House repainting advice

[SwedishChef]

I need to repaint the side of my house which is rendered and painted over in white paint. In several places the paint has started to crack and peel away in quite thick clumps. It looks as though quite a few old coats of paint have come away together. If I just paint the wall all over then that will leave noticeable 'depressions' in the surface where old paint has come away. What's the best way to deal with this? I don't want to be in a situation where I fill the holes and paint over them only to find out later on that other areas are peeling away.

 

[confidentincompetent]

How old is the House ? sounds like original coatings are cement based and many 'modern' masonry paints have been applied on top. which is leading to cracking an blowing. What is the surface like where paint has blown? is it back to sound render? Or! is the render dusty ?.. Afraid in either case if you want a sound job you will have to scrape as much off as possible, use a light hammer and old stripping knife (scraper) on the stubborn bits. Brush down well with a stiff hand brush (not wire) Wetting the old paint may help.. If after you done all that and surface seems chalky, dusty, then you will need a stabilising primer. Dont use stabiliser unless it is chalky or the paint will fail. So. If you can run palm of hand over wall and no dust then you are ready to coat up with a masonry paint. I use water based masonry paint. For bare surfaces thin down by at leat 20%.
The next coat a bit thicker.. then leave for 15 yrs ......
good luck....

 

[SwedishChef]

The house was built in 1929. Where the paint has blown the render is chalky/dusty when you run a finger over it (but not crumbling) and so is the surface of the paint where it hasn't blown.