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Old 06-29-2015, 04:15 PM   #1
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Sealing Subfloor - Polyurethane vs Penetrating Epoxy

Hi guys,

I recently sealed the original subfloor of my 1970 Overlander with a high grade polyurethane floor sealant. (It was in decent shape, but had a couple of small rotten spots that I cut away and sealed off).

However, while I was scouting around on Vintage Trailers.com, I found that they recommended using Smith & Co CPES Penetrating Epoxy. I'm wondering, is it worth sanding down and removing the polyurethane seal and replacing it with this product? Apparently polyurethane totally seals out moisture, while this Smith and Co epoxy product penetrates and allows the wood to breath while preventing fungus from taking over.

For those of you who have sealed with polyurethane, have you had any issues?

Thanks for any and all advice - happy Airstreaming!

Andre
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Old 07-29-2015, 12:21 AM   #2
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I'm thinking about using the penitrating epoxy before installing vinyl flooring.
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Old 07-29-2015, 06:19 AM   #3
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Sealing the floor with anything such as oil based paint, or a poly varnish is fine. Figure it lasted over 45 years with nothing on it so coating it with something can only help prolong it. Penetrating epoxy is used mostly for rotted wood to give it back some structure rather than replace it. It would be serious overkill to strip off what you did just to put that down, just focus on something else that needs fixing and be happy.
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Old 06-21-2016, 12:20 PM   #4
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Epoxy Recommendations

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Originally Posted by larry smith View Post
I'm thinking about using the penitrating epoxy before installing vinyl flooring.
Due to the leak between the bumper plate and shell on my 2009 25FB I experienced some damage to the floor. Not bad enough that anything needs to be replaced (fortunately) but I would like to use some kind of epoxy which can soak into the floor in the areas where the water has penetrated the plywood.

I've heard of Rot Doctor. Is this what should be used or are there any other recommendations?
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Old 06-21-2016, 12:55 PM   #5
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In boat building we always used WEST System epoxy to pre-coat all the marine plywood. First, we would roll a layer of epoxy onto both sides of the full sheets, as they lay flat on a work bench so the epoxy could soak in. You have to let the first side cure/harden before flipping the sheets over to do the other side. [edit -- see below for sanding the sheets]

Then after cutting the plywood up into the final pieces, before assembly, we would brush epoxy onto all the cut edges, which are especially vulnerable to water soaking in, sometimes years later. You can use a fast hardener for this step, and it sets up in a couple of hours. If you know that you will not need to remove the piece of plywood, you can set it in place with the epoxy still wet on the edges, but don't even think about removing it later if there is a problem.

This may seem like overkill for trailer assembly, but it does not require much additional labor and materials, just planning for the time required.

And you can rest assured that the floor will last . . .



PS edit -- If you are going to bond anything to the plywood later, like another sub-floor, linoleum, or some composite flooring, you should sand the epoxy-coated plywood lightly when it is still in full sheets, to remove the "blush" from the epoxy chemical process/hardening.
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Old 06-21-2016, 09:11 PM   #6
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I don't plan to remove or replace the plywood as it is not rotted beyond use. But is has had water damage.

What type of epoxy product have others used on the floor? Has anyone used Rot Doctor?
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Old 06-21-2016, 10:15 PM   #7
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Then after cutting the plywood up into the final pieces, before assembly, we would brush epoxy onto all the cut edges, which are especially vulnerable to water soaking in, sometimes years later.
The importance of this step can NOT be overstated. If you can NOT seal the edges of the wood, do NOT use epoxy. I learned from experience.

I coated a plywood floor heavily with epoxy both top and bottom on a Scamp. I even drilled several tiny holes all over it almost full depth of the wood and used a watery very slow-drying acetone thinned mixture so that it had a water-like flow and viscocity that allowed it to absorb everywhere throughout the wood. It dried hard and sturdy as a rock. You could JUMP on it without worry. BUT...I could not get to two sides of the edges of one section so I wasn't able to treat them. I figured it didn't matter...the rest was sealed AMAZINGLY well. A few years later I had a leak that I couldn't see; water was draining between the exterior and interior walls in the front bathroom, and oozing slowly down into a corner that was hidden. Water was being soaked up into the floor like a sponge through the non-treated edges. Just soaking and soaking up water that I couldn't detect or see. Even being able to see the wood through the clear epoxy (I never put anything over it), you couldn't SEE the water inside the wood.

The water could get in, but it could NOT get out. It stayed like that for months on end without me knowing, just sitting there rotting from the inside out. One day I dropped a 12oz can of Coke on the floor and it literally broke about a 2" chunk out the wood floor about 1/2" deep. I was STUNNED. The wood, while still coated with thick clear epoxy sealed on the top and bottom and throughout, was basically rotted out like balsa wood or styrofoam between the top and bottom sealed surfaces. It had no internal strength. If I step on that section I'm sure I'd go right through it. The epoxy is strong, but not nearly strong enough to stand on with the rotten wood between the top and bottom.

Remember, if water can get in, it MUST easily be able to get out. If you can't seal the wood TOTALLY, do NOT use epoxy. This is the same way many boat transoms rot from the inside while being enclosed in fiberglass; water gets in and it can't get out.

Take the time to do it right on ALL edges of ALL the wood and sealing it with epoxy will grant you a lifetime of use without rot.

Hope this helps!
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Old 06-22-2016, 05:55 AM   #8
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Quote:
Originally Posted by RareStream View Post
The importance of this step can NOT be overstated. If you can NOT seal the edges of the wood, do NOT use epoxy. I learned from experience.

