pre-soak&seal w/ cheap polyurethane and mineral spirits

[working on it]

OK, my build has been forced to "tighten its belt" for economic reasons. I'm having to substitute cheaper items for those originally planned in order to continue. Waterproofing and painting are being "downsized" also. I originally planned, Plan B, to do two coats of (moisture-cured polyurethane) Aluthane as a waterproofing/prime coat, then finish coat with Aluthane (if it looks good) or with Tractor Supply Enamel (MF gray) and more TSC black enamel for trim and highlights. Need 1 gallon of Aluthane minimum, and/or 1 gallon of TSC enamel(s) as well. Over $200 at least. Not including shipping. I chose Aluthane because I want a silvery gray appearance,waterproof,heat-reflective, and the dealer claims two coats will completely seal the wood. My research here indicates that a generic polyurethane mixed with mineral spirits will do the same. So my question is...if I use a cheaper, locally bought poly to pre-seal the plywood, can I get by with less of the more expensive Aluthane as a primer, and have a better finish by using it as a pure topcoat? I am not explaining this well at all, so can you more experienced guys read between the lines and extract the gist of my intent?

[48Rob]

I think your best bet would be to pose this question to the manufacturer of the final finish you plan to use.

Thinned polyurethane for the first couple coats, and then a few more full strength with light sanding in between will seal the wood, and work well as a primer for a similar oil based paint, but for Aluthane?
(Be sure to apply extra coats on edges, as that is where the wood will soak up/need more material to be water proof)

A foundation for the rest of your build is not a place to pinch pennies...that said, the specs for Aluthane http://www.epoxyproducts.com/dataaluthane.pdf seem to support using pretty much anything as a base, as long as it is clean, and well adhered.

Rob

[working on it]

48Rob-thanks for your comment. I've reconsidered the Aluthane approach...for two reasons: 1). I can get the desired waterproofing and heat reflective properties another way, and 2). my research shows only one other on this forum having used it before, but coated over it. The cheap poly, mineral spirits 75/25 mix espoused especially by GPW looks like a winner to me, and it can be coated over with TSC HD Aluminum Paint and trim painted with the TSC enamels favored by some others here too. All products are compatible, since they are all oil based alkyd resins, and can be purchased locally. $50-60 for the min.spirits/poly mix, $30+ for the Aluminum paint, and $6 apiece (rattle cans) for the trim paint. Roughly $100, w/no shipping costs, should have leftovers for touch up or additions, and no learning curve on usage. I was hesitant about using the moisture cured Aluthane due to application advisories on MCU's, and the fact that the surface appearance was not liked by the other TD builder "guinea pig" . I may still use Aluthane at some future date, probably on my racecar hauler, but I really can't afford to experiment on my TT. I have used polys, paints, enamels, and thinners before with satisfactory (though not professional) results.

[parnold]

I seem to remember that Aluthane is NOT uv friendly. I sell a product, that for all I can tell is the same thing as Aluthane, but marketed under a different name, and I know the stuff I sell has to be top coated if exposed to sunlight.

[working on it]

In my searches on the web, I never saw whether or not Aluthane or MCU 100 or various other names for the same product were UV resistant. But, it's shown being used on outdoor structures and is aluminum filled, so perhaps it is. Still want to try it at some time, somewhere.

[48Rob]

I may still use Aluthane at some future date, probably on my racecar hauler, but I really can't afford to experiment on my TT. I have used polys, paints, enamels, and thinners before with satisfactory (though not professional) results.

A "professional" look is nice, and is the result of a pro who has developed real skill in his/her trade.
However, we amateurs can still get pretty nice results by slowing down and doing our best.
The coating doesn't have to be mirror finish perfect, but it does have to be applied carefully and correctly so that it will do the most important thing it is designed for, which is to protect.

Good luck with your project, and please post pictures, it will be neat to see what you choose and how it comes out!

Rob