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I have an old house with a lot of trim. Baseboards, wainscoting, crown molding, built-in cupboards. The walls are probably 50% trim. I also have a lot of old, solid wood doors.

From what I can tell, all of this was originally clear-coated with a varnish or something similar. Then at some point, a previous owner painted over it all, but didn't sand or strip the varnish, they just painted over it, several times.

I had the house repainted when I moved in, but quickly found that the paint would come off the trim really easily, which is when I noticed the varnish. It's been less than a year and there are already a lot of bare areas on the trim and doors.

Stripping down all of the trim and doors, or replacing it all, seems like a monumental task in this house. So I'm wondering if there's anything I can do at this point, maybe something I can coat the painted wood with, that would help a new coat of paint bond to it better?

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    Coating a poorly-bonded layer just leaves you with a thicker poorly-bonded layer. There's really no way around removing it. Doesn't mean you have to strip the wood completely--you just need to remove the latex or whatever's over the old finish.
    – isherwood
    May 5 at 13:32
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    Also, this strikes me as a warranty issue for your painter to deal with.
    – isherwood
    May 5 at 13:33
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    That's a good point, the painter should have noticed that would be an issue. I'll get in contact with him and see what he says, thanks.
    – Chris.B
    May 5 at 13:53
  • Upon re-reading I see that the painter you hired wasn't the first to overcoat the old finish. I retract that suggestion. A painter is really only liable for a good bond to the current finish.
    – isherwood
    May 5 at 15:34
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    That makes sense, however when he painted about 50% of the previous coats was chipped off with the bare wood exposed, so he should have seen there was an issue. Anyway, I'll probably just contact him and get him to come by to offer suggestions for how to move forward.
    – Chris.B
    May 5 at 15:43
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Paint needs pores to adhere properly.

If the substrate is very smooth or glossy then it should have been prepped in some way such as:

  • Shellac primer
  • Lightly sanded
  • Rubbed down with denatured alcohol
  • Oil-based primer
    • Oil-based paints tend to self-etch the surface

The painter is probably not at fault here since you probably paid them to just paint the trim and not fix the previous owner's mistake.

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Most likely you have old-school varnish, which contains chemicals not really in use anymore. Modern latex paints won't hold because they are designed to be weaker for easy cleanup.

The best solution here is to strip the boards before painting. Once the boards are stripped, scuff sand the boards (200+ grit) and then apply an oil-base primer (mineral spirit cleanup) (there are now some water-based shellac products as well, but I am not sure how well they would work here). This should adhere to whatever is in the wood and give you a solid surface to put latex paint.

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You have to go down to a stable substrate...

Which means any non-adhering paint, or paint layers which are poorly adhering to each other, must be removed.

If your layers are A B C D, and there is poor adhesion between layers B and C, then anything you paint over layer D will simply fail, and you will find the C-D-E layers will be peeling up in a sandwich.

That's just science, and that is a fact no matter how inconvenient it is.

Fortunately "latex" emulsion paint is pretty wimpy stuff, and weak paint strippers will tear it off that won't do much to underlying alkyd coats.

... And then, prep for Pete's sake

Once you are down to a reliable surface, you will need to prepare it for new paint to adhere. This is where 'the last guys' went wrong.

You will need to "scuff-sand" the entire surface carefully. The goal is to roughen the surface so it is microscopic jagged hills and valleys - the Rocky Mountins, not the Utah salt flats. You do not need to dig through any thickness of material. I'm fond of 3M green Scotchbrite pads, as they are less prone to burn-through.

Most "flat" surfaces are relatively lumpy microscopically. Glossy surfaces are mirror-like (that's what gloss is) and they need the most attention. Gloss is your enemy.

Then you need to lay down a primer, another step people love to forget. This is a paint-like substance which is tuned to do a good job grabbing on to inconsistent substrates, and will provide a consistent surface for the paint to adhere to, so the paint looks the same in all locations, has the same color so that substrate color differences don't print through, has the same texture and absorption.

An alkyd primer like Kilz will perform better, at the trade-off of being stinky and slow to dry.

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