Alpenlite Foamcore

Question

Greetings. My 1989 29' 5th-wheel had a soft spot in the floor of the rear kitchen, so I am now in process of repairing that. A LOT of exploratory surgery revealed that most of the lower half of the rear wall was moist, as well as a lot of the floor extending 8' forward in places. It appears that there was no single large leak, but rather several small contributors that totaled a lot of moisture. So far, I have found several small screw-sized penetrations of the lower half skin. Both of the lower mounts of the rear awning look very bad. Hiding where the retracted awning frame rested against the skin, I found 2 quarter-sized areas of full-depth cracking. Most of the screws in the horizontal aluminum channel holding the upper edge of the awning were rusted and/or loose. Finally, 4 of the 5 top rear marker lights had very wet surfaces where the wiring was run thru the foamcore. (I believe the marker lights were the primary leak sources) Enough backstory. I'd like to connect with someone who has actual experience with the fabrication process for the Alpenlite foamcore. I think I have deduced most of the layers and bonding secrets so I can recreate the foamcore panels, but I still am unclear as to the purpose of the strips of 1/2" and 2" clear packing tape (for holding all layers in place during bonding process?) And I'm scratching my head as to why so many water-soluble materials and adhesives were used in the foamcore assemblies. Anybody out there who has actual knowledge of the Alpenlite procedure? Or can you direct me to another possible source of the info? Thanks for your time and assistance.

troubledwaters · Answer

I don’t have any experience with Allenpenlite foamcore process or materials but we have made foamcore materials for show props where we wanted the finished prop to be light weight, robust, easily assembled and disassembled, and easy move and store. We cut the styrofoam with a hot wire, then coated the styrofoam surface with moisture activated gorilla glue, mist the surface with water, lay the plywood on top, weight it down, and allow to dry. Turn it over and bond the other side(s). For you, The psi rating of the styrofoam and the thickness of the plywood are key in developing a suitably sturdy finished floor/sidewall. I don’t have any advice on that - my prop building days are far away in my past.

ardeebee · Answer

Hmmmm, interesting reply. The info that you provided (thanks much!) fairly closely parallels the plan high points that I had come up with for re-creating the original foamcore. But about the "moisture activated gorilla glue". I should tell you here that even mentioning the "m" word (moisture) around an RV-er can strike fear into our hearts. 😂 When the rain leak moisture reached the wall/floor layers, it caused some unidentified layer to dissolve into a saturated, fibrous mess that was probably either some kind of a paper facing, or the outer de-laminated layer of the super thin luann ply, or some kind of adhesive that was water-soluble. On most RVs, the bonded foamcore panels provide both insulation AND structural strength. Any input as to the durability of your engineered foamcore, or the resistance to water of the cured gorilla glue? Thanks, again!

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