How to prepare a concrete wall for plastering?

Question

The last the last time I painted my daughter's room, the paint started peeling off in strips, and it seems that the render had never been sealed.

This time around, we've had to strip the paint back to the plaster , and it's come off relatively cleanly on all of the other walls, except for this wall, which is the one that faces the external part of the house

Because we've chipped the plaster and/or render and there are some bits of exposed concrete, I now need to apply (I think) a skim coat / topping coat of plaster.

Questions:

* I have some Bondcrete all ready, should I do a seal coat and bond coat before applying the skim coat or can I just apply the skim coat?
* How fastidious do I need to be about the removal of the paint? You'll see in the photo underneath the window there are some patches where there are still some remains of paint left on the wall. Can I just do the skim coat and (if needed)  bondcrete over that, or do I need to be really diligent and about removing every last bit of paint before I do the next step?

I probably know the answers, but hoping their might be a life hack or top tip as this simple repaint job is killing me!

Thanks in advance

MitchellMc · Answer

Hi @melaniegoesmia,

The Dulux Sealer Binder is to seal the porous repair compound prior to painting. It allows the paint to bind properly otherwise it will flake off. There is no need to seal the current surface prior to patching. For this step, the key is to remove any deteriorated material to allow your patching the best chance to adhere.

Mitchell

melaniegoesmia · Answer

Thanks Eric, and  just to be sure, the Dulux sealer binder should be applied once the wall has been repaired? And there's no need to also do it before?

I feel really confident now - thanks for all your hard work.. it really makes a difference!

EricL · Answer

Hello @melaniegoesmia

As suggested by Jacob in his last post, it would be better if you did not use the Bondcrete. The plaster/lime mix will be sufficient to cover your wall. I don't recommend applying a Bondcrete sealer over the plaster/lime render. Instead, I suggest using

https://www.bunnings.com.au/dulux-1l-precision-white-sealer-binder_p1400879

to bind the surface of the plastered wall. Please remember to lightly sand the primed surface if you are going to use a water-based topcoat.

Before we go any further, one of the reasons paint peels off is because of hydrostatic pressure. When heavy moisture gathers behind the wall and comes through the masonry or brick surface and pushes the paint off the wall. Another reason is poor preparation, if the wall was not properly sanded and primed and paint was directly applied over it, the topcoat will not adhere properly to the wall and will eventually peel off. If your wall exhibits heavy condensation on its surface, it's possible that moisture is coming through and it must be addressed before you plaster or paint the wall.

Yes, you can use the plaster/lime mix as a filler to repair your other walls. In regard to the ratio mix the Gyprock Data Sheet advises:

Please remember to wear personal protection such as gloves, goggles and a mask.

If you need further assistance, please let us know.

Eric