Exterior seam molding source needed

Yeah, GDE, that's kinda what I was thinking of, but the more I look the more I find they don't use that kind of stuff on RV's. I'm going to go with a marine grade caulk (the kind used on seams below the water line,) which I figure should be good enough. Then 2-3 layers of marine grade paint should do the trick, and no visible seams ;?), although I'm going to use heavy duty, self-sealing, large flange pop rivets to reinforce the 3M VHB tape on the vertical struts so those might show, but then I'm not trying to win any beauty contests at this stage of the build. A little more work, but it'll do for now. Thanks for your input. ;?)

Cym wrote:
Thanks for that link, but looking at these I can't figure out what most of them are for :? (and of course no description as to their purpose, lol) although I suppose you're supposed to know what you're looking for in the first place. I could be completely off base, but what I thought I need is a piece that essentially has a double-sided u-shape so both pieces of plywood can fit into each channel, but maybe I'm thinking of stuff you'd use in a tub enclosure. If you could point out which piece serves that purpose I'd really appreciate it, and thanks again for your help ;?)

I think I have an idea as to what you want..

Kind of like

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Or a "H" on it's side..

Sort of hard to draw using keyboard text..

I don't think there is any off the shelf stuff made for the size of plywood.. Most of the stuff I have seen is designed for thin materials like bathtub surrounds or FRP panels..

You might be able to find some aluminum carpet edge trim to cover the seams but you would have to use screws to hold it in place.

Alternately you could take a look at vinyl siding "J" channel trim (J channel back to back would give you the effect of covering both plywood edges) or any other vinyl siding trim pieces and creatively "adapt" those to your usage..

The link posted is mostly for the fillers that go into the aluminum trim molding. There are also some window glass retainer moldings in there. I purchased lengths of trim molding at Arlington RV in RI but I would expect any RV parts store would have it. They have some that goes along a flat seam or on a corner. Butyl tape it used between the molding and the seam.
Hopefully this link works: Flat Molding
At least that is the profile. No idea how long the piece is. You would need to call someone.
You will need a vinyl filler piece to cover the screws.

Thanks for that link, but looking at these I can't figure out what most of them are for :? (and of course no description as to their purpose, lol) although I suppose you're supposed to know what you're looking for in the first place. I could be completely off base, but what I thought I need is a piece that essentially has a double-sided u-shape so both pieces of plywood can fit into each channel, but maybe I'm thinking of stuff you'd use in a tub enclosure. If you could point out which piece serves that purpose I'd really appreciate it, and thanks again for your help ;?)

DrewE wrote:
The best I can suggest is checking out the PVC moldings at a big box store. I've seen some variations on panel joints and T moldings and such, I think. You might also have success applying eternabond tape over the seams once you've completely finished the plywood, though I think it would look rather poor.

On the whole, this scheme of covering sounds somewhat problematic to me, for what it's worth. Typical current practice is to have a seamless sheet of flexible filon or similar (a sort of fiberglass laminate, I think) over whatever substrate is used, or else interlocking corrugated aluminum siding strips. Maybe I just lack some sense of adventure or don't have enough faith in unconventional approaches.

Hey DrewE, well not sure about the PVC as it might not be exterior grade UV resistant. That's why I was looking for RV parts. Yeah the tape is not an option either.

As for the covering, that may be true if you're thinking strictly in RV terms, but for marine applications it's not unusual to simply seal then paint over wood. There will be a lower section with another seam running the entire length and I have thought of adding a layer of some sort to protect if from damage from road debris, but still searching for the seam material to see what's available and then work with that stuff, if it exists.

I wonder if there's fiberglass tube somewhere that I could cut to make the corners. Personally I hate working with fiberglass cuz I have a some bad memories as a kid. My dad bought an old fiberglass boat and one summer he had my sisters and me working almost every day re-glassing, sanding and painting that sucker. To this day the smell of fiberglass resin makes me ill, lol.

The best I can suggest is checking out the PVC moldings at a big box store. I've seen some variations on panel joints and T moldings and such, I think. You might also have success applying eternabond tape over the seams once you've completely finished the plywood, though I think it would look rather poor.

On the whole, this scheme of covering sounds somewhat problematic to me, for what it's worth. Typical current practice is to have a seamless sheet of flexible filon or similar (a sort of fiberglass laminate, I think) over whatever substrate is used, or else interlocking corrugated aluminum siding strips. Maybe I just lack some sense of adventure or don't have enough faith in unconventional approaches.

Btw, I meant quarter round corners, lol, so anyone know where on the web one might find this kind of molding?
:h

DrewE, thanks for the information, I didn't want to get into fiberglassing it if I didn't have to, that's another expense and ton of time I don't have. I've coated the plywood with 3 coats of spar varnish for marine applications. I was thinking of caulking the joints and then painting the whole thing with a couple of coats of white paint. But then a friend suggested using a molding at the joint which he thought I'd find at an RV parts store, but I haven't found that particular molding (not sure but I thought I've seen RV's with such stuff on it but could be mistaken). Same for the corners, just trying to save time if I could find some kind of pre-made 3/4 round plastic or fiberglass parts. Any idea where I might find such an animal?

Are you planning on any outside material over the plywood, like fiberglass or something? If so, I think typically you'd use that to cover the seams, after making whatever preparations are needed to ensure they stay tight and even.

I think boat hulls frequently just use a backer/butt block at the joint to hold the pieces in alignment, or else scarf and glue the joint to basically form a continuous piece of material. (Scarfing is easier for narrower widths and larger thicknesses than it is for a full 1/4" sheet of plywood!) Often they're covered over with a layer or two or three of fiberglass cloth for protection and waterproofing, and possibly a gelcoat or other finish.

There are various ways of forming a rounded corner, depending at least somewhat on the radius needed. For fixing up the bottom curve of the cabover on my class C, I put a seriese of strips around plywood formers, somewhat like barrel staves, with a layer of fiberglass epoxied to the front and back to tie them all together structurally. It made a fairly light and stiff and strong construction, though was a good bit of work to put together. I didn't use one, but a bead and cove router bit set applied to the edges of the strips would allow them to interlock where they meet and make for a stronger and better job overall.