On 23/03/2013 07:42, harry wrote:

It was common practice years ago. The blocks will likely be proper
breeze blocks, ie made out of power station fused ash & very light..
The gap under is probably due to the timber warping/shrinking as it
dried out.
So long as there are no cracks/other visible damage, leave alone.

And I thought that lightweight concrete block such as Thermalite were
significantly lighter than breeze? I always think of them as being a bit
lighter than the heavy concrete blocks, but much heavier than
lightweight blocks.

Anyone care to confirm - or otherwise?

--
Rod