Trillium 4500 - repairing wood under bench - Fiberglass RV


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Old 05-21-2020, 06:41 PM   #1
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Name: Nancy
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Trillium 4500 - repairing wood under bench

Hey there. I am a new owner and have been getting to know the floors today. There has been water getting in a couple of the dinette windows, but the good news is that it appears to be isolated to the benches alone- the wood over the water tank looks perfect.
In the curb side bench the wood feels hard, but the screws are rusted. On the road side bench the wood is now dry, but soft to poke at. I can't remove the wood all the way through though. When I stepped in the dinette near the edge of the trailer I heard a crunching and it if felt as though my foot might go through.

I can't find photos showing the anatomy of the inside bench area. How should I proceed in taking up the soft wood? Would there be a layer of plywood sitting directly on the fg? I have read that there is a pontoon hollow under there, but I am not sure where and don't want to start with a circular saw and damage anything.

Do rusted screws on the curb side dinette suggest that there is hidden water damage, and I should remove the wood there also?
Thanks!
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Old 05-21-2020, 07:20 PM   #2
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As you have probably figured out by looking and poking around in all of the cabinets and benches, there is a layer of plywood between the inner fiberglass components (floor, rear benches, front bench, closet/furnace/converter cabinet, and kitchenette) and BOTTOM of the outer shell. The "pontoons" or bumps extend down 3 inches or so along the curbside and roadside edges of the bottom of the outer shell.

I would use a pick or sharp screw driver and poke the plywood in the bottom of all of the cabinets and benches. Base your decision to repair on that. Rusty screws is not sufficient evidence to deem the plywood rotten. There is no rotten plywood in the bottom of my Trillium 4500, but several of the eight bolts holding the body to the frame were rusted to powder.
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Old 05-21-2020, 07:31 PM   #3
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A couple of additional notes:

1. Isolated patches of rot are not a major problem, unless those patches are providing structural support. For example, rotten plywood surrounding a bolt that is holding the body to the frame IS a problem and should be repaired to strength at least equal to the original construction.

2. Both of your photos show the heads of bolts that hold the body to the frame.
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Old 05-21-2020, 07:56 PM   #4
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"felt as though my foot might go through"

If by the edge of the trailer you mean the side, that's the pontoon area. And yes, there is a hollow pocket below the plywood there. That is not a critical area in the sense that the plywood there is not providing much structural support. Still you should repair it to provide a solid bottom to the storage compartment, and to restore the stiffness that the plywood there provides to the fiberglass shell.

I have repaired a couple of rotten patches in the plywood subfloor in my Boler 17. The plywood is 5/8" thick. To remove the rotted plywood, I used a versacut saw which has a 4" blade and is capable of "plunge cutting" into the plywood. Just proceed carefully to avoid damaging the bottom of the outer shell.

EDIT: Also, the center of each rotten area in my Boler 17 had (you guessed it) a body to frame bolt, so I patched the plywood and added a larger second layer of plywood above that before installing a new very large washer, larger bolt paired with a nylock nut below the frame.
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Old 05-21-2020, 09:59 PM   #5
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Thanks for the detailed information John. Is the layer of fibreglass in the benches a thin coating on the wood? If so, then it must have just chipped away over time and exposed the soft wood on the one side.
I'll get to cutting tomorrow. Thanks again!
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Old 05-21-2020, 10:00 PM   #6
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Hello Nancy,

John "in Michigan" has shared some sage advice and direction, and the more you poke around the more you'll get a sense of how the components in your Trillium work together, and how much restoration/repair is necessary vs cosmetic or personal preference.

If you become familiar with the frame and corresponding areas inside the trailer, this can give you some idea of which areas provide critical support. As John mentioned, the outer edge of plywood over the "pontoon" is less critical, does a good job of keeping your stored items out of the puddle of water the pontoon is supposed to collect and drain. Conversely, the plywood area around the bolts to the frame needs to be sound.

I am lucky to own a '79 4500, and have a wee patch of partial thickness soft plywood in the same area. Both rear storage areas were lined with pieces of Ensolite and foam sheets like you'd pack your plates in. Really impaired ventilation. Your photo makes it look as though some square item sat in your storage area and held moisture against the plywood, in that case the soft area may be localized and require more patch/treatment than removal.

As an alternative to replacement, some owners treat wood with has small, or thin, or non-structural defects, with epoxy and or wood hardeners.

If your water tank is under the floor, at the rear of the trailer, you may be able to lift off the cover and, with some contortions, see the edge of the storage area plywood you have questions about. This inspection might allow for further evaluation. Will add, just in case, if you take the water tank out, DO NOT STEP IN THAT COMPARTMENT! Pretty likely you will crack your shell, and possibly step through.

Lastly here's a screenshot of a current 1300(?) build. Might help visualize how they are put together.


Hope you enjoy your trailer.
MJ
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Old 05-22-2020, 06:09 AM   #7
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Quote:
Originally Posted by Nanph View Post
Thanks for the detailed information John. Is the layer of fibreglass in the benches a thin coating on the wood? If so, then it must have just chipped away over time and exposed the soft wood on the one side.
I'll get to cutting tomorrow. Thanks again!
Nancy, during the manufacture of my 1978 Trillium 4500 thick pigmented polyester resin with no fiberglass material was applied over the plywood in the benches. This provided a protective coating.

OTOH, the main floor fiberglass (top layer) between the kitchenette and the closet was formed in a mold shared with the furnace and converter cabinet. Near the kitchenette is a gap in the fiberglass floor where that mold ends. In that gap, you can see a bit of the plywood subfloor.
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Old 05-22-2020, 02:58 PM   #8
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I found the plywood under my seats was soft too, but as it was about 1/4” thick I believe the purpose of this wood was only to provide a flat floor in the storage area. I don’t believe it’s structural.

The first thing I did was to drill a discreet drain hole at the lowest point in the “fender” or “pontoon” behind the wheel to allow for drainage. Then I removed all traces of this thin shelf of wood, installed new galvanized frame bolts with large backing plates and sanded and painted inside the locker.
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Old 05-22-2020, 06:41 PM   #9
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Thank you so much! I think that I am going to proceed the same way that you did Phil. John, I found exactly what you were talking about with the plywood. I am glad that I was expecting it otherwise I might have wondered if it was a former repair. The photo that gtblue posted was so helpful! I wish there were more if those online. Another sunny day tomorrow with more windows to remove and floor to inspect. This is the right way to isolate.
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