How can I fix these issues with damaged plaster?

NibblyPig

I'm selling my house at the moment and I need to paint a lot of bright walls white again. In the process, I want to try to repair various problems with the plaster.
I've done some googling and watched some videos but I see a loooooot of different information, namely, arguments over types of plaster to use, if you should use stain block, damp block, diluted PVA (?) that kind of thing.

I've never done anything with plaster before other than polyfilla on cracks and stuff. Below is an album of some photos of issues I've taken.
I intend to pop to wilko or screwfix to grab the various bits I might need to fix it. I wish I could find some way to learn about these things in person like on a course or something.

My plan was basically to sand the problem areas a bit (I'm not sure sanding will remove the paint though, or if I even need to remove it), then slap some pre-made plaster stuff on from wilkos, try to sort of skim it flat, then wait for it to cure a bit I think ? then skim it a bit more then when it's done just prime it with diluted paint and then finally paint it. Does that sound right? The yellow wall and the white problems around the window were from penetrating damp (now fixed by weathershielding the front of the house) and I read some stuff about using stain block or damp block on first (not sure if before or after plaster?).

Some articles said that you shouldn't use pre-mix plaster when patching up areas caused by damp because you want a different type (although I could only see like 20kg bags from B&Q of the different type I forget its name now and I suppose I just need a handful), so not sure about that.

I'm basically lost at sea and I wonder if anyone could offer some advice!

Photos: https://imgur.com/a/njrh4wO

grumbler

I don't like polyfilla.

IMO for small corrections decorators caulk is much better, although it shrinks a little when dries that may require second sanding and application.

Yes, old paint is better to be sanded first and IMO wetting with PVA won't hurt.

NibblyPig

I thought you couldn't sand caulk, it's just rubber isn't it?

JIL

We used some ready mixed plaster inside a cupboard that used to house the boiler and we had lots of holes to fill. It wasnt difficult to use and it sanded down really well. 
Bought it from screwfix. 

grumbler

NibblyPig said:

I thought you couldn't sand caulk, it's just rubber isn't it?

You can gently - with fine or medium sandpaper and usually it's fine without sanding. Yes, it's a little rubbery, but not silicone.

NibblyPig

Does what I put sound right? I'm really worried about doing this wrong

Jeepers_Creepers

Hi Nibbly.

You've pretty much got it right :-)

You'll need -
a sanding block (so you can sand filled areas completely flat),
80 grit (coarse) sandpaper to quickly flatten raised bits on your wall prior to filling and to 'key' surfaces before filling),
120 grit paper (medium) to smooth out filled bits and prepare surfaces for painting,
a filling knife ideally wide enough to span the parts to be filled so the surrounding wall surfaces act as the depth guide, and
filler.

The idea is to first go over the rough areas with the coarse grade paper on a block, going as light or firm as needed - until you remove any 'high' spots such as that previously (badly...) filled patch in your second photo. This will also 'key' the surfaces ready for fresh paint. If the sandpaper leaves lots of visible score marks, it's either too coarse or you are pressing too hard; this might well show through your new paint, so ease off or switch to the 120 grit. 

Once the high bits have been flattened down, you then need to fill the dents and hollow bits up. I've read good things about Toupret ( https://www.screwfix.com/p/toupret-powdered-interior-filler-2kg/4911h ) and I personally prefer powdered fillers like these that you mix up to requirement as these actually 'set' chemically, and don't just 'dry out'. Mix small amounts at a time. For shallow holes especially, make sure the surface you are filling has been keyed with the 80 grit for a good grip. Try and add as little filler as needed to fill the holes - hold the filling knife at a low angle as you finally pull it over, so that all excess filler is removed - you don't want to spend too much time sanding back a too-high fill...

Two basic approaches here - one is to firmly level off using the surrounding walls as your guide. This will mean less sanding afterwards, but will also likely mean a second - even thinner - wipe-over with a further layer of filler will be required to get it truly flush afterwards. The other is to apply it in a thicker - higher - layer than actually required (tho' trying not go excessively high...), and then be prepared for a bit more sanding afterwards, but hopefully only once. I prefer the first way - I hate sanding :-)  

You don't have any deep holes from what I can see, but that would be a similar process - fill it up to virtually level, allow to set and then apply a thinner levelling-off layer afterwards. 

