Does Flex Seal Work on Boats?

Flex Seal is a great temporary fix for a lot of problems like a leaky roof, or a tire leaking air, or a crack in a gutter. But, is Flex Seal strong enough to seal a hole on a boat? The answer is, yes it is! There are a few stipulations to this answer, so before you whip out a can of Flex Seal and go to town on your vessel, keep reading to find out exactly what kind of repairs you can make with this product and how to properly apply it.

Flex Seal

Flex Seal was invented in 2012 by Alan Swift and Phil Swift. It is a liquid rubber that can be poured into cracks and leaks and hardens over time. It can not only be used to patch holes and cracks, but can be used to weatherproof whatever you need. It can also be used as a rubber coating for your tools handles so you can have a comfortable grip.

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Flex Seal is a very popular product for stopping leaks and repairing cracks. The brand has a few different products like glues, tapes, caulking, and waterproof sealant.

Flex Seal’s waterproof sealant is advertised to commonly repair roof and gutters, ponds and bird bath assembly leaks, basement and foundation cracks, cars, trucks, vans, RV repairs, campers and trailers, boats and watersports equipment, and DIY projects.

They recommend use on surfaces such as concrete, glass, brick, stucco, wood, copper, plastic, tile, fabric, wire, vinyl, fiberglass, ceramics, porcelain, metal, aluminum, stone, foam, asphalt, PVC, polyurethane, and much more.

The product is popular for forming a weatherproof and durable seal to cracks that is resistant to rain, snow, sun, wind, hail, air, moisture, UV degradation, natural weathering, water, and mildew. It is also non-hazardous and non-flammable as well as safe around plants and animals.

It is great for emergencies!

Most anglers will keep flex seal and flex seal tape on their boat in case of an emergency. Some people have used the tape to easily repair wiring that would take a large project to replace, and even though the wiring is exposed to water, they say that it has held up and have not had a problem. Other common fixes include sealing thru- hull ports, seacocks, or hatches. A seacock or any other hose break can be sealed with Flex Seals tape. The thru-hull can be sealed using the Flex Seal Flex Tape or the Emergency Plug.

This will help fill the void in the side of the boat long enough for you to travel to safety. The hatch is probably going to be the hardest thing to repair with Flex Seal products, but hey, if there is an emergency you can either go down or do what you can to stop it. You can use the Emergency Plug to plug the hatch, then put the Rescue Tape around it to hold it in place, and then put the Flex Tape around that to hold it all in place and seal the edges. This will give you enough time to make it to shore.

What boat material does it best adhere to?

Flex seal is advertised to adhere to fiberglass and aluminum, so you should have no problem with it sticking to your boat. It also sticks to a variety of other materials like concrete, glass, brick, stucco, wood, copper, plastic, tile, fabric, wire, vinyl, fiberglass, ceramics, porcelain, metal, aluminum, stone, foam, asphalt, PVC, and polyurethane.

So, what about a permanent fix?

Flex Seal should never be used as a permanent fix. Even though it has an excellent ability to patch holes and cracks, it was not intended by the manufacturer to be a permanent fix for anything, especially if that something is consistently submerged in water.

How to use Flex Seal on your boat:

If you do need to use Flex Seal temporarily on your boat, you should at least understand how to properly apply it. There is some prepping involved and technique, so let’s look at what steps you need to take to successfully seal your boat:

1. First, you obviously need to find the leak. Whether it is a hose or a hole in your boat, you need to know exactly where to repair it. If your leak is in a hose, you can run water through it and watch where it starts to seep out. Mark the area with a permanent marker before you turn the water off so you know where to go to repair it. If you are looking for a hole in your boat, this can be a little more difficult. The best way to find a hole in your boat is by taking the boat out of the water and rising it up on either a trailer or a lift. After it is properly mounted, you can fill the interior of the boat with water and watch below to see where the water is escaping. Mark the area with a permanent marker and then drain the boat out.

2. The next thing you should do is completely clean the area. Flex Seal is recommended for use on a dry surface, so make sure after you are done scrubbing the area free of debris, grease, barnacles, algae, or whatever else is on the underside of your boat that you wipe it down completely dry. If you want to make extra sure it is dry, you can use a product like rubbing alcohol and waiting until it dries. You should be cleaning and drying both sides of the leak inside and out. If you are trying to patch a hole in a hose, obviously you can only clean the outside of it.

3. Next it is time to apply the product. If you are patching a hose, you will be using flex tape. Do not take the tape from the roll until you are ready to apply it. Once you take the tape off, you will wrap it very firmly around the hose. If you are experiencing an emergency, you can kink the hose first to resist the flow of water even more and then tape it. If you are patching a hole in your boats hull, you will patch the underside first, and then the inside.

4. The next thing you need to do is wait for your patch job to dry. Now, Flex Seal will become dry to the touch within 2-3 hours but it is not actually fully cured. It will take at least 24 hours to fully cure, so don’t put your boat back into the water until you wait the whole 24 hours. The tape will obviously hold immediately.

How to Remove Flex Seal

Once you are ready to prepare for your permanent repair, you will need to clean the flex seal off of your vessel. The best product you can use that wont damage your vessel is Toluene. Toluene is a type of paint remover, so you will need to be careful with it as it will probably remove the uppermost layer of paint on your vessel. If you have an aluminum boat, you can use acetone and a rag to scrub off the flex seal. The stronger the acetone the better, so I would look for 97 percent acetone or higher.

Common Flex Seal Complaints

Although the company has a lot of great reviews on the durability of its products and has a track record of adequately temporarily patching holes and cracks, like any other company it is going to have some nay-sayers. A common complaint that Flex Seal gets is that it causes mildew and mold, even though the company claims their product is mildew, moisture, and mold resistant. Although the product is resistant to these types of things, it is not meant to be sprayed on top of them in an attempt to stop them. Mold will grow through just about anything if it is covered so if this is the goal, do not attempt to use it in this manner or yes you will get mold through the product. As for the product actually growing mold, the company has no response.

Another complaint we have seen is that the product flakes off of the surface. This problem seems to be associated with applications to outdoor areas. If you are using flex seal on an area of your boat that is constantly exposed to the sun, you may or may not run into a similar problem. Area’s like decks and roofs seem to be the most common place of application for this type of complaint, so it could be assumed that under heat for so long the product dries out and starts to crack and flake.

A common complain that people submit is that it does not work when applied to areas that are under pressure. Flex Seal does say that their product will not work under certain amounts of pressure and they use the example of a bicycle tire.

Other than those few product performance complaints, the only other type of complain is with their customer service quality. Shipping delays and poor responses to customer complains are the number one complaint in this category.


If you are wondering if flex seal is going to be a good permanent fix for your boat, the answer is no, it is not. If you just need to use it as a temporary repair until you save the money to properly repair your boat, then yes, Flex Seal is a great product for a temporary fix. Make sure that if you are using this product that you apply it properly, and you should get a good amount of time from the product.

Flex Seal is a very popular product to have on hand for emergencies. Every angler or skipper should keep a can of flex seal spray and a roll of tape on board. Heaven for bid you get a hole in a hose or a leak in your boat, Flex Seal could make the difference between your boat sinking or being able to make it to land. Anglers and Skippers swear by keeping the product on board for situations like this and it makes sense!

Flex Seal will stick to your boat and it is waterproof enough to use on your boat even if the area is completely submerged by water. Remember to let the product cure for the whole 24 hours before placing your boat back in the water.

Once you have properly prepped, have applied your product, and are done letting it cure, you will be ready to get back on the water! But don’t forget to pinch your pennies and prepare for a repair in the near future because Flex Seal is not meant to last forever.