Do you need to paint latex over oil?
Maybe you need to paint the trim on an old door. Maybe it is the door itself.
Regardless, if you have existing oil paint on a surface and you want to paint latex over oil, here is what you need to do if you desire the best interior paint job you can accomplish.
Have a look at the existing paint.
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Cracking ~ Peeling
Is the existing oil paint badly cracked? If it is, it means that the oil paint that is on there is well past its useful life, and has cured slowly over many years to the point that the paint film has pulled itself apart.
If that oil paint is old enough to crack up, likely it will be peeling too, as the two often go hand-in-hand.
That being the case, if you topcoat this cracked, peeling surface with anything, as the oil paint continues to shrink, the cracks will reappear.
And if peeling of the oil is happening now, it will still continue to happen, and your new paint will peel off with it.
If you want a good finish, then you must strip the oil paint completely, and start again from clean, bare wood.
We have already covered what must be done if the existing paint is cracked and peeling.
If the existing coat is just peeling in a couple of spots scrape the loose paint off back to firm paint.
Check carefully elsewhere for loose paint that hasn’t come off yet, and remove it.
Using a #150 or similar grit sandpaper, scuff sand the entire surface to dull any gloss.
Sandpaper the edges of any peeled paint to smooth the transition areas between the old paint and the bare wood.
Wipe the surface clean. Since you are top coating with water-based products, I would use a damp rag.
Make sure the surface is completely clean, free of dust or particulates, oils, grease etc. Then wait until the surface is completely dry.
Since paint binds to an undercoat via mechanical or chemical means, latex over oil does not bind well.
There is a little mechanical interface between latex and oil, and there is virtually no chemical reaction between the two.
Some folks might suggest you can paint modern, 100% acrylic latex paints right over an oil paint.
I cannot fly in the face of advertising that claims this. However, I can tell you my personal thoughts.
My strong suggestion is, if you want a good bond with latex over oil, you need to use a transition primer.
Water Based Primers
Transition primers are designed to bond to virtually any well-prepared substrate.
The lock into what paint is on the surface already, and at the same time, are able to be bonded to by the new paint you are putting on top.
You could use an alkyd based transition primer over an alkyd paint.
The drive to lower VOC’s means that alkyd based primers are going to disappear.
That and the complexity of dealing with the by-products of using oil-based paints have given rise to a range of excellent, high performing, water-based transition primers.
A water-based transition primer is a product I suggest you acquire and use to move from your existing oil-based paint to more easy-to-use, environmentally friendly, latex paints.
One brand is Gripper, that from the Glidden or Dulux paint stores. Other manufacturers have their equivalents.
It may not be necessary to prime just the bare spots first before you coat the entire surface of the project with the primer, applied as per the directions on the can.
The primer is a sealer too, and will even out the paint voids so they don’t absorb more than the painted surface.
The Gripper transition primer ( and probably most others ) will dry quite quickly and should be ready for re-coat in a matter of hours.
Topcoat Latex Over Oil
Now your project is ready for a nice, easy to use, low odor, low VOC, latex topcoat.
If the project is one subject to a lot of touching, like door trim, the usual selection is a semi-gloss that resists dirt penetration, and the potential for burnishing from aggressive cleaning.
If it is a wall, consider a low sheen paint, like a Matt or Flat finish.
Since I’ve learned about how VOC’s affect the atmosphere and the breathing environment in my house, I always try to purchase a 100% acrylic latex paint, that is as close to zero VOC’s as possible.
Depending on what you are painting, you might use a brush, a roller, or even a sprayer, though most DIY-selfers would opt for brush and/or roller.
Apply sufficient coats of topcoat, using the roller and brush painting techniques found on this website, to coat the project to your satisfaction.
Enjoy the fruits of your labor.