Keeping your Hummer H2 watertight is essential for both off-road adventures and regular road use. One of the most common sources of leaks in the H2 cab comes from the gutters and cab marker lights. In this guide, I’ll walk you through the process I used to waterproof these critical areas. It’s a time-consuming job, but if done right, it will save you from dealing with frustrating leaks and water damage later.

Step 1: Inspect the Gutters

The first step to waterproofing your Hummer H2 cab is to check the rain gutters. From the factory, the drip gasket that runs down the center of the gutter doesn’t fully cover the body joints in the gutter, and over time, this can allow water to seep in.

The Problem with Factory Gutter Seals

The gutters on the Hummer H2 are strangely unfinished, with paint applied directly over polyurethane seam sealer. If cracks or leaks are present, the entire drip gasket needs to be pulled up for proper repair. Half-measures like squeezing in a tube of caulk won’t do the job. Proper prep is key to making sure your repairs last.

Under the topcoat of paint is the original polyurethane. The black is a prior owner’s poor repair.

Step 2: Removing the Old Gasket and Adhesive

To fix the leaks, you’ll need to remove the factory gasket and clean the old adhesive. Here’s how I tackled it:

Tools and Materials: I used a can of 3M Adhesive Remover, which is safe on paint but effective for loosening stubborn old adhesive. A plastic razor scraper also helps prevent scratching the paint while removing the old material. Be prepared—this step can take time, especially if the previous owner applied a poor-quality caulk like in my case.

After a few hours of scraping, I also decided to remove the roof rails to clean up the loose adhesive foam tape under the side rails. Remember, when you’re waterproofing, thorough prep is everything—rushing through this step can lead to more problems down the road.

The 3M adhesive remover is key. I alternated between the plastic wire brush and plastic razor scraper. If you are the first to repair your gutter you won’t have to work as hard to get the gutters clean.

Step 3: Cleaning the Gutters

Once all the old adhesive is gone, clean the gutter thoroughly. I used soap and water followed by rubbing alcohol to ensure the gutters were completely free of debris and oils.

Step 4: Reinforcing and Sealing the Gutters

Now that the gutters were prepped, I knew I needed to fully span the gutters with a durable material to ensure long-term waterproofing. Simply applying a sealant would not be enough.

Materials I Used:

3M Professional Grade Black Polyurethane: This provides a flexible, waterproof seal and adheres well to clean surfaces.
Fiberglass Tape: I chose thin fiberglass tape to help reinforce the gutter. It gives the polyurethane something to grab onto and improves the durability of the seal.

Application Process:

After cutting the fiberglass tape to fit the gutter, I applied the 3M polyurethane in a zigzag pattern along the gutter.
Using a plastic putty knife cut to the exact gutter width, I spread the polyurethane evenly through the gutter, ensuring good adhesion to both the gutter surface and the fiberglass tape.

I let this sit and cure for 48 hours to make sure everything set properly.

Cut a plastic putty knife to the width of the gutter and smooth the polyurethane in.

Step 5: Adding a Finished Look with EPDM Roof Gasket

After the polyurethane cured, I wanted to give the gutters a clean, finished appearance. I found black EPDM roof gasket on Amazon and installed it over the gutters. This not only enhanced the look but also provided an extra layer of protection.

Step 6: Testing for Leaks

Before installing the EPDM roof gasket, I ran a water test. I noticed that water flowed from both the front and rear of the gutters, but it was seeping underneath the front and rear cab marker lights. This was an important discovery.

Testing Tips:

Open your front doors and watch how the water flows. You may also see water running down the interior door panels if there’s a crack in the door gasket at the roofline. If this happens, you can apply a little polyurethane to the gap.