Replacing rotted plywood under bathroom sink

[street glide]

Hello all,

I purchased a 2006 18ft Work and Play toy hauler earlier this year, which has been a great rig so far. Luckily it hasn't required any major repairs besides a new awning, if that counts. However, I believe my luck has come to an end...

When camping this weekend, I noticed water under the bathroom sink. After taking a closer look, I found it was a fast drip coming from the cold water connection to the outside shower. The leaky connection is the simple fix...The not so simple fix is the damage to the wall.

There's probably a 1.5 x 2 ft section of the wall that is completely rotted. Rotted to the point it would take very little pressure to stick a screw driver through and make contact with the exterior wall. Obviously, the leak has been there for some time. (Shame on me for not taking a deeper look under the sink around the divider when purchasing the unit.)

Since this is a beginner rig for me (and I prefer to DIY), I'd like to avoid taking it to a shop to be repaired. However, I'm not sure what the proper procedure for replacing the wood is...

Is it as simple as just cut out the rotted wood and adhere another piece in its place? Are any special material and/or tools required? Or, can all the supplies be found at the local hardware store?

I've searched the forums, but haven't seen any specifically addressing repairs made to a unit where the plywood sits right up against the exterior wall. The ones I've seen have studs and insulation in between.

Any help/guidance you can provide is much appreciated.

Thanks!

[bikendan]

Pics are always helpful.

[street glide]

Here's one. This is just under the cut out for the outdoor shower.

I'll take a few more when I get home.

[street glide]

Here's a few more pics.

[Bama Rambler]

You may get lucky still and just have to cut out the bad pieces and replace them with new wood.

I looked at at a few units on the internet, but I cant tell if the outside walls are fiberglass or sheet aluminum? If they're aluminum, all you need to do is remove the bad plywood and replace it with new, and adhere it to the sheet metal. If it's fiberglass, you still may be able to do the same thing, depending on if it's fiberglass sheets or if it's filon that was vacuum bonded to the plywood.

[jeff64]

I can see where that would happen. I noticed some seepage under the plumbing chase to the rear of the toilet on mine on a prior outing, and some damage starting on the vanity cabinet. I believe the outdoor shower was the culprit and disconnected it and capped off the lines. Also noticed on the outside, the proflex which sealed the od shower to the fiberglas was cracked. Had to reseal that and both sides of the "V" where the flashing and fiberglass meet. Ran a dehumidifier in the vanity for a couple days and it sucked out about a quart, that's after I mopped up the floor. Hope I got it in time

[street glide]

Bama Rambler, the exterior is fiberglass. However, I'm not sure which one of the categories of fiberglass you mentioned below it falls in. Is there a way to tell the difference?

[Bama Rambler]

If it's fairly thick and substantial then it's sheet fiberglass.

[Rednight]

I repaired a small section about 6"x 8" under my fender well with a fiberglass repair kit. I gouged and scraped all of the loose rotted wood I could until I got back to solid wood. Don't worry with making it square, just remove the bad wood. With all the bad wood removed I mixed up a small portion of the fiberglass resin with hardener and painted the patch area extending past the good wood. Let that cure a day or so. Get piece of cardboard and cut out a pattern that will fit down flat against the fiberglass outer wall then transfer that to a piece of plywood and cut that out. I used a scrap piece of treated plywood. Back at the patch area use some 80 grit sandpaper and rough up the area where you applied the fiberglass resin. Test fit your patch to make sure it lays flat on the outer wall, if not trim until it will. Mix up another batch of the resin and paint the sanded area and the bottom of your plywood patch. Press the patch into the repair area and tape securely across one way leaving 2 ends exposed. With the remaining resin cut strips of the fiberglass cloth in the kit and soak the strips in the resin. Lay the strips into the exposed ends of the patch and smooth down. Let cure a day or so. Pull the tape off and again sand the area to roughen up the surface. Mix up another batch of resin and cut the cloth into strips sufficient to fill in the remaining ends that were taped over. Let that cure. (For an interior wall like yours I might just omit the next step) I finished the project by sanding down the rough spots and using the pattern I had cut out before made two fiberglass cloth patches that extend past the repair an inch or so. Mix up your remaining resin and soak the patches and apply over the repair area. When that cured I fine sanded down the rough spots and sprayed the patch area with undercoating paying attention to any exposed wood not covered with the resin. Done! Messy and slow but the end result is a patch that would meet or exceed the original. I apologize for the long winded post but I used to develop training material for a living and just can't give the short response. And I will give a shout out for the US Navy, they sent me to school to learn how to do this. We did a lot of hole patching in the Gator (amphibious) Navy...

[Rednight]

Another school of thought might be do you really need to do anything with it. From the pics it looks like it is inside the cabinet so no outward indication of damage. That section is not supporting any structure like a floor wood. The wood interior may be spongy but it is still intact. If it is crumbling and you just want to stabilize it scrape the bad area down about a 1/4" and fiberglass a patch over that area. Cover your repair with some finish paneling glued over it. Any repair that involves screws in the wall is a no no in my book. You probably have a paper/wallboard/plywood/fiberglass laminate and the plywood section is not too thick plus the chance of screwing through the siding.

[beyerjf]

A Work and Play is constructed of FRP (Fibreglass reinforced Plywood. There is a thick gelcoat on the outside, and a thin sheet of fibreglass on the inside. In between is 3/4 " plywood. Any place there has been a cutout or hole drilled for a fastener(the cutout here being the outside shower) leaves the potential for water to soak into the plywood between the fibreglass layers and slowly rot, undetected for years, until the inside or outside walls start bulging.
I have battled this on my 2007 34FK since I got it from the original owner in 2012. You can remove the rotted sections where you can get to them, and use marine grade glue to put in new plywood. It is a race against time, since there are many sections that are rotted in these units that are yet to be discovered. Tapping below any cutout with a padded hammer( like finding a stud in a wall) will reveal lots of areas that will be unrepairable, like behind kitchen cabinets or around the frig or under windows.
That is why they most dealers won't even consider taking them in on a trade.