Latex on oil...what a rookie mistake.

October 14, 2007 10:18 PM

paintingfilter: Latex on oil, not a great plan, I know. What is the best way to undo the mistake?

Three years ago, when my husband and I moved into our new house, we accidentally used latex paint on all of the trim and the banister, without realizing that the previous owner used oil. As you can imagine, the paint does not stick at all. Now we are finally ready to tackle the job of finishing the banister and moving past the blunder. We're talking about 33 individual spindles, so the labor could be overwhelming if we need to scrape every single one. Yikes. So: is there a way of removing the latex from all of those spindles without having to scrape every single one? Can we remove most of it and then prime over all of it then reapply the correct paint?

posted by ms.v. to home & garden (6 comments total)

I was going to suggest emergency contraceptives when I first read this. But after seeing the more inside, I suggest a power sander.
posted by reformedjerk at 10:21 PM on October 14, 2007 [1 favorite]

I've had some luck encouraging peeling of the latex coat by washing in 3:1 hot water:white vinegar solution, leaving that on for 15 to 30 minutes, and then heating the latex to low temperatures (130° - 150° F) with a heat gun, and then quickly rubbing with disposable tack cloths. The combination of a vinegar water wash and low heat seems to promote delamination of the latex paint, and the tack cloth has just enough adhesive action to want to bond with the latex, pulling it off effectively, in sheets. It won't be perfect, but you'll be sanding later with 120 or 150 grit anyway, to break the shine of the oil paint, and you can devote a little time during such sanding to cleaning up line details, and small remaining adherence chips of latex. Overall, this is many times cheaper and easier than sanding off the whole latex coat. But you do need to keep the heat gun moving, and work on the latex paint with the tack rags while the latex is still warm, and amenable to pulling off in sheets. It's best to work in relatively small areas, keep the water:vinegar solution hot, and don't get too far ahead of yourself with the water:vinegar solution, before you heat the area with the heat gun. You're not trying to blister paint with the heat gun, in the conventional sense a heat gun is often used to remove paint; you're actually just trying to encourage the latex to "fail to adhere" as its natural chemistry is already trying to do, if that makes any sense.

After you've sanded and tack ragged the oil paint again, be sure to prime with an appropriate primer coat, before applying a semi-gloss, or gloss latex or latex enamel topcoat.
posted by paulsc at 12:11 AM on October 15, 2007 [1 favorite]

i like paulsc's suggestion a lot, which is why i favorited it, but i would be careful with chemicals. i had the same problem because of the previous owners of my house, and when i used some chemicals (i went overly harsh, sigh) it just turned into a nightmare.
posted by taumeson at 6:44 AM on October 15, 2007

For future reference, generally you are okay applying latex over oil paint, particularly if it is interior paint and not glossly. Generally manufacturers don't recommend putting latex over more than five coats of exterior oil paint.

The problem you had was not latex over oil but inadequate preparation of the surface before painting. Most likely the old oil paint was a gloss finish. This glossly finish must be removed by very light sanding even if you are repainting with oil.

So once you finish with Paul's suggested preparation, you should have no problem getting latex to adhere properly.
posted by JackFlash at 11:53 AM on October 15, 2007

I've dealt with a similar problem, though it was on flat trim instead of narrow spindles. I was able to remove a lot of the badly-adhering paint with tape. Blue painters' tape isn't supposed to pull paint off, but it did in that case. If you need something stronger, try regular cream-color masking tape. Apply the tape to the surface, and rub it by hand to increase adhesion; wearing gloves, you can generate some heat without hurting yourself. You may be able to tear the tape and paint off right away, but the tape seems to stick more securely if you wait a day, as I recall.

JackFlash is correct; alkyd paint can be used on a properly-prepared, sound latex surface.
posted by wryly at 12:17 PM on October 15, 2007

Wryly, perhaps you have a typo or misunderstood me. I said exactly the opposite.
posted by JackFlash at 12:39 PM on October 15, 2007