I coated a plywood floor heavily with epoxy both top and bottom on a Scamp. I even drilled several tiny holes all over it almost full depth of the wood and used a watery very slow-drying acetone thinned mixture so that it had a water-like flow and viscocity that allowed it to absorb everywhere throughout the wood. It dried hard and sturdy as a rock. You could JUMP on it without worry. BUT...I could not get to two sides of the edges of one section so I wasn't able to treat them. I figured it didn't matter...the rest was sealed AMAZINGLY well. A few years later I had a leak that I couldn't see; water was draining between the exterior and interior walls in the front bathroom, and oozing slowly down into a corner that was hidden. Water was being soaked up into the floor like a sponge through the non-treated edges. Just soaking and soaking up water that I couldn't detect or see. Even being able to see the wood through the clear epoxy (I never put anything over it), you couldn't SEE the water inside the wood.

The water could get in, but it could NOT get out. It stayed like that for months on end without me knowing, just sitting there rotting from the inside out. One day I dropped a 12oz can of Coke on the floor and it literally broke about a 2" chunk out the wood floor about 1/2" deep. I was STUNNED. The wood, while still coated with thick clear epoxy sealed on the top and bottom and throughout, was basically rotted out like balsa wood or styrofoam between the top and bottom sealed surfaces. It had no internal strength. If I step on that section I'm sure I'd go right through it. The epoxy is strong, but not nearly strong enough to stand on with the rotten wood between the top and bottom.

Remember, if water can get in, it MUST easily be able to get out. If you can't seal the wood TOTALLY, do NOT use epoxy. This is the same way many boat transoms rot from the inside while being enclosed in fiberglass; water gets in and it can't get out.

Take the time to do it right on ALL edges of ALL the wood and sealing it with epoxy will grant you a lifetime of use without rot.

Hope this helps!
It helps a lot. Thanks for taking the time to explain and it makes sense.

I saw a product called CPES which is designed to soak into the wood. Would this work better than just epoxy?

I don't need to replace the floor as it is not rotted. I just wanted to give it some strength because of having water damage. Or would it be better if I just leave it as is?

Thanks!
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Old 06-22-2016, 06:19 AM   #9
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I do not recommend the WEST system for penetrating into existing soft/rotted areas. They used to make a product called Git Rot but I have never used it. There are probably epoxies which are very thin and designed to penetrate.

One caution for any epoxy used -- the chemical reaction after adding the catalyst/hardener is exothermic, which is to say that it generates and gives off heat as a by-product. One must be careful not to pool up the epoxy into too-thick puddles, as overheating can occur, forcing the chemical reaction into a more dangerous state of "excitement" which can produce fire and toxic fumes. No fun!

Leftover pots of mixed epoxy should be put outdoors, and ideally poured onto a flat surface like a plywood scrap, so that the epoxy can spread out and cool off as a flat-ish material, not a bulky tub of hot material.

All safety precautions should be followed including gloves and respirators. A fire extinguisher is good to have on hand.

Good luck!

Peter

PS the CPES mentioned by Hans627 sounds like it is designed to penetrate, however I am not familiar with it. If it is not a two-part epoxy material, I would keep looking for such a thin epoxy.

Edit -- sounds like the right stuff, I would research more and give it a try.

http://www.rotdoctor.com/products/cpes.html
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Old 06-22-2016, 11:28 AM   #10
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I used good quality 5/8 plywood for my subfloor. Not marine grade however.
I used Smiths penetrating epoxy.
Over a year ago when I coated my sheets I did a scrap piece.
The scrap piece with epoxy has been outside ever since under the eve of garage.
No rot at all! Even on exposed edges.
Can't imagine my floor will rot away in my lifetime.
I'm clam happy with the results.
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Old 06-23-2016, 10:14 AM   #11
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My experience with boats is what leads me to protect the top surface of the wood, but leave the bottom untreated. Water infiltration in trailers is (generally) from the top down to to leaks. There are also various fasteners penetrating the top surface of the floor, both through the C channel and from the various cabinets, battery boxes, etc. Leaks in seams, vent gaskets, etc. often can run down the inside of the skin and lead to water puddling on top of the fasteners that penetrate the wood; this is between the exterior and interior skins in the C channel. Since it's not practical to bed all the elevator bolts and other fasteners w/ sealants, or drill oversize holes and coat the holes w/ epoxy, water infiltration into the wood seems inevitable if there's a leak in the trailer.

I prefer to leave a way out for the water.


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Old 06-24-2016, 12:26 PM   #12
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Hans627,
I am about to do the same to my 25'FB. I too got lucky, the floor is wet, stained and feels a bit soft in some spots, but is not rotted. I'll drill some holes in the top and apply some type of epoxy sealer, probably CPES or similar.

I plan on not doing anything to the bottom of the subfloor, but have removed the foil insulation and will be adding spacers and some stiff foam board insulation to allow moisture to run away from the floor (other threads have covered this extensively).

Hope your project goes well,
Chris
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Old 06-24-2016, 12:43 PM   #13
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The assumption -- that water intrusion in all the hidden places in a trailer will come from above and obey the laws of gravity and free-runoff (ignoring capillary action and wind-forced "running uphill") -- it seems to me is misplaced.

Water does not follow logic.

Pre-coating all plywood surfaces and cut edges is by far the best insurance against future rot, if possible.

There is no perfect solution, and Bart's point about not trapping water inside the ply is well-taken.

Each solution is a compromise dependent on the exact circumstances of each situation.

Happy Trails!

Peter
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Old 06-24-2016, 01:13 PM   #14
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Peter,

I agree with your statement, and in a perfect world I would do it that way. In this case, my subfloor isn't really that bad, and it would be a massive PITA to remove it and treat it the right way. I don't have the time or skills to do that. I just hope this lasts a long time (it should do better than the original since I'll fix the biggest water leak around the rear bumper).

Chris
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