Subfloor lifting up

[funkill]

Hi all!
I decided to start my flooring evaluation on my ‘73 Overlander today and found that one piece of my subfloor has raised up about 1/2”. When I step on it, it goes down some (and squeeks), but not flush. I can see a few of the metal corrugated joints used to secure this panel to the adjacent one. The fasteners are rusted and bent and could actually be preventing me from being able to fully seat the floor. Hummm

Anyway, what is the easiest way to assess what is going on here? I know my fresh water tank is under this area.
On Airstream Addicts, it was suggested to use self tapping screws to reseat the floor but I'm a little worried about placement of the fresh water tank and actually hitting the frame.

Other tidbits of information:

+ The water lines have been drained and dry for over a year.

+ The plywood in this area looks poor but is solid.

+ There are no visible screws securing this panel to the frame at this edge. Only the corrugated pieces affixing it to the adjacent panel.

+ The plywood has old adhesive and some bondo (used to try to smooth surface damage caused by prying off old, glued on laminate).

+ I had the frame inspected, 1 outrigger and the entire rear bathroom floor replaced a few years ago.

+ I intended to sand it smooth and then add 1/4” plywood over the entire floor before laying my new vinyl.

Thanks for any ideas you have on why this subfloor panel has raised and how best to investigate it further.

[funkill]

After a little internet surfing, I found some pictures of where the tank may reside...

If this info is correct, it doesn't appear that there is a frame cross member in the area where my subfloor has raised. That would explain the use of joining fasteners rather than screws to a (possibly non-existent) frame cross member.

And, if this info is correct, then how do I get this piece of plywood to lay flat again? Or even if there is a cross member here, do I dare grab self tapping fasteners and try to pull it flat?

HELP... Please HELP...

[Belegedhel]

Well, looking at the picture of the guy standing next to the frame, and the picture of your lifted plywood, it looks like the warped joint is immediately in front of the wheel well, in which case it looks to me like there should be a frame member there you could screw into.

If my recollection is correct, from when I replaced my floor, there is always a frame member where sheets come together, and typically a single sheet covers the entire area where the water tank is stored. But, for all that, your best bet would be to drop the water tank, and then you could do the repair ensuring that you won't put a screw into your tank. As I recall, I had to trim some screws in the area of the tank before installing the tank. Dropping the tank isn't rocket science, but typically the wood panel supporting the tank has welded itself into the angle iron slides, and pulling it out may take a come-along.

It would probably be a good idea to see what is going on underneath the subfloor anyway. Maybe the subfloor at the joint is held down with wood screws that were put in from below, and they have torn loose from the plywood, but are still keeping the wood from being pushed back down into place. Or maybe that frame member has completely disintegrated.

good luck!

[batman]

IMO Your flooring looks sketchy to me. But if you say it's solid that is your business.

I believe Most folks use #10 or #12 self tapping elevator bolts to attach the subfloor to the frame and cross members. Something like these from VTS.

https://vintagetrailersupply.com/flo...crews-vts-387/

or these,

https://vintagetrailersupply.com/flo...bolts-vts-375/

Not a bad idea to inspect from below before you start screwing the ply down. The bottom could be rotted or otherwise compromised. Plus you get to see the cross member locations and see how your screws will work.

I have used 1/4" "Underlayment" on top of the subfloor to achieve a ultra smooth surface to install Marmolium on. I used mastic/glue and finish nail gun to install the underlayment. You will need to remove the holding tanks to make sure you don't put holes in them. then cut and grind smooth.

Best of luck,
-Dennis

[57Vintage]

Considering the amount of delamination in your subfloor I agree with Batman and Belegedhel, its time to remove the tank and check the underside.

Considering the time and expense of adding 1/4" and new flooring I'd want to make sure that area is structurally sound.

IMO I'd replace that piece at least out to the frame rails. I wouldn't be confident that the bondo will stay attached to the subfloor or that glue/nails will stay secure to the bondo for the 1/4" you install on top.

[funkill]

Thanks for the feedback guys. It sounds like more work than I anticipated- which seems to be par for the course! Since I’ve put so much work I to all the other refurb work, I agree that it’s not time to start cutting corners.
I’ll formulate a plan to attack this and “get ‘er done”.
Thanks again!

[funkill]

Well I dug in the floor today. As many of you pointed out, the delamination of the plywood in the center (from prying up old flooring) was starting to wear on me. And I knew it would be compromised.

The good news is that the floor was pretty solid around the perimeter. And my frame looks good underneath. The bad news is that since it was so solid, it was a real bear to get out of the C- channel - especially when encountering a few frozen bolts. Will finish pulling up the center piece next weekend. Oh... and as soon as I opened the drain handle, the trapped air in my freshwater tank escaped and the floor went back flush. Proving the plywood was significantly compromised. And that the vent on my tank was not working??

I’m hoping that my getting the new piece wedged back in place goes easier…

Thanks all.

[Belegedhel]

Impressive that your FW system could hold pressure that well!

[Belegedhel]

Or should I say "scary." Yes, your vent/breather should have allowed air to escape.

[funkill]

I finally got that piece of flooring replaced.... it was easier fitting this new piece in the c-channel than digging the old piece out. Glad this is done and I am able to move on to the next item.


Laura

[Daytonacoupe]

Likely not much help at this point but the fresh water tank on my 1987 is aligned directly under one of the cross members, so add screws beyond the edges and puncture the tank. This is nOt the case with the grey and black tanks, which sit between. Likely why the factory used those corrugated metal fasteners on some seams.

[funkill]

I was surprised to find that there was a good amount of clearance bet even the fresh water tank and the frame crossmember above. Still nerve wracking to screw into it blindly, but possible!