Old paint / new plaster removal

[Quiddy]

Hello - this is my first post and I'm looking for some (probably rather basic) advice about old paint and plaster!

I've been a bit of a lurker on here recently after buying an old house last year that has seen a lot of modern interventions over the years and is in need of some TLC. Seeing all the projects and discussion on these forums has given me the confidence to start some of my own work, but even after reading a some of the previous posts about this particular topic a few doubts remain, and so any guidance would be much appreciated!

1. Old paint removal - one bedroom was entirely covered in thick wallpaper which we've mostly removed to uncover several layers of old paint beneath - couple of pics below. It's directly on top of the original lime plaster which is generally sound but needs patching in places and i think eventually a new skim (but i'm guessing we can only do this once the paint has been removed). However I'm unsure the best way to go about removing the paint. I've tried just using a dry paint scraper which works ok for the orange stuff, but proven tricky for the yellow/green not to just sand off some of the lime in doing so. I've also used a home swab test to check for lead in the paint (seems to be negative) so main concern is avoiding too much damage to the plaster... any tips?




2. New plaster removal - our surveyor also noted in that room some possible damp issues around the chimney breast - suspecting that behind the wallpaper was some modern plaster which (alongside uncapped cowls) was causing moisture ingress/build up. That certainly seems to be the case as there's a big patch of very hard, smooth, grey material (the top half section in the pic below). I'm not entirely sure what it is - it's absolutely rock hard, but had thought gypsum was pinkish in colour not grey. But any advice on how best to remove while minimising damage to the brickwork beneath would be super helpful. If it's a careful hammer and chisel job then so be it...

 

[Cubist]

What's your plan for final finish of the walls once the plaster has been repaired where its necessary?

The hard material above the fireplace could very easily be a cement mortar. Paint a small area with a little vinegar to see if it fizzes - if it does its most likely a lime based render or plaster but thats doubtful to my my mind.

 

[Quiddy]

What's your plan for final finish of the walls once the plaster has been repaired where its necessary?

The hard material above the fireplace could very easily be a cement mortar. Paint a small area with a little vinegar to see if it fizzes - if it does its most likely a lime based render or plaster but thats doubtful to my my mind.

The plan is to repaint with something breathable (claypaint or similar).

Interestingly there was a very small bit of fizz when I tried the vinegar just now... but seems strange when it feels so hard and cement-like to the touch. It's definitely a different material to the rest of the plaster.

 

[Cubist]

The vinegar test is far from being absolute but it's a fair indicator, If it indeed lime based it could have been blended with almost any fine aggregate and pigments so colour is not much of a guide. Before tackling the paint it's best in my view to tackle the plaster repairs. First I would use a solution of PVA and water to paint all the walls. This will help to stabilise the plaster, and incidentally may help to loosen/remove some the paint. When dry, a a skim of a fine lime based plaster can be used to fill the bulk of the minor surface damage and polished back with a sponge to a smooth finish. Any rough edges or prominent ridges in any of the old paint that remains can be feathered back with a fine sand paper (by hand) so that when the new paint is finally applied those ridges and rough edges disappear. BTW - its a good tip from professional painters is to use your fingers to sense whether the feathering has been successful rather than relying on your eye.

 

[Quiddy]

That's really helpful thank you - wouldn't have thought of PVA and skim over the existing paint but would certainly make the job simpler. I'd read somewhere that to lime skim over older lime plaster i'd need to scratch it up first with a devil float to get a good key - assume that's not needed with the PVA?

I probably need to do a bit more investigation on the harder material and whether it's actually causing an issue or not in terms of damp. The ceiling plaster immediately above it at the wall join is certainly loose, but there's a chance the root cause is actually in the loft space which is yet to be thoroughly inspected...

 

[paulc]

First I would use a solution of PVA and water to paint all the walls. This will help to stabilise the plaster, and incidentally may help to loosen/remove some the paint. When dry, a a skim of a fine lime based plaster can be used to fill the bulk of the minor surface damage and polished back with a sponge to a smooth finish.

If you are putting PVA on the wall with the intention of skimming with lime, I'd bung some silver sand in to the mix first. The sand will provide something for the lime to key on to.
I've used Febond Blue Grit in the past with a 3-5mm thick lime skim over the top. Seems to be working quite well so far.

 

[Lacan07]

That's really helpful thank you - wouldn't have thought of PVA and skim over the existing paint but would certainly make the job simpler. I'd read somewhere that to lime skim over older lime plaster i'd need to scratch it up first with a devil float to get a good key - assume that's not needed with the PVA?

