Routing edges of subfloor to allow greater thickness

[JoleneAS]

Hey guys. Doing a full gut of a 76 Overlander, shell on. All of the subfloor needs replacement. The existing subfloor is 1/2”, which is kinda flimsy. I have been thinking about taking 5/8” or 3/4” and routing down the edges to fit the c-channel. What are the negatives in doing something like this? Obviously a little more weight. I will allow enough room for the interior skins to slide into the groove between elevated subfloor and shell. I don’t plan on using any of the original cabinetry, so the slight change in height will not impact that.

Any thoughts?

[Bill M.]

Sounds good to me. I have done that for a small patch. I have see such a rout in places on my trailer that Airstream did at the factory. Seems the OSB was thicker than the channel from the start. The dado is on the top which makes sense.

[Isuzusweet]

I used 3/4" Coosa board in place of my 5/8" plywood; 40-45% lighter than plywood; will not rot or promote mildew; just as strong, if not stronger than plywood, less than 1% water absorption rate. Very easy to machine to any profile.

I first did a 1/4" deep cut 1 3/4" to the inside of the blade on the edge fitting into the C channel; then machined the 1 3/4" to 5/8" thick; then machined an angle on the last 1 1/4" to aid insertion into the channel, since it's only the inside of the channel that needs support. Not the best picture below, but you'd get the drift.

Cheers
Sidekick Tony

[Del Gurney]

JoleneAS:
Airstream always installed 5/8 sub-floors.
1/2” is not possibly strong enough nor
Thick enough to accommodate the
Elevator bolts to hold everything together.
Back to the drawing board.
What ever you chose for sub floor be sure
to seal it and epoxy all around the edges.

[steve46]

Your idea is just what I did on my ‘76 TradeWind Land Yacht. I used 3/4” tongue and groove “plytanium dry ply” and routed the edges down to the original ~1/2” thickness and it worked very well. Be prepared for a huge mess of sawdust when you rout the edges. I was more concerned about floor thickness and integrity than losing 1/4” of interior height. I also built flashing at the rear to avoid the wicking of water into the floor. See the photos and good luck with your project.

[SuzyHomemakr]

I was able to pry up the c-channel and jam in 3/4" ply on my shell-on floor replacement section. This was about 4' of the end, so fairly substantial. So no need for routing?

Be sure to drastically seal the edges if you're using plywood. And use some nice, lightweight marine ply or that Coosa board ($$$).

[Iansk]

Originally Posted by Del Gurney

JoleneAS:
Airstream always installed 5/8 sub-floors.
1/2” is not possibly strong enough nor
Thick enough to accommodate the
Elevator bolts to hold everything together.
Back to the drawing board.
What ever you chose for sub floor be sure
to seal it and epoxy all around the edges.

My '77 has/had 1/2" subfloor. Tape measure and caliper confirmed.



Ian

[Bill M.]

Stiffness goes up in proportion to the cube of the thickness. Well worth it to use the 3/4” nominal at whatever actual thickness it is.

[Crackerman]

Prying the channel open is probably the easiest way to get 3/4" wood in there.

It's soft enough to open with a piece of 1/2" wood, like a fence picket, then the plywood fits in fine. After it's installed, tap around the bottom of the channel to close the gap back up.

[JoleneAS]

Wouldn't prying open the C-channel result in rivet holes not lining up? It doesn't seem like it'd be too hard to use 3/4" ply and route the outer edge to 1/2". I just wanted to make sure that this was a reasonable idea since there are posts on this sub stating "don't use non-factory thickness, you will have problems!" I suspect that is for people using original cabinetry and such.

And I agree with Iansk. My subfloor thickness was confirmed by caliper and tape measure at multiple areas. This subfloor has never been replaced, so the 1/2" was definitely factory on this model.

[bradt]

If you indeed have 1/2" original flooring, I would recommend replacing it w 1/2" Coosa board. No routing, no sealing, light weight, easy to work with, stronger than plywood, and will never rot. It costs more but will give good results and make your project go faster. I had 5/8 plywood and replaced it w 1/2 Coosa and added 1/8 aluminum shim stock underneath the Coosa.

When removing my rotted plywood floor, it was apparent that the factory sealing of the surface and edges with black sealant didn't help so much. Once inserted in the c-channel, lots of holes get drilled for screws and bolts. It is no longer sealed. Plus, moisture can wick in to the plywood thru these penetrations, and then can't dry because of all the sealant. It becomes a moisture trap.

Good luck with your project!
Brad

[JoleneAS]

Huh... I hadn't thought about the risks of rot after drilling through the treated wood. That's a good point. Can you screw into coosa like wood though? Like if I wanted to install cabinetry and such?

[Crackerman]

Coosa doesn't hold screws as well as wood. Threaded inerta are recommended.

[Iansk]

While coosa looks interesting, I personally can’t justify $2100 + tax + shipping to do my subfloor.

As for holes drilled I’d probably just dribble some spar urathane in there before bolt insertion.

