RV Roof; When You Can Use Lap Sealant Over Old Sealant

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RV water leaks can result in mold, delamination, dry rot, and eventually damage your RV frame. So can you put lap sealant over old sealant on an RV roof? Or do you need to remove the old sealant to put in the new lap sealant?

You can put lap sealant over old sealant on an RV roof if the old sealant is still intact without any sign of it falling off. However, if it shows signs of coming loose, remove the old sealant before putting on the new sealant.

In the rest of this article, we’ll discuss the factors to consider when putting lap sealant over old sealant on an RV roof and provide instructions on how to apply lap sealant on an RV roof.

What To Consider Before Using Lap Sealant On Old RV Roof Sealant

Before starting your new sealant layer, you’ll need to consider a few factors. Let’s look into this in more detail. 

Is the Old Sealant on the Roof Solid?

One of the first things to consider when putting lap sealant over old sealant on an RV roof is whether the old sealant is still intact.

If the old sealant has started to peel or crack, you should remove it before applying the new sealant. 

To confirm if the old sealant is peeling, look for dust particles under the sealant. If dust is present, then it’s likely that the sealant is slowly releasing adhesive. If the old sealant is intact and doesn’t show signs of peeling or cracking, you can put lap sealant over it.

Is the Roof and Old Sealant Clean and Dry?

Mold, dirt, and debris can interfere with the adhesion of the new sealant. This is why it’s crucial to ensure that your RV roof and old sealant are clean and dry before applying new lap sealant. If the old sealant is brittle, you’ll need to scrape it off before cleaning it.

Is the New Sealant Compatible With Your Roof Material?

Different types of sealants can be used for different roof materials. The one you use will directly affect how well it adheres to your RV’s roof, so be mindful to choose the correct one.

Before applying lap sealant over old sealant on your RV roof, ensure that the new one is compatible with your RV roof material. Check the manufacturer’s recommendations to ensure you’re using the correct type of sealant.

To learn the difference in how to reseal different RV roof types, you can check out this article where I explain it.

How To Apply Lap Sealant Over Old Sealant on an RV Roof

If you’ve determined that the old sealant is still intact and the roof and old sealant are clean and dry, you can apply new lap sealant over it. Here are the steps to follow:

Preparing the Area

Even if the area seems clean, it’s best to prepare the old sealant and the roof surface thoroughly. Follow the steps below:

1. Use an RV roof cleaner such as the Dicor roof cleaner. Rinse the cleaned area with water and allow it to dry.
2. Once dry, wipe over the roof with a cloth. This should be dampened with denatured alcohol to ensure all the dirt has been removed. 
3. Wipe the area dry.

Refrain from pouring the denatured alcohol directly on the old sealant or roof. Instead, apply it directly onto the cloth and squeeze out the excess before applying. 

Apply Sealant

The type of sealant you’ll use depends on the surface you’re applying it on. If applying the sealant on a surface level with the roof, use a self-leveling sealant such as the Dicor self-leveling lap sealant.

If applying the sealant over a vertical or raised surface, such as the skylight or antennae, you should use a non-leveling sealant, such as the Dicor Non-Leveling lap sealant. Both these sealants are compatible with most TPO and EPDM roofs and adhere firmly to fiberglass, aluminum, and vinyl roofs.

Here’s how to apply your new sealant:

1. With a standard caulking gun, squeeze the sealant onto the old sealant and spread it over the area.
2. Using a flat knife dipped in water, level the sealant by applying light pressure across the surface of your RV’s roof.

The self-leveling lap sealant will do just as the name suggests and “float” out itself so you won’t need to spread it out evenly, it does that automatically in a couple of minutes.

The advantage of applying lap sealant over old sealant is that you use less sealant to cover the whole area. 

Allow Lap Sealant Time to Dry

After application, you’ll need to wait to ensure it has dried fully: 

• Within four hours, the sealant will now be waterproof. 
• In 3-6 days, it will be 80% cured.
• Within 30 days, it will be 100% cured.

If you don’t wait for the sealant to dry and use your RV as normal within the first day, you’ll have to reapply. 

How Do You Remove Old RV Sealant? 

If you notice that the old sealant is cracked or peeling, you may need to remove it.

Here are a few tips on removing old RV sealant:

• Using a scraper is the easiest way to remove old RV roof sealants. However, a scraper can only be used during warm weather.
• If you want to remove old sealant during the cold season, you’ll have to use a heat gun to soften the hard caulk.
• Use a plastic scraper if your RV has a rubber roof. You have a bit more leeway for aluminum roofs and could try a regular scraper, although carefully not to make scratches to the paint.
• If you don’t feel like spending hours scrapping, you could use an oscillating tool to speed up the process. Ensure the speed is tuned to slow and the tool is angled, so the blade removes the old sealant.

Use a Removal Solvent

If you had previously used silicone sealant, removing it will require using silicone removal solvents such as mineral spirits or turpentine.

Using these solvents isn’t advisable if your RV has a fiberglass roof.

Tip: If you’ve used silicone sealant in the past, you’ll need to completely remove it before reapplying the new sealant. This is because the new sealant won’t adhere properly to silicone.

Final Thoughts

Ensuring your RV roof is waterproof is integral to its maintenance process. We hope this article helped you understand if, when, and how you should apply lap sealant on old RV roof sealant.

When applying lap sealant, follow instructions to the letter, as an improper application can compromise your roof sealant and your entire RV.

And with your roof now fixed, you can look into other issues, including how to keep your motor home warm this coming winter.