I probably need to do a bit more investigation on the harder material and whether it's actually causing an issue or not in terms of damp. The ceiling plaster immediately above it at the wall join is certainly loose, but there's a chance the root cause is actually in the loft space which is yet to be thoroughly inspected...

If you're going to lime skim that wall you'll need to scratch up the surface first with a devil float. There's no point using lime plaster if you're going to cover the surface in PVA / water, that's usually reserved for gypsum plaster. The PVA will seal the wall and it'll be unbreathable. Lime is more expensive than gypsum.

On the upper floors people sometimes compromise and skim gypsum internal walls, your wall is obviously external so its up to you, its not the end of the world as long as you satisfy yourself its dry and there are no issues. Looking at the photos I wonder if that harder (cement) plaster has been a repair on a leak. I would get into the loft and check that area. Damp chimneys can be tricky, especially if they've been repointed with the wrong mortar in which case the issue will be intermittent.

 

[Quiddy]

Cheers both - think i'm leaning towards a lime skim, partly to keep things breathable, but also because it'll be a good opportunity to practice - there being other areas of the house downstairs that will likely need something similar once the wallpaper is removed. But at the risk of starting an argument... is there not a consensus then on PVA being breathable/compatible with lime?

I'm a complete novice plastering wise, but have done a fair bit of research on the subject and using lime in particular, so keen to give it a go.

Looking at the photos I wonder if that harder (cement) plaster has been a repair on a leak. I would get into the loft and check that area. Damp chimneys can be tricky, especially if they've been repointed with the wrong mortar in which case the issue will be intermittent.

It does look that way, our surveyor noted some parts of the exterior brickwork had been repointed in cement, and also recommended we put ventilated caps on the cowls / open up the fireplaces to help the chimneys air out. Will brave the fibreglass this weekend and have a look.

 

[Cubist]

All I can add is that a PVA solution worked for me. At the time I was dealing with existing plaster that was very friable and without being stabilised first any new material I added simply pealed away bringing more of the old plaster with it. There are other stabilisers on the market but I have not tried them but know that some of the ones I looked at at the time, and much the same as PVA, also reduce breathability. What I couldn't find out though was whether the final level of breathability was significantly better/or worse than any of the other products.

 

[malcolm]

PVA isn't all that breathable which makes it good for stain blocking. Probably most of the other plaster preparation products aren't too breathable either.

For a lime skim it's useful for the wall to be absorbent so the lime has a chance to make a good bond. Scrape off the loose stuff and wet the wall until it gets to the point where it stays a little damp without drying out instantly before applying a lime skim. If the water doesn't soak in at all you have a waterproof surface which could be emulsion paint.

If you are plastering over any waterproof surfaces lime won't normally stick quite so well but there are some restoration lime plasters that will stick to anything and still breathe fairly well.

 

[Sam W]

For any walls where you won't need to reskim l I would recommend Peelaway for paint removal. They do 2 versions, Peelaway 7 and 1. Broadly speaking the 7 is for modern paints and the 1 for older paints. They do test pots so you can find out which one you neeed, and if you've got modern paint on top of old paint you may need to use the 7 first and then redo with 1.
After using the Peelaway and thoroughly cleaning off, most of our walls were sound enough to repaint with clay paint. There are a few areas which are hollow when you tap them, given the cost and effort of reskimming I've taken a risk and just painted over them, at present (12 months on) all seems fine.
If you are going to reskim with lime, might still be worth paint stripping as any non-breathable paint has obvious potential to negate the benefits of using lime.

 

[Lacan07]

Cheers both - think i'm leaning towards a lime skim, partly to keep things breathable, but also because it'll be a good opportunity to practice - there being other areas of the house downstairs that will likely need something similar once the wallpaper is removed. But at the risk of starting an argument... is there not a consensus then on PVA being breathable/compatible with lime?

I'm a complete novice plastering wise, but have done a fair bit of research on the subject and using lime in particular, so keen to give it a go.

Yes, there is a consensus. Let's not get confused here, watered down PVA is solely used by gypsum plasterers to get their muck to stick to the wall. As others have stated it can be useful to spot repair lath & plaster walls where the lime has separated from the lath, but lath & plaster walls are not usually in critical areas of the house. Make no mistake if you slobber your walls with PVA they will not be breathable.

