laid on a thin adhesive joint a few millimetres thick. This joint conducts almost no heat, but it doesn't forgive unevenness. We set the first course on mortar using a level, because any error in it carries up through the whole wall.

Unground blocks are laid on a thermal mortar, which uses a lightweight aggregate instead of sand. The joint is thicker and laying is slower, but it is easier for the crew to get each course level. We don't use ordinary sand and cement mortar on external walls: every joint becomes a cold stripe, and in winter condensation can appear along them on the inside.

We use the mortar or adhesive from the system that the manufacturer specifies for its block. Course height, half blocks and corner blocks differ from one manufacturer to another, so we never mix blocks from two manufacturers in one wall.

A brittle block on site and in the finished house

The thin webs inside the block crack easily on impact, and you can see this as early as unloading. We lift the pallets off with a crane truck, we don't throw the blocks down, and we include an allowance for breakage and cutting in the order from the start. We cut blocks with a saw to marked lines, prepare the make-up pieces for openings and corners in advance, and never pack the gaps next to openings with broken pieces.

We cut chases for cables and pipes with a wall chaser. A hammer drill makes the webs inside the block collapse, and the chase sinks deep into the wall. Horizontal chases in load-bearing walls go only where the design allows them, so we plan the electrical runs on the drawings.

Positions for heavy items are decided before the walls go up. For the air conditioner's outdoor unit, the water heater, kitchen cabinets and a TV on a bracket, we build solid inserts into the wall or move the fixing onto the concrete ring beam. We mark these points on the plan, and they go into the handover file.

Seismic design: blocks in a frame or with ring beams

Porous clay handles compression but copes poorly with shear and impact, so we don't build with it without concrete. There are two schemes. In a low, compact house the blocks can carry the load themselves, provided the masonry is framed by reinforced concrete ring beams at every storey and vertical cores at the corners and next to the windows. In a taller house, or one with large windows, the load is carried by a cast-in-place concrete frame, and the blocks fill the bays between the columns.

In both schemes we tie the masonry to the concrete with reinforcement or ties in the joints, taken into the columns and cores. Before the ring beam is poured, we cover the top of the masonry with mesh or a strip of roll membrane. Otherwise the concrete runs down into the vertical voids of the blocks: consumption goes up, and the wall gets an unnecessary thermal bridge. The general rules for seismic design are collected on the page about earthquake-resistant construction.

Facade and moisture

Fired clay doesn't hold on to water: in wind-driven rain the block gets wet at the surface and quickly gives the water back, as long as there is no dense layer on the outside. So we choose a vapour-permeable facade. Most often that is mineral render on mesh, less often facing brick with a ventilated air gap, or a ventilated facade.

The weak spot of such a wall is where clay meets concrete. A single-leaf wall keeps the heat in by itself, but the ring beam and columns in it are colder than the block, and in winter a corner can darken on the inside along their outline. If the block system and the calculation allow, we pour the ring beam and lintels in U-shaped clay blocks with an insulation insert on the outer side; otherwise we cover the concrete with mineral wool. Under the render we bridge the joint between the two substrates with reinforcing mesh lapped well onto both sides, and then no crack runs along the line of the ring beam.

A clay block house in Batumi: where it fits

The block is good for a house lived in all year round. A single-leaf wall keeps the heat in, its mass evens out the daytime heat, and damp doesn't harm fired clay. That is why we often recommend it when people are building a house for permanent living or a house in mountainous Adjara, where the heating runs in winter.

It is less suitable if:

• the plot is on a steep slope with no access: brittle pallets are hard to lift, and breakage goes up;
• the design has a lot of large openings and cantilevers: the block then only fills a frame, and its advantages are lost in the price;
• the crew hasn't worked with porous clay block before: experience with aerated concrete or brick doesn't carry over directly;
• the walls have to carry heavy equipment anywhere along their length, as in a workshop or a commercial kitchen.

If wall mass and a facade without render matter most, a brick house is closer to what you need. If price and speed matter more, look at aerated concrete houses: that block is cheaper and lighter, but more sensitive to water during the build.

How much a clay block house costs

The shell of a house built from porous clay blocks costs from 840 to 1,020 ₾ per m² of floor area. This price includes the foundations, masonry on thermal mortar with ring beams or in a concrete frame, floor slabs, the roof and delivery of the blocks to the plot. The facade, windows, building services and finishing are separate lines in the estimate, and the design and plot are not included. Turnkey, a clay block house costs from 1,830 ₾ per m².

Large-format block wall masonry with materials costs 210–265 ₾ per m². An aerated concrete shell costs from 750 ₾ per m² and a brick one from 960 ₾, and clay block sits between the two. The most expensive items are the material itself and delivery, and the saving comes on insulation, which a single-leaf wall hardly needs. If the wall is insulated under render after all, a turnkey ETICS facade (insulated render) adds 205–250 ₾ per m² of facade.

We'll send an approximate estimate based on the house plan 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, when the ground, the block format and the supplier are known.