Our motorhome is 17 years old and I have had several occasions to fix just this kind of problem. Most of the problems are a result of the factory glue just letting go. The biggest repair I did was caused by a leak that allowed water under the rubber and caused the glue to let go on an area approx 2? x 4?. That damage also caused part of the sub-roof plywood to buckle. I have had to do approx 6 repairs during the past several years.
Whether the repair is small or large it is basically the same method to repair. Re apply a glue to reattach the rubber to the sub-roof and seal any slit(s) needed to apply the glue. On a simple scale, it is no different than putting a patch on a bicycle tube. The steps are to insert the glue, smooth and even it?s thickness, apply pressure overnight to the reglued area, then seal the access slit(s).
Obtain a rubber roof repair kit(s), I use the DICOR brand. Determine the size of the area to reglue and cut one or several 1? to 2? slits to allow access to squirt in the rubber lap sealant (referred to as glue). I place the slit in the middle of the effected area. Spread out the glue to a uniform thin film, ~1/8?. Re-squirt and re-level as needed. I use a 6? x 3? wide caster to spread and even it all out. Place a heavy weight (5-10#) on a board covering the area being reglued. This is an important step. Without the overnight clamping weight, the outgassing of the glue will prevent the entire area from becoming reattached. After the overnight period the rubber should be attached. The glue will be soft if you need to shift things around slightly. Clean the access opening and apply a patch, per package instructions. The glue will continue to cure over weeks and most of the waviness will fade over time.
If the area is large or if you miss a spot, this process can be done in stages, on the same or different days. If you are unsure of your abilities, try a small area first. The patch will be inherently water tight when done due to the glue used around the cut access opening.
The external patch is for added insurance. The process may take 1-2 hours.
Glad to asnwer any questions. Good Luck.
Robert Flight
Rochester, NY
