Chris Bacon wrote:
alanjones wrote:
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?


I think it was because you used waterproofer and did the second coat a
week later. After a week the render is probably fully cured and ther
will be no suction available for the second coat because the
waterproofer wil not allow it. I'm no expert so its just a guess.