Getting an even base on uneven brick walls

by Will
(Manchester)

Hi Paul,

I've now successfully skimmed three walls and am delighted with the results. The final wall in the room, however was in very poor condition with very loose (original) plaster. When I removed the skirting large chunks simply fell off! I decided to remove the rest of the plaster as I felt this would make achieving an even backing coat easier. Unfortunately my efforts with sand and cement haven't been great and I've struggled to overcome the uneven brickwork - some bricks stand out 10mm proud. I don't seem to be able to manage to get the plaster on thickly and evenly enough to provide an acceptable to surface for skimming. I'm now considering dot and dabbing plasterboard over the top of this half-done wall. I've read elsewhere that using a timber battens instead might be better for uneven walls, although I imagine this would be rather fiddly and not entirely sure why that would be better than dot and dab. I was wondering if you had an opinion on this and also if you could give some advice on plasterboarding window reveals - is it best to do them first?

Many thanks,
Will

Answer
Hi Will

If there is some suction present then it should be possible to easily apply a good thickness of plaster. The suction does want to be about right though - so do a suction test by applying a small patch of plaster to the wall to see how quickly it becomes firm. If it starts to firm up in a few minutes then the wall needs soaking with water, if the plaster remains unchanged in a few minutes then you're probably good to go.
Applying the backing coat
The trick is to apply a very thin tight 1st coat to the immediate area that you are going to plaster, this ensures a good bond is achieved by putting firm pressure on your trowel to squeeze a small amount the plaster firmly into the crevices and all areas of the wall. Only put this tight 1st coat on a small area just prior to putting the real thickness on as it does not want to become too dry but should stay moist and sticky. Then thicker amounts can be applied with your trowel.
Trowel Angle
The trowel angle is important - the flatter to the wall, the greater the thickness will be applied, but view your trowel as a tool to apply a good thickness of plaster and remember to view the straight edge as the tool that will give you the flatness. But the straight edge will only do it's job if you've applied the correct thickness of plaster.
Before you even think about flatness be sure that you have the correct thickness - always think thickness then flatness
Once you've run the straight edge over the wall you will see where the straight edge has and hasn't touched. Then you can apply more plaster to the untouched areas and run the straight edge over to take off the highs. Keep repeating this process until there are no more low spots.
It is surprising just how much plaster you may need to put on.

Dot & Dab

This is where I have to say I am not an expert on dot & dab, as I very rarely do it and would not therefore like to advise, but all I can say is that - if I have a rough wall, I find it much easier to dot and dab rather than using battens.

Paul