Walls - Wash then sand or sand then wash?

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Paper was stripped off a while ago. Walls were painted before being papered (not by me) - just round to re decorating. The paint is crazing/flaking off - which I believe is down to the paint that had been used reacting with the wallpaper paste left on the walls after stripping....
I know I need to get the wall paper paste off completely if I want to not use lining paper and just paint the bare walls or the new paint might do the same.
After a rewire there are a few areas that have been re-plastered, quite a few cracks/holes I've filled - planning on using an electric wall sander to get them smooth enough.
Have dry scraped the worst loose flaking paint off (it was like snow), given the fresh plaster a mist coat (60:40 trade matt emulsion:water). Then had a go at getting the paste off with water and a scraper. It isn't really bringing the paint off but there is obviously quite a lot of paste still on the walls - really messy and time consuming...someone said using sugar soap in the water might help? Is that true?
But then I thought seeing as I am going to have to give them a really thorough sand anyway ... I could give them a good sand with a coarse-ish paper/mesh (which should take the old paste off), then with fine paper, wash them with sugar soap to get any remaining paste off and then another mist coat - as I imagine the coarse sanding will take a lot of the old paint off too. Fill any imperfections that shows up, fine sand where necessary, possible another base coat and then top coat.
Does that sound like a reasonable plan - or do I really need to get the paste off first.
Also plan on using vinyl matt as the top coat - with the (non-vinyl) matt I've used for the mist coat - both water based - should be ok?
 
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The last bloke who painted the walls has painted over paste and every time you now paint the walls you'll reactivate the paste causing crazing to happen. Your best bet now is to give it a good sanding, dust off and coat the walls with Zinsser Gardz, this will cure the paste reactivating problem and is a lot quicker and less messier than trying to wash off paste, which is behind emulsion. Gardz is an outstanding product and will save you a load of arm ache and grief.
 
I've seen Gardz mentioned before - so it really works? - (its not cheap if it doesn't)
I guess that means I can skip doing another mist coat if I use it and just give them a base coat of white matt emulsion to give them a more even colour/tone and highlight any imperfections...act like a primer (White cos cheap and final paint colour not decided but will be a light one)
Just thought - It isn't the same as PVA on new plaster - from what I've read seems to work at first but can cause problems after a few years? Has it been around that long?
 
Gardz is nothing like pva, I've used it for a fair few years now and never had a problem with it. Make sure your walls are all sanded properly and then coat it with Gardz, it's a clear coat so make sure you cover all areas, you're then ready to first coat with emulsion, fill, spot prime filler, second coat emulsion.
 
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Ok - Great - I'll give that a go....
Plan is if I can't get a good finish after sanding I will give up and use lining paper...(semi-wish I'd had all the walls skimmed instead of patched after the rewire - but it was a whole house so would would have been a big job/expensive and I didn't know I was going to have this flaky paint problem...)
 

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