Polyester/epoxy resins and styrofoam

[Terry Coombs]

  Live and learn , it's expensive ! So about 14 years ago we bought a camping trailer . One of those super lightweight units . The problem is , nobody ever said a word about checking the caulking (roof mostly) every year or two ... now this unit is made of bonded foam/plywood panels with 1 1/2" thin-wall aluminum square tube framing . And there's water damage that has caused the plywood to delaminate . I've repaired the floor panels and laminated a layer of 3/8" plywood using a latex-based engineered wood adhesive . Next step is regluing those delaminated plywood panels . The interior ones I'm going to just replace using the same/similar water-soluble(when uncured) adhesives . The outside skin is another matter entirely . I have purchased both epoxy and polyester resins and have formulated a plan to hold the panels firmly against the substrate (the styrofoam) while the resin cures . HOWEVER I have been cautioned by a local (kinda) RV repair place that the resin MAY cause damage to the foam core - like dissolve it . I know there are at least a couple of folks here with chemical backgrounds , I'm looking for an answer - is the resin going to dissolve the foam cores of these structural panels ? A corollary question is : are all styrofoams created equal ? I have several pieces of styrofoam insulating board leftover/used and removed , etc that I can use for testing , ass/u/ming that it's all made from the same stuff . FWIW it looks like the original bonding agent was a rubbery adhesive , I'm guessing a latex-based contact type adhesive .  And I'm working to a deadline - my wife wants to go visit her old and sickly mother later this month . I can't leave the dog home and Max would run her mother bugnuts crazy in under an hour ... and there ain't a motel I know of that'll let us have a 70 pound dog in the room . I guess I could just send her off to Kentucky alone and Max and I could stay home ... which would suit me just fine , but y'all know how women can be about this sort of thing .

[Clare Snyder]

Polyester resin will disolve styrene. Epoxy will not

There is ipen cell (blown) expanded styrene and closed cell expanded styrene. Otherwise known as "bead board" and" Styrofoam SM". Both are styrene and will be disolved by the solvents in plyester resin. There are also IsoFoam, urethane foam, andseveral other foam board products that will stand up to polyester - but they are not as commonly used in things like travel trailers. Take a small chunk and put it into a jar of gasoline. If it melts, DO NOT use polyester resin!!!

[Terry Coombs]

  OK so I will use the epoxy for rebonding the outer skin . After I test it on some of this foam board to make sure . This stuff came from an outfit in Utah , the kit is expressly designed for rebonding delaminated camper skins . Came with mixing cups , gloves , syringes and tubing to inject the resin where it's needed . They recommend injecting from an edge if possible , drilling holes in the skin and patching them later if necessary . I'm no way going to get this thing totally repaired in time for the upcoming trip , just gotta get it roadworthy . And fit to stay in for a couple of days - toilet is top of the priority list ,

   The panel cores appear to be the same stuff they make foam cups with . The pour foam I used to repair the floor panels is rigid urethane , 4lb/cu ft density . I'm not concerned about that stuff . After pouring the foam in the cracks, gaps , etc in the sagging floor panels , I floated it level and (reasonably) smooth with a floor patch compound with a latex admix . I then bonded some 3/8" b/c plywood to that with the engineered wood flooring adhesive . Also used 1" drywall screws at 6" on center into the aluminum framing , which is 16" O/C . Did I ever mention that while I retired as a cabinet maker , I spent nearly 20 years as a floor mechanic ? I specialized in vinyl flooring with subfloor damage . Did my own subfloor repairs because carpenters just couldn't f****ng understand you MUST stagger joints in subflooring .

  I'll be using the water-soluble adhesive for the interior panels on the back wall , looks like I'll be saving that poly resin for another project .   Thanks Clare !

[Thomas]

Upcoming trip? Cover it with a tarp.

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That is correct. Polyester resin is cures by cross-linking with styrene and the monomer would attack the polystyrene