Peter Taylor wrote:
"alanjones" wrote in message
oups.com...
I built a concrete block wall this summer and rendered it about a month
ago. I applied 2 layers of render the first was well scratched before
the second was applied a week later. I used sand:cement 4:1 with
waterproofer 1:25.
About a week ago the top later detatched itself from the base layer and
fell off. The other walls I did are also losing thier top coat (they
sound hollow).
What did I do wrong?
Was the cement too old (about 3 months)?
Did I over float the top coat to get it level?
I thought I'd done a very nice job and wish I'd stuck at one coat of
render!

Many thanks Alan of Exeter.


Had exactly the same problem about 2 years ago. Bricked up a window and
had to rended the surface to match the house. Problem was the render
had to be about 1 inch thick ( given my inset bricks) so I put it on in
two layers..First layer went on fine...Left it for about 4 weeks during
which time it also got a bit dusty, then got around to doing the second
before chucking lots of wee pebbles at it to match the house. 2 weeks
later I thought it looked blown and tapped it..HOLLOW sound. prodded
away and the whole 2 feet by 4 feet lump slid off! Kind of realised
what I had done wrong..Got out watered down PVA solution and soaked the
wall in it..Really soaked the wall until it stopped drying out quickly
then re-did the render.. Suffice to say its still up there!

Ged