Using lightweight blocks - gen advice please.

[Ladybrickie]

Hi all, I've been surfing the net trying to find answers but am not getting anywhere. Can you give me general advice about using Thermalite blocks. I understand that before I can rest structural timber on them they need to have a course of concrete commons. Is that right? It makes sense to me. What are the other rules please or can you direct me to a web site which would help me. Can 'normal' blocks be mixed with 'Turbo' blocks for speed or is that frowned upon? I don't want to use plasterboard but wish to plaster after but read somewhere that the thermal efficiency is lowered. What, if anything can be done about that? ?An upgrade in block density perhaps? Any sage advice would be gratefully appreciated.

 

[noseall]

Structural timber can rest directly onto aerated blocks.

The use of concrete commons in conjunction with lightweight blocks is prohibited. What you may have seen is lightweight coursing bricks used as a make-up course to achieve ceiling or plate height.

Similarly, it is frowned upon to use any masonry other than that which is of the same or similar thermal value. However, similar sized aerated blocks can be mixed together.

Rendering/plastering these blocks is risky due to shrinkage etc.

If it were me, and the customer insisted on wet plastering, i would be thinking about using fibolites or similar. As far as i'm aware you can still achieve the latest thermal reg's values by going say - 100mm external masonry - 100mm full fill dritherm - 100mm fibolites - 18mm lightweight render and skim.

 

[themiddleagedun]

Concrete bricks... no
mixing types of blocks .. no.
The only thing in favour of thermalite type blocks, IMO, is the lack of weight. I don't like 'em, but loads are used everyday so I may be just biased! I'd use concrete blocks.

 

[stuart45]

At my age I prefer thermalites. Let the spreads worry about the rest.

 

[Ladybrickie]

Hi,
Thanks for the replys. In every other respect they are Ok for attaching wall starters, joist hangers etcetera and ad infinitum, yes?
Does anyone know about the relative sound transfer for the two types of blocks? I imagine Therms are more blocking in that respect? We are near a noisy road. Thanks for all your help!

 

[^woody^]

As all the others have said, there is not much difference to using aerated blocks to concrete ones

For fixings, some normal fixings can work loose or pull out easier, so for high loading, a longer fixing or expansive bolt type may be better.

Sound wise, block are categorised in density (ie 3.5N) and there wont be much difference in use at similar densities. But it is the whole wall construction which has the greatest influence, not just the blockwork

Also remember that the mortar strength should be a lot weaker than with normal concrete blocks to allow for greater shrinkage and expansion - something like 1:6 or 1:9 - see the manufacturers recommendations

I prefer lightweight concrete to lightweight aerated blocks, as the aerated are too dry and have a slight dust coating which makes the mortar on the perp joints not stick too well when laying. And they dry too quick, so any slight knock or tap looses them

 

[Ladybrickie]

Thanks everyone. Plenty to think about there (sound of chin scratching)
All have a good day and cover up in that sun eh? Best wishes. LB