Soft new render surface

Hi

I've built a single skin block garage and have just rendered the rear wall which is around 3m2 as there's a window in the middle. I did a 10mm scratch coat with a 4:1 mix, left it for a couple of weeks then did another 10mm coat @ 5:1 + waterproofer. I floated the second coat to a nice flat finish and was initially really happy with the result. I left it around a week to dry as it's south facing it dried out really quickly.

When I started painting the first cost of Leyland Pliolite Masonary Paint everything looked fine until the roller took off a 3"x3" patch of render about 3mm deep. I thought it was down to the pull from the roller because the paint is really thick and oily then another patch got pulled off. If I prod the render with a flat screwdriver the 2 to 3mm surface of the render seems to be really soft, almost blown off the render underneath.

Any ideas what could cause this?

Floating too much can bring the sand to the surface weakening it, or the frost has got to it, or its not been mixed thoroughly enough.

alastairreid said:

Floating too much can bring the sand to the surface weakening it, or the frost has got to it, or its not been mixed thoroughly enough.

Click to expand...

Thanks, possibly floating too much.