lowest temperature to apply "the mix"

[ChrisW]

What's the coldest temperature anyone may have applied "the mix" (mineral spirits/poly) to seal your TD? Also, how did you like the finish and how long did it take to dry (which I'm sure temp/humidity would impact)? I want to use is as a base coat and was hoping to apply it yet this fall. Any other advice regarding the mix would be appreciated. Following that up with a good primer and paint.

[working on it]

I tested using the "mix" in lower 50's temperatures, with overcast skies, and it took over an hour to dry. A 75/25 % mix (polyurethane/paint thinner) variant that I followed with, took even longer. But, the actually application on my trailer was done in much different weather conditions, at 106-110 degrees, and direct sun, and dried very quickly. Hopefully, you will be applying your"mix" in conditions somewhere in-between these extremes. However, the "mix" worked out fine in both cases, with no problems, at least for me.

[Andrew Herrick]

Hello there!

Though I admit it with some shame, I tried applying polyurethane in the low 40's. Not a bright idea. It flows like molasses. It doesn't dry quickly, and therefore becomes a sticky flytrap for all sorts of gunk and junk. Oftentimes, when it's in the 40's and 50's, it's in the evening, and in most of this nation, that means the humidity rises well over 50% - sometimes up to 100%! That humidity will often get trapped in the polyurethane and cause blooming in the finish. I would recommend at least heating the polyurethane/mineral spirits mixture to a minimum of 60-70 degrees, even if the work surface is colder.

On another note: You mentioned covering up the polyurethane with a primer and paint. This is a little rare. What exactly are you trying to waterproof?

[ChrisW]

Thank you both for the advice. Both of your trailers look great!
Andrew, I have bare plywood and thought it would be a good base coat to help seal the wood from any potential rot as I saw that a few people on here had used it. Originally, my plan was just the primer and paint, which of course would be easier. Do you (or anyone) know if there is really much benefit to using the mix under primer and paint? It will mostly be stored inside and hopefully only see rain or snow rarely (because I'm sure it will only sunny when I camp and travel with it )

[Andrew Herrick]

Thank you both for the advice. Both of your trailers look great!
Andrew, I have bare plywood and thought it would be a good base coat to help seal the wood from any potential rot as I saw that a few people on here had used it. Originally, my plan was just the primer and paint, which of course would be easier. Do you (or anyone) know if there is really much benefit to using the mix under primer and paint? It will mostly be stored inside and hopefully only see rain or snow rarely (because I'm sure it will only sunny when I camp and travel with it )

Chris,

Whether or not your plywood would benefit from extra waterproofing depends on the quality of the plywood. Many people use imported Russian Baltic Birch, which is close to void-free and manufactured with exterior WBP glue. Chinese Baltic Birch and many other cheaper (<$50/sheet) plywoods are nowhere close to void-free and not made with WBP glue. You might already know all this, so I'll abridge this lecture on plywood If you using plywood for your exterior skin, I say: Buy the best you can find.

The main issue I see with using "the mix" is that painting over polyurethane can be difficult. Sanding/etching the polyurethane and using an exterior oil-based primer is an absolute must. Here's how I see it: If you use a high-quality primer and paint, you'll seal your plywood against the elements. Pine, which is not a rot-resistant wood, is the standard for wooden clapboard siding, and as long as it's painted, it stands up for decades.

If you want an extra layer of protection, a lot of teardroppers use CPES (Clear Penetrating Epoxy Sealer), which does a much better job guarding against rot and mildew than two or coats of thinned polyurethane. I believe it also bonds to primers much better.

[working on it]

...I have bare plywood and thought it would be a good base coat to help seal the wood from any potential rot as I saw that a few people on here had used it. Originally, my plan was just the primer and paint, which of course would be easier. Do you (or anyone) know if there is really much benefit to using the mix under primer and paint? ...

Whether or not your plywood would benefit from extra waterproofing depends on the quality of the plywood....The main issue I see with using "the mix" is that painting over polyurethane can be difficult. Sanding/etching the polyurethane and using an exterior oil-based primer is an absolute must.

• I used the "Mix" over bare plywood, which I bought for $25 a sheet (for 3/4" , a killer price), without sanding before application, nor between coats. The Plywood was pre-sanded ACX, with phenolic resin between plies, so I knew it was ideal, for the price. My multiple coats of mix, poly, and oil-based acrylic paints bonded together because I painted the entire trailer exterior under very hot conditions, with high VOC ingredients, with coats following coats in quick succession...they merged together, so to speak.
• It might've been a freak occurrence for paint over poly to work so well together, but there's been no problem with it, for six years, now, though I re-coated one part due to accidental overspray of an adjacent project. However, my trailer resides in a garage bay, unless camping, so that might've made it last much better than expected. I was fully prepared to have to overcoat it by now, or switch to a durable bedliner-type coating, but it's not needed. One major point in favor of the paints I used was that they were made for outdoor use on silos and farm equipment, so they were designed to last under adverse conditions that my trailer mostly avoids.