SubFloor Replacement - What to use, Seal or not Seal?

Discussion in 'Roof/Floor Repair & Maintenance' started by jmatasov, May 19, 2017.

  1. jmatasov

    jmatasov "Never tell me the odds." -Han Solo

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    Aug 19, 2016
    Western NY
    I currently have a post going in the full restoration forum, and am just about to the point where I pull off the old OSB subfloor and put down a new one. This is a '99 Starcraft, and the existing subfloor is an OSB of some sort that was painted/stained black underneath.

    I have done a ton of searching and have not found a consensus among people, so I am looking for direct feedback from you guys.

    1) Do I use Marine Plywood (fir, probably), or an exterior OSB? I am leaning towards a plywood of some sort, because it seems that it reacts to water a bit better than OSB, but I am looking for thoughts on this. we will be putting a linoleum/ vinyl flooring over it.

    2) Do I seal it underneath in any way, or leave it bare? I will probably paint/seal/cover with something all of the edges and cutouts and holes through the wood, but I'm looking for experiences that you guys have had who did this already. Did your method work? What would you do if you had it to do over?

    I believe I have a way to keep the water out of the corners of the walls, so water coming from the top should not be a problem anymore. Anyways, looking for info on what I should do with the subfloor.

    Thanks!
     
  2. roybraddy

    roybraddy Active Member

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    Mar 23, 2016
    King George, Virginia
    My 2008 Starcraft 14 R/T has the OSB flooring that is painted black on the bottom side. It has held good over the years. I did have a weak section just inside the front door which I beefed up on the bottom using some angle metal. I sealed all around the bottom of the door jam etc... Haven't seen anything there since then... I don't know if this was any water damage or just a poor support area from the bottom. It is nice and sturdy now since I added the angle metal sections from LOWES...

    My floor is covered inside the POPUP trailer with 2X2 foot BLUE stick-on squares with the board under the tent bed areas using GREEN 2X2 foot carpet square sections. This really helped out keeping things warmer in the winter and cooler in the summer. The downside of course is carpet squares really draws in the leaves and other woods small things. I picked up one of those grated folding steps from Camping World to stomp on real hard before entering the trailer... Seems to have helped...

    [​IMG]

    Roy Ken
    [​IMG]
     
  3. jmatasov

    jmatasov "Never tell me the odds." -Han Solo

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    3
    Aug 19, 2016
    Western NY
    Thanks, @roybraddy for the insight. After doing a ton of research, I came up with a plan I think might do the trick.

    I found a local supplier for 1/2" marine plywood at $64/sheet. I am buying 3 sheets, using Titebond III on shiplap joints to connect them together, then using Titebond III brushed around all of the edges and holes through the wood to seal it. After that I will probably use an exterior latex paint to paint a few inches in from every hole or edge to help seal it.

    So that's the plan, right now.
     
  4. Helmsman Spar Urethane is an excellent breathable yet waterproof sealer for wood products.
     
  5. jmatasov

    jmatasov "Never tell me the odds." -Han Solo

    55
    3
    Aug 19, 2016
    Western NY
    @Fless - that sounds like a good option, but I just got back from my wood run and Home Depot run with the marine Plywood and the Titebond III. [:D]

    It seems people are split on whether to seal the bottom or not. Most feel that the bottom needs to "breathe" and if I seal it I will seal in any moisture that gets in and will encourage rot. The top will have vinyl over it, so I am not worried about that. Right now my main thing is to seal the edges, and the titebond III should do it, from what I have read.

    Anyone have any experience that would say otherwise? I have a plan to seal the corners properly, so water from the top shouldn't be an issue...
     
  6. Be-Ce

    Be-Ce Member

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    Apr 5, 2017
    Albany, Oregon
    Are you going to reinforce the frame any with the deck off? My floor is in good shape, but I can feel deflection when I walk around inside... I like Roy's idea of angle iron support; I was thinking of scab'ing in PT "joists". I'm less of a metal worker than I am a wood worker.
     
  7. jmatasov

    jmatasov "Never tell me the odds." -Han Solo

    55
    3
    Aug 19, 2016
    Western NY
    Agreed. I can see it getting spray if driving in the rain, but other than that it should be dry...
     
  8. jmatasov

    jmatasov "Never tell me the odds." -Han Solo

    55
    3
    Aug 19, 2016
    Western NY
    So in talking with the various people I know that are engineers and woodworkers and such, incorporating the knowledge gained from you folks, here is the revised plan:

    I will shiplap the joints with Titebond III to waterproof them. All edges and about 6" in from the edges will be sealed with the Spar Varnish, to weatherproof them. The rest will be left as is, to allow the wood to "breathe".

    This will work for this camper because it will be stored inside when not in use, so even if the underside gets wet from road spray it will have the chance to fill dry out.

    That seems to be a reasonable middle ground.
     
  9. jmatasov

    jmatasov "Never tell me the odds." -Han Solo

    55
    3
    Aug 19, 2016
    Western NY
    Just as a followup, I pulled the linoleum/vinyl off the floor of the camper, and the ring of damaged flooring shows me that sealing the edges and running a the spar varnish at least 6" in from the edges should do the trick, for as long as we own the camper...
    [​IMG]
     
  10. jmatasov

    jmatasov "Never tell me the odds." -Han Solo

    55
    3
    Aug 19, 2016
    Western NY
    Ok, so this thread is about my evolving thought process on the subfloor...

    As I was talking through the subfloor and my plans for it (outlined above), I came to a realization.

    My chosen wood for the subfloor is Marine Plywood. The big selling point for Marine Ply is that the plys are glued together with waterproof glue. So...if every layer of the plywood is waterproofed and essentially sealed from every other layer of the plywood, it is not going to "breathe" in the sense most people mean. Regular OSB will, but not Marine Ply. It's 5-7 layers that are already sealed between them. Is my thinking correct? Please correct me if I am not understanding how Marine Ply works, but that is my understanding.

    So the conclusion I draw from that is that since I am using Marine Ply I am best off completely sealing the underside with something that will flex with the camper, since the only part truly exposed or "breathing" is the bottommost layer.

    Does that logic hold?
     
  11. mstrbill

    mstrbill Member

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    Mar 17, 2013
    Austin , Texas
    I say no. If Marine plywood is already waterproofed by using waterproof glue, why would you have to do anything else? This sounds like it the same as the Structurwood used on Coleman campers and they specifically state not to coat it with anything.
     
  12. jmatasov

    jmatasov "Never tell me the odds." -Han Solo

    55
    3
    Aug 19, 2016
    Western NY
    OK, I hear you on that, but if it everything but the bottom ply is already waterproofed via the glue, wouldn't I want to protect that bottom layer too?
     
  13. kreeves

    kreeves She and her two dogs

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    10
    Dec 4, 2016
    West Virginia
    I'm going to Paint/seal mine with a solid stain from Lowe's. Top edges will be sealed as well into the main floor area on top before new flooring goes down. My thought is seal it to keep moisture from getting in so you don't have to worry about letting it get out.
     

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