Rust-Oleum Leak Seal vs. Flex Seal (Which Is Better and Why)

Gaps, cracks and holes aren’t fun! Although they are a normal consequence of the deterioration of any material, they can certainly cause many annoying problems for home and car owners. The number one problem caused by these tiny enemies is certainly leakage.

Leakage is more than just an inconvenience. Leaky pipes, roofs, toilets, water heaters, doorways, windows, etc., have one thing in common — they need to be fixed quickly and efficiently. If you do not attend to the leakage problems immediately, you might end up paying bundles of money in the long run.

OK, you’ve heard us loud and clear. And the question that pops up now is how you can deal with your newly discovered leakage without wasting a lot of money and time. The answer is rather simple — grab a liquid rubber sealant and fill those problematic cracks up!

Rust-Oleum Leak Seal vs. Flex Seal


You’ve started your search for the best liquid rubber sealant there is, and you’ve determined that Rust-Oleum seals are the most popular ones. But they offer two types of sealants that might work equally well. Which one is better, Rust-Oleum Leak Seal or Flex Seal?

This is a question that you will have to answer based on your preferences and the characteristics of these 2 sealants. And we are here to help you get to know their characteristics better, so let’s start.

To cover the basics, we will first discuss all the important factors to consider when purchasing a liquid rubber sealant. Here is the list of items to consider when making the decision:

  • Material compatibility
  • Surface compatibility
  • Durability
  • Application method

Material Compatibility: Leak Seal vs. Flex Seal

The first aspect of Rust-Oleum Leak Seal vs. Flex Seal comparison we should discuss are the materials. Both Leak Seal and Flex Seal can be used on a vast number of materials. You can use them on wood, metal, glass, masonry, cement, concrete, etc. You can also use them on some types of plastic, vinyl and rubber — but not all. Therefore, it is highly important you do your due diligence and get the information from the seller or the producer on whether you should apply the sealant on your specific plastic, rubber or vinyl surfaces.

Speaking of specific materials that sealants are compatible with, people often ask if leak seal and flex seal can be applied over caulk. The simple answer is yes, you can apply the sealants over the caulking job you did. However, if you’ve used silicone for caulking, then it is not recommended to use either leak seal or flex seal. The reason is that they won’t adhere well to the silicone and what you get won’t be what you expected.

As you can see, none of the 2 sealants we are discussing has advantages over the other when material compatibility is concerned. So in this case, there’s no clear winner of Rust-Oleum Leak Seal vs. Flex Seal battle — you can use both sealants successfully on a multitude of materials. But here’s a tip. Before you start using either sealant, make sure you first test it. Spray a small amount in an inconspicuous area and see how it adheres. After you confirm it behaves as expected, you can apply it to the rest of the surface and finally get rid of that annoying leakage.

To sum up this section of our Rust-Oleum Leak Seal vs. Flex Seal comparison, let’s take a look at frequently asked questions:

Can I use Rust-Oleum Leak Seal on an RV roof?


Yes! RVs are particularly vulnerable to leakage. With all those cracks, seams and moving parts, it is almost impossible to avoid leakage. Luckily, Rust-Oleum Leak Seal can be used on RV roofs. We even recommend using Rust-Oleum Leak Seal vs. Flex Seal in this case, as it is more resistant to temperatures and other weather conditions.

Does Rust-Oleum Leak Seal work on wood?

Yes. As we’ve already mentioned, Rust-Oleum Leak Seal works on a plethora of materials, wood included. What you should do, however, is make sure the wood is prepared for coating.

Does Flex Seal work on wood?

Yes. This is basically the same question as the one above, but it concerns Flex Seal. Even though the answer is the same for those 2 questions, we’ve decided to keep them separate and make it crystal clear they both work on wood. If you have a cracked wood problem you would like to seal, don’t hesitate, and apply Flex Seal on it. You can rest assured it will do a wonderful job on this material.

Does Flex Seal work on roofs?

Yes, you can most definitely use Flex Seal on your roof. It is a good option, as it has enough flexibility, so it can expand during hot months and contract during cooler months without cracking. However, if you live in an area that has extreme temperatures, you should avoid using Flex Seal outdoors. It is vulnerable to very high or very low temperatures, so you would be better off with Leak Seal in this case.

Does Flex Seal work on gas tanks?

No. Neither Flex Seal nor Leak Seal should ever be used on gas and oil tanks. Keep the sealants away from any fuels and other flammable substances.

Does Flex Seal work on toilets?

Yes! Just make sure you dry the toilet tank well before applying the Flex Seal coat.

Surface Compatibility: Flex Seal vs. Rustoleum


Surface compatibility is another important factor to consider when making the Rust-Oleum Leak Seal vs. Flex Seal decision.

Materials, which we’ve already discussed, are an important characteristic of any surface. However, when we speak of different surfaces, there are other elements that play an important role in deciding which is better, Rust-Oleum Leak Seal or Flex Seal.

Before you decide to apply Rustoleum rubber sealant vs. Flex Seal on your surface, you should take into account whether you’re coating an outdoor or an indoor surface. Although both sealants can be used outdoors and indoors, there are some advantages of Leak Seal when it comes to outdoor usage.

That major advantage is Leak Seal’s better resistance to temperature. Even though you might live in an area with a mild climate, we recommend going the safe way.

Another thing to consider when resolving the Rust-Oleum Leak Seal vs. Flex Seal mystery is the purpose of the surface you want to treat. Do you want to repair your toilet tank or do you want to fix your kitchen sink? This is a very important question to answer, as it can save you from some very serious consequences.

Basically, you should never use neither Flex Seal nor Leak Seal for any surfaces that are in contact with drinking water, food or kitchen utensils. Also, you should never use these for fixing something your pets use (and can lick, eat, etc.). This means that although both Flex Seal and Leak Seal can do wonders for glass surfaces, you should never think about using them on your fish tank.

To conclude, information about the surface can help you resolve the Rust-Oleum Leak Seal vs. Flex Seal dilemma up to some point. If your surface is indoors, where you can easily control