My house is about 30 years old. I recently painted over exiting off-white trim in two rooms with white alkyd enamel. The new white paint turned yellowish tan in about 4 weeks.
I then painted over the discolored alkyd enamel with a coat of Zinsser shellac based primer. The bleed through continued. I then painted over the shellac based primer with an Oil Base primer. I waited two weeks, and then repainted the trim white again, this time with latex semi-gloss. The two primers did not solve the bleed through problem.
The trim along the floor is bright white (for now), and the trim around the doors and windows is a very noticeable darker shade of off-white. I have new carpet scheduled for installation in two weeks. I’m desperate and in need of some sound advice.
This is a tough question. You already tried a great primer that is known to seal stains and stop them from bleeding into the finish paint. This makes me think that something else might be happening.
Possibly what is happening is you're seeing the original color on the trim and not a true "bleed through" as with a water stain or crayon. In other words, the finish paint has very little hiding abilities.
The reason for this is that all paints and primers contain solids and it is the solids that give then hiding abilities. The problem is as a paint becomes shinier the amount of solids it contains decreases. So, a flat paint covers the best and a full gloss the worst. Add to this, the color bright white has little or no added tint.
It's possible the trim needed another coat or two. When you primed with the shellac primer you added back some yellow to the surface, all primers are a off white color.
The only way to test this theory is to repaint a piece of trim. This time use a 100% acrylic exterior flat after priming, exterior flat covers the best.
Apply 2 coats, in your chosen color, and then apply a coat of acrylic finish paint in your favorite sheen. Allow each coat to dry for 4 hours before proceeding with the next.
If this works then all should be well, if not then the "bleed through" should return within 3-4 days.
Tried your recommendation
I'm currently trying out your suggestion on a test area of one of my windows. That is where the trim is experiencing bleed through, and is darker then the trim along the floor. Results: I primed the test area, and 24 hours later applied the 1st coat of 100% acrylic exterior flat. As it was applied, it was fairly white, pretty much as it is right out of the can. Within one minute, you could see the color begin to darken. Within 5 minutes, the color completely changed to off-white. The final color so closely matches the rest of the off-white trim, it's hard to tell where I just painted. I will apply a second coat, and then a final topcoat, but I can pretty much guarantee the final result; the color of the trim will remain off-white, even though the primer, the two coats of flat acrylic, and top coat are bright white. Bottom line, the shellac primer, the oil base primer, and the two layers of flat are not stopping the bleed through. Does anyone have any other suggestions?
Two more coats of BIN
My experience with BIN shellac based primer is you need 3 coats. I spot prime all of my knots on exterior pine trim 3 times before I prime it. I have had no problems doing this. Try a second and third spot prime over the stains.
I was raised in my late fathers paint store. The yellow that never goes away, is creosote, from a heater or old stove. It always comes back yellow, primers will not work. Only thing that will is aluminum paint, then prime and paint.
Sounds like a hassle. remove and replace the trim. Prime and repaint. Or paint it a darker colour.