Splicing subfloor

[JoleneAS]

Hey guys. I know I'm posting a ton and eventually I'll create my own trailer build thread.

I have my 76' Overlander stripped to the frame, cleaned, and about to POR15. I am doing a shell-on approach, but I was able to get all subfloor out intact. This will make tracing the new subfloor much easier.

At any rate, I read about people splicing their subfloor together. What is the best approach for this when someone is installing all new subfloor? Is there a preferred method for this?

I purchased the recommended self-tapping screws from Fastenal and stainless steel bolts / washers / nylock nuts for the perimeter / C-channel, for what it's worth.

[Bubba L]

There have been numerous comments on what some have done to keep the plywood joints in perfect alignment. When we adjusted the crossmembers on our chassis to accommodate the tanks, we adjusted to also accommodate the plywood joints. We also went a step farther and used a biscuit joiner and added biscuits on 12” centers along the butt joints. I glued the biscuits into one sheet but not the other so expansion wasn’t compromised. I’m sure this was overkill, but it didn’t take any time to do it. In your case, I would make me a dimensioned sketch of crossmember locations and hit spices on crossmembers where you can. Another simple way is to screw a 3/4” x 2” strip of plywood to the bottom of one sheet edge and set the other on top of the piece of strip hanging over the edge of the first sheet. You just don’t want a spongy feel at the joints. I’m sure others will chime in with other suggestions. Good luck

[Isuzusweet]

When I did my Coosa subfloor I used a 3/4" half lap joint.

Set up router with a 3/4"x usually 1/2" cutter, with bottom bearing, (link below)

https://www.homedepot.ca/product/fre...set/1000407377

Cut just a hair over halfway into the edge of the sheet. You want the joint to be a hair under flush to allow for silicone or PL premium nails to be applied into the joint. The beauty about a half lap joint, is you only need one fastener to fasten both sheets, and the bottom half lap keeps the sheets flush, no matter what the frame is doing below; or will support the other sheet if crossing between frame supports.

In the photo below, you can see the half lap joint. Whenever I was joining sheets together over a frame, I would cut the sheet 3/8" longer than the center of the frame work, so my fastener would be into the center of the frame.
Notice the one line of fasteners attaching sheets to the frame below.

Cheers
Sidekick Tony

[TheGreatleys]

My 74 originally had plywood strips (7/16" maybe, not positive on the measurement) under each of the plywood seams, and the subfloor sections were screwed to those before being bolted down. The frame members at the joints were lower to accommodate these strips.

You can see the strips in the first photo of this post:
https://thegreatleys.com/journal/201...va?rq=Subfloor. Unfortunately I don't think I have a good photo of them put together.

Not sure if that's what Airstream did for your year, but I'd suggest just duplicating what was already there. If it lasted this long, it should work out fine.

[JoleneAS]

Is there any chance mine did not have any splice pieces? Each subfloor piece joined over the crossmember where a metal zigzag looking piece joined them together and then a bolt into the crossmember. Once I removed the bolts and cut out the zigzag pieces I was able to separate them. That said there were some old, barely distinguishable screws at the seams that didn’t seem to screw into anything. The subfloor pieces don’t look like they were routed at all to accommodate a splice and the crossmembers seem to sit pretty flush with the rest of the frame.

I’m still confused about how to squeeze in a splice when the frame and crossmembers are flush. I’m having trouble visualizing the recommendations by Bubba and Isuzu. :/

Thank you guys for the help!

[JoleneAS]

Maybe this is kinda what is already being described but I was thinking of something. The original subfloor measures very close to 1/2”. I purchased 3/4” and will be routing down the entire perimeter to fit the c-channel. What if at the seams I routed the underside edge by 1/4” about 3” deep on both sides, then used 1/4” thick x 6” wide strips to span the width of the trailer and glued and screwed the subfloor into that. Does that make sense?

A crude drawing of what I mean.

[OTRA15]

Any time you want strength for assembling wood joints like this, it pays to take the time to use a good marine epoxy like the WEST products, and to pre-treat all the surfaces to be glued with a carefully-applied-thin-first-coat -- before assembly -- and letting that coat dry. Then sand it lightly.

When you assemble again with a fresh layer of epoxy, screw/clamp it all ASAP, and let everything cure for 24 hours without moving it, standing on it, etc..

"WEST epoxy" AirForums search results FYI:

https://www.google.com/search?q=WEST...com&gws_rd=ssl

Good luck,

Peter

[JoleneAS]

Thank you kindly for the reply. I already have myself West epoxy and will be using it on all subfloor pieces (I even planned to pre-drill and pour a small quantity into holes where screws will go into the frame and through C-channel to help prevent rot in these areas.)

I'm still just having a difficult time mentally visualizing how people are making these splices. D'oh.

[OTRA15]

It might also be a good idea to pre-coat all your ply/Coosa board subfloor sheet material with a thin coat of WEST applied with a roller, on both sides. If you also then coat all freshly cut edges with WEST, the possibility of rot is greatly reduced. Pre-coating plywood with WEST makes a great base for painting later, although that might not apply to an Airstream's subfloor.

Peter

[JoleneAS]

Thanks, I do plan to use the West system on all pieces of wood and on all sides. Now I just need to figure out a good method for splicing.

[Isuzusweet]

Originally Posted by JoleneAS

I’m still confused about how to squeeze in a splice when the frame and crossmembers are flush. I’m having trouble visualizing the recommendations by Bubba and Isuzu. :/

Thank you guys for the help!

Just Google half lap joint

https://en.wikipedia.org/wiki/Lap_joint

The great thing about this joint is that you don't have to follow the framework. In my picture you'll notice I've laid the Coosa across the frame work, instead of with it. As I said the bottom part of the lap joint supports the top half; once you have an adhesive in the joint, it's not comng apart.

Cheers
Sidekick Tony

[JoleneAS]

Originally Posted by Isuzusweet

Just Google half lap joint

https://en.wikipedia.org/wiki/Lap_joint

The great thing about this joint is that you don't have to follow the framework. In my picture you'll notice I've laid the Coosa across the frame work, instead of with it. As I said the bottom part of the lap joint supports the top half; once you have an adhesive in the joint, it's not comng apart.

Cheers
Sidekick Tony

Thanks much for the reply. I guess the part I don't understand is that the original subfloor pieces were 4' long, and I've purchased 4'x8' subfloor to replicate what was already in there. I get the idea of a half-lap, but I don't understand how to make the replacement sheets overlap if they are the exact length as previous? Or would I need to change the lengths of the sheets so that they no longer overlap the crossmembers?

[JoleneAS]

Looking at this thread, a spline joint sounds like it would make the most sense for me: http://www.airforums.com/forums/f36/...ed-142903.html

Given that I want the dimensions of my subfloor pieces to match the original and overlap over the existing, thin crossmembers, this would seem like a reasonable setup for me.

If there's any wood aficionado's out there, would be happy to hear about specific cut recommendations. If my wood is 3/4", I figure I'll make the spline a 1/4" and the depth 1" on each side for a 2" spline. Is this a reasonable setup?