Allow filler to FULLY dry before sanding or else it'll clog your paper.

Do NOT coat your walls with PVA! Any of this stuff which remains will 'reactivate' when you apply paint and risks making a mess of the job. It usually isn't needed - just 'key' the surfaces and you should be fine. If you do use PVA, then make sure it's all below filler level.

The trickiest 'fills' are the really shallow ones like where paint has flaked off - you will struggle to fill a layer as thin as a coat of old paint... You might manage it with 'fine surface filler' but again you need to have fully keyed the surface first or it won't grip well. You might find that you are better off just sanding around these areas to reduce the surrounding paint level to the lower one, and 'feathering' it in. Start with coarse paper to speed things up, but use your judgement as you sand. 

For the damaged window reveals (second last pic), trim off all loose paper using a craft knife, and then apply a thin layer of filler by working from the edges backwards - this'll leave a sharp extra edge of filler along these edges which can then be sanded down gently down to match the original edge profile.

I also wouldn't use 'decorator's caulk' for the reason given earlier - difficult to sand - but perhaps there are better ones available these days? If so, it might be a good bet for filling really thin parts like the missing paint flakes.

Finally, there are sandpapers and there are sandpapers, and the best aren't even sand. I think you'll have good results with ali oxide - https://www.screwfix.com/p/oakey-liberty-green-sanding-roll-unpunched-5m-x-115mm-120-grit/56823

If you have a lot of 'flattening' to do, then a 'block' with a handle might well make sense - https://www.screwfix.com/p/aluminium-hand-sander-240-x-84mm/12688

Finally, what paints are these - the first green and the others? If they are 'silk', then a light keying with 120 grit might be essential before repainting. This time stick with matt as it simply looks better, but also helps to hide blemishes. If you need durability, chose matt vinyl. 

NibblyPig

What a fantastic post, thank you so much for going into so much detail. I'm going to repaint everything white because I'm trying to sell my house and the green was a mistake from the start lol.
The bits I am worried about are those like the yellow where they're caused by water, I already sanded that down and painted it and the ring of water damage is still clearly visible, so I am not really sure how to fix it, I can aggressively sand it down but I'm not sure if putting some of the plaster stuff on it would help or if it needs something else entirely.
But I'm just going to have at it and hope for the best. I feel much more confident now. Thank you again.

sol2017

Great advice earlier!

I can only agree that Toupret fillers are great, they sand easily and leave a great finish. I do prefer ready mixed ones though (I've used https://www.toolstation.com/toupret-ready-mixed-filler/p51702 for bigger repairs and https://www.diy.com/departments/toupret-fine-finish-ready-mixed-smoothover-finishing-plaster-1kg/1849584_BQ.prd?rrec=true for skimming). They do cost a bit more but will save a lot of time and effort compared to some cheaper fillers.

You will need some sealant for the water stains. I'm currently dealing with a similar issue and have used Zinsser Bin for spot priming/sealing. It seems to do the job but isn't the easiest to cover with emulsion (flashing). So hopefully someone will come along and recommend a different product or advise how to work with Bin.

Jeepers_Creepers

If the water marks are dry, then this should hopefully seal them permanently: https://www.screwfix.com/p/no-nonsense-stain-sealer-white-400ml/31649  I haven't used this actual product, but no-nonsense items are usually pretty solid. 

Sol's 2 suggestions for filler look good too, and ready-mixed is certainly easier. The second product - the 'smoothover' - can only be applied thinly (up to around 2mm) so should be great for most of your filling - only the few deeper holes would either need building up in layers (each must dry fully), or else use a different filler for these. 

NibblyPig

Thank you that's incredibly helpful.  Do you put the stain block on before or after you plaster? For fixing damp spots I read that the quick drying powdered type can be better in case there is residual water in the walls, because it's unaffected by water whereas the mix with water type can be reactivated by the water in the walls. The green wall has only recently been treated outside to prevent water ingress so it is probably not dried out yet. I would wait but I am trying to sell my house and I badly need to fix and repaint it... but perhaps I can get away with it