kylights have been part of the RV’s roof landscape for many years, offering additional height in showers and natural lighting. For the most part, these plastic domes have a good lifespan (unless, of course, you collide with a low structure or tree limb), but the seal that ensures a tight fit on the roof can deteriorate over time, requiring attention to prevent moisture intrusion. Hence, skilled service technicians recommend inspecting the roof seals annually, or immediately after any driving mishap.
When we aided a friend in examining the roof of his five-year-old fifth wheel, it was plain that the seal around his skylight was weathered, dried out — and a prime candidate for creating problems inside the rig. Allowing water to penetrate the roof, or any other place in an RV, leads to costly dry-rot damage and long downtimes — usually at the most inopportune times.
The skylight in the fifth wheel was original from the factory and was well-sealed, meaning plenty of “goop” applied could be found around the edges. Long-term exposure to the sun allowed the lap sealer to shrink and develop voids where moisture could eventually make its way into the roof structure. For the record, the manufacturer did a good job sealing this skylight, which further demonstrates the level of wear-and-tear that should be expected from the intensity of the sun and continued exposure from other damaging elements.
Working on the roof takes some agility when the real estate is consumed by nearby solar panels and other accessories, so be careful. After exposure to the elements for five years in a full-time environment, the sealant around this skylight was dried up and no longer capable of protecting against water intrusion.
Resealing the skylight (and any other accessory on the roof) does not require special training, but there are a few precautions to consider. First, you’ll be on the roof, so it’s important to be aware of your surroundings and possible trip hazards. In this case, much of the roof real estate is occupied by solar panels, so footing was important. Second, removing old sealant from a rubber roof requires patience, care and the right tools — you don’t want to damage the roof membrane. Lastly, do not lean on the skylight while removing and reapplying sealant; a friend learned that lesson the hard way — and ended up having to replace the skylight because the plastic cracked when pushed on by an errant hand.
In order to properly re-seal the skylight, the old material must be removed first. Chances are your roof has an EPDM or TPO membrane, which can be damaged very easily. If you are new to this type of repair, you might consider using a plastic putty knife; steel putty knives will “dig” into the membrane easily, creating large gaps between the skylight flange and roof. The skylight re-seal for this project was completed by RV Enthusiast contributor Bill Gehr, who has done this job hundreds of times and has the right “feel” when using steel putty knives. Use of a plastic putty knife will slow down the process, and in some cases make it difficult to remove stubborn sealant, but it’s the safer alternative. The bottom line? Work slowly and carefully and take breaks if the job becomes too tedious.
Obviously signs of cracking in the original sealant was a red flag and led to the decision to remove the old sealant and replace it with EternaBond tape.
Once all the old sealant was removed, the surface was washed with a commercial cleaner, followed with a wiping of alcohol. At this point, you can elect to use a lap sealer designed for your roof type or seal the flange to the roof with EternaBond tape; for this project the latter was chosen. EternaBond (https://amzn.to/3IPpIBP) is some of the stickiest stuff on the planet. It was originally designed to seal pipes underwater, so weather has little adverse effect on its ability to provide a tight seal. Granted, EternaBond is expensive, but if you use this tape you’ll likely never have to re-seal the skylight again unless it becomes damaged and needs to be replaced. And that’s the caveat: it’s brutal to remove, which is why it does such a good job sealing out moisture. If it becomes necessary to replace the skylight, the only way to get if off the roof is to cut the tape at the edges of the flange with a razor knife (and exposing the screw heads will take some time and patience). Nevertheless, it’s normally a “reseal it and forget it” proposition.
Applying the tape takes some thought and should be done in sections. This is not the easiest tape to work with, and you’ll only get one shot at placement; once the adhesive touches any surface, it pretty much cannot be moved. But it’s not hard to do it right. After cutting the tape to the needed length, it’s laid down to confirm the fit. Then the liner protecting the adhesive is removed, which can be maddening if not done correctly. Simply scrunch the leading edge of tape using two hands until the protective liner separates enough to get a grip and pull back a manageable length of liner. Carefully position the tape on the flange/roof and work it to the other end while continually pulling back the liner; the process is repeated until all four sides are covered. Be sure to cut the sections so that the ends meet without unnecessary overlap — not exactly critical, but the final job will look better.
The key to ensuring that the adhesive sets up properly is to roll the tape so that contact is uniform. Steel EternaBond rollers for this purpose are available from Amazon (https://amzn.to/3m0FEHR) or other tool sources, but we couldn’t find ours, so we improvised by “ironing” the tape surface with the head of a hammer. After about an hour, the job was completed and the skylight once again was protected from exposure to the elements, including water intrusion.
Four-inch-wide, black EternaBond tape provided a good amount of overlap for the skylight flange and roof membrane. The EternaBond tape was rolled across each side of the skylight to determine the right length and then cut with scissors.
EternaBond tape is incredibly sticky, so you only get one chance to apply it correctly. Once it touches the surface, it’s there for the duration.
It took about an hour to remove the old sealant and apply the EternaBond. Owners can expect this seal to last for many years.