Thermal clay block for single-leaf walls: how to choose

What is a thermal clay block and what is it used for?

A thermal clay block is a large-format, low-density fired clay unit designed to build the wall as a single leaf instead of combining several layers (outer leaf, cavity, insulation and inner leaf). The Oñati thermal clay block from Vetonek is a unit of this type: it simplifies the building envelope into a single masonry wall with high thermal efficiency, and it is aimed at builders and self-builders of housing.

If you are used to traditional brick, the most visible difference is size: the face of the block measures 30 x 19 cm, so very few units are needed per square metre. If you are still not sure which unit you need for each wall, start with our guide to clay bricks.

Oñati block sizes: standard range and ECO range

According to the technical data sheet, the block is made of low-density red clay and comes in two ranges:

Standard range (30 cm long x 19 cm high): widths of 14.2 cm (6.4 kg), 19.2 cm (8.5 kg), 23.2 cm (10.4 kg) and 28.5 cm (12.3 kg).
ECO range: 30 x 29.5 x 19 cm (13.9 kg) and 24 x 24 x 19 cm (9.1 kg).

In the shop the models appear as Bloque Termocerámico 14, 19, 24 and 29, and Bloque Termocerámico ECO 24 and 29.

How to choose the block width

The thickness of a single-leaf wall is set by the project, not by the catalogue. What you can compare is the data for each format: the wider the block, the heavier each unit (from 6.4 to 12.3 kg in the standard range) and the fewer units per pallet (90 units at 14.2 cm versus 45 units at 28.5 cm). Before choosing between the standard and the ECO range, ask for the technical data sheet, which includes the thermal values and is available on request, and check with the technician in charge of the works, especially if the wall is load-bearing. The ECO range is the one with the higher insulation.

What walls it is used for

The data sheet for the Oñati block lists three applications:

External walls.
Load-bearing walls.
Dividing walls.

Whether a particular unit is suitable for a load-bearing wall or a specific facade is not decided in the shop: the project sets it, and the architect or site technician confirms it. With the data sheet in hand it is easier to justify the wall and to decide between standard and ECO.

How many units you need: a calculation example

In the formats that are 30 cm long, the yield is 17.5 units/m². For 40 m² of wall using the 19.2 cm width: 40 × 17.5 = 700 units. That equals 9 pallets of 75 units (675 units) plus 1 pack of 37 units, 712 units in total, with a small margin for cuts. These are the sales formats:

14.2 cm: pack of 45 units (2.57 m²) or pallet of 90 units (5.14 m²).
19.2 cm: pack of 37 units (2.11 m²) or pallet of 75 units (4.29 m²).
23.2 cm: pack of 30 units (1.71 m²) or pallet of 60 units (3.43 m²).
28.5 cm and ECO 29.5 cm: pack of 22 units (1.26 m²) or pallet of 45 units (2.57 m²).
ECO 24 x 24 x 19 cm: pack of 40 units or pallet of 80 units.

Pallets weigh a maximum of 1,000 kg.

Laying: the basic steps

Set out the wall and check that the foundation or slab is clean and level.
Lay the first course on a perfectly level mortar bed.
Place the blocks with mortar, staggering the vertical joints.
Check plumb and level on every course.
Make cuts with a disc cutter and follow the project instructions at lintels and junctions.

Openings, partitions and other wall units

A single-leaf wall also has to deal with door and window openings. Clay units such as the reinforced clay lintel Ordizia or the clay shutter box Deba exist for that, and we review them in the guide to clay floor blocks, lintels and shutter boxes.

For light interior partitions there are thinner units, such as the Hondarribia hollow brick; in the guide to partition walls we compare the options. And if you need a more solid unit for load-bearing or party walls, the Gernika perforated brick measures 24.5 x 11.2 x 9.5 cm and is used in that type of masonry. For garden walls and fences in concrete block, see the concrete blocks buying guide.

Frequently asked questions

What is a thermal clay block?

A thermal clay block is a large-format, low-density fired clay unit that lets you build a single-leaf wall with high thermal efficiency. The Oñati block measures 30 cm long x 19 cm high and weighs between 6.4 and 13.9 kg depending on the width and range.

How many thermal clay blocks do I need per m²?

In the formats that are 30 cm long, you need 17.5 units/m². For example, 40 m² with the 19.2 cm width comes to 700 units, ordered as 9 pallets of 75 units plus 1 pack of 37 units (712 units with margin).

Which width of thermal clay block should I choose?

The one set by the wall project. The standard range offers widths of 14.2, 19.2, 23.2 and 28.5 cm; ask for the data sheet with the thermal values and check with the technician in charge of the works.

Can a thermal clay block be used in a load-bearing wall?

The data sheet for the Oñati block includes load-bearing walls among its applications, but whether it is valid in a specific case is decided by the structural project. Always check with the architect or the technician in charge.

What is the difference between the standard range and the ECO range?

The ECO range is the one with the higher insulation and it has two formats: 30 x 29.5 x 19 cm and 24 x 24 x 19 cm. The exact thermal values for each range are in the data sheet, available on request.

Find all the units in the Clay bricks and blocks collection and in the main Building ceramics category.

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