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Just primered the kitchen ceiling with 1-2-3 water based primer. The ceiling was previously painted with oil based paint. In preparation, I used TSP rinsed it well, then used liquid sander. Now the primer can be scrath off with finger nail. I need help please. what is the best way remove the primer without having to sand the 25x11 ceiling?

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Sounds like either the liquid sander didn't, or the liquid sander is leaving a residue which is interfering with bonding with the new primer.

I have never heard of a "liquid sander", and I would expect the recoating industry would jump all over that if it works. So I suspect it is "snake oil". But I mostly paint over alkyds (oil paints), maybe it only works on old latex coats; that wouldn't be a surprise, latex is very chemically different from aklyd. Also, etching an alkyd would require extremely harsh chemicals, and I doubt they'd be allowed to be sold at Home Depot.

Regardless, it should be perfectly obvious that the new primer has to go, as it will be the "weak link" for any coating painted over it, and will cause that coating to fall off too. Do it ASAP while it is still soft. I would use a scrub brush and water; water makes still-curing latex paint/primer softer.

Sorry you have to go through that, but not too sorry; that's what you risk when you try to take shortcuts.

Adhesion has two parts:

  • The old surface is roughened, so at the microscopic level there are many jagged grooves and peaks (like a mountain range) so the new coat can physically attach.
  • The old surface is entirely clean of contaminating material. An example of contaminating material would be "snake oil".

You don't need to go crazy with sanding. All you need is a "scuff sand" to remove the gloss and create those jagged edges. My favorite scuff-sand method is a 3M Scotchbrite sponge with the green abrasive, wetted if necessary. You'll know when the gloss is gone because the surface will look dingy. I mean honestly, I don't see how rolling out a chemical and the cleanup that follows is any easier.

Also, I realize people like latex products because of less smell and easy cleanup, but since you're dealing in primer, they come in both latex and oil base. Since you're painting over alkyd/oil, oil-based primers are a perfectly reasonable choice. Primers like Kilz Original, BIN etc. are designed to have latex laid over them.

  • Thank you for you help- it is truly a nightmare- it took me 1 1/2 hrs to scrape a small section of 18x18 inches. Tomorrow I will try out your recomendations. The product I used is from Klean strip and it's called "sander degloser" sold at big box stores. Aparently it didn't work. – Ramon Sep 22 at 18:44

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