Using Sikaflex 715 to Reseal an RV Skylight on an EPDM Roof

Updated 09/29/2026 | Published 06/23/2026

Question:

I’m getting ready to reseal around a leaky skylight on my EPDM rubber roof this weekend, and I’m looking at using Sikaflex 715. Since it’s labeled as 'semi self-leveling,' will it stay put on the slightly sloped edges of the skylight frame, or is it going to run all over the place? Also, the previous owner used Dicor, so can I just clean that up and apply the Sikaflex right over the old caulk, or do I need to scrape it all off first to make sure it adheres properly to the plastic and rubber? Lastly, it's supposed to rain here in a few days how long does this stuff actually take to dry and fully cure before it can handle a downpour, and is it really that much better than traditional lap sealants?

asked by: Bob

Expert Reply:

Bob, Sikaflex 715 part # SI78FR is a good choice for resealing your skylight on an EPDM roof.

Since it's a semi self-leveling sealant, it will flow just enough to smooth itself around the skylight flange and cover fasteners, but it isn't so runny that it's going to pour off the sides on the slight slope around the skylight. It gives you a cleaner finish than a fully self-leveling sealant while still filling gaps nicely.

For the best long-term results, I would recommend removing as much of the old Dicor as you reasonably can before applying the Sikaflex. While some people have successfully applied new sealant over cleaned existing Dicor, the safest approach is to remove the old material, clean the surface thoroughly, and apply the Sikaflex directly to the EPDM roof and skylight flange. That will give you the best adhesion and help avoid compatibility issues between old and new sealants.

As far as drying time goes, Sikaflex 715 will typically skin over in about 30 to 45 minutes, but it usually takes between 2 and 5 days to fully cure depending on the temperature and humidity. Since rain is in the forecast, I'd try to give it at least 24 hours of dry weather before a heavy downpour if possible. The longer it has to cure, the better.

One of the reasons people like Sikaflex 715 is that it stays flexible, resists UV exposure, and doesn't shrink as much as some traditional lap sealants over time. If you're taking the time to remove the old sealant and prep the surface properly, it can provide an excellent long-lasting repair.

Are you just resealing the skylight, or are you planning to freshen up anything else while you're up there?

expert reply by: Heather A

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Laura

9/28/2026

Is this product good for 10 years?

Heather A.

9/29/2026

@Laura Yes, Sikaflex 715 is a durable RV roof sealant and is designed for long term roof sealing, but I would not promise that it will last a full 10 years without needing attention. Sika specifically describes Sikaflex 715 as having very good UV resistance, flexibility, and durability for RV roof applications, but they do not give a 10 year service life rating. How long it actually lasts will depend on the roof material, installation, weather exposure, and how well the roof and existing sealant are prepared. I would still recommend inspecting the sealant regularly for cracking, lifting, or damage and touching up any problem areas before they allow water to get underneath the seal. If you are looking for a sealant to apply now and hopefully not have to worry about for many years, Sikaflex 715 is a good choice for RV roof sealing, but I would not guarantee a 10 year lifespan.