Why is the paint completely peeling off the plaster?

[SensibleHill]

 

Hello! Another post from my whole-house renovation! While removing an old built in robe, some paint peeled and I found I could peel all paint from the entire room, leaving only plaster.

I’m assuming this might be due to the walls never having been primed or possibly a latex or similar paint in the 80s (it feels rubbery). This paint only appears to be like this in the bedroom. Is there any other cause, and is it something to be worried about - or can I rejoice in having a nice plaster base to work from?! 

many thanks,

k 

[MitchellMc]

It's likely due to not being appropriately prepped with a suitable primer, @SensibleHill. If the plaster is nice and smooth, you'll be good to go with Dulux PRECISION Sealer Binder White. It's an oil-based product specifically designed for sealing bare plaster. Standard water-based primers can delaminate like this due to the powdery surface and are better suited to paper-backed plaster.

Although the sealer is oil-based, it's suitable for all Dulux topcoats, so you'll be fine going over it with standard water-based Dulux Wash and Wear.

Since you appear to be on a roll, I recommend removing the remaining paint in the room and sorting out all the walls. That way, you don't have to worry about the other walls or remove their paint in the future.

Please let me know if you have any questions.

Mitchell

[SensibleHill]

Thanks so much @MitchellMc - that’s what I suspected but I couldn’t find a clear answer online for a brick, rendered and plastered wall context. I’ll get that oil based primer onto the walls, pronto! 

There’s one spot that is softer than the rest - it feels damp, and doesn’t have the same kind of coating. Backs onto the shower where there’s been water damage. I’m assuming the plaster hasn’t been sealed - or, water damage might have brendan repaired and that wasn’t sealed. Should I do anything to that area first before priming? 

Thanks for all of your help! 

[MitchellMc]

Damp plaster would indicate there's an active water leak @SensibleHill. If this leak were some time ago, one would assume that the plaster should have had adequate time to dry out.

There's not much you can do from the room side to solve moisture in the wall without addressing the moisture source. You could attempt to dry it out with a room heater and then wait to see if the dampness returns. However, you really need to track down where the moisture is coming from. Now, depending on how far along you are with the bathroom remodel, this might involve some exploratory work on the other side of the wall. Ultimately you'll need to access the wall cavity to determine what's going on. If you're still planning on relocating the shower, I'd suggest doing that work on the bathroom side, but if not, you can cut into the wall on the room side. It will likely either be leaking pipework or a failed waterproofing membrane.

If it were me, I'd dry the area and paint it just to complete the room. Next, I'd remove tiles in the bathroom, cut the wall open, search for an active leak, and resolve it. Or, wait until you begin remodelling and get the plumber to check for the leak source whilst they're capping off the old water pipes to the shower. Worst case, the water returns to the wall and blows the paint off in that area, and you'll need to re-paint again. If you weren't moving the shower, I'd say open the wall in the room; otherwise, you'll destroy the shower's waterproofing membrane in the exploratory process.

Mitchell

[SensibleHill]

Thank you! We are getting the plumbers in within the next few weeks, so will flag this with them. 

[LivMitch]

Hi Mitchell,

I've had a similar problem. I put undercoat on plastered patches covering fine cracks in my walls (1960s flat).  The undercoat paint began peeling as I painted. I had to wash the paint off the walls - about 15 buckets of water for 3 small areas! 

1 Do  I need oil-based Dulux Precision Surface Prep Sealer Binder?  Or can you recommend a water-based product ?   

2 How long should I wait for the washed plaster to dry before applying the Sealing product ?  

3 There's still fine smears of paint on the plaster, will that be ok? I had to stop washing as the plaster was coming off.

4 Does it matter if I apply a paint brush to apply it, then roller for the undercoat and top coats?

5 How long do I wait for Sealer to dry before applying Dulux Ultra Air Interior Primer?  1 or 2 coats of Interior Primer?

Thanks for your further help Mitchell.

Liv 

[MitchellMc]

Welcome to the Bunnings Workshop community @LivMitch. It's sensational to have you join us, and many thanks for your question about painting plaster.

