The Right Glue for Bonding Filon Fiberglass to Plywood

One question that regularly comes up on RV forums and chat rooms is how to rebuild water damaged RV walls using new materials and specifically how to bond Filon to plywood. We found no easy answer, so we looked into the situation. Here's what we found.

In the past many RV manufactures built the walls in a factory by gluing layers of fiberglass, wood, and Styrofoam together with contact cement. The main advantage of contact cement was the immediate bond that occurred when the parts were joined together. Contact cement worked well, however flammability and toxicity issues pushed manufacturers to find an alternative that was easier to handle and store.

Currently a number of manufacturers are using hot melt glue, which is a high performance version of the "hot glue" you might use for crafts. This product has proven to be durable as well. It is easy to store, relatively non-toxic, and gains strength very quickly. However, the process requires a large, heated vessel to hold the melted glue, and an elaborate system of rollers to apply the adhesive. There is also a limited working time because the glue skins over as it cools.

We focus on DIY and one of the caveats of our testing included the availability of potential adhesives, as well any required special processing equipmen. We contacted a supplier of a contact cement that was the industry standard for years, however they we were unwilling to provide a sample. They did send us to a distributor, and the cost of a 5-gallon pail was around $1000. The product is pricey due to the high flammability rating and toxicity, (not legal to use in certain parts of the country), and must be shipped by truck freight. We deemed this product impractical to the average DIY'er, so we did not test it. However, we did select 3 off-the-shelf contact cements to test.

We also eliminated hot melt adhesive even though we feel a good DIY'er could build a backyard system. We contacted Henkel, a primary supplier, but were unable to get a sample for testing. Part of the problem is the holt melt being packaged in large bulk blocks. We were not even offered a chance to get it even if we were willing to pay for it.

That leaves us only a couple of options that we feel a DIY'er could find with reasonable effort and cost.
1. Off-the-shelf contact cement.

One-Part Construction Adhesives, and Marine Adhesive Sealants
Two-part epoxy

We purchased Filon and the adhesives from an online supplier as well as the local big box home improvement stores. We did a few initial trials to determine product compatibility and general bond characteristics. We culled the products and settled on final contenders. We fabricated 8" x 8" test panels consisting of a Filon/plywood/Styrofoam/plywood sandwich.

The materials were cleaned and prepped. We also used a heavy-duty roller (www.rvroofandwall.com) to assist in getting a good bond. Then we placed the samples in a homemade press where they cured for 24 hours at 70 degrees F.
We ran the parts through a heating and cooling cycle, and then tested at temperatures starting at 200 degrees F. An RV wall with dark decals or dark paint can reach temperatures as high as 160 degrees F in the summer.

Please note that we are not a scientific test lab. Our tests were developed by seat-of-the-pants methods and are not to be confused with a technical analytical study. The information we are sharing represents our opinion and observations.

Summary:
Building RV style walls in not an easy task, but well within the reach of skilled DIY'ers who have the space, tools, and ambition to tackle the project. The 2-part epoxies form Composet Products L.L.C. were the overall favorites, followed by the Loctite PL Marine. There are a few specific tools needed (roller, notched trowel, adhesive roller, press/clamp). We found a good online sources are www.rvroofandwall.com and www.delamrepair.com

RVSHIPSHAPE.COM


	Composet SLV	Composet CompoBond	Loctite PL Marine	3M 5900	3M 90	Benders 631	Weldwood Red	Stabond 440
General Description	2 part epoxy trowel grade paste requires clamping long work life minimal gap fill	2 part epoxy flowable liquid requires clamping long work life gap fill to 1/8"	heavy bodied paste trowels easily requires clamping short work life gap fill to 1/8"	heavy bodied paste difficult to spread requires clamping very short work life gap fill to 1/8'	aerosol contact cement flammable, fumes no gap fill clamping recommended	aerosol contact cement flammable,fumes no gap fill clamping recommended	liquid contact cement flamable,fumes no gap fill clamping recommended	liquid contact cement highly flammable fumes no gap fill clamping recommended
Substrates	fiberglass,wood metal, Azdel, foam	fiberglass,wood metal, Azdel, foam	fiberglass,wood metal, foam	fiberglass,wood metal, foam	fiberglass, wood	fiberglass, wood	fiberglass, wood	fiberglass, wood
Styrofoam Safe	YES	YES	YES	NO	NO	NO	NO	NO
Work Time	45 minutes	60 mimutes	25 minutes	15 minutes	Immediate Bond	Immediate Bond	Immediate Bond	Immediate Bond
Bond Strength	Very High, Temperature to 160 F	Very High, Temperature to 160 F	Very High, Temperature to 200 F	High Temperature to 150 F	Medium, Temperature to 140 F	Medium Temperature to 120 F	Low Temperature to 120 F	Not tested
Application	roll, brush, trowel	roll, brush, trowel	trowel	trowel	spray	spray	roll	roll
Coverage	75 sq/ft gallon	50 sq/ft gallon	50 sq/ft gallon	40 sq/ft gallon	10 sq/ft can	16 sq/ft can	16 sq/ft can	Not Tested
Price	Medium	Medium	Medium	High	Very High	High	Medium	High-Unavailable