If you want to keep that wall breathable you'll need to remove the paint first. Check for lead paint as this is considered breathable and the original surface may well be distemper which is also breathable and damned near impossible to remove!! Hacking off the paint may well leave your exposed lime surface rough enough to just skim straight over without the use of a devil float. As Malcom said the wall will need a good watering first. I would avoid NHL if I were you and go for a putty based ready mix, its much easier to use and will stay fresh in the bucket all day.

 

[larry]

I've said this on another post but I've had some luck DIY plastering with 'Breathaplasta' (smooth) and the "magic sponge trick". I used a big 40cm stainless trowel.
Have also tried a few other ready mixed brands and got on best with this one. A close second was "lime solo".

Didn't use a hawk but just a 10l old paint bucket and mixed fairly small quantities at a time.
Used galvanized beading from Screwfix.
Pleased with results. Though I dare say if a pro saw it they'd scoff...

Definitely don't use PVA, liquid cling film for your walls....

 

[Toby Newell]

PVA is very breathable. No one researches it, just assumes the recieved wisdom that anything resembling a plastic is obviously impervious to water.

This is incredibly facile. Oil finishes are plastic. There are hundreds of thousands of polymers both natural and man made with widely varying properties.

Plastic is technically not a material, rather it is a generic descriptor of a property that many polymers possess that has fallen into general usage, ie the ability for large volume deformation before failure. They are not all the same. Knowledge is a good thing, as is not trusting 99% of what you hear, including the reductive reasoning from your own brain. Your plastic shopping bag is not identical to a PVA bonding film. The former (LDPE) has a water absorbency of 0.01% over 24hrs, PVA? 40% over 8hrs, so that's 4,000 times as much, or 400,000%.

You could also try the power of thought.

Why is a weak PVA solution so fantastic at promoting bonding to water borne products?

Precisely because it is (partially) permeable! This is incredibly obvious and deductible with little thought.

IF PVA was highly impermeable then what would happen? Simple. The applied coating, be it a filler, finish, adhesive, plaster, render or other cement would not be able to bond to the substrate, akin to trying to coat onto a plastic bag.

So why use PVA? Obviously to REDUCE the permeability, slightly, to retard moisture uptake so that the water is not wicked by capillary action so fast that the interface layer effectively dries out and stops the applied medium from curing correctly. Cementatious compounds cure with moisture and / or reaction with the air, water based paints often have to stay wet (in the 'open' state) for a minimum period also becuase they too often need to dissolve parts of the air (normally oxygen compared to carbon dioxide for non hydraulic lime) to fully cure and this is most effectively achieved whilst solubised.

In some cases you can simply apply water directly to the substrate ( plaster) or add more water to the finish (paint) to make up for the wicking effect, whatever the case, if water based compounds dry out too quickly there will be a poorly cured intermediate layer that has poor adhesion, which is why non diluted paints direct to plaster often bubble and peel. It is irrelevant what form the dewetting process is, for example excessive heat or forced air movement will accelerate water evaporation and so also often lead to poor curing. Concrete plants in the middle east spend millions pre-cooling their aggregate with freezing water, adding dry ice to the mix and transporting it in refrigerated trucks to ensure it doesn't dry too quickly.

A secondary function is to reduce dust and micro friability that may reduce adhesion.

So, is PVA breathable? Yes, obviously, otherwise it would be a bond reducer, not bond promoter!

Does PVA reduce permeability? Yes, obviously, otherwise it would also not work!

You should also note that PVA bonder is extremely cheap, because it is so basic, if you were to use ten times more expensive D4 PVA (which has resins that cure to be waterproof) then obviously that would not work as well. All 'plastics' are not the same, all PVA's are not even the same!

"PVA is sensitive to moisture absorption and has high moisture permeability, which is a shortcoming of PVA film as a packaging material. On the other hand, for items that generate water vapor after packaging, it is an advantage that no mist will be condensed in the film. Therefore, it is often used for packaging of finely processed fabrics whose temperature has not yet been completely reduced after drying."

"The pure PVA films have the highest moisture absorption compared to blend and pure starch films. The value of moisture absorption of pure PVA film at 8 h is 41.97%. This is different from pure starch films which only have 36.50% in these conditions."

The fact is PVA is one of the most hygroscopic polymers whose permeability can be modified and controlled, this is why it is used as a bond promoter as it allows moisture through at a controlled rate. Using it therefore will necessarily reduce permeability, but that may be offset by the increase in adhesion. To say it is highly non breathable is simply incorrect.

