Not prefered. Oil (alkyd) paint dry to a stiffer and harder film than latex. Putting a harder fil over a softer film invites cracking of the harder film from movement of the softer layer underneath. Just spot prime with latex.

When I did my FPE sample boards, I just used two coats of C2's SAP (Sandable Acrylic Primer-Latex) a couple hours apart, and let them sit 'till the next day. These sanded-off nice. (You can use Zinsser's 123 primer as well.) You CAN do 2 or 3 coats of primer to give yourself SOME grain-filling function and sanding-cushion. I then did two coats of FPE's ECO-series (Latex) White....WOW! Bottom-line...you can thin primer. Cans often state "No thinning" 'cuz sometimes people use the wrong stuff, or way too much, etc. * A very good "relaxer" for Oil primers is XIM's X-tender for Oil paints & primers. There's a version for Latex paints/primers too. * You won't need it with FPE stuff though! * Most SW stores have some XIM stuff. I've got it @ the ACE where I work, but ACE itself doesn't carry it. We've got to order lots of stuff directly from vendors. Faron

Professional, licensed painting contractor here. Only age 30, we do very high end work. I do surface testing myself using scientific method and also read a TON of textbooks, literature, etc. The best primer to use is oil-based or alkyd-based, and I’ll tell you why. THEN, I’ll tell you why unfortunately some in the industry LIE. And it has to do with money, special interests, and EPA regulations. IN SHORT: Oil-based primer is better than latex primer because of the binder (oil), preventing moisture from intruding into the wood. (Oil and water don’t mix) Wood swells and expands when it’s surface gets wet. The oil primer prevents the rain from entering wood. This prevents paint chipping and peeling. Latex primer- even if it bonds great to the wood- still doesn’t prevent rain from soaking into the latex paint and latex primer, and then into the wood. When the wood expands, the paint chips/peels because paint has low elasticity. For a more scientific explanation: Ever seen how accidental oil spills in the ocean, result in the oil sitting on top? This is because oil and water do not mix. They cannot mix. This is because water (liquid H2O) is held together by hydrogen bonds. Whereas oils and fats not have any polar part and so for them to dissolve in water they would have to break some of waters hydrogen bonds, which they will not do, so they remain separate. All of the paint advancements in the world, cannot change the fact that the binder in latex paint remains water, thus it is WATER SOLUBLE. This is a problem when it rains. You can paint interior cabinets (just not in bathrooms) with a urethane acrylic (water based) paint and it’s generally fine. But outside wood, where it’s going to rain? It’s a very, very bad idea to use latex based. WHY THE INDUSTRY LIES: Paint Manufacturers (Corporations) receive money directly from our USA government as well as European governments, in order to promote what they call “environmentally friendly policies”. As oil-based paints are less “environmentally friendly” due to a higher VOC count, this results in paint manufacturers and paint stores feeling obligated- generally FINANCIALLY OBLIGATED- to push customers to purchase latex primers over oil based primers, even when oil based primers are much more effective according to science. Oil-based solid stains have actually been cut out of circulation completely… you cannot buy them in the USA anymore. For oil-based semitransparent stains (which are much better than water based stains), only a few states manufacture them and our state needs to have them shipped in. This is because of EPA regulations. I want to reiterate that I am certainly in support of helping the environment, and I understand the importance of that. I think both sides of the aisle can and should agree on that. However, I don’t agree with government corruption or misleading consumers in order to push incorrect claims. Any agendas should be based on truth and honesty, nothing else. There’s a reason the girl, in a comment above, mentioned How she had applied oil based primer to her deck and siding and it held up perfectly, whereas the latex primer and paint over that had peeled. Because latex primer on wood outside, fundamentally does not work on a molecular level. Corruption and EPAA regulations and government funding are the reason why companies incorrectly tell you to do this. But if you get a skilled and intelligent painting contractor, that really knows what they are doing, they’re going to tell you otherwise. And again, I’m 30, I grew up in a time period where I could do experiments/ tests on both oil and latex primers and come to factual conclusions based on the data. I have no bias, except I want to do the best job and make the most money obviously. And jobs hold up better and look better with oil based primer on EXTERIOR wood.

Contaminants aren't likely to slow the drying. They will affect adhesion or such things as "fish eyeing". In warmth and reasonable humidity, a primer should have dried overnight. It is not impossible that you just got a bad batch of primer. Oil products do have chemical driers put in them, this is what Japan Drier is. Years ago, I used to use a lot of Ben Moore's Oil Satin Impervo.. One of my few complaints is that once in awhile, it was like they forgot to put the drier in! Occasionally, i would apply a coat of Impervo at no later than 4PM and then find it still tacky a 8AM the next day! I learned to add a cap full of Japan Drier to assure it being dry in the morning. Applying an oil paint over not thoroughly dried oil paint can also retard the drying of both coats. Oil paints need oxygen to dry and cure. Putting that second coat on too soon, deprives the first coat of oxygen and results in both coats being tacky for days. They will eventually dry, but it will take days. Water based paints are generally ready for re-coat as soon as the water has exited, about 1 or 2 hours later. They are not fully cured, but can be re-coated. Not so oil paints. Their minimum dry time is several hours.