What is a poriso brick?
A poriso brick is a solid clay brick made porous by blending a burn-out additive into the clay — sawdust, coal slurry, silt or fly ash. During firing that additive burns away and leaves pores throughout the body. The result is a yellow to red-brown unit with a density of around 1,300 kg/m³: clearly lighter than an ordinary solid brick, but still massive.
Poriso is a Dutch and Belgian designation; in English-speaking practice these are simply called porous or lightweight solid clay bricks. Unlike many porous blocks, the poriso brick has no large vertical cavities — all of the porosity sits in the material itself.
Where it is used
The poriso brick is an internal wall unit. Its relatively high compressive strength makes it suitable for both loadbearing and non-loadbearing internal walls, for instance as the inner leaf of a cavity wall or as a partition.
It is not intended for external use: a porous body absorbs water, which makes it vulnerable to frost damage and staining.
Variants
- Render grade — a more robust unit meant to be plastered or rendered, often with tongue-and-groove ends so the perpend joint does not need filling.
- Facing grade — a unit that looks like ordinary brickwork and can be left exposed.
Points to watch
- Sound insulation is the weak spot. Airborne sound insulation comes from mass. For separating walls between dwellings the construction has to be calculated against the applicable building regulations, and in practice that means a much heavier wall or a twin-leaf, acoustically isolated build-up.
- Tongue-and-groove saves work — but not always. If a wall has to perform acoustically or in fire, the perpends must be closed too. Check the manufacturer’s data sheet.
- Choose the right fixing. A porous body breaks out easily. Use anchors tested for porous masonry and drill without hammer action.
- Match the mortar. An absorbent unit draws water out of the mortar. Follow the instructions on pre-wetting or on the use of a thin-bed mortar.
Related terms
- Porous brick
- Poroton
- Brick
- Perforated brick
- Calcium silicate brick
- Aerated concrete
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