Please help with undercoating options for floor

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Please help with undercoating options for floor

Postby jamorgan3777 » Fri Nov 20, 2020 10:20 am

Dont know if I am overthinking this, but I am looking for the best practices for how to coat the exterior wood floor of my first TTT build. I have tried searching, but have not found much on the topic.

Construction will be 1/2" sanded clear plywood with a 2x4 frame filled with 1.5" rigid foam insulation (pink sheets) with a 1/2" clear sanded plywood interior skin. The inner and outer skins will be glued and screwed to the 2x4 frame to give a torsion box construction for added rigidity.

Anywho, I am wondering about a couple of things. First, what is the best seam treatment on the underside? I will have two seams running across the width of the trailer as its 5'x9' floor. Cant do that with 4'x8' sheets and less than 2 seams. Second, what surface treatment (exterior) has been successful? I am considering the following but open to anything. I am leaning away from fiberglassing or a separate rigid skin (i.e. filon, aluminum, etc) but could be convinced if other "applied" solutions are all sub par.

Option 1: standard exterior house paint. Oil based and give it 3-4 coats. Would seal the seams and screw holes with paintable silicone caulking and.

Option 2: 3 coats of oil based poly thinned 50, 25, and 0% with MEK and then overcoat with two coats of Monstaliner. Not sure about the seams and screw holes in this case. Could use paintable caulk or bondo body filler.

Option 3: Behr (or other brand) of deck resurfacing paint. https://www.homedepot.com/p/BEHR-PREMIUM-ADVANCED-DECKOVER-1-gal-SC-102-Slate-Smooth-Solid-Color-Exterior-Wood-and-Concrete-Coating-500001/308486653 Would apply directly to the wood with a couple coats. I would assume bondo or paintable caulk for seams and screw holes.

Any other suggestions I would be greatly appreciative.
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Re: Please help with undercoating options for floor

Postby linuxmanxxx » Fri Nov 20, 2020 11:10 am

I'd do option 2 but modified. If you do monstaliner it should seal seams and screws. If you figure the poly is plenty good then seal them with e6000 glue and you'd have an easy to clean very hard durable undercoating. That much poly should be fine on its own. The mix is mentioned here a lot and could be used and easily touched up after several years if needed. Lots of ways to skin a cat and after doing my last with just the mix, won't ever return to the nasty black crap. Thinned enough the mix penetrates and dries fast. I used gloss poly so once I started seeing a subtle shine knew it was good to go. I think I just did thinned coats about 25% poly 4 or 5 of them.

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Re: Please help with undercoating options for floor

Postby jamorgan3777 » Fri Nov 20, 2020 12:27 pm

Thanks Much Steve!

I forgot to mention "the mix". I didnt know if that would be good on its own.

Will give it a look!
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Re: Please help with undercoating options for floor

Postby saltydawg » Fri Nov 20, 2020 12:35 pm

You night want to do a little research on bed liner on ply wood. I have seen a few people say not way to that. Monsterliner maybe different but its worth 15 mins of research for safety.
https://expeditionportal.com/forum/thre ... it.202829/

edit I dont know if this is over sealed wood or raw wood. or if its just one brand that is a problem.

I dont have a suggestion for wood under there. ( ps I am anti wood )
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Re: Please help with undercoating options for floor

Postby tony.latham » Fri Nov 20, 2020 12:49 pm

In prehistoric days, builders used roofing tar. :frightened: If I used that stuff, I'd be banned from the house...

I use epoxy. It soaks into the wood and plasticizes it. In the past, I have used thinned oil-based polyurethane. It too soaks in as long as you give it multiple coats while it's still wet. I'm convinced both will do the job.

What I don't recommend is a product that simply skins the plywood (such as paint). Any peeling will expose bare wood.

At $200 a gallon, Monstaliner is an expensive choice and I don't see the need. I used it on my last build for UV protection and color on the walls and roof. If you feel the need for a color-coat, use an oil-based paint over thinned poly or epoxy.

:thinking:

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Re: Please help with undercoating options for floor

Postby jamorgan3777 » Fri Nov 20, 2020 2:49 pm

Thanks for the additional inputs. I think I am going to go with "the mix" on the bottom and then overcoat with the same oil based acrylic that I am going to put on the trailer frame. I will save the Monstaliner for the walls and roof.
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Re: Please help with undercoating options for floor

Postby Sparksalot » Fri Nov 20, 2020 3:56 pm

I did the old school tar mess. After 12 years and 30,000 miles there are still areas that have never gotten dirty. If I were doing it again, I’d probably just do some good quality exterior paint.
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Re: Please help with undercoating options for floor

Postby noseoil » Sat Nov 21, 2020 7:32 am

We used white roof coating (2 coats rolled on pretty thick) from a home supply store & it's nice to have a white surface to work under, there plenty of light & a car wash keeps it looking new. For the seams, I'd just use a good glue like Titebond when the panel is assembled.

The floor on our TD is a 3/4" face frame made out of 3/4" poplar, 3/4" foam insulation & 1/8" Baltic birch top & bottom. I doubled up the skin in the galley & added an extra layer where you enter the cabin backwards to sit & swing your legs in. The mattress will distribute the load pretty well when sitting or laying down. This has been plenty strong enough. I think building with 2x4's & 1/2" plywood is way too much weight, unless you're not planning on building with a steel a frame & using the floor as the attachment point for an axle & tongue to save weight. Take a look at my build journal to see how we saved a bit of weight on the floor & walls.
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Re: Please help with undercoating options for floor

Postby halfdome, Danny » Sat Nov 21, 2020 5:50 pm

I always put plam ( plastic laminate) on the top and bottom of the floor.
It’s impervious to water especially that far off the road surface.
:D Danny
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