Thermalite / aircrete

[ladwey]

The planning notes from the architect recommend Thermalite Turbo and Shield lightweight blocks for the cavity walls. I've not used them before; they look great from an insulation and handling point of view, but a builder friend has said that he's had problems with them cracking in the past. He recommends using the standard blocks instead. Has anyone used these 'aircrete' or similar blocks and had any problems with them? Was my mate just unlucky or are they bad in some applications?

 

[^woody^]

"Recommended" or "specified"? I suspect the later, and its not up to the builder to use the cheaper things on offer at the merchants or that they just be randomly swapped

The issue is whether alternative blocks have the same performance and meet the same u-value in the wall.

These "recommended" blocks, as well as and the ones the builder recommends are basically the same, and are each just as likely the crack. Each needs a weaker mortar to prevent cracking, and certain storage and handling precautions to minimise the risk of cracking.

 

[ladwey]

I should have been more specific, sorry -- the construction notes say 'Thermalite Shield ... or similar' at the relevant points. Don't worry about a builder swapping in cheaper materials!- I'm buying things directly myself and just wanted to check that this was a place where the architects weren't out of touch with what people find useful and durable to actually build with. The u-value of the walls is an important concern and I wouldn't do anything to compromise it.

 

[^woody^]

The block is normally chosen in conjunction with the wall insulation to get the overall wall u-value to meet building regulations.
Alternatively, a lazy designer just cut and pastes from his last plans.

Either way, you need to check that if you do swap the block, the wall still meets the required u-value, as sometimes you may need to swap insulation too if the block has lower performance

There are also 100mm and 110mm versions of the blocks, so again make sure its the specified/agreed type.

 

[jks7492]

Yes its quite common for thermalite blocks to crack

 

[noseall]

Yes its quite common for thermalite blocks to crack

Especially if the wall has been soaked while under construction.

 

[ladwey]

Thanks for the useful comments all! I was actually just speaking to a structural engineer this morning about an unrelated thing, and he mentioned that he'd just come from a house where they'd discovered that the thermalite blocks in their kitchen had cracked and were panicking -- he said he sees it all the time, and that one of the chief reasons is that while they're very structurally sound and excellent insulation, the thermalite blocks tend to crack with thermal expansion and contraction. He stressed that it's just a cosmetic issue and doesn't at all affect their structural integrity, so if you're (eg) drylining the walls it's not something to worry about at all. He also mentioned as Woody does above that the harmless cracking can be eliminated by using a weaker mortar mix.

 

[phatboy]

At the moment, you may find the biggest issue is finding the things!

We were going to do an extension with them, or other aircrete variants (Durox or Celcon), but in December they were all on allocation, and best case 3 months wait

Reverted to concrete.