PMF question...ever had this happen?

[GPW]

Remember the “sock” effect meaning all edges should be overlapped and glued (?) securely ...

The Skin is the Strength of the trailer … The edges are the weak points … I overlap and use “reinforcing strips" over that , then sizing and paint …

[MatBirch]

Remember the “sock” effect meaning all edges should be overlapped and glued (?) securely ...

The Skin is the Strength of the trailer … The edges are the weak points … I overlap and use “reinforcing strips" over that , then sizing and paint …

For a foamie, this is a good school of thought! On plywood though, it would already be strong, and strips of canvas glued down would be durable and far more waterproof than “traditional” trailer covering methods. Aluminum siding, fiberglass siding, even FRP coated plywood with the little filler strips would all allow more points of ingress than overlapping strips of painted canvas.
Just my humble opinion at this stage of my own build.

[GPW]

Mat , our first trailer was plywood , and if we had covered it with canvas , it would probably still be here … Paint alone wasn’t enough to prevent delamination … especially in our DAMP climate … If it wasn’t for that , I’d have never tried a FOAMIE !!!

[John61CT]

Not "little strips" though, the dropcloth sheets are bigger than the pieces they are covering.

[MickinOz]

I believe the PMF method involves saturating the timber with Titebond?

Personally I like the idea of taking wood out of the picture completely, would prefer the core structural to be materials that never rot, e.g. aluminum + insulation foam.

I've been pondering this.
I think that removing plywood from the picture takes the teardrop out of the hands of the home builder to some extent.
Once you move to aluminium, or even steel, you are talking mig welders, special extrusions to get nice looking joins, special adhesives, etc.
Sure, there are guys here doing a great job with aluminium cladding, but generally over plywood though.
And I do think working with metal is harder - could just be me.
I do find it interesting that quite a few people don't discuss the glue used in their plywood.
Some people seem prepared to use less than waterproof gluelines and rely on sealers to avoid delamination.
As I type, the only piece of plywood in my whole build that doesn't have a water proof A-bond is the inner head liner on the front curve.

[John61CT]

I def mean using metal for frame / support, e.g. I want 500# load bearing roof rack up top.

PMF+ foam only for skinning for me

And nothing wrong with cut &bolt, or getting a pro to help out in spots afaic.

[pchast]

Have you looked at long run foamy's?
Most use less frame than expected above the trailer base.
Its really not much different than using wood sheet goods.

[Patrio]

Today, I went out and re-covered with the old sheet. It went way better than I expected. TB, rolled on full strength a foot at a time, the canvas rolled onto a long dowel and unrolled over the fresh glue, pressed down by hand, then ironed flat under a hand towel. Advice: do not let the iron slip onto the latex paint, especially if the iron belongs to your wife. She will NOT be happy.



The little "lines" near the middle are where I accidentally hit the paint with the edge of the iron. In the second pic, you can see how flat it glued down. You can see, though, it stretched out nice and flat.



Where I had stored the canvas, it got a little dirty. I'll probably wipe it down with a damp cloth and apply another topcoat. In addition, I'll have to put 3 coats on the parts where there's now bare canvas.


John61CT, I agree, the risk of delamination might be higher. I can't say how much. But, if you can apply PMF over PMF, there is probably no penetration into the first coat either. I can't see where this is greatly different from that. On mine, the glue is soaking into the plywood and is soaking into the canvas.

I can say, part of the original problem was "undergluing" on that part, which didn't adequately seal the plywood, which led to paint getting in a gap, which led to swelling. I didn't make that mistake again!

The back side of the fabric does show some paint flow-through, but not like you'd think. There's lots of "virgin" fabric there to soak up glue. In the end, I think it will be OK.

GPW: I intentionally left my edges long. I'll trim them back to 4-6 inches or so then overlap them onto the other panels once I begin assembly. Reason being, once I begin assembly, I will have to move outside, meaning I need to minimize the time the camper is exposed to the weather before it is sealed up.

[Patrio]

Oh, and just wanted to say...if you want a high quality, waterproof tarp, get some latex paint and one of these dropcloths and paint both sides.

When I had that off the camper, it reminded me of the old tarps my dad used to have when I was a kid...before everything turned to plastic!

[John61CT]

To me the term PMF is the whole process, not just one of its components.

And the critical part is the cloth fibres getting 100% saturated, to me meaning "as above so below", the cloth fully embedded, one continuous thick layer of fluid not just "saturating" but totally encapsulating that cloth.

Having a stiff impermeable layer glued on one side then painted on the other

may well be "good enough" standing up to certain conditions for some period of time,

but personally I'd prefer to waste some materials and "get it right" as best I can, at least according to my vision of best practices.

[Patrio]

To me the term PMF is the whole process, not just one of its components.

I'm not as concerned with the term as I am the results.

And the critical part is the cloth fibres getting 100% saturated, to me meaning "as above so below", the cloth fully embedded, one continuous thick layer of fluid not just "saturating" but totally encapsulating that cloth.

If you're using glue above and paint below, you're not using a continuous layer of thick fluid. In fact, you'd be surprised how much the paint doesn't penetrate the fabric, even after four coats. I expected it to be the same color on the front as the back. Wasn't even close! If I get a chance, I'll show you a pic off the back side of the canvas.

Having a stiff impermeable layer glued on one side then painted on the other may well be "good enough" standing up to certain conditions for some period of time but personally I'd prefer to waste some materials and "get it right" as best I can, at least according to my vision of best practices.

I get it. It's about the level of comfort you have with it. Being here and seeing first-hand how solidly this application went gives me confidence that it will be just fine for my intended purpose. I'll keep you posted on how it works out!

[John61CT]

If you're using glue above and paint below

I think you mean glue on the inside, paint on the outside?

If so then my requirement for fully encapsulating the fabric, would be in relation to the glue.

The interface between the outermost glue face and the waterproofing coating would then be where strength against peeling is critical.

Personally, my goal is to use just one coating that has excellent adhesive and primer / sealant / waterproofing properties, so one less compatibility issue.

The outermost (very thin) paint layer is then just for color and UV protection, but of course also adds more waterproofing.

As we agree, to each their own, and I very much hope what you've done lasts a long time.

[Patrio]

It didn't, because you made me paranoid...lol.

I ripped it off and re-coated it with fresh canvas.

I don't know how long it would have lasted, but it certainly didn't want to come off.

I'm going to use it for seaming and patching when I get my camper assembled.

Thanks for all the advice.

[John61CT]

Darn would have been an interesting experiment!

But that's what I would do, let others collect the arrows 8-D

[Patrio]

I edited my first post, just in case anyone happens upon this.

If you try to fix plywood "checking" like this, beware that it WILL come back. Maybe not immediately, but eventually.

It happened to me all these months later. Exact same place, exact same characteristics.



Except now, on an ASSEMBLED camper in the middle of winter, which will be much more difficult to repair! I may wait until Spring anyway and let this run its course, so I'll know how much wood I ultimately need to replace. I plan on cutting out only the affected section and replacing with good wood.

After reading about plywood checking on the Internets, once this kind of checking starts, it'll keep going. Even using fiberglass resin and cloth on it will NOT stop it from continuing to check. Best remove the offending piece and replace.