I want to attach a ceramic house number plate to a plaster wall with somewhat crumbly paint. This is an old house, and I assume the paint is some kind of traditional whitewash (though it is light pink in colour).
If I rub my hand on the wall some of the colour comes off.
I was given some Bostik PolyMax glue to attach the numbers. But I'm not sure if I should scrape away the paint where the numbers are to be attached, or if the glue will bind the paint under the numbers.
Any suggestions or advice gratefully received.