Did you ever paint anything (indoors) in high humidity, and if so, did it cause issues with the paint?

Aren’t you painting inside an air conditioned house? If the temp inside is controlled it shouldn’t matter that it is humid outside. I just painted the entire outside of my house and part of the inside. It was in the 90’s two of the days, and fairly humid, and no trouble with paint inside or out, although, it stands to reason high humidity would mean longer drying time.

I think the board must have had some sort of sealer on it? So you need to strip it with a chemical or sanding. Did it specifically say unfinished?

That’s my guess. I am not expert that’s for sure.

Yeah I have painted block walls in a very humid basement before and the paint literally fell off the walls. Lots of runs and drips. Try running a fan while you paint. Your wood beadboard still may have some moisture in the boards. It would have been a good idea to open the boxes of it and stacked it log cabin style in the room you were going to install it or once you installed it don’t paint it for a few days to a week or so. That gives the wood time to acclimate and often packaged lumber has a lot of moisture in it still and needs time to naturally dry out some. Too much moisture in the wood can cause the paint to not soak in good and also as it dries it shrinks and the paint on it kind of has to clump up and will do weird things.

I’ve painted a bicycle in humid weather and the results were horrendous, particularly because it was pressurized in a spray can. If there is any humidity, there is bound to be water in the paint.

Go rent or buy a de-humidifier. That should take care of the problem, I hope.

Just a thought. Since your bathroom is always going to be high in humidity, have you considered buying paint that’s resistant to mildew?

More important than simply the ambient humidity in the room in which you’re painting is the relative difference between the material you’re painting and the air itself.

For example, if the board was stored under cover but in an otherwise uncontrolled environment, then it will have absorbed moisture. If you then bring that into a dry environment (indoors, air-conditioned), then it’s going to take some days for the moisture in the wood to work its way out. That’s what causes your problems, more than the ambient humidity of the room itself.

And if the bathroom has been used for a hot shower after the board was installed, for example, then you need to re-start the clock on drying the wood. Depending on the material and the application, it may take days of drying before it’s ready for paint.

@CWOTUS That makes a lot of sense. Like how a glass sweats when you put an iced drink in it. So you think it might be similar to a condensation on the surface that causes the paint not to adhere.

That’s a different thing, @JLeslie. When condensation beads up on a cold glass it really is all about the ambient atmosphere. That condensation is from water vapor that had been in the air and now condenses on the glass. (If water is coming out through the glass surface then you need a new glass.)

But what I’m talking about is when a “wet” piece of wood is brought in from a place where it had absorbed water vapor and is now shedding it from the inside out. In other words, it’s undergoing a slow drying process.

However, you raised an interesting issue, and one that I don’t know how to address. That is, what to do with a piece of material to be painted which is at a significantly different temperature from ambient. That is, if the wood were brought in from a cold garage, for example, and had not yet equalized with the air temperature in the room.

@CWOTUS I never had thought it through like that before. Thanks.

If the paint is bubbling, I’d be worried that the beadboard is going to warp. Just like wood flooring, the beadboard should have been acclimated indoors in an ideal temperature.

Ideally, prior to installing the beadboard, you’d have had it flat on a floor indoors for a few days. Then you’d paint when it’s 75 degrees or less in your bathroom.

If you have the A/C on, give it a couple of days before you paint this again. If you don’t run your A/C, then don’t paint this until the humidity and temperature are both lower.

I do paint in summer, but also keep my A/C at 69 degrees during the day. Besides the A/C, I run fans and a dehumidifier in the room I’m renovating/painting.

You may want to read up on moisture testing for wood floors. This will give you an idea of how to best prepare the beadboard in your bathroom.