Floor replacement. Keep me from going down the wrong street. AGAIN.
Unlike other threads which talk about tongue and groove or lap joints in 5/8” plywood, the existing floor in my '69 GT was 3/4” plywood with butt joints connected through plywood splice plates about 6” wide glued to the underside. Generally, every other cross frame is set low to accommodate the thickness of these plates. Has anyone else seen this type of installation? Here is how I propose to proceed with the floor replacement. At this time, the inner skin and floor is out, the belly pan is off, the wheel wells are out and the only connection between the shell and the frame is across the front where a formidable steel plate is installed to prevent frame separation. The shell is supported by a system of shores between the frame and underside of the shell roof. After completing repairs to the frame, priming, painting, replacing the axle and the wheel wells, I will start replacing the floor. This will involve gradually shimming the shores so that the separation between shell and frame varies from 3/4” in front to 2” or 3” at the rear. I will then install the floor with five pieces of plywood running the width of the trailer (about 92”) starting at the front. I will use the same method of joining the pieces as was used originally (see above). I realize that this will require selective removal and replacement of the shores as each piece of plywood is installed. Once the floor is in place and interior bolts installed, the shell will be lowered into place and secured to the frame at the outriggers and to the floor only with screws elsewhere. I do have some questions. First, what are the potential pitfalls of this approach? Second, vinyl resin has been recommended to seal the edges (and perhaps the entire underside) of the floor. No West Marine is nearby. Is it acceptable to use the resin sold with the fiber glassing kits at the big box stores that costs about $35 per gallon? They don't mention that it is vinyl. Finally, does anyone know what the width of the original floor in a '69 GT was?
Since this post is already too long, I have not related how my first approach to replacing the floor ended in failure. Let me know if you would like to hear this cautionary tale.
Hi John. My '68's flooring was installed just as yours was, so you're not alone. I admit I'm not going to say how I replaced the floor because there may be an outcry (it really goes against the grain of lots of people here) but your concept looks like the best true shell on replacement I've come across! I stayed with the butt joints and the "shim" underneath the joint like the original design also.
And I'll be back on in 10 years to let me know if my subflooring replacement concept worked out well...
A little concerned
"Once the floor is in place and interior bolts installed, the shell will be lowered into place and secured to the frame at the outriggers and to the floor only with screws elsewhere."
I assume that you will bolt the floor to the frame using elevator bolts and that this is what you mean by "interior bolts".
One of the best visuals I've found on construction is post #20 of this thread:
On my '65, I found that the c-channel was trash and had to make up a new one. I would definitely inspect it well, replace if necessary and buck rivet the shell to that c-channel and NOT use screws to connect the shell to the frame. It's a critical part of the monocoque construction.
On Epoxy, you're not confusing West Marine with West Systems Epoxy, are you? They are totally separate companies. West Marine is not the only place to get West Systems Epoxy. Head east to a good boat store if you want to find it, you're not far from the water.
The previous thread I mentioned and this are great resources:
Be careful, you're on a critical part of your project. Research it well!
The Bondo box store resin is a polyester - and would be better than paint but not by much. "Polyester resin is the cheapest resin available in the marine industry and offers the poorest adhesion, has the highest water absorption, highest shrinkage, and high VOC's"
I used 700 Vinyl Ester Resin which is extremely hard resin - the vinyl ester is superior when you want to encapsulate medium and large grain woods, fine grain woods like cedar and redwood should have epoxy. The price has gone up some but not much.
VE withstands higher temperatures (250F+) than epoxy or polyester. I thinned the first coats with 5% xylene and watched the endgrain soak it in - took 3 coats before it stopped wicking in. I finished both sides - the clear glass coat on the inside is a bit brittle, drop a heavy tool and it cracks a birdseye but the plywood is failing, not the resin.
No clue about your floor width...
I did a complete floor replacement on my 71 GT on this thread
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