It is acrylic.

It is PPG "ACRI-SHIELD MAX 739-10"

Maybe the stucco was not power washed evenly.

I have had problems with fiberglass, due to wax.

Are you the only owner? Was there an addition? Someone spray for insects?

Thank you for your response. We are not the original owners but have lived there for 10 years. No addition and no insect spraying on the home at least since we have been there. One theory from another painter this morning is that there was not adequate drying time after power washing and there ia Trapped moisture. His opinion Was to wait a month and see if it eventually disappears. I am having someone from a stucco company come out this afternoon to take a look and give me their opinion.

No primer was used initially. Just the power washing and then 2 coats of the paint. This was the recommendation of PPG, "2 coats will get the job done." When the yellow started appearing, a primer was applied in some test spots along with an additional topcoat of paint, that's 4 coats total and yellow still came through after a few days. They also tested an area using cover statin with the same end result after a few days. It always appears to have worked but by day 3 or so the yellow reappears. What doesn't make sense is why it is not yellowing everywhere and why does the back of the house look almost perfect? Could this just be a part of the process where some yellow will pull through and eventually go away or will it continue to look worse over time? More coats of paint will do nothing and only take away the texture of the stucco which I do not want to lose. I appreciate your time and opinion.

my guesses are based on the location of yellowing in the pictures.

there is a “pattern”..... around utility boxes, windows, patio trim.. maybe a sealant/caulk?

based on my experiences with fiberglass, there is a contaminate on the surface.

The primer used after the fact, may not have been the right type of primer. The house should have been primed with a good shellac based primer before the first bit of paint ever was put on it.

Thank you. I haven’t heard of that. What is the reason for that?

The reason is that it seals the existing surface, so there is no bleed through to new paint.

Thanks so much for your feedback. It is hard to see in the photos but the yellow is also showing up on the walls as well, just not on the back of the house. We have 2 covered doors and the yellow is coming through on those walls and also on walls exposed to the sun and the elements. We just can not figure out the common denominator.

This is why you don't paint stucco. I know everyone does, but you shouldn't.

Stucco is a cement product. It is porous. There are things in the pores of your stucco, and now they are coming out from underneath, because the vapor in your house is used to passing through unobstructed and now it can't.

Now, if you do paint stucco(which you shouldn't), in order to have any chance of success, you need to have it cleaned, sealed, primed, and then painted, in that order. Congratulations, you now have painted stucco. If you ever want to repaint you are looking at a sandblast, and you have also drastically altered the vapor permeability of your house in an unknown fashion which can bring all sorts of headaches with it.

Stucco should be recolored with a very thin sprayed on special mixture of pigment suspended in a cement. End of story. That is the only "right" way to do it. Painting it with latex is a series of compromises you shouldn't make.

I have the same issue with my shop which was painted in July with PPG sun proof paint in a medium gray. The side of the building that does not get direct sunlight has turned completely yell

Prime it in oil base primer...it should go away with the oil ...and tint it to near finish color

Careful when using Shellac based primers exterior. It's meant for spot priming only. If you do the entire surface with a shellac it will crack. Shellac dries hard and does not expand with the elements. You'd be better off with oil based primer. Oil based primers seal the surface and stop things from coming through to the surface. Water based pants can actually draw things out onto the surface. This is what is most likely happening.