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Open Roads Forum  >  Travel Trailers  >  Vintage TT's

 > How to treat a Subfloor?

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drsteve

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Posted: 12/29/19 09:13am Link  |  Quote  |  Print  |  Notify Moderator

Marine grade plywood is really good stuff, but it's not waterproof, nor is it treated. It is high grade plywood, five to seven ply, sanded on both sides, with no voids allowed. The glue is waterproof.

It is also horribly expensive.


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pianotuna

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Posted: 12/29/19 09:14am Link  |  Quote  |  Print  |  Notify Moderator

Hi,

So is there a waterproof plywood?


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Posted: 12/29/19 10:38am Link  |  Quote  |  Print  |  Notify Moderator

GrandpaKip wrote:

Most CDX is not suitable for vinyl sheet flooring (telegraphed defects) and has a twist that can difficult to deal with in close quarters.
BC plywood can also be used, though not as flat or smooth as AC.


Good point. For the OPs, also consider snap lock type “floating” flooring. Economical, again much easier to work with, especially in tight quarters and many more aesthetically pleasing options.


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Posted: 12/30/19 07:45am Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

Hi,

So is there a waterproof plywood?

Yep, if you fiberglass it.


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Aubrey0418

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Posted: 12/30/19 07:57am Link  |  Quote  |  Print  |  Notify Moderator

Okay so I'm really torn on what to get as the base plywood which would be going directly on top of the metal frame and exposed to the weather. We were planning on doing a base plywood then insulation then the subfloor and then vinyl wood planks on top of that. For the base plywood I'm torn between marine grade or exterior grade? I know marine grade is expensive and would need sealer. Honestly though, which one is the better bang for the buck?

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Posted: 12/31/19 08:27am Link  |  Quote  |  Print  |  Notify Moderator

Most contemporary trailers use the plastic corrugated sheets as the bottom layer that is closest to the road. No sealing, no rot and lower cost. Most people call it an underbelly cover. I have bought some at Home Depot in the past.
I suggest you go take a peek under a trailer at an RV dealer.

Grit dog

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Posted: 12/31/19 11:20am Link  |  Quote  |  Print  |  Notify Moderator

GrandpaKip wrote:

Most contemporary trailers use the plastic corrugated sheets as the bottom layer that is closest to the road. No sealing, no rot and lower cost. Most people call it an underbelly cover. I have bought some at Home Depot in the past.
I suggest you go take a peek under a trailer at an RV dealer.


^ This is what I was describing, but appears the OP is intending to make a plywood sandwich with foam insulation in the middle on top of the floor framing.
Is this how the trailer was originally built? If not, have you accounted for the additional floor thickness or height?

Bottom line, the water resistance of the bottom plywood is being scrutinized far too closely, IMO. It is not submerged, it is not constantly exposed to the weather from above. It only gets wet while driving in the rain and then is sheltered and dries out.
For example, I have a "temporary" plywood ramp I built into the back of the shop about 9 years ago. wood frame, don't remember if I used treated lumber or not, with a piece of MDO plywood on top. It has been 100% exposed to the wettest weather (Seattle) from above and has yet to rot out.
Pretty much all cargo trailers have exposed plywood on the bottom, some are pressure treated, some traditional plywood or other material like Advantech (exterior grade OSB basically). Have a 15 year old trailer that runs only in the winter (wet/salt/slush) and sits outside. Floor is fine, like new still.
Any exterior glue plywood with a coat of paint, stain, varnish, waterproofing sealer will likely out last the trailer again as it is only occasionally exposed to road spray and sheltered the vast majority of the time.
Barring re-constructing the floor the way RVs are typically built. 1 layer of flooring above the joists, insulation in between the joists and a thin "skin" under the joists, if your doing the sandwich floor...
I'd think 1/2" ply bottom, 1" 30-40psi foam board, 1/2" plywood on top.

Grit dog

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Posted: 12/31/19 11:22am Link  |  Quote  |  Print  |  Notify Moderator

Or just sheet the floor with 3/4" and be done with it. What is the expected use? Winter camping, I could see insulated floor being an advantage maybe, but not in temperate or warmer weather.

Cost/effort/benefit analysis here.

busterja21

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Posted: 12/31/19 11:45pm Link  |  Quote  |  Print  |  Notify Moderator

I'd 2nd the recommendations for advantech. I've had it in my snowmobile trailer for 10 years, which is constantly exposed to salt, mag chloride, standing water, ice and snow. No issues with it breaking down, warping or sagging.

If your really worried about it, then use an underlayment

on the vinyl flooring (assuming its plank or similar), i'd suggest something rated for non climate controlled otherwise it can contract in cold environments and separate at the seams.


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Posted: 01/01/20 09:22am Link  |  Quote  |  Print  |  Notify Moderator

If you are going to put everything on top of the fame, then I would do as Grit dog suggested, though with some solid framing between the foam edges.
You could also wrap the bottom layer in Darco, a waterproof fabric, before installation.

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