Painting

[Stigmorgan]

So it's now the summer holidays and one of the jobs on my list is to repaint several of the classrooms, normally not a problem but one of the rooms has an external wall and most of the paint was flaki g so I've scraped it off and now have exposed plaster, there are several cracks in the plaster and in some places the plaster feels like it's floating rather than being stuck to the blockwork beneath, should I seal it with some PVA before painting? I have some white emulsion to use as an undercoat before the colour goes on. Or will the main course be fine straight onto the plaster? I'm going to be using Dulux tough and washable.

 

[Spectric]

Dulux, I avoid at all cost and it survives in the market where people know no better, there are better paints out there that give a better finish and with less effort. For many task Johnstones is great and they can color match F&B or LG.

https://www.johnstonestrade.com/product/covaplus-vinyl-matt
and for those tough jobs Benjamin Moore

https://www.thepaintshed.com/benjam...MI1vHb2uafgAMVhIrtCh2wVwjnEAQYASABEgLlpvD_BwE
If you want to seal the wall then use something like Coo Var

https://paintwell.co.uk/coo-var-ant...MIkKOiz-efgAMV0NbtCh2MnQ-lEAMYASAAEgLlr_D_BwE

 

[joncooper27]

What sort of wall is it? Is a solid wall or cavity wall, stone brick or block?
There could some sort of damp issue there? You may be better with a breathable paint?

 

[Stigmorgan]

Dulux, I avoid at all cost and it survives in the market where people know no better, there are better paints out there that give a better finish and with less effort. For many task Johnstones is great and they can color match F&B or LG.

https://www.johnstonestrade.com/product/covaplus-vinyl-matt
and for those tough jobs Benjamin Moore

https://www.thepaintshed.com/benjam...MI1vHb2uafgAMVhIrtCh2wVwjnEAQYASABEgLlpvD_BwE
If you want to seal the wall then use something like Coo Var

https://paintwell.co.uk/coo-var-ant...MIkKOiz-efgAMV0NbtCh2MnQ-lEAMYASAAEgLlr_D_BwE

The paint has already been purchased and accounts are closed now until September so I have to make do with what I've got and that's white emulsion for an undercoat where needed, I can use PVA glue from the stores and water down a little to help the paint bond just wondered if anyone here with experience decorating would know if it's worth doing, it's only that 1 wall because the existing paint is practically falling off, I suspect it's something to do with being an external wall and probably poorly insulated.
I've use dulux everywhere for the 6 years I've been here and have no complaints so far

 

[Stigmorgan]

What sort of wall is it? Is a solid wall or cavity wall, stone brick or block?
There could some sort of damp issue there? You may be better with a breathable paint?

Brick/block cavity wall, I don't think it's damp. The bosses won't go to the cost of getting things done properly so I have to do what I can with what I've got, as I've said I have white emulsion to undercoat, just not sure if it's worth putting on a coat of pva to seal the cracks or if the emulsion will do that.
All other walls are fine and just need a clean before applying the new paint, which is good considering I have 6 classrooms in total to do as well as the list of jobs longer than my arm

 

[Spectric]

If our schools are looking to get jobs like decorating done on the cheap then why have they not just given the kids a brush.

 

[Bingy man]

Several watered down coats prior to a coat or 2 of full strength emulsion work well on bare/ new plaster . Don’t try to do all the coats in 1 day eg at least 5-6 hours between coats . I’ve not used pva prior to painting but I’ve used a stabiliser to seal off any friable surfaces . A friend of mine chose not to take this advice and 6 months later the paint began to peal and within a short time he was back to the new plaster . I’m not saying there isn’t a better way but this has worked for me over the years ..

 

[Stigmorgan]

If our schools are looking to get jobs like decorating done on the cheap then why have they not just given the kids a brush.

General redecorating is part of the cartakers/site manager job, I've no issue doing it and have done most of the school with no issues over the 5 years I've been here, normally it's a simple task but this wall in particular seems to have an issue that has caused the paint not to adhere to the plaster very well, I just wondered if pva would help seal the cracks that have formed and help the paint stick or if that would be a waste of time and just use the white emulsion straight onto the plaster then the colour coat on top.
At the same time I have fought tooth and nail to avoid always going for cheapest option where it matters.

 

[accipiter]

If our schools are looking to get jobs like decorating done on the cheap then why have they not just given the kids a brush.