Do you have a bare plaster (no paper coating) wall? When you say the undercoat peeled off, was this an old undercoat over the bare plaster or a new one you'd just painted? I see you've removed the paint, but have you removed all the undercoat that was peeling?

1) Typically with minor repairs, you'd just use a water-based undercoat like Dulux 1Step Prep Primer, Sealer & Undercoat 1L. If it was a whole wall like in @SensibleHill's situation, it's best to use a sealer/binder. After a couple of coats of undercoat, you'll be fine to apply your topcoat wall paint.

2) It sounds like you've fully saturated the plaster so I'd recommend giving it the best part of a week to dry out. You could run a heater in the room periodically to speed up the process. Make sure it doesn't get too warm though as you'll risk cracking the plaster. Keep it under 30 degrees celsius.

3) Fine smears of paint on the plaster should be fine and is certainly better than washing away the actual plaster.

4) The sealer binder can be applied with a brush or roller, and then you can apply your topcoat with either as well. However, I'd suggest using a roller for both as it will eliminate brush strokes. 

Dulux PRECISION Sealer Binder White can be top-coated in 24 hours, also depending on weather conditions. If it's cold or humid, it's best to wait 48 hours. To clarify, you only need two products, the Dulux PRECISION Sealer Binder White and your wall paint topcoat. There is no additional undercoat required, the sealer binder is your undercoat. If you are using the Dulux Ultra Air Interior Primer over the sealer binder for its Low Voc qualities, the same 24-hour rule applies.

Please let me know if you have any questions.

Mitchell

[LivMitch]

Hi Mitchell

Thanks for your quick reply!   The photos are SensibleHill's walls, not mine   

My walls have been previously painted 17 years ago (and before that, it's a 1960s block of flats). Sorry but I don't know what you mean by a bare plaster (no paper coating) wall... 

The plasterer applied plaster to long, fine cracks in these walls – patches are approx 1m square  each. 

I sugar soaped the walls.  

I applied an undercoat paint to the 3-weeks dry plaster patched areas (undercoat paint was 17 yrs old but recently used with no issues on window frames).

As I applied the undercoat paint, it was not sticking to the wall properly, peeling off as I painted (using a roller).

So I washed off as much undercoat as I could (water and a Chux super wipe).

Now I will:

* exchange the oil-based Dulux Precision for the Dulux 1 Step, Prep Primer

* apply 2 coats of this

* 1 top coat of Dulux Ultra Air Interior Low Sheen Walls

Thank you! So grateful for your expertise and quick help. 

Liv Mitchell  

[MitchellMc]

Hi @LivMitch,

I apologise, as I might have assumed more similarities with @SensibleHill's project than there were. Their paint and undercoat completely delaminated from the bare plaster. It's an older style of plaster that doesn't have a paper coating like newer plasterboards. 

If the undercoat you're using wouldn't stick to the cleaned wall then it sounds like some type of incompatibility. The wall's not painted in gloss paint, is it? I'd suggest doing a test section with the Dulux 1 Step. Apply it to a small area and wait for it to dry completely. Place Painter's Tape over it and wait five minutes. Tear the tape back off and see if it removes any of the undercoat. If it removes the undercoat, then you might have to look at sanding the wall for better adhesion.

Mitchell

[LivMitch]

Hi Mitchell

My bad, it's me not understanding apples vs oranges re Sensible Hill. The undercoat I used wouldn't stick to the plaster. It was a normal undercoat not a 'primer' or 'sealer' or 'binder'. It was also 17 years old (perhaps the age of the undercoat was the issue)

I will do a test patch of Dulux 1 Step 1 as you suggest and masking tape.

My concern is that the Dulux 1 Step product says it is for use on:

"Apply it confidently to most surfaces including brick, masonry, paper-faced plasterboard, timber, MDF, render, concrete, cement sheet, galvanised iron, Zincalume steel, PVC and previously painted surfaces."

1. Does new plaster, on top of a previously painted wall, fall into any of those categories?

Doesn't sound like it. That's why I brought Dulux Precision which says:

" For porous surfaces including plaster, cement sheet ...."

2.   Is Dulux 1 Step definitely what I need? 

Thanks Mitchell.