Different blocks used for inner walls, why?

[websan]

Hi,
Could someone please let me know what the difference between these two kinds of blocks are and why would it be used this way. This is a new build and I am a bit concerned on why it would be so.

 

[stuart45]

Both AAC blocks, just different makes. Top one looks like Thermalite other like Durox.

 

[noseall]

They are both lightweight aerated blocks and will have similar thermal performances.
The lower ones are probably Durox fellas. Crap to lay - hate 'em.
The change in block type looks like it has occurred at wall plate height. This is a distinct stop-start part of the building process where the brickies have built up to roof height and are waiting for the roofers to build the roof structure so that they can then build the gables to the shape of the roof. The smaller blocks would be easier to cut up the gable.

 

[stuart45]

The lower ones are probably Durox fellas. Crap to lay - hate 'em.

Theory is that because they are longer the wall goes up quicker. What they don't tell you you is that it takes 10 times as long to butter the perps.

 

[Wendelspanswick]

I was faced with a similar problem, I was buying Celcon blocks (grey) from Travis Perkins but they have run out and will have no stock till October (it's a national shortage).
I could buy Thermalite blocks (white) from a different supplier but I managed to track down enough Celcons to finish the job.

 

[jeds]

Aerated blocks - all manufacturers - are in VERY short supply at the moment. I have a 5 house site starting in the next 6 weeks and we are collecting blocks from 4 or 5 different sources. We even considered changing the spec to allow use of medium density blocks. So my guess is they just couldn't get the Durox block so used what they could get. As above though, not really a problem as long as the block is the same thermal value, which it looks like it would be.

 

[tony1851]

Slightly off-topic here, but just a general question; two of you have pointed out that aac blocks are in short supply. Is there any particular reason for this? - just wondering.

 

[Wendelspanswick]

A severe shortage of fresh Crushed Fly Ash, a by product of coal power stations. As we reduce our reliance on coal the CFA is becoming scarce. Apparently there are huge stockpiles of old CFA but this requires a different process to turn into blocks and the manufacturers are in the process of changing over.