How do I choose a water-based primer?

Question

I am about to paint a room with a water based enamel. Old coating is matt latex, I must be overly zealous when priming and painting it.

My main problem is finding a good primer, shopping around I have found and tested 2, both acrylic, one tinted (primer 1) and one not tinted (primer 2). Testing them on melamine (to simulate poor adhesion) I have found that:

Primer 1 is very thick, easy to apply, dries dead matt but is easy to wash off and strip with just water, even after 3 days.

Primer 2 is thick, calls for a 4:1 water/primer dilution (runs and drips like crazy) but when used undiluted on melamine is a tad easier to apply, covers well, dries slowly to a semi glossy sheen and cannot be removed with water, I have to use ethanol or scrape. Unlike primer 1 this one did have adhesion issues in one test (see attached photo, I have reproduced it with a paint).

My questions are:

• Will the fact that Primer 1 can be removed with just water affect the adhesion and durability of it in a moist room? What about the paint's?

• Will the gloss in Primer 2 affect the paint's adhesion? I know gloss surfaces do not stick as nicely, and I can't sand.

• Those are all acrylic primers, Primer 2 has a decent solid content and high viscosity, would an acryl-styrene primer with an even higher solid content be better? Or is acrylic the way to go?

TIA

Answer 1

Will the fact that Primer 1 can be removed with just water affect the adhesion and durability of it in a moist room? What about the paint's?

Yes. There's a reason that very little paint is oil-based, but a decent amount of primer is. Latex is designed to be weak against water and anything similar. When in doubt, use oil-based. Harder to deal with, but it adheres better to anything that is not paint. I had to paint some old drywall on the ceiling of a room I was renovating and the latex paint bled the old yellowed drywall paper. A gallon of oil-based primer solved that. Using the wrong primer means more paint and painting.

Will the gloss in Primer 2 affect the paint's adhesion? I know gloss surfaces do not stick as nicely, and I can't sand.

It can, but a light scuffing with a high number grit (200+) won't leave any visible marks. If you don't sand, your job is harder.

Those are all acrylic primers, Primer 2 has a decent solid content and high viscosity, would an acryl-styrene primer with an even higher solid content be better? Or is acrylic the way to go?

Don't be too focused on the acrylic part. This is primer after all. My experience is the base (oil or latex) is the important part.

Answer 2

If you want good paint performance, it's less about the paint and more about the surface preparation. You have to remove dirts and oils from the old surface, and scuff up the surface so there is some microscopic roughness for the new paint to adhere to.

Scuff-sand with a Scotchbrite style kitchen sponge lightly passed. If you're galling up clumps of paint you are doing it too hard. There's no significant risk of lead dust, but if you're worried about that, keep the sponge wet instead of moist.

I hear "can't sand". The paint doesn't care. If you don't roughen the surface, it won't stick and will fall off in a few years.

Clean with Tri Sodium Phosphate or equivalent product, but thoroughly rinse it off.

If you're looking for a "product in a can" that will do this prep for you, there's no such thing.

As far as thickness, emulsion/latex paints are supposed to be very thick. Most come out of the can ready for application by roller, brush or airless sprayer. If you must reduce, follow the can's instructions.

If you have a very challenging surface, you need first tip-top prep, and if you must hire it, do so. And then you need an oil primer. Fooling around with water based primers is a risk.

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Once the prep is done, if I must use a water based primer, it's Kilz 2 simply because it's available everywhere. For bare metal I insist on at least oil based Rustoleum 7769 Rusty Metal Primer (which still needs prep to SSPC-SP2 bare minimum, pref. SSPC-SP3).

Answer 3

If I'm ever in doubt about priming and sealing I just go straight to the Super Stick 777. It's expensive but it is the best primer for those really tough jobs. It's not horribly thick and sticky during application. When dry it sticks to everything. I've used it on tile several times.

Para Super Stick 777

Para

About your specific questions

The fact that you can wash the paint off after 3 days doesn't indicate a problem. Paint dries in hours but takes weeks to cure.

Primer is designed to sick to surfaces and leave a surface that has a rough topology at a microscopic level. It's sheen doesn't indicate a problem.

Acrylic and acrylic styrene have similar properties except that acrylic styrere fades under UV light. I don't know how that would affect the primer but if the room gets lots of light I'd stick to the acrylic.