internal render

[hawkman37]

what is the correct quantities for sand and cement render please, we were arguing today i said it was 3-1 for first coat then 4-1 for second coat is this right? also is just using building sand ok

 

[roughcaster]

4 plastering sand, 1 cement, 1 lime. Scratch.
5 plastering sand, 1 cement, 1 lime. Top coat.
The lime in the mix gives it flexibility, you will also need to use a combined waterproofer/plasticiser mixed in with the water, especially in the scratch coat,, even though it is internal render. Makes the top coat a lot easier to work with whether it's rendering indoors or out.

Roughcaster.

 

[hawkman37]

do i need to pva first or just wet the wall, as ive been told in the past it kills the suction

 

[roughcaster]

Once you've mixed up your mortar, give the brick/blockwork a good wet down. Put on your scratch-coat evenly, scratch it as you go, and leave it to go off/cure. Because you have put waterproofer in the scratch coat mix, there would be very little suction. When you are ready for the top coat, wet the wall down again, let the excess drain off, and then put on the top coat. So now,, because of the scratch coat having w/proofer in, and the wall being wet down before putting on the top coat,, there's no need for pva, because if done correctly,, there shouldn't be any suction at all.

Roughcaster.

 

[hawkman37]

excellent thanks for the reply, its a great help