breeze block wall drying with loose blocks

[browfish]

I have laid the first couple of courses of breeze blocks for my extension. The are Celcon solar blocks laid with 5:1 mortar (builders sand, mastercrete cement and plasticiser). Most of the blocks have set ok however there are a couple of blocks that are loose and can be lifted off. There are a few others that move ever so slightly when wobbled so i have cut these out. Any idea what could cause this?

 

[^woody^]

You probably need to damp the blocks down before laying. And once laid, don't mess with them or knock them

 

[browfish]

I did think that but the weather hasnt been great and the blocks have been stored outside so i assumed they would be damp enough. Som of the blocks at the centre of my stacks were alot dryer so maybe it was these that have come loose. I shall have to make sure i dunk each block from now on.
thanks

 

[simonjay]

I did think that but the weather hasnt been great and the blocks have been stored outside so i assumed they would be damp enough. Som of the blocks at the centre of my stacks were alot dryer so maybe it was these that have come loose. I shall have to make sure i dunk each block from now on.
thanks

These blocks do the job and have advantages, but have issues too. If not wet enough the mortar does not stick, if too wet, they shrink a lot as they dry. Dunk them quickly or spray them but don't soak them.
Make sure you include horizontal mesh reinforcement every few rows to limit the run of cracks. However, the shrinkage cracks are usually jagged in nature and do not destabilise as much as you would think. You may need to dig out joints and repoint a few blocks after the roof is on and the walls have dried out.
Also, a 100mm wall with no load or lateral support is a bit wobbly, especially with lightweight blocks.
Do not pour a floor against freshly layed blocks without support or cavity infill - they may well fall over !!

Simon.

 

[browfish]

Thanks
The wall is not 100mm. It is a cavity wall (90mm), both skins in Celcon solar as the outside is a combination of render and cedar cladding.

Have already filled the cavity with concrete up to ground level (1 block below DPC)

what mesh should i use, is it like plasterers lath? This seems to come in sheets 2500x700mm. Assume this wont rust and cause more problems? How many courses should i do between this? Assume this should be used on inner and outer skins?