The Brew Cabin

Why do clay pavoirs vary in size? I know that each manufacturer states that this is due to the firing of the clay but surely this applies to all clay products - including house bricks etc. Also why do some have nibs and others not. Interested in a tech reason as it does puzzle me!

thanks - fantastic site.

I'm not sure whether you mean that pavers from one 'brand' vary in size, or that there is variation in size between pavers produced by different manufacturers.

Within any batch of clay pavers, there is some variation due to the fact that the pavers are manufactured from a natural material that behaves in somewhat unpredictable ways when fired. The exact nature of the clay, the temperature of the kiln, the position of the paver within the kiln - all these can and do have an effect on the finished dimensions of the paver, and this is 'covered' in the tolerance requirements of BS6677.

There is also a noticeable difference in size of pavers from different manufacturers. Some produce "metric" blocks, typically 200x100x65mm, while some other produce pavers based on traditional brick sizes, and so we get 205x102.5x63mm pavers. It's a pain, but that's the way it is.

As for the spacer nibs, I'm sure there is a determined policy amongst manufacturers to design spacer nibs in such a way that ensures their pavers are incompatible with any others! Given the legendary petty mindedness of some manufacturers, this is not as far-fetched as you might imagine.

Basically, it's down to the manufacturers to decide how many spacers nibs, if any, they wish to use on the pavers, and where these should be positioned on the pavers. Some manufacturers provide spacers on all 4 sides, while other have them on 2 sides only. The spacer-less pavers are normally those reserved for rigid paving, where a 8-13mm mortar joint is used, rather than a 3-6mm sand joint.

Hi Tony

Thanks for that. I did mean variation in size between same type of pavior/brick. Just wondered why there is so much emphasise on this as house bricks must be around about the same tolerence levels. Guess that the amswer must be that house bricks have a standard 10mm mortar and this variation in brick size will be masked by that.
Clay paviors would not have this benefit and variation in size much more noticeable.

Like the description that the variation in size highlights the natural element of the material. Bit like " romantic Scottish mist" as a description of our sometimes terrible climate up north.

The tolerance requirements for facing bricks are quite similar to those for paving bricks - both are notoriously variable due to firing and material differences, but you're right in suspecting that the 10-12mm mortar beds and perpends with masonry are intended to accommodate these variations, rendering them less visible than is often the case with flexibly-laid block paving.