How do I fix white desk after using oil based polyurethane?

I would sand the top coat and just do a coat of the white paint

Yep you can sand it and paint over it. I would use a good primer though to seal that poly in or it will probably bleed yellow through your paint. After you prime, paint again and then use a water based poly called polycrylic - that won't yellow your finish :)

Hi Ellen, you can just sand the top coat off, Any water based polyurethane will go on clear and will not yellow over time. Oil-based finishes start yellow and get more amber as they age. ... For now, all you can do is remove the finish and start over, or simply paint over the polyurethane with primer and white paint.

A quick sand and repaint should do the trick. You want to find a water-based clear acrylic that says "non-yellowing" or "crystal clear" on the label.

I'm so sorry that happened to you, Ellen, but, yes, polyurethane will yellow. I've even seen the poly pull tannins out of the wood through the chalk paint. Was the desk a dark color? I would lightly sand and and repaint with a latex enamel. Then you don't have to worry about a topcoat.

You have a couple of options...

1. Sand and repaint it in white.
2. Use a good primer (KILZ) to seal off the existing paint and sealer then repaint, then seal with a water based acrylic-this will not yellow.
3. Just paint with chalk paint and then apply a protective wax, otherwise the chalk paint will chip off.

I've seen a yellow tint when I put poly over white as well. Do what Redcatcec suggested!

with chalk paints you are supposed to use a wax to seal them that could by why you are getting the yellowing

https://www.bobvila.com/posts/196237-poly-urethane-coating-turned-yellow#:~:text=Water%20based%20poly%20will%20show,than%20one%20thicker%20coat...&text=Both%20epoxy%20and%20poly%20yellow,is%20thin%20layers%20and%20sanding.

Polyvine (water based) would be a better choice. You can try removing just the poly but you will probably have to do some paint touch ups.

Yeah oil based poly has a yellow cast and does yellow over time. Water based poly goes on milky but dries clear and does not yellow. Lightly sand the piece with 220 grit sandpaper, prime with Kilz primer then the topcoat. Seal with three coats of a water based poly.

I'd remove the poly and then use a wax to avoid getting the yellowish tint.

As a temporary solution, if the lightbulbs you have in the room are incandescent or fluorescent, you could try replacing the them with LED to see if they change the perceived color on the desk. LED light can sometimes have quite an effect on what color wall paint looks like.

Oil bases poly tends to yellow. Water based doesn't.

I would recommend sanding all the oil based poly off. and add a new coat of chalk paint so the colour is even then add you water based poly. Another thing to look out for is to select a waterbased poly that does not yellow. I have had some in the past that still went yellow.

You could try a light sanding and put a good primer/sealer on, then re paint

I would sand it off and apply a primer then paint the color you would like.

Chalk paint usually gets waxed, not poly. I don't know how you can sand off the top coat without damaging the white unfortunately.

I've only ever sealed with wax... Once you repaint, if you do it with chalk paint, I'd just get a good name brand wax sealer (I use Minwax clear or if I want a chippy, beautiful finish without all the work, but a little stinky while using it, I'll use Bri-Wax) and seal it really good and see how it goes. You may find you like it much better without the poly. I've honestly been using chalk or milk paint for yrs and only have ever sealed with wax and love the results