Tony Bryer wrote:

On Wed, 28 May 2008 00:35:51 +0100 Bruce wrote :
Uses included roof and wall cladding. It was often used as permanent
formwork for suspended concrete floors. I have a feeling that this
use was restricted or after problems with some of these structures
which were concealed by the woodwool. But it was very popular and
there will still be a lot of it about.

Yes, it looks like woodwool to me. The problems you refer to came to light
at New Malden House, a tower of about 12 storeys (IIRC) in SW London. The
floors were made by using woodwool slabs as permanent shuttering,
reinforcement and concrete on top. What happened was that when the
concrete was poured, the woodwool acted as a lovely vibration soak,
leaving the concrete far from compacted, but, as you say, this could not
be seen as the woodwool was not removed.


Thanks, Tony.

Those were the days ... failures due to improper use of woodwool and
high alumina cement, alkali-aggregate reaction (a.k.a. "concrete
cancer" ... !

With woodwool, the concrete needed extra careful compaction. I think
the biggest problems were with slabs that incorporated downstand
beams, and it would have been difficult to ensure proper compaction.
The biggest problem of all was that you never got to see the concrete,
as the woodwool was left in situ. At least when you stripped
traditional formwork, problems like this could be identified and
remedial action taken.

Ironically, modern concrete mixes require far less compaction and they
would make woodwool a very sensible alternative to conventional
formwork. But once a product has a bad name, that's it.