Tuesday, October 3, 2023


RV window seals shrank, exposing opening. How to fix?

Dear Dave,
The outside seal on one of my RV’s windows has slipped, exposing part of an opening in the corner. The molding is hard and will not move. Do have a suggestion as to how to fix this? Thanks for your attention to this and your help. —Lewis, 2005 Coachmen Leprechaun

Dear Lewis,
This is a very common issue with windows and the rubber molding as it dries and shrinks when exposed to the sun and heat. Usually it happens at the corners because when the molding is applied, it is stretched tight around the radius and has some tension at that point.

In a dual pane window, this creates an opening for air and moisture and ultimately condensation forms between the two pieces of glass and fogs up. It will eventually etch the glass and can be pulled out and repaired, but it’s typically cheaper to replace the window unless you can do it yourself.

You have three options depending on the severity of the shrinkage and gap.

Option 1: Stretch the molding

I have done this myself a few times and sometimes it works for a short period of time, others for more than a year. Apply a generous coating of 303 Protectant and heat the rubber with a hair dryer or heat gun on low setting. Be careful not to melt the rubber or burn the paint or decal. Apply more 303 and work slowly until the rubber gets soft and can be moved. You will want to do this at least 6” on each side of the corner to provide enough soft material to stretch.

The molding typically has a bulb and a channel that the glass fits into. Once the material is soft enough, use a small flathead screwdriver to stretch it back to the edge of the glass and push the channel behind the glass. I have found an angle pick like this one works well to guide the channel around the corner.

If the molding is extremely hard and brittle, it will either not soften or won’t stay after stretching, which means moving on to Option 2…

Option 2: DAP Dynaflex Ultra Sealant

Over the years I have tried several DIY products for sealing windows, including silicone, EternaBond, and the “King of Fix”—duct tape! One product I came across this winter at the Florida RV SuperShow at Tampa, talking with a few service techs, is DAP Dynaflex Ultra. You cannot use just plain silicone or most other sealants found in a home improvement store that will work on materials typically found on an RV such as fiberglass, aluminum, and rubber. This sealant is easy to apply and made for exterior use.

You will need to clean the gap with mineral spirits and let it dry for at least an hour. If the window needs to slide back and forth behind the gap area, I suggest taping some wax paper on the glass, then sliding the glass back to the corner. Apply a bead of the Dynaflex to the gap and feather it to match the rest of the rubber. Let it sit for 24 hours and gently remove the wax paper. You might need to run a razor blade on the back side to release the sealant from the wax paper.

You can find it on Amazon here.

Dynaflex Ultra will help re-seal RV window seals

Option 3: Replace the RV window seal

The window is most likely a Hehr or Hurd brand, and you should be able to find a replacement molding from them or from Trim-Lok, which has just about every molding made. You can find them at www.trimlok.com.

 You might also enjoy this

Check those seals around your RV’s compartment door frames

Click here to read.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

Read more from Dave here


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Dave Solberg
Dave Solberghttp://www.rv-seminars.com/
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


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Bill Byerly
3 months ago

Thanks for the info Dave!

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