Painting solid plaster & Rising Damp

[rscho]

Are water-based sealers/undercoats suitable for solid plaster walls?

We've had some problems with rising damp (hopefully fixed now) and the guy told us to use water-based paints & undercoats as they would allow any water vapour from the walls to pass pass through the paint and avoid it building up.

However the water-based products don't specifically mention they are suitable for plaster, only plasterboard.

So now we're looking at Dulux Prepcoat sealer-binder which is oil based. Does anyone have any advice?

[johnc]

I would not use an oil base undercoat in that situation as it will lift if you do have a moisture issue. Just use a waterbased sealer and top coat, it is no guarantee but will reduce the risk of paint failure in that application. It is correct that there is a limited amount of moisture that can pass through waterbased paints. The plasterboard type sealer will be fine.

John

[Tools]

Plasterboard sealer is not suitable for new solid plaster .You must use the oil based sealer, or you paint will eventually peel off in sheets.

Tools

[johnc]

Plasterboard sealer is not suitable for new solid plaster .You must use the oil based sealer, or you paint will eventually peel off in sheets.

Tools

Not so, have a look on the Dulux site if you are using a waterbased top coat such as Dulux 101 the recommended base coat is Acrylic Primer Sealer Undercoat which does work. The oil base is not suitable when the moisture is coming from behind as in the above. For sealing something such as cement sheet in a bathroom I would prefer use oilbase there to prevent moisture getting through to the sheet as the moisture is coming from the opposite direction.

John.

[Tools]

I can find nothing that says it is ok to use acrylic sealer, just sealer / binder which is oil based. What product are you advocating is suitable?

Tools

[Tools]

Maybe I have misunderstood here.I assumed that you have had the rising damp fixed, and have replaced some of the plaster at low level. Is this correct?

Tools

[rscho]

That's right,

Some of the plaster near the floor was in poor condition and we re-plastered. Over the years the original owners tried a few different coatings but most didn't seem to last. When we bought the place we fixed the source of the damp so hopefully it doesn't return.

Only the sealer/binder which is oil based specifically mentions it is suitable for plaster as opposed to paper covered plaster.

[glenn k]

i had rising damp in a solid wall put in a damp course to stop it but the wall was still wet. put a blow heater on for a few days and painted and got water stains. So i painted with bondcrete (PVA) then painted over the top. The water stains moved up above the PVA so i painted much higher with the pva problem solved as I was selling the house and didn't have time to wait.

[johnc]

This is the sealer Dulux refers to on its site,
"Dulux Professional<SUP>&#174;</SUP> Acrylic Sealer Undercoat (Interior)

High opacity, excellent adhesion, excellent sealing. Easy to use and clean up, ideal for interior masonry, plaster, paper faced wall boards and suitably primed timber and metals. APAS approved. "

I'd be doing a bit of homework on this one, the board has produced two different opinions, and I would not consider either correct if it was my wall.

Cheers, John.

[rscho]

Johnc, I took your advice and did some homework. I called the dulux product info line and their advice was that if the wall (or significant parts of it) has been sanded back to solid plaster then it should be re-sealed with an oil based sealer-binder, followed by either acrylic or oil based under coats and top coats. They said if I used the plasterboard products I'd have to use multiple layers to get a consistent finish as the exposed plaster sections of the wall would suck up all the water from the first few coats while parts of the wall that were still sealed would take up very little.

I mentioned about possible future rising damp and the the advice was that the source of the problem should be addressed. Furthermore if the wall was not sealed then any rising damp may eventually show through as a water stain.

As we couldn't find an acrylic sealer from any manufacturer that was recommended for solid or set plaster (as opposed to plasterboard) we decided to go with an oil based sealer binder followed by acrylic undercoat and top coat. The sealer-binder (Dulux) spec sheet stated that it is suitable for use under either acrylic or oil top coats.

Thanks everyone for your advice