My wife is one of the cleaners at a local school. Part of her area is the "cookery" room and "needle work" room. I've no problems if imagining the catastrophic outcome of letting the kids free with decorating paint and brushes after the descriptions of the state the rooms are left in which my wife cleans. Imagine pastry, jam, pasta, egg, flour, sugar on the worktops and cookers plus loose threads, needles, pins on the carpets... Neither the kids nor the teachers clean away before classes end.

 

[accipiter]

@Stigmorgan emulsion won't stop the cracks from reappearing. It will cover them for a short time but youd be better off using a fine filler such as "Diall interior ready-mixed smoother" from B&Q or a flexible decorators caulk rubbed into the cracks. Both will sink back slightly into the cracks when dried. Paintable 24 hours after applying. I doubt trying to use/add plastic would seal the cracks.

 

[Stigmorgan]

@Stigmorgan emulsion won't stop the cracks from reappearing. It will cover them for a short time but youd be better off using a fine filler such as "Diall interior ready-mixed smoother" from B&Q or a flexible decorators caulk rubbed into the cracks. Both will sink back slightly into the cracks when dried. Paintable 24 hours after applying. I doubt trying to use/add plastic would seal the cracks.

Thats why I thought maybe using a pva coat first would help close them up before painting. I have a fine filler for the endless pin and staple holes that need filling before anything else.

 

[accipiter]

@Stigmorgan Sadly I know from my experience of trying to close up/cover up cracks, especially in the ceilings, when redecorating the old house I've been in since December 1986. House built 1796. Used to use the well known make Polyfilla but it would still crack over time as the old house moves. Haven't decorated for a few years but doing so now so using the flexible caulk to see if it's any better. Try the fine filler you have. Probably be okay for a while.

 

[Bingy man]

Thats why I thought maybe using a pva coat first would help close them up before painting. I have a fine filler for the endless pin and staple holes that need filling before anything else.

Before painting the new plaster you will require a sealer to prime the surface a lot like adding wax to a new piece of oak furniture for example. Contractors often worryingly think PVA will work as a sealer. Do not use PVA. PVA is the mortal enemy of paint …I’m thinking the cause of the paint flaking is the common sense approach- is it damp , excessive heat or other environmental issues. Your post mentions that the plaster sounds like it’s no longer adhered to the wall ( blown ) if tapped lightly does it sound hollow. If yes then ( I’m not a builder) it could be movement of some type from the building or footings ( any visible cracks inside or outside) if it’s damp I’d expect the signs to be there - mould, effervescence damp smell etc . So ruling out pva a suitable primer is probably required bearing in mind the above .

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Something like these - you also mentioned that the paint has been purchased and your superiors don’t consider or budget for doing the job properly and there in is your 1st problem- if they won’t support the additional cost of a suitable primer/ stabiliser then keep it simple and go with the watered down coats and then final coats of undiluted . Edit. After all you can only do your best with the materials you have at your disposal. Just explain that it won’t be successful due to the existing surface issues sand your covered.

 

[trvlr]

if paint flakes... either inadequate undercoat etc. preparation; and/or damp (water penetration in some way or other)

If plaster feels it's "floating" then it's lost it key - again due to moisture ingress (weather penetration). Any signs of rain water constantly running down the outside of the wall(s) affected and not actually free to dry out in the sun etc. (as per other walls do), or rising damp? To check for those you need a damp meter.

Simply sealing the surfaces with a "water sealant" is no proper solution to the problem(s); it (they) will simply reappear in the near future.

 

[Henniep]

Where PVA is flaking, scrape off all loose paint and paint entire walk with a solvent based bonding liquid, then apply new PVA (Arylic PVA would have been ideal)

 

[Henniep]

Edit.....entire wall with solvent based ....

 

[stuckinthemud]

I have always sealed plaster with mist coats of watered down emulsion but can you explain why PVA is the mortal enemy of paint? This is pertinent as tomorrow I am rubbing down and repainting the inside of an exterior wall subject to damp where rain runs down the wall, and had intended to base coat with PVA….

 

[Bingy man]

How and When To Paint New Plaster - Promain Resource Centre
Re not using pva to seal walls prior to painting.

Edit
The reason paint often peels when PVA is used to seal a wall is that the paint sits on the film of the PVA instead of the wall. This impacts the ability for the paint to remain adhered to the surface, unlike a mist coat that will absorb into the plaster.