External leaf - Any disadvantage to thermalite?

[Delinquent]

As my house is rendered and rather exposed on a steep slope, to up the insulation factor and ease the build (no access, period! long walk with blocks) both the bricky and a supplier I use suggested doing both leaves of the cavity wall with thermalite (or equivelant), which the BCO has accepted no problem.

Don't know why, but it just feels.... wrong! Couple of other people have screwed up their noses as well when discussing it but haven't been able to give any sort of real reason not to - other than it's "usual" to have concrete blocks externally.

I've heard of issues with rendering lightweight blocks before but a mate in the trade gave me a technical number, who when called said it was no problem at all IF you sealed the blocks before render, a stage often missed out.

Any other problems I may encounter?

 

[^woody^]

The only issues I can think of are that when rendering, it is possible for the blocks to suck the moisture from the render too quickly - leading to a poor fix or cracking of the render. This can be addressed during application.

The other possible issue is perhaps initial shrinkage of the blocks following laying. Sometimes if saturated or the mortar is too strong, then these blocks develop vertical cracks when they shrink - this can crack render. Again, this can be adressed by taking precautions during construction.

The people who say "don't use them" are the people who don't know how to use them.

 

[Delinquent]

Many thanks Woody,

Re: "
The people who say "don't use them" are the people who don't know how to use them."

Funnily enough, that is almost word for word what the technical chap said as well, only he added something a little less forgiving at the end