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I have a problem in that I have a lot of interior painting to do and in some cases it is holding up carpentry because I want to prime, for example, baseboards before installing them. However, after priming with an oil-based paint, I need to sand but I can't sand because the oil primer is rubbery and will tear out if I sand it. I have heard that it is supposed to "cure" and then will sand to a powder, but the problem is that it looks like it may take weeks before it dries that much and it is holding up the whole project. How do I deal with this problem?

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    Paint takes as long as it takes to dry but that depends on many factors, none of which you have mentioned here. What's the temperature in the building? Is there good air circulation? What does the paint manufacturer say in their literature?
    – jwh20
    Feb 12 '20 at 14:57
  • I have never used it, but seen it in the stores... Look up Japan Dryer and see if that might help.
    – JPhi1618
    Feb 12 '20 at 15:23
  • What is the temperature in the room it is drying in? If I paint in a 50 degree room it might be 3 full days before I would sand.
    – DMoore
    Feb 12 '20 at 19:40
  • Oil primer or oil paint? There is a difference
    – Machavity
    Feb 12 '20 at 20:01
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24 hours is normal

The problem is, people who have only painted with latex paint have funny expectations about drying.

Painting, and then sanding, in the same workday, is out of the question. 8 hours of dry isn't going to cut it for any alkyd, if the next step is to sand or switch from prime to topcoat.

If it's taking more than 8 hours to get tack-free, or if it's taking longer than 24 hours to be sandable, you may be dealing with adverse conditions such as low temperature or poor air circulation. You need to change the air periodically because it will saturate with the paint solvents, and that slows drying. (just like high humidity slows drying of water). If your conditions are good, the next step is to talk to your paint supplier, because some paints are extra slow - they may have quick-dry additives available, to bring them into a "24 hours to sand" expectation.

By the way, "curing" is a red herring. For 1-part paints, curing takes months or even years. If it won't sand, it's not even dry.

Use primer for priming

In my experience, alkyd primers dry much faster than alkyd topcoats, which is why I'm surprised you're having a problem with primer. If you're actually painting a topcoat, and relying on some advertising claim that the paint is its own primer, yeah, that's a lie. That's always a lie. You'll never see a pro painter doing that.

At the risk of stating the obvious, read the instructions

I think that's actually a law: it can do environmental damage, so you must use the product consistent with its instructions or labeling. A careful read of the paint-can fine print is essential, and if the fine print says "See instruction booklet" (as my 2-part paints do, as there isn't enough room on the label for critical warnings and also instructions), then you need to do that. Not reading the instructions is the surest way to have mis-set expectations and a failed application.

Also note that it is likely the instructions will call out certain "re-coat windows" which you have to hit. This is because of the (superior) nature of alkyd paints. You generally have two recoat windows: between X and Y hours (when the paint is dry enough to be stable yet soft enough to chemically bond to the next coat); and beyond Z hours (when chemically bonding is no longer possible, but the paint is nice and hard so it can be scuff-sanded so the next coat can mechanically bond). Adverse conditions can warp those numbers; conditions for slow drying extend them, etc.

Chemical bonding has superior performance to mechanical bonding. If you've ever seen paint layers separate, that is someone relying on a mechanical bond and failing to do proper surface prep by scuff-sanding and cleaning.

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  • For what it's worth, some semigloss latex isn't going to be sandable in a day either. They stay rubbery quite a while after they dry to the touch.
    – JPhi1618
    Feb 12 '20 at 16:33
  • I am actually priming, not painting. Feb 12 '20 at 18:07
  • @TylerDurden You were not specific as to which product you were painting, what its instructions say, how long you are letting it dry, and what the conditions are. As such, I was forced into a generalist answer. GIGO, my friend... but on the upside, it makes it more broadly useful to other readers, and that suits SE's format. Feb 12 '20 at 18:23
  • @JPhi1618 - just FYI - a good latex that is applied correctly will take weeks before it should be sanded if it is a climate controlled home. I mean you can always do it a couple of days after but high chance you will rub it off or end up with a sort of "ridge".
    – DMoore
    Feb 12 '20 at 19:26
  • @TylerDurden, it's been my experience that oil based primer like Zinsser Cover Stain will dry in hours. If it is made to be a primer, its normally formulated to dry quick because they know you will need to do more to it as soon as you can. Something might be wrong with the "primer" you are using?
    – JPhi1618
    Feb 12 '20 at 19:38
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You can get a paint dryer, or oil drying agent, also known as siccative, from professional paint suppliers.

https://paintersworld.co.uk/rustins-paint-driers-300ml

(This is related to the process known as "japanning".)

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  • Yes, but I'd consult the manufacturer, dealer or instructions as to which one to use. The days of using J random Japan Dryer in K random alkyd are long gone... thanks to 12-state VOC laws, they are innovating a bit too much for my tastes in alkyd chemistry. For instance, "waterborne alkyds" are pushing very hard into consumer retail, and my local store mixed me one without even telling me that. Feb 12 '20 at 16:53
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An "oil base" paint will have solvent ( not water) vehicle ; drying depends on which solvent and the temperature and air circulation. But as you note it must "cure" - (polymerize) to develop film strength before you can sand, cure rate also depends on temperature. Increased temperature and air circulation is the most practical way to speed it up. In a worst case situation , a coating will never cure properly at some low temperature.

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  • It needs to cure "a little bit", but I'd hardly call that true curing. It takes months or even years for 1-part paint to fully cure. I have some equipment with at least 50 year old alkyd paint, it's as hard as my LPUs get in 28 days. Feb 12 '20 at 16:46
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When we are doing trim on a house we often use oil based paints including primer. It simply lasts longer and looks great. If we are under a crunch they will dry faster with a box fan and a space heater. Either one will help, both make the drying time way faster.

You still need a good 16 hours - so usually if crew primes trim on day 1 and at end of day throws on a box fan and space heater - then we are good to go the next morning. I will also add when sanding the foam sanding pads (sometimes used for sanding mud) are your best bet here. They are less likely to tear the paint because you can sand with less direct pressure.

(Note that the process of adding heat - even at 85-90 degrees - can cause lighter colored oil based paints to "yellow". This is normal and will happen over time no matter what. If you use a heating element to help dry expect a shade or two difference which may be undetectable unless you put the colors right next to each other. Also having a room at 85-90 is fine with airflow. You should not have a space heater right next to a piece of trim making that area 150 degrees.)

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