Advice on Repairing Bathroom Floor

[JohnnyAustin]

I am remodeling the interior of my 29 foot 1988 Airstream Excella. Someone had previously replaced the floor to presumably fix some water damage. The fix was working but not particularly solid as there was some give to the floor when it was stepped on. I tore out the old plywood and the attached pictures show the current state.

The first picture is just a view looking down from the entry to the bathroom. The second show the back of the opening that is closest to the wheel well/ water heater. The third photo shows the part that is closest to the shower.

I plan to clean and respray the cross member to prevent any further rust. It would be ideal to be able to support the replacement section of the floor on the frame on all four sides. In the second photo you can see that the previous repair cut the original floor at the edge of metal beam. I intend to cut the floor a bit wider such that the replacement will ride partly over the beam. That solves the support for one side; however, I am looking for some advice on how to support the other three sides

1) It's is hard to see in the third photo, but there is metal support that runs just under where the floor was cut out. The support appears to stop at the grey tank inlet from the shower. I don't know how solid that support is but my intent is to also enlarge the cutout such that the edge of replacement will rest in part of the support. Does anyone know how solid this support is? Is there any reason not to to use it for support.

2) There is no metal support available to rest the plywood on toward the center of the trailer. In the first photo, you can see a piece of plywood that was screwed to the underside of the original floor and provided a lip to set the replacement on. This seems like an OK solution (although not ideal). Does anyone have a better idea of how to handle this.

3) There was no support for the back part of the replaced floor. I can remove the wall so one solution is to extend the cutout back to the next cross beam (making the cutout about another foot longer). Anyone have any thoughts on doing this?

Finally, I intend to glue all joints. I've recently tried using some Git Rot on a small section of floor that had some minor water damage. I don't know how well it would work for sealing the seams between the replacement floor ant the original floor, but conceptually it seems like it'd be a good solution. It's an epoxy that wicks into the fibers of the wood which would seem to provide a better bond than glues that rely on a mechanical bond to the surface. Has anyone else tried this or is there something better that I should be using?

Thanks!
John

[Belegedhel]

The wood you see screwed to the bottom of the existing pieces in order to support the patch is a recommended practice according to the Airstream service manual for my '73. Probably not easy to get much more support than you would get from that.

Any metal you see exposed under the subfloor is likely to be either a frame rail or a cross member. The cross members should be spaced 2' apart to form kind of a "ladder" structure. So, if the piece of metal you are looking at is not 2' from another cross member, and it is of a different width or thickness, it may not be a structural part of the floor--could be a support for the tank, etc..

As far as strategies for a stiffer joint go, if you have a biscuit joiner, you could mount the biscuits in the patch, and then cut biscuit shaped cuts in the existing sections of floor that will allow the protruding biscuits in the patch to drop in. You would then have to patch the tops of the slots with bondo or something.

Another strategy may be to cut your mating edges at 45 degree angles, and give your patch a corresponding angle so that the patch is supported by the existing floor at the edges. This would probably take a lot of iterations to get it right.

As far as glues go, I don't imagine you would have very good luck with a butt joint unless you used a very thick glue like liquid nails. Anything thin enough to wick into the pores of the wood will just run out of the joint and end up in a puddle in your belly pan. Pretty much any wood working glue is intended to enter the pores of the wood and provide more than a surface adherence, but when you glue two boards together in a butt joint, the edges are precisely planed to match, and you put a few pipe clamps onto them to impose the pressure that drives the glue into the pores. Neither of these will happen with your floor patch.

Good luck!

[Kvsterling]

Gosh John, I feel your pain. Just completed some subfloor patch work myself. We were able to cut back to frame on all 4 sides of the patch so had at least 1/2 of the old floor and other half new floor on a frame. Then did countersunk washer/screw with liquid nails at the edges. Feel it is a sturdy repair

Trimming your current opening back to allow new board to rest on a frame edge would definitely be more sturdy. Can you get to the next frame section with an oscillating saw?

[JohnnyAustin]

Thanks for the help. There's actually nothing preventing me from cutting the opening wider to reach all the way to the frame on the other side of the trailer so perhaps that is what I should plan on doing (the cabinets and closet are already removed). The one thing I've been trying to avoid is pulling out the old shower, but honestly the only reason is that I was hoping that was just something I wouldn't have to do. The most important thing to me is to do it right!!! I want to get a lot of use out of this trailer when I'm done so whatever I need to do now to have the best solution is what I want to do.

[Kvsterling]

I pulled everything out, including the shower pan. I damaged it and then threw it away. I’m really regretting that now; think removal...not demolition

[JohnnyAustin]

So I thought I should provide an update. After being gone for several days of vacation and finishing up some painting, I got to working on the floor repair. I cut out three sides to rest on the frame but opted not to cut all the way across the trailer to support the fourth side. Since there's only a 2 foot span between supported sides, I decided the fourth side could rest on the plywood patched in below the floor. I bought an oscillating saw and cutout the floor. I tried to leave as much wood as possible around the existing screws which led to a rather odd looking cutout. I used some fiber board to get a decent template of the cutout and then traced that on my plywood before cutting.


The attached a couple of pictures of the fix. The first shows the floor after I finished the cutout (and before I repaired the rust with POR-15). The second shows the plywood in place but not screws down (waiting on my screws to arrive).