Soaking thermalite blocks before use??

Thermal blocks must be dry when used. They expand enough when wet so that when they later dry, they will crack in half. This happens when left uncovered out in the rain on building sites before use. You can moisten the surface for plastering, but don't soak the whole block.

Mortar does bond to brick and blockwork, but the main function is to hold them apart, and blockwork itself doesn't have much tensile strength, so there's little point in forming a strong bond, as you would just pull the block apart under any significant tensile forces (as happens above).

I think it varies depending if the blocks have been baking in the sun for weeks, or left out in the rain - I'd expect the bricky to act accordingly, only soaking them if necessary.

The concrete foam type of light weight block is unlikely to benefit from soaking. You may need a bit of dampening depending on how hot it is when laying them, but I can't see it being an issue this time of year.

(all the load is in compression anyway, and the light weight blocks have little strength in bending, torsion, or tension - so the strength of the bond is relatively unimportant as long as the mortar was hydrated enough to allow proper curing)

You can check various technical guides here:

k. Specifically she felt that the mortar wasn't bonded to the blocks prope rly as he hadn't soaked the blocks before laying them.

I seem sure it must have)), but can't find anything.

used to soak his as this prevents them from immediately sucking all the moi sture out of the mortar joints and messing up the bond.

a post in a less august forum.

rickies, etc). Was don't soak the blocks (as it can lead to cracking when t hey dry out), but use a wet mix and get them down quick (one or two did say they had been on site and seen them being soaked). But then, they may be more interested in how quick they can get paid and move onto the next job, rather than the longevity or otherwise of the structures they build.

It's normal for mortar on lightweight blocks to crack as it dries. For medi umweight blocks it's not.

NT

I recently had to remove the top two courses of blocks from a four foot high wall and was surprised at how weak the mortar bond was: it seemed as if only the weight of the blocks (the dense kind) was keeping them in place.

I found myself wondering if a serviceable (if not too tall) block wall couldn't be constructed by using adhesive rather than mortar.

Assuming of course they really are the real mcoy so to speak. I recall seeing somebody kind of painting water on the surface to be mortared many years ago, so the wetting rather than soaking sounds about right to me. Brian

Thermalite blocks are horrid things - seen exactly what you describe.

It seems they only get strong when 1/2" of plaster goes on them...

There are "landscape" adhesives sold for just that in America e.g.

I checked with Henkel if it was available over here, they said not and nothing similar, which is when I ended up looking for (and eventually using) CT1 to glue down the edge pavers on my driveway, it didn't have quite the numbers in terms of holding pressure, but not far off ...

Yes it is done. The idea is to reduce heat loss through mortar joints. EG

I wasn't familiar with CT1 and had to look it up: it's considerably more expensive than most gun adhesives though I suppose the spec is higher. But wouldn't any of the high-performance tube adhesives, Stixall and the like, do an almost comparable job?

As someone whose skill with mortar and cement is approximately zero this approach holds considerable interest.

And here's someone building a block wall using Gorilla glue:

Don't think they'd hold up to car traffic (especially steering wheel turning against pavers) I only needed a couple of tubes, don't think I'd want to pay for enough to build a wall, plus it dries with a lot of rubbery stretch/give to it, so not ideal for a wall.

I did use solvent gripfill to put in a temporary paving slab "half-step" for a neighbour who found the normal height had got too much for her, and it held OK, though it didn't take much force when the time came later to remove it.

Argh! I think I'm seasick ...

Yes, I suspect you're right; I was thinking more of walling than paving.

replying to Bert Coules, Giuseppe wrote: In Italy, for interior walls, with similar blocks, a glue made especially for joining them is used, you can also use the simple glue for the tiles