Fiberglass/plywood floor repair questions ... - Fiberglass RV

Thread Tools Search this Thread Display Modes
Old 12-10-2011, 04:02 PM   #1
Senior Member
Name: Fred
Trailer: 1978 Trillium 4500
Posts: 232
Fiberglass/plywood floor repair questions ...


I ran into a bit of a bump in the road on my restoration of my 78 trillium. The floor Under the rear right dinette seat is composed of some epoxy/resin/?? over a plywood sheet over the fiberglass bottom.

Somehow water had gotten in here (lots of it) and it has fully rotted out the wood. It came out in chunks about 1 inch in size and the consistency of soaked shredded wheat cereal (no joke). There was a small puddle of water in there too.

I cut out 99% of it. This wasn't too hard except for the two major bolts that hold the egg to the frame. These go thru the wood. I worked one free from its rust -- well actually I broke the bolt trying. See pict.

* What should I replace it with? All fiberglass? FG with metal / wood reinforcements?
* What fiberglass materials and techniques are needed to bond with the existing fiberglass shell?
Attached Thumbnails
IMG_1710.JPG   IMG_1711.JPG  

IMG_1712.JPG   IMG_1713.JPG  



--Fred and Natalie
1978 Trillium 4500 "Bernerwagon"
freddo411 is offline   Reply With Quote
Old 12-10-2011, 09:26 PM   #2
Name: Jon
Trailer: 1981 Scamp 13 ft / 2005 Volkswagen Golf TDI
Posts: 40
I had a similar failure on my '81 Scamp. Unfortunately, this happens top lots of fiberglass trailers. The problem with having the resin/glass under the plywood is that it keeps water from getting out of the wood just as well as it keeps it from getting in. Even small leaks from windows, side rivets, etc. can dribble enough water in to do this.

I'm replacing my entire floor with marine plywood. I used material from a local specialty distributor which also contained some flame retardant, probably borate, which interfered with curing of the repair resin I coated the bottom side with. Most marine plywood won't do this. However, I strongly advise testing the resin on your plywood before attempting the actual repair just to make sure there is no reaction (or lack thereof). If you shop on-line for marine plywood for pontoon boats, you'll likely find the right stuff. You may, however, end up paying more for freight than plywood. I also noticed that common permanent marker ink turned the resin into slimy goo! Make your cutout markings with a carpenters pencil.

The resin itself is common peroxide-cured polyester / styrene - the same as you would use to repair a car or a boat. 3M/Bondo makes it (don't use regular Bondo body filler!) as do lots of other companies. If you want a stronger resin, use vinylester, which will stick to the existing resin just fine, but costs quite a bit more. You can get all kinds of fancy resins and fillers from specialty distributors. Just google fiberglass resin composite distributor with your zip code and you'll find tons of them. Auto body repair or boat repair supply houses have lots of the same stuff. The resin needs to have fiberglass added to it, whether it's chopped strands or glass cloth. The easiest thing to do is buy the resin with chopped glass added to it already, since it doesn't look like you'll need to patch any structural joints. Woven glass cloth saturated with resin (without the chopped glass) is really good for that. You can find the premixed resin and glass at lots of auto parts shops and big-box stores. I bought my Bondo-Glass at a local farm supply store. Bondo(R) Bondo-Glass(R) Fiberglass Reinforced Filler, 272, Quart (US) Can (Net Wt 2 lb 9 oz), 12 per case

Unlike my rig, yours has a resin/glass bottom with wood over it. Cleaning out the inside of that panel without going through it may be a challenge, depending on condition and thickness. It may be prudent to sand and recoat the underside with resin after the wood replacement. just to make sure any holes are sealed.

Just like painting, body repair will fail without proper prep. You absolutely have to get the old surface clean before you start. Having air-powered tools is a big help, but not absolutely necessary. I used a cheap air die grinder with a double-cut carbide burr to cut old glass/resin out, but you could use a Roto-Zip for this as well. A high-speed sander or angle grinder will clean away dirt from the surfaces you need to bond to. Flap sanding discs and wire brushes may do less collateral damage than simple sanding discs. Clean at least a 1" wide band going up the wall to ensure a strong bond. Vacuum thoroughly and then clean the surface with acetone on a rag. Wear nitrile rubber gloves and do this with LOTS of ventilation.

If using power tools, get a good HEPA or ULPA dust filtration mask. Wear eye and ear protection when sanding or cutting. Wear old clothes you can throw out when you're done. The dust may make your shirt permanently itchy.

There are lots of good how-to tutorials and videos on youtube and resin manufacturer and distributor web sites. Most will be specific to cars or boats, but the materials and methods are basically the same, especially when it comes to wood/glass repairs on boats.

The remains of that bolt you dug out aren't very recognizable. I bought some closed-bottom threaded inserts and an application tool from to reinstall my floor. You may need to do the same. Somebody who is familiar with Trilliums may be able to steer you to the correct fasteners to use. That water may have corroded your frame where the fasteners went in. Make sure that connection is really solid. You may need to drill new holes nearby and and seal the old ones.

Oh yeah, don't forget to find out how that water got in. You probably won't want to do this again in two years.

