Saturday, September 29, 2012

Backwall Install (Epoxied-Over Plywood)

Had to trim the interior skin of the panels on the rear of the camper to accommodate the rear wall panel. I just cut through and removed the interior skin and polypropylene honeycomb, leaving the protruding exterior skin intact.  This protrusion would serve as a shelf to hold the plywood when installed. 

The reason I chose this manner of installation was because I was overly concerned as to the potential of a sharpened edge on plywood, created by at 45 degree cut.  My thoughts were, if forces caused the rear wall to shift some in transit, that edge could possibly cut through the fiberglass cloth tape joints along the corners much like a knife.  So instead of using 45-to-45 mating here, I decided to go with a butt joint instead.  Squared cuts all around the plywood's perimeter and allow it to sit upon and butt up against these protruding exterior portions.
 

 For the backwall I decided to go with a decent grade 3/4" Plywood and using 635 Thin System 3:1 Medium Epoxy from US Composites, coated the exterior of the plywood with three separate coats for waterproofing. This plywood used was not cabinet grade plywood however, for it would not have benefited me to do purchase such a higher quality wood.  This good grade of plywood that I did purchase should suffice, for the application of epoxy bonded really well leaving a 'built up' hardened, waterproof finish.

The small fibrous facing on this general plywood serves as more surface area for the epoxy to saturate and thus create not only better saturation, but ultimately a better cured bond across the face.

After multiple applications, the exterior of the plywood turned out really nice.  I also coated the edges to provide waterproofing along the edges also.  The neat thing about epoxy is that you can indeed create a stabilized surface by filling up the surface pores, preventing any moisture absorption.

Should be able to sand later on and paint the backwall with the same marine paint that I will use on the entire camper.






Interior corners were filleted using 635 Thin System Epoxy as well for this wood-to-fiberglass mate.  Epoxy bonds to wood really well, polyester resin not so much so.  I have to mount many accessories upon the backwall plus a door install, so decided to go with plywood here instead of a composite panel.  

Now I just need to glass the interior and exterior corners.  I should have glassed over top of the filleting while it was still wet, but I was unsure if the epoxy was going to cure at all, after the addition of a lot of structural filler material that I added when making this structural compound.  I did not want to glass over the fillet with several layers of cloth and then it not cure underneath because the filler material might have had disturbed the epoxy to hardener ratio.  That would have been a mess.

I waited until the next day and it had cured thoroughly.  
Now, I have the interior corners of the backwall fiberglassed with epoxy.


The rear panel has been cut and tied into the top now.


jump forward to November to see rear wall completed

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Chris