Homasote or Plywood underneath?

[Gone Kayaking]

Getting ready to start rebuilding (hopefully tomorrow). I have a question about what to replace the Homasote with?
I see people referring to Celetex, but I'm afraid I'm not familiar with that product. When I google I get celotex and there are a ton of different products.

I do have some tar paper around. I was thinking it could make sense to use 3/4 inch CDX with tar paper on the underside. Or does it make more sense to coat it with something after installation that can fill the seams.

[vikx]

I call the old fiber belly material Celotex, but after doing a search, I'm not sure what the true name is...

Any good coating should protect the floor underside. It's a matter of repelling water from the road. I think the tar paper is a good idea too. You can do both.

[Gone Kayaking]

after a bit more puzzling I'm thinking that Homasote might actually be a pretty good alternative and would like thoughts from anyone that's used it. www.homasote.com/products/

Here's the site for Homasote which seems like the closest thing to the original product that I've seen. But I'm still kind of scratching my head for what might be the best thing to use. The original stuff after all did last for 50 yrs.

I'm thinking about using 440 440 SoundBarrier® is a special-density, structural board made from 100 percent environmental Homasote® cellulose fiber, a homogeneous composition manufactured with uniformly distributed protection against termites, rot and fungi and resistance to moisture. It also insulates, with twice the R-value of wood.

or NCFR Homasote which is fire rated and spec'd for use in marina exteriors (that's a lot of moisture!)
N.C.F.R.® Homasote® is a structural building board and substrate for interior or exterior application, offering constant insulation against air, moisture and noise penetration. It is a UL fire-rated structural building board and UL recognized component in floor protectors and wall shields. Fire Rated N.C.F.R. Homasote is made with 100% recycled, all wood fiber material completely impregnated with fire retardant chemical ingredients, treated for protection against termites, rot, fungus, and moisture absorption, and compressed into high-density, structural exterior building board.

[vikx]

The marine Homosote sounds good. I would still undercoat the exposed side. VK

[joek]

I've used many sheets of Homosote for interior applications as sound insulation material. I'm embarrased to say tah ti don't knwo which product I have used, I just ask for Homosote and they give it to me. From the link, it sounds like it was probably the 440 Soundbarrier. I woud not guess it to be particularly water proof, but have never exposed it to water. The original belly material looks to be impregnated with tar or oil, which kept the bugs and water out.

All that said, if I were doing a new floor in a trailer, I'd probably use 1/2" foam insulation board and 1/2" pressure treated plywood. And I woud seal the seams of the plywood with a peal and stick butyl flashing like Protecto 6610 (available at Piedmont Lumber and close to Margurite).

[flyingham]

Fwiw, I went with the Celotex (from Home Depot) and ply on top. I staggered the sheets (as you would) and am going to seal the underside soon (probably with more bedliner material)

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[Gone Kayaking]

Thanks for all the ideas! I'll see what's available locally and then go from there. Joe when you say foam and plywood...do you mean foam on the bottom and then plywood or the other way around?

[joek]

Yeah, foam on the bottom, plywood on top. For the insulation, I'd use the aluminum foil faced stuff. And for the plywood, after rethinking it a bit, I think I would just use CDX plywood instead of presure treated plywood. It isn't going to see much moisture, and the pressure treated plywood could give you headaches, literally because of the offgassing and figureatively with adhesive for flooring.

[elewayne]

My very old trailer (1948) was built with the old black Homasote under the whole frame. I think this is the same stuff that would be used under siding on a house. You don't see it used much anymore, there are better things on the market today for that purpose. Celitex is a product I've used for years in the cabinet shop business for making tack boards for office applications. It would be covered with fabric and put against the walls in cubicles and such. Celitex is usually a light grey color and very dry, not sticky at all like Homasote.
Anyway the old Homasote under my trailer has kept the frame nice and dry and rust free for 64 years. Can't go wrong with that.
Wayne