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Does Anyone Treat Their Plywood Subflooring?


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Hello, I've been reading the various threads - several on floor replacements with laminates, vinyl, new carpeting, etc. and I also read recently the thread about water pressure/regulators, some mishaps, etc.


So my question is : Is it wise to treat the plywood subflooring with a marine poly, varathane, etc. when one has the chance while replacing flooring to help safeguard against potential water damage in the future? Anyone do it, and with what? Is it a bad idea because....?


I'll say thank you now to anyone who wishes to comment.



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I have done it on a 17 foot trailer. All new plywood floor and before installing I brushed on a very liquid clear low VOC epoxy to act as a water barrier/moisture barrier. I did top, bottom and the edges.

Something like this stuff





good luck

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The inherent problem with doing so is, you seal the exterior but the interior of the subfloor material is still untreated. This means if you miss one little spot, water can enter and saturate the interior of the subfloor and might never dry out completely because there is only that unsealed spot for any chance of evaporation.

I would much prefer to purchase pressure-treated, exterior subfloor material in the first place.

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Hi RayIN, thanks for those thoughts. Recently at Lowe's I was told that there is really no such thing as 'pressure treated wood' anymore because of the chemicals that used to be used to preserve it and deter bugs (arsenic, copper, etc) ; now they inject the wood with salt water, and then he said: In essence, there no longer is pressure treated wood as we knew it.


Just when I was leaning towards sealing,you got me thinkin' - again! :)

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I've been thinking about this for a few days, so here's my thoughts based on experience in dealing with some rot in my trailer and 50 yrs in the woodworking racket.


Sure you could gut your trailer and coat everything you could get access to but are you going to pull up the floor, coat both faces and all edges then replace? While in my rig, looking at my floorplan, I doubt it. What about your wall plates and studs, are the wood or aluminum? You may have to pop your slideouts beyond normal range of travel to gain access, let alone remove the interior slideout facia and backer and that is no easy chore let alone the crown or decorative trim around the top.


What about where the wall plates sit on the subfloor, that's about 1- 1/4 inches, how will you access that and what about the outside edge of the slideout floor covered by the fibreglass skin on the outside of the wall, how do you plan to get at that?



What about your steps coming into the trailer or going up to the bathroom or bunk area? Are you going to tear them out to get at all sides and faces of the steps and all that is under?


I can answer that because I did it on my bedroom slide. The floor was rotten 'cus someone else didn't do their job properly and it was a difficult job to replace it and I have all the tools required.


Do you have any idea how much your neck and back ache when working for even a short time in a very awkward position. I'm 5 10 trying to work in a 5' space with my head trying to look up under the slideout floor.


And that was just 1 slideout let alone the other slides and floor.



You're opening up a huge can of worms.


Check for rot now.


Tap outside the trailer, underneath the slideouts when deployed, tap with your knuckles. If there is rot, it will sound and feel mushy, not a hard rap.

If you have a corner sink, reach in where the plumbing comes thru both the slideout and trailer floors. There will be fittings on the end of the pex pipe. They need to be tite or will leak like mine did. Feel the floor in or on both to see if it is wet or black. Cut an access panel in the back of the corner sink unit, reach in with you camera on flash and take some pics in behind the sink cabinet.


I'm off my soapbox for now.

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Used to work in a lumber yard. I was very impressed with the propaganda we would get on "Thompson's Water Seal".


Apparently people even use it on their drywall in wet areas and it has proven it's worth when they have had floods.

I found out it does NOT work on a farm wagon bed. I bought dried oak boards from a sawmill and replaced the bed a few years ago. Painted everything with Thompsons first, then bolted them in place. Went back a week later and re-painted the boards. Last year I began replacing rotted, water-soaked boards as they broke, almost have another new bed now.

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( re: Mike and Claudia and Ray's comments) I've used Thompson's around an outdoor hot tub -- worked wonderfully at first, but seemed to wear off quickly on the decking around it. Mixed feelings now about treating or not treating the subflooring. I guess whatever one can treat completely, is potentially saved from damage. I'd do two good coats--top, bottom, edges; but like Ray said - if you miss a spot and the wood gets soaked, then it won't dry, and that's more trouble. Roger laid it all out there quite nicely. I've also used the epoxy coating suggested by RVFan, but never on wood; worked great on cement flooring. Hmmm. Thank you one and all for your time and input.

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