Elementary Building Questions

[TheScullster]

Hi all

As regular posters will know, I am having an extension at the rear of the house re-furb'd. The DIY bit is the electrics, preparation, partition wall etc etc... The builder has started blocking up to cill level (where a patio door was situated previously). He has used (what I think are called) Thermalite blocks for both inner and outer leaves. The extension is going to be rendered on completion, so they won't show, but should these be used on the external leaf of a build, even one that is to be rendered? I have seen blocks used in the modern houses prior to rendering, but assumed these to be more substantial items.

TIA

Phil

[Andy Wade]

[Christian McArdle]

Thermal blocks may be used almost anywhere on a 2 storey house, even as the main wall construction, or as buried foundations. They are surprisingly strong. They can even be rated up to 7Nmm2, which is pretty good.

Christian.

[TheScullster]

Thanks Christian/Andy

Following Andy's link, I contacted Thermalite to check this out. Looks like I am worrying unnecessarily!

One reservation I have is that, where these have been used previously in the house, they seem to crack readily and also loosen easily i. e. become detached from the mortar bonding. I do like to feel that the house is solid!

Phil

[Christian McArdle]

That may be more to do with the craftmanship of the brickie, or perhaps some settlement.

Christian.

[Andrew Gabriel]

That's because they expand and contract as they get wet and dry. They are often laid rather damp, drying after the mortar has set, and crack because the mortar doesn't also shrink when it drys. It seems this is just accepted.

This is important when plastering them too. You mustn't wet them too much, or when they later dry out, they shrink and lose key with the plaster.

[TheScullster]

That seems strange! You would think that wetting them would reduce the amount of water sucked out of the plaster mix and lead to a stronger joint. Looking at the block edges, the moisture from the mortar can be seen creeping an inch into the block.

Phil

[Mike]

I trust he is also insulating the cavity substantially. Thermalite blocks aren't that good an insulator.

[TheScullster]

Yes, Mike, he is.

This is all coming under general building inspection scrutiny, although I think my nightly inspections and reports/questions to this group are likely to prove more onerous. Went home last night to find that he had drilled through two cables, one going right back to CU. That's my Saturday morning taken care of then!

Phil