powdery scratch coat

[williamglossop]

Hi

I had a go at exernal rendering yesterday for the first time - its only 8 sqm so not loads.

I used a 4:1 mix with plastering sand and used a combined waterproofer/plasticiser. Applied directly to a new dense concrete block wall that i wetted down before applying...

Render went on fine, flatted it out and scratched it up - but today, after its dried, the surface is powdery - if i rub it with my hand i can almost rub the comb lines out. Will it be OK to apply the top coat on to it? Was gonna use a 1:1:5 mix for it - cant understand why its gone powdery though. Its very solid and really well bonded to the wall, just wondering if it will be a problem.....

 

[joe-90]

Your problem is that it has dried out rather than cured. Draping a wet old blanket or sack over it would have helped. It'll often harden a bit later on (that's what my missus says).

 

[Micilin]

As joe says.

Also, be careful not to let it mix for too long as this also kills it