However interesting as a science lesson, this is all somewhat moot as PVA may not be suitable for lime or various coatings for other reasons, one of them being precisely because it absorbs 40% water. Highly caustic lime could possibly cause accelerated breakdown of a thick PVA layer over time on a damp prone substrate (and thus cause adhesion problems) specifically because PVA is so hydrophilic. (Lime and other inorganic substances are generally only caustic ie acidic or alkaline when hydrated and the ions are thus dissociated)

The takeaway being that your plastic shopping bag is not identical to PVA bonding film. The latter having 400,000% increased water absorbency. PVA is certainly a lot more breathable than all the deductive reasoners assume. Permeability being film thickness dependent just use a more diluted / thinner coat.

To be safe, do not use PVA with lime for the reasons stated earlier, especially on known damp areas. For any other cement or coating you can always experiment, try an extra thin, extra diluted coat. Reducing micro friability ('chalkiness') will improve adhesion. It's possible a very light coat on a known dry area might not do much harm. Always follow manufacturers instructions, unless you know better, or enjoy experimenting.

On another note, removing old coatings is by far the best way to ensure adhesion. PVA is not magic, if there is any loss of adhesion of the old paint patches, PVA will not help. In fact, PVA being so permeable will absorb and retain moisture in damp environments that may then attack any remaining weakly bonded paint layers making them more likely to fail.

 

[Toby Newell]

For any walls where you won't need to reskim l I would recommend Peelaway for paint removal. They do 2 versions, Peelaway 7 and 1. Broadly speaking the 7 is for modern paints and the 1 for older paints. They do test pots so you can find out which one you neeed, and if you've got modern paint on top of old paint you may need to use the 7 first and then redo with 1.
After using the Peelaway and thoroughly cleaning off, most of our walls were sound enough to repaint with clay paint. There are a few areas which are hollow when you tap them, given the cost and effort of reskimming I've taken a risk and just painted over them, at present (12 months on) all seems fine.
If you are going to reskim with lime, might still be worth paint stripping as any non-breathable paint has obvious potential to negate the benefits of using lime.

Peelaway 1 is a thixotropic alkaline stripper, NaOH and CaOH, basically oven cleaner mixed with starch wallpaper paste, you can make your own for pennies.

Peelaway 7 is a less effective Benzl alcohol solvent stripper meant to replace DCM. It is less toxic but works much slower, probably a better idea on large walls whereas DCM would still be better on wood work.

 

[Toby Newell]

Hello - this is my first post and I'm looking for some (probably rather basic) advice about old paint and plaster!

I've been a bit of a lurker on here recently after buying an old house last year that has seen a lot of modern interventions over the years and is in need of some TLC. Seeing all the projects and discussion on these forums has given me the confidence to start some of my own work, but even after reading a some of the previous posts about this particular topic a few doubts remain, and so any guidance would be much appreciated!

1. Old paint removal - one bedroom was entirely covered in thick wallpaper which we've mostly removed to uncover several layers of old paint beneath - couple of pics below. It's directly on top of the original lime plaster which is generally sound but needs patching in places and i think eventually a new skim (but i'm guessing we can only do this once the paint has been removed). However I'm unsure the best way to go about removing the paint. I've tried just using a dry paint scraper which works ok for the orange stuff, but proven tricky for the yellow/green not to just sand off some of the lime in doing so. I've also used a home swab test to check for lead in the paint (seems to be negative) so main concern is avoiding too much damage to the plaster... any tips?

View attachment 10983
View attachment 10984

2. New plaster removal - our surveyor also noted in that room some possible damp issues around the chimney breast - suspecting that behind the wallpaper was some modern plaster which (alongside uncapped cowls) was causing moisture ingress/build up. That certainly seems to be the case as there's a big patch of very hard, smooth, grey material (the top half section in the pic below). I'm not entirely sure what it is - it's absolutely rock hard, but had thought gypsum was pinkish in colour not grey. But any advice on how best to remove while minimising damage to the brickwork beneath would be super helpful. If it's a careful hammer and chisel job then so be it...

View attachment 10985

View attachment 10986

Removing as much paint as possible is the key. No pun intended. Pretty sure some of the paint contains lead. The lowest beige paint layers will be aged oil based lead paint primer with added natural resins, these are a pig to strip and often turn to toffee with heat / solvent stripper. Most times they are very brittle by now so scrape nicely but normally much more difficult than subsequent layers.

It's a shame you have to refinish really, the breast has a lovely Klimt / Monet effect going on.

