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Old 07-30-2021, 07:32 PM   #1
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Join Date: Jul 2021
Location: Nashville, Tn
Posts: 9
Soft subfloor around the toilet

I'm a brand new RV owner, I have a 2003 Monico Diplomat and the floors around the toilet and in front of the toilet door are soft. I've built my own house, so I'm pretty handy, but I'm a little worried that replacing subfloor on an RV is going to be insane. Any thoughts?

Tommy H
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Old 07-30-2021, 07:34 PM   #2
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With your background, shouldn't be that different than if the subfloor in a house were soft. Remove the floor covering and see if the subfloor needs to be replaced or if get-rot or one of the epoxy products could be used to strengthen it.
Brett Wolfe
Ex: 2003 Alpine 38FDDS. Ex: 1997 Safari Sahara. Ex: 1993 Foretravel U240
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Old 07-31-2021, 05:42 PM   #3
Join Date: Jan 2013
Posts: 88
Just finished the same repair on our 1999 Diplomat 36B.

The sub-floor beneath the ceramic tiles consists of 2 layers of OSB which disintegrates when it gets wet when the foam gasket between the toilet and the flange wears out.

The bottom layer spans the 2" X 2" steel subfloor which is filled with blue StyroFoam insulation. On ours, there was a 2"X2" crossmember just in front of the toilet flange.

If you are lucky, only the top layer needs to be replaced. I wasn't and had to remove about 2/3rd of the bottom layer in the toilet room.

Use an oscillating multi-tool to cut the epoxy grout between tiles, remove the tiles and cut out as much damaged OSB as necessary to get back to solid wood. I cut back the upper layer about 3" more than the lower to provide an overlap.

The toilet flange needs a solid mounting surface so I used 3/4" fir plywood to replace the OSB.

I was unable to remove the toilet flange from the black water tank so I ended up having to install each layer of plywood in 2 pieces with the layers at 90 degrees to each other.

I then screwed the two layers together for strength and rigidity, fastened down the toilet flange, levelled the edges with levelling compound and then covered with vinyl plank flooring (48" long pieces reduces end joints).

As far as i can see the whole problem is due to the design of the Sealand (Dometic) toilet and gasket.

Unlike a conventional toilet where the outlet is the same size as the 3" wastepipe and the tapered area of the floor flange is sealed with a wax gasket., the Sealand outlet is 4" wide and uses the toilet flange taper to reduce to the 3" waste pipe into the black tank. The foam gasket sits between the top of the flange and the bottom of the toilet and deteriorates with age.

Replacing the gasket should be a semi-regular maintenance item to prevent leakage and the resultant sub-floor damage.

Good luck in fixing yours.

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Old 08-01-2021, 08:05 PM   #4
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Location: Nashville, Tn
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wow thank you for that very detailed reply! The floor literally is soft all around the toilet room, and I'm thinking I might have to take out a curtain wall or two to get it right. Ever done that?

Also, there's a spongy spot to the right of the shower, so I'm assuming something is messed up, i.e.. drain, around the shower. Ever taken out one of those?

Thanks again,
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Old 08-02-2021, 05:11 PM   #5
Join Date: Jan 2013
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I have never had to go to the extent of removing a partition wall although there is nothing complex about them.

There have been several recent threads where members have extensively rebuilt /remodelled Monaco products (Ted Dupuis has some excellent videos) which provide an overview of the underlying construction.

While the source of water damage which occurs around a leaking fixture may be easy to identify, there are a couple of hidden failure points which can slowly cause damage.

One of these is the flexible drain line from the kitchen sink where the sink is located in a slide-out. The 1 Ĺ” flex line is hidden inside a wall and unless it ruptures completely it may be hard to identify if it is leaking. On ours, the ABS fitting to which it was only partially glued eventually leaked enough to lift the tiles under the slide roller.

If your shower is immediately adjacent to the kitchen slide out this may be a possible source of leakage in that area. (Bob Jones had a good thread on repairing this a couple of years ago).

It is also possible that at some time in the past, the water and drainage systems were not properly winterized and a p-trap or supply line damaged. I have replaced several sections of pex line where the fittings were constantly weeping.

When the OSB subfloor damage extends right to the exterior wall, you may have to get creative providing support for the replacement OSB or plywood since the original subfloor was sandwiched between the 2” X 2” steel substructure and the exterior wall structure. I have used pieces of angle iron screwed to the steel subframe to support a ĺ” plywood subfloor.

If you are having to replace large sections, it may be worthwhile trying to locate the 2X 2 subframe members to provide the needed supports. It also provides an opportunity to remove the ceramic tile and update the flooring in that area.

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Old 08-02-2021, 08:47 PM   #6
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How can I find Ted's videos? And again, thank you for the time you've taken to answer these questions!

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Old 08-02-2021, 09:34 PM   #7
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DH had to replace the rotten soft sub floor in our TT.

Make shallow cuts in the subfloor as it can be very close to the black tank. Other posters have given you very good detailed instructions. Find this repair on You Tube. I am confident you are handy enough to do this repair. Wear the best knee pads known to man.
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floor, toilet

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