Plywood stretching advice...

[TimC]

I'm building a ply-foam-ply sandwich floor on a 4x8 trailer which is actually 49 1/2" wide. I'm looking for suggestions on how to build it 49.5 wide with 48" plywood. I'm not concerned about the foam portion as I can fill an area on each side with lumber. I'd like to avoid buying 5x8 plywood as it is not available in 1/4" thickness and 3/4" is pricey and heavy.

Would you rip the ply down to two 2' sheets and fill in the 1 5/8" void at the center? (Saw kerf plus 1 1/2")

Thanks for your ideas.

Tim

[eLink]

Use two 4x8 sheets, cut them to 49.5" x 48". The waste can be used for some other project.

[TimC]

Thanks Erik. That would work. I'm leaning against that strategy because it would require four sheets to accomplish what I'm trying to do, it results in a seam which I hope to avoid and I don't have a use for the cut-offs. If the cut-offs were AC plywood I might go that route but it is crappy CD ply.

After some thought I have decided to go with coroplast for the bottom. This results in an even lighter structure and eliminates the need to coat the entire bottom surface with waterproofing. So I'm looking at 1/4 plywood top, 1" rigid foam inside and coroplast bottom. I'll build a frame out of pressure treated lumber and cut rabbets in the lumber to accept the ply and coroplast. I should be able to "stretch" the plywood all the way around the perimeter of the trailer bed consisting of pressure treated lumber to make up the difference in width.

[Pmullen503]

What kind of glue will you use on the coroplast?

[TimC]

I did a little research on gluing coroplast and came up with Todah Tear's comment about using Great Stuff. I have an old coroplast sign and a little bit of Great Stuff in a can that I can experiment with. I will use mechanical fasteners as well so hopefully the two methods will work well. Besides those the coroplast will be held in place on top of the trailer frame cross members every two feet.

Testing coroplast glued with GS to rigid foam. Will post results.

https://www.tnttt.com/viewtopic.php?f=55&t=64999&p=1168366&hilit=COROPLAST+EXPANSION#p1168366

[QueticoBill]

I think facing same issue I would mill edge pieces to fit between plywood skins but also extend 3/4 ", sort of a squashed fat "T". could be 2 pieces - one foam thickness and one foam +ply thickness - but I would prefer 1 piece. I guess you'd have to trim foam a little.

I would stick to ply both sides for skin strength, and no framing except perimeter.

YMMV

[TimC]

...

I would stick to ply both sides for skin strength, and no framing except perimeter.

YMMV

Yup, I'm thinking I might go back to the ply-foam-ply method. Strength would be better for sure. And coating the road side wouldn't be that difficult or expensive. The foam is more to prevent moisture penetration than insulating value. I'll have a six inch mattress to accomplish that.

[Squigie]

Most people tend to opt for a scarf with thinner ply.
With thicker ply, biscuits or half-laps seem to be the methods of choice.

I don't recall who did it, but one of the members here stretched their ply with butt joints and bowties.

You can always half-lap or half-lap with a filler.

quarterlap.png (11.83 KiB) Viewed 350 times

Hmm. That cropped and resized weirdly.
Whatever. Still gets the point across.


Are you sure you need the full 49.5" width in a continuous sheet?
Wouldn't it save some time and energy, without sacrificing strength, to possibly increase the width of the internal framing and then just use a filler strip on one or both sides abutting the ply?

[TimC]

...
Wouldn't it save some time and energy, without sacrificing strength, to possibly increase the width of the internal framing and then just use a filler strip on one or both sides abutting the ply?

That's an interesting question. And a real possibility. 3/4" on each side frame would need to be filled. It turns out the trailer bed chassis is 96 1/4" long. With PMF and maybe some sort of front surface rock deflector that extra 1/4" is no problem.

I'm rethinking how my 2" rigid foam, standing on edge on the frame would benefit from a different attachment method than I was planning. I planned that I would attach a cleat, 3/4" x 3/4", centered on the 2" foam and attched to the floor framing. Drawing below. I'm expecting I'll be planing the 2X Trtd lumber to a thickness to match the 1" foam and two 1/4" ply sandwich thickness. Also considering keeping the 2x 3 1/2" wide and trimming the 1" foam to fit the remaining space. Might be stronger than having the vertical joint lining up from trailer frame to 2" foam wall.

A dado on the end of the foam would marry the foam to the floor structure. And I don't have the required drip edge drawn in yet. Contemplating having a removable cabin but I don't know why. I don't need another utility trailer.

Still thinking...

Original plan with cleat and 2" XPS wall

[TimC]

Decided to go with the plan I sketched. Figured I'd make a final decision while I can still get the HD 11% rebate deal. Thanks for the ideas.

[Pmullen503]

The cleat functions primarily to keep the sides aligned while gluing, Its wrapping the canvas around the bottom edge that secures the walls to the floor.

For my next build I was going to do the same: cleat to align the sides while gluing but I would then unbolt the floor from the frame, prop it up on 4x4s so I can wrap the canvas around the floor to past the frame.

[TimC]

Yup, that's probably why I keep thinking of making the cabin removable. Thanks for the reminder...

My TDs have always had six anchor points, three on each side. Is that how you bolt yours down to the chassis?

Tim

[Pmullen503]

It's been a while, but it's at least (10) 1/4" grade 8 (for corrosion restance) bolts. Over kill but it's on an HF trailer. The cabin strengthens the trailer instead of the other way around!