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Building an RV Style Composite Wall Panel
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We decided to put our testing to work in a practical application and build a small section of RV style sandwich composite wall panel.

The typical RV wall is a composite structure.

The outer skin is a manufactured fiberglass panel about .060” thick with a very thin layer of gelcoat on the exterior side. We’ll call this layer the “skin”.

The skin is bonded to a backer, traditionally a 5mm thick mahogany plywood typically referred to as Luan Plywood. This a good product, unless it is exposed to moisture. Moisture can cause the glue bonding the plies together to dissolve. More recently a new product has hit the market under the brand name “Azdel”. Azdel is a composite plastic-based material that is water resistant. There have been “skin to Azdel” delamination issues reported due to potential “resin starvation” issues whereas the Azdel absorbed too much resin and there was not enough residual adhesive left to adequately bond the Azdel to the fiberglass skin.

The backer is bonded to a Styrofoam core that is embedded in the cavities created by the framing structure. The framing is either wood or aluminum. The thickness of the Styrofoam and framing members is typically 1”. Welded aluminum is generally superior to wood framing.

The final layer is bonded to the opposite side of the Styrofoam/framing matrix. This is the interior decorative wall panel that provides the interior finish. A number of different products have been used, though a manufactured compressed wood fiber material with a wallpaper type outer skin is typical.

Traditionally, a high performance solvent-based contact adhesive was used to bond the fiberglass-to-backer layer. This layer is subject to temperatures exceeding 140 degrees F and consumer grade contact adhesive products can “soften”, causing delamination. The high performance product is not readily available to the consumer or DIY’er due to toxicity, flammability, and extreme cost.

More recently a reactive hot melt has been used by RV manufacturers in a spray-applied application. This seems to be a good process, however it is also not available to the general DIY’er or consumer.

To build our test panels we used epoxy resins produced by Composet Products LLC. Composet has two products used in the repair of delaminated RV walls. The epoxy did very well in terms of strength, environmental durability and heat resistance. However, the process requires building a fixture and clamping for 24-hours.

The Composet Products epoxies can be found on these two websites:
This shows the fiberglass skin, plywood backer, Styrofoam/framing, and interior panel.
Surface preparation is a critivcalchieving high performance bond.
Each layer is coated with the epoxy resin to a specific thickness
The layers are assembled while wet.
Different adhesives are used for each layer.
The "sandwhich" is placed in a press until cured.
The finished product.