 

[malcolm]

This is incredibly facile.... You could also try the power of thought.

I'm not so sure we are all idiots on here as so often accused by @Toby Newell But it's true we ought to have thoughts so I'll present mine.

Firstly to the opening poster nothing on that wall looks like it needs any PVA. Don't use it. Scrape off as much muck as you dare to get back to something breathable. That wall is why I insist on lining paper on new lime plaster. Someone is going to paint it in something stupid and it's impossible to remove stupid paint from soft lime plaster. They can paint what they like on lining paper and that can be removed and replaced without damaging the lime plaster. Zinsser DIF might be worth a try. It's for wallpaper but also works on paint a bit with the help of a good paint scraper like the Bacho 665.

PVA is great. I used to rent an old 1911 farmhouse. You could plaster PVA on the walls before painting and it would hold the damaged plaster snd paint together a bit and stop the stains getting through when redecorating. There was an underlying problem but it wasn't my problem because I was renting. Stopping the stains is not something that breathable coatings tend to do. In my mind PVA is not all that breathable and should be avoided where possible.

 

[Zebra]

Have you tried a heat gun for removing the paint? I'm not sure that it would work, but might be worth a try?

 

[Toby Newell]

I'm not so sure we are all idiots on here as so often accused by @Toby Newell But it's true we ought to have thoughts so I'll present mine.

Firstly to the opening poster nothing on that wall looks like it needs any PVA. Don't use it. Scrape off as much muck as you dare to get back to something breathable. That wall is why I insist on lining paper on new lime plaster. Someone is going to paint it in something stupid and it's impossible to remove stupid paint from soft lime plaster. They can paint what they like on lining paper and that can be removed and replaced without damaging the lime plaster. Zinsser DIF might be worth a try. It's for wallpaper but also works on paint a bit with the help of a good paint scraper like the Bacho 665.

PVA is great. I used to rent an old 1911 farmhouse. You could plaster PVA on the walls before painting and it would hold the damaged plaster snd paint together a bit and stop the stains getting through when redecorating. There was an underlying problem but it wasn't my problem because I was renting. Stopping the stains is not something that breathable coatings tend to do. In my mind PVA is not all that breathable and should be avoided where possible.

Grow up.

If that were the case I would be accusing the entire human race of being idiots.

It's rather pointing out that we are all susceptible to received wisdom and reductive reasoning. For example, anything plastic is bad. This is an important and helpful thing to remember. Like oil finishes are natural and hardwearing or that your plastic is actually recycled.

PVA is quite breathable for people worring about such things, so perhaps they can worry less.

As I also said, the perfect amount of PVA is no PVA. From working on site I suspect it is overused as a shortcut.

Spending more time on preperation including stripping as clean as possible will always give the best result.

As you correctly pointed out PVA stabilisation is one of its greatest strengths.

I just thought it was a little ironic that the main reason for not using PVA is that it is too breathable and absorbs too much water.

You are however wrong though. It is breathable, I have quoted the science. Your opinion does not affect the facts. You are free to think what you want.

Do you have scientific evidence of why all stain blockers are non breathable? No, because you don't know, you are making an uneducated guess, maybe I should qualify, an unresearched guess.

Because it seems like more reductive logic. It is possible you appear to be assuming a stain blocker precludes the passage of water. I have no idea why that is relevant.

Stains are not made of water. Rather they are made of much larger molecules, usually nicotine and metal sulphates and carbonates for example. A substance that is hygroscopic and lets water pass might not let these larger molecules pass.

Thus it is perfectly feasible for a substance such as PVA to block the solutes that cause staining and yet allow water vapour to pass. I have not heard of using PVA as a stain blocker, so I don't know how good it is.

The only stain blocker I know that I have used is Zinsser shellac.

Shellac is breathable, like D1 and D2 PVA and yet the best stain blocker.

I try to be helpful on here by writing facts, as far as I can best make them out.

Carry on.

 

[Toby Newell]

Every day is a school day. For everyone. Forever. Even for AGI when that comes along.

The fact I have studied finishes for nearly four decades and went to university where one of my courses was titled 'Polymer science' means zippo in the final analysis.

Yes, it means I have a good basic understanding both from the practical and molecular level, but I still need to study.

In fact I probably need to study more than most because I find concepts very difficult to accept unless I can visualise them.

I never accused anyone of being an idiot.

You are free to think whatever you want but the facts are out there if you look hard enough.