You don't need to "knock back" the gloss on a painted surface. That's only for painting something that wouldn't normally absorb paint, like tile.

Since you don't know if the previous paint was oil or latex, you should use a primer. That will also help tone down the bright yellow and brown to make the white need fewer coats.

But wash everything down with TSP before starting.

Robo, thanks for the reply. A beautiful smooth finish is not realistic for this room. I'm pretty sure the existing paint is all latex. I was actually one of the people who painted it yellow (someone else chose the paint color!) and I'm pretty sure it was latex.

A few days ago, just to get an idea of color, I put on a coat of primer. It might have been BIN 123 and I don't remember it having a strong smell. Although it appeared to go on okay, within a few minutes it beaded up a bit. Not really beads, but effects of the gloss underneath having its way. The sexton (custodian) came by and said the surface needed to be washed down first.

I don't want to do unnecessary work, but I want the new paint to cover well.

amberm, thanks. I'm pretty sure the existing paint is latex. Yes, I was told to wash everything down with TSP before starting.

I thought knocking back (don't know if that's the correct term, maybe sanding?) was necessary to give the paint some tooth so it will grab and not slide. Will the primer take care of that?

Yes, the primer will take care of that.

Hmm, I think the Zinsser product I used that didn't cover well was:

Wow, that 1-2-3 primer is great stuff and usually my first rec. You can generally apply over latex or oil without any sanding. Did anyone apply a wax or polish over the paint that might be what is causing the beading. I would try washing down an area and then applying some of the primer. You can also try a light sanding, but it sounds like there is something other than the semigloss at work here.

You can also use KILZ or another laquer based primer (the water based would be like the 1-2-3 primer). I use that in special circumstances, but the fumes can be bad in a closed area and the clean up is a pain. I wouldn't want to turn volunteers loose with it. Even the 1-2-3 sticks so well that if you don't clean up quickly, it may not come off where you don't intend for it to stick (in your situation, perhaps drips on floor or furniture -- even your hands).

lascatx, I don't think anyone applied a wax or polish over the paint. One thing, if it makes any difference: the beading was evident only on the cabinet door but not on the textured wall (now I'm not sure if it's plaster or not).

Honestly the yellow is so vibrant it's hard to tell what's going on. I think I'll wash a small area and see what happens.

The old beadboard could have a tung oil, some other oil or laquer finish -- but that is under that yelow paint that seems to have adhered just fine. It may take a little trial and error to figure out what will work.

Yeah, I think I'll wash a section with TSP and then see how the primer takes. The yellow is so strong and overbearing that you can't even assess sample colors in the room. I'm surprised we've tolerated it for 9 years.

Wait. If you're using 1-2-3, read the caution: Do Not Use TSP to clean.

I recommend Dirtex for paint prep. TSP is not for indoor use unless you can flood rinse it.
Read Surface Preparation

Linelle, what product TSP do you have? Someone on the paint forum the other day was mentioning the liquid form will say 'substitute' somewhere small on the product packaging, adding that it doesn't clean and degloss like the powder that must be mixed. I must not have bought any in a while, I didn't know it came in liquid form, but I have taken the shine off oil-based painted woodwork with powdered TSP mixed with water, so it would then accept an undercoat and fresh paint.

Most primers will not adhere to TSP residue. Use Dirtex instead.

Even BIN will fail over TSP residue. Read the Surface Prep Label before proceeding.

morz8, I don't have any TSP yet. I've never used it myself, although years ago when my BIL painted one of my bathrooms, he used TSP (dry mixed with water) on the walls. I don't remember him flooding them afterwards. Perhaps wiped with damp sponge?

Brushworks, thanks so much for the advice! I found Dirtex in several forms online, e.g.,

I've never flooded, only wiped down with a damp cloth. Hate to sound conflicting, but my painting projects have turned out well over the years. My go to undercoat (primer) is Ben Moore Fresh Start. I like it well enough I have to pick it up out of town when making Costco or other trips, no one in this small coastal community carries Ben Moore any longer.

The gallon makes 16 gallons. That's the best choice of the three.