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Fifthwheel sidewall repair

by Robert Penn

. This repair started when my friend James embarked on a 15 minute project to caulk a small gap in the gasket around the lower edge of the slideout. But he soon discovered serious water damage and, before it was finished, we had spent numerous man hours.

. James had recently purchased the unit used and had already been on a four day shakedown trip. As he pulled the rubber gasket away from the fiberglass siding to clean out any debris, James noticed water standing in the bottom of the U shaped gasket. This led to removing the gasket and checking the edge of the outer wall of the slideout. The wall, consisting of a quarter inch plywood panel covered with a thin fiberglass sheet, was totally saturated from the lower edge upwards about 12 inches. The plywood glue had failed and the wet wood was in several very thin sheets.

. We decided to replace the lower section of the panel, and started by removing the trim pieces at both ends and the lower edge of the slide. Then we carefully separated the fiberglass outer layer from the plywood. The glue which was used to bond the plywood and fiberglass was apparently good stuff, and a thin layer of wood had to be painstakingly removed from the fiberglass. A dull chisel and hammer was used, taking care not to damage the fiberglass. It was slow work, and the final splinters of wood were removed by using a belt sander (we had to get it all since we assumed that any wood left adhered to the outer panel would show through in the repair because the fiberglass was very thin). We clamped a board to the lower edge of the panel and held it up and out of the way by wires hanging from the ceiling of the garage.

. Since we wanted to replace only the damaged wood and not the whole wall, we cut the plywood just above the damaged area. A chalk line was made for guidance and a dremmel tool with a small saw blade was used to cut the plywood. The blade lacked about 1/32 cutting all the way through (we didn't want to saw the aluminum frame members the wood was bonded to), and we completed the cut with a box cutter. Our plan was to replace this section of the wall with an aluminum panel to eliminate future problems with water in the U channel gasket.

. At the rear end of the slide we got bad news; the outer corner was also saturated from top to bottom and about 18 inches out both walls from the corner. This 15 minute caulking project was beginning to get complicated. We removed trim and two windows and used the same technique to peel back the fiberglass from the corner, and cut out the saturated wood. The good news was that the roof looked solid and did not require any work except to loosen and pull back the edges where it lapped over the sides. Because of the care required to avoid damaging the fiberglass, we had about two man weeks of effort into the project at this point.

. James located some 1/4 inch marine plywood, and 3/16 inch aluminum to replace the removed sections. We made patterns from the removed sections and fitted the new plywood into place. Unfortunately the existing plywood was not marine grade and was slightly thinner than the 1/4 inch marine plywood by about 1/32 inch. This difference required us to taper the mating edge of the new wood to avoid a discontinuity which would show through the thin fiberglass panel. Fortunately the aluminum replacement panel, being slightly less than a quarter inch, matched well enough to avoid having to do any tapering. We used construction adhesive commonly available to bond the new wood panels to the aluminum frame. The aluminum panel was bonded with 2-part epoxy. Both panels were also screwed to the frame.

Things were looking pretty good so far, and now the task was to get the fiberglass outer layer bonded back down without creases or bubbles. We were prepared to use a contact cement by 3M ($50/gallon) for this bond and the label cautioned against using it in a high humidity environment. Since we were using an unheated garage in the winter, and it started raining and kept raining for four days, we had to take a week off. When the rains stopped we used heaters to get the humidity down to an acceptable level and resumed the effort. We used contact cement with a 30 minute working time, rolled the cement on both sides, let it dry with paper and boards separating the two pieces. Then, starting from the undamaged edge we rolled the two layers together, trying to avoid any air pockets. We then used wood blocks and hammers to pound against the fiberglass to get a good compression on the bonding surface. At this point we stood back and admired our work; It actually looked pretty good, no telltale creases or bubbles. What a relief!

The work remaining was simple; Re-bond the rubber roof where we had loosened it at the corner, replace the windows, and trim and caulk all the seams. Interestingly, the windows were not caulked all the way around at the factory. They had been set in place with a foam rubber weatherstrip and a small bead of caulk on the outside, just over the upper edge of the window. We put in new weatherstrip and caulked all but the bottom edge of the window on the outside. We left the bottom edge uncaulked with the idea that any water that did get in would be able to drain out the bottom. We used butyl rubber caulk under the trim pieces (the same as the factory had used) and silicon caulk at the edges of the trim and windows.

A special glue/caulk supplied by the manufacturer of the rubber roof was used to attach the EPDM rubber roofing material to the plywood surface forming the roof. The edges of the EPDM rubber roof were caulked using a caulking gun and special EPDM caulking. Polyurethane caulking will not adhere properly to EPDM roofing material; therefore, the special caulks are required. They may be procured from RV dealers.. A lot of man hours went into this repair. At a commercial repair facility, the cost would have been significant. However the work is straightforward, and easily accomplished by anyone with a reasonable familiarly with tools and a lot of patience - once you get past the unpleasant thought of pulling the side off your RV.