Jon W is offline   Reply With Quote
Old 12-10-2011, 10:47 PM   #3
Senior Member
Name: Fred
Trailer: 1978 Trillium 4500
Posts: 232
Wow, thanks for the thoughtful reply.

I was wondering if it is possible/advisable to embed steel/aluminum in the resin in place of the wood? A 1inch x 2 foot bar would give good purchase for the bolts and would never rot out.

--Fred and Natalie
1978 Trillium 4500 "Bernerwagon"
freddo411 is offline   Reply With Quote
Old 12-10-2011, 11:19 PM   #4
Senior Member
Name: Brayden
Trailer: Boler
Posts: 144
Rust out lol

I'm in the middle of restoring yet another
boler and this one has (had) a rotted out floor
I used normal 3/4 plywood
Took out all the old wood and used it as a stencil
When the new wood is cut
I used the wood treatment (green) stuff they use on decks And coated every inch of it

Than put the new treated wood in place
And re fiber glassed it to the shell
I also added fiberglass mat to the surface of the wood for extra protection

Than on the underside
I fiber glassed it to the shell again
Than sprayed the bottom with rubberized under coat
Siris is offline   Reply With Quote
Old 12-11-2011, 04:59 AM   #5
Senior Member
Posts: 787
I'm not 100% clear on what your plan is, but if you are going to add back plywood over an existing layer of fiberglass (see - I managed to not write 'glassfibre') then you need to encourage the two to stick together. One thing I would regard as essential is to drill decent 'ventilation' holes all over the plywood so that you don't get a big bubble of trapped air holding the two apart. In ideal workshop conditions, 1/8" drill holes on a 3-4" grid (yeah, that's a lot of holes) would be enough but I suggest you use larger holes, say 3/8-1/2" so that they don't easily get clogged. Anything can be used to fill these holes afterwards (Bondo is fine) though structurally it doesn't matter if you leave them open

I imagine you will need some support under the floor to push the bottom fiberglass layer up against the plywood until the two stick together. A nice tool for that is strips of thinnish plywood cut just too long so that they need to get bent to fit, which keeps upward pressure on the fiberglass.
Andrew Gibbens is offline   Reply With Quote
Old 12-11-2011, 06:11 AM   #6
Senior Member
Trailer: Bigfoot
Posts: 604
My understanding is that the only difference between normal plywood and marine plywood is that marine is free of voids. Best screw/drill hole fills are round toothpicks "twiddled" in epoxy; insert and break off flush.
Cam A is offline   Reply With Quote
Old 12-11-2011, 08:45 AM   #7
Name: Jon
Trailer: 1981 Scamp 13 ft / 2005 Volkswagen Golf TDI
Posts: 40
Originally Posted by Cam A View Post
My understanding is that the only difference between normal plywood and marine plywood is that marine is free of voids.
Freedom from voids is only part of the spec for marine grade plywood. All contain waterproof glue, but so does plain old exterior grade plywood. Some types also contain wood preservative. Mine was made with preservative, flame retardant and resorcinol glue. I bought it because it was locally available.

Because the wood I bought inhibited curing of resin, I covered the bottoms with 1/16" aluminum cemented on with silicone caulk. I also cut and trimmed 2" wide aluminum pieces for the outside edges of the tops and riveted them together. That way, I'm bonding to tempered marine-grade aluminum, not my goofy plywood. I sanded the edges to expose fresh wood and make the aluminum flush. Overkill? You bet. Would I do it again? Nope.

Even though some people think it's evil, Scamp has been building their trailers with OSB floors for a few years. I thought it was a bad idea, too, until I had some work done on my house. A stack of leftover Louisiana-Pacific 3/4" OSB has been sitting out in my yard in the rain and snow for a few months now. So far, there has been no crumbling, peeling or rot. I'm going to use it for decking in my attic soon. If I had it to do over again, that is what I'd use in my trailer. It wouldn't survive being sealed up inside of glass and resin any better than plywood, though.
LP Building Products | Why Choose OSB Instead Of Plywood?

I still have to fiberglass the panels in. I got delayed reassembling it due to an inconvenient home renovation. The glass egg will roll again next year.

Jon W is offline   Reply With Quote

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Plywood subfloor over original floor???? shumiron Problem Solving | Owners Helping Owners 5 10-15-2015 02:00 PM
Trillium 4500 Plywood Upper Cabinet Repair David Tilston Care and Feeding of Molded Fiberglass Trailers 8 11-12-2011 09:29 AM
Plywood floor - what do I look for? Melanie Problem Solving | Owners Helping Owners 6 07-03-2011 08:38 AM
Fiberglass repair Questions Kenny H Problem Solving | Owners Helping Owners 9 09-04-2008 10:20 AM
Question – fiberglass repair– gap between wood-floor and “wall” of ori lenny247 Problem Solving | Owners Helping Owners 11 09-03-2006 03:27 PM

» Trailer Showcase

Boler Bear



» Upcoming Events
No events scheduled in
the next 465 days.
» Virginia Campgrounds

Reviews provided by

Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities

Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 05:56 PM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.