Ian

[JoleneAS]

Yeah, after I posted my reply yesterday I spent some time reviewing coosa posts on here and I just can’t get behind paying $2000+ for something I can’t dorectly screw into. Sounds like it’s be a pain in the ass to work with. I’m going to stick with wood and treat the bolt holes prior to insertion. I’ll stick with 3/4” acx, route the edges to 1/2” to fit the c-channels, and waterproof the underside, edges, and bolt holes. Thanks for the feedback, guys!

[Re-Pete]

Originally Posted by Isuzusweet

I used 3/4" Coosa board in place of my 5/8" plywood; 40-45% lighter than plywood; will not rot or promote mildew; just as strong, if not stronger than plywood, less than 1% water absorption rate. Very easy to machine to any profile.

I first did a 1/4" deep cut 1 3/4" to the inside of the blade on the edge fitting into the C channel; then machined the 1 3/4" to 5/8" thick; then machined an angle on the last 1 1/4" to aid insertion into the channel, since it's only the inside of the channel that needs support. Not the best picture below, but you'd get the drift.

Cheers
Sidekick Tony

Hey there SideKick Tony or Anyone, I am also going to be using 3/4" Coosa (To the naysayers: I already have it, so no need trying to discourage me), and the "C" channel on my 92 Excella will only take 5/8" material. When you say you machined the 1 3/4" along the outside edge to 5/8" are you referring to using a router? I'm not very experienced with using a router or adding a rabbet to the edge of something. Please walk me through how you did this if you can, with as much detail as possible. Thanks

[ehodg66]

[QUOTE=bradt;2208896]If you indeed have 1/2" original flooring, I would recommend replacing it w 1/2" Coosa board. No routing, no sealing, light weight, easy to work with, stronger than plywood, and will never rot. It costs more but will give good results and make your project go faster. I had 5/8 plywood and replaced it w 1/2 Coosa and added 1/8 aluminum shim stock underneath the Coosa.

Bradt,


Do you have any pictures showing your coosa and shim process?

thank you

[Minno]

Interesting. On our '72, the subfloor was 3/4 inch plywood. We replaced with 3/4 inch sanded down slightly on the edges to enable us to slip it into the C channel easily. I wonder when they changed to 1/2 inch, or did they use what came in when they could get it at the factory?

Kay

[bradt]

[QUOTE=ehodg66;2209429]

Originally Posted by bradt

If you indeed have 1/2" original flooring, I would recommend replacing it w 1/2" Coosa board. No routing, no sealing, light weight, easy to work with, stronger than plywood, and will never rot. It costs more but will give good results and make your project go faster. I had 5/8 plywood and replaced it w 1/2 Coosa and added 1/8 aluminum shim stock underneath the Coosa.

Bradt,


Do you have any pictures showing your coosa and shim process?

thank you

Yes, I have some photos of the process to share. I will work on posting some. Regarding screws, I talked to the app manager at Coosa and he said to use normal wood screws, I found sheet metal type screws also worked fine. I also used a 1/4" pneumatic stapler to secure the vinyl flooring and Coosa firmly gripped the staples, just like wood. The only fastener issue i had was when using a power screwdriver, I had to use care to stop in time or the screw head would go in too deep. I'll just say I saved every little scrap, because it seemed it could be useful for other things, too.
Coosa is light weight and helps you shed a few pounds from your trailer. It is easy to work with and doesn't need sealing. So your repair work goes faster. If you get a leak later, it won't rot. Alternately, if you decide to use plywood, just be sure to spray both sides and edges with a 10% solution of Timbor. Then it will not ever rot either.
Brad

[Isuzusweet]

Originally Posted by Re-Pete

Hey there SideKick Tony or Anyone, I am also going to be using 3/4" Coosa (To the naysayers: I already have it, so no need trying to discourage me), and the "C" channel on my 92 Excella will only take 5/8" material. When you say you machined the 1 3/4" along the outside edge to 5/8" are you referring to using a router? I'm not very experienced with using a router or adding a rabbet to the edge of something. Please walk me through how you did this if you can, with as much detail as possible. Thanks

I thought about this and realized that others out there arn't the skilled cabinetmaker with 30+ years behind him, that's use to saws and such.

So here's how I want you to do this. Set up the saw fence 1 3/4" away from the blade and set the blade to 1/4" depth. Run the Coosa board through top face down to get a 1/8" x 1/4" deep groove on the outside edge of the Coosa.
Then using a sacrificial fence, (piece of MDF or whatever), screwed to saw fence, set a 10 degree angle with the blade up 1 3/4" high eating into the sacrificial fence. Your going to run the Cossa with the groove side towards the blade; slowly adjust the fence until the blade cuts an angle going from the edge to 1/4" away from the 1/4" groove. Remember to always keep your pushing hands behind the blade on the uncut side, as once cut the material will want to rotate towards the blade.
Once angle is cut, straighten angle on blade to 0, set blade height to 1 3/4" and saw fence 5/8" away from blade. I would clamp a block of wood on the outside of the blade to keep your fingers guarded from the saw blade. Then run Coosa groove side out away from the fence to machine that last little bit near the 1/8" groove to 5/8" thick.

Clear as mud?

Cheers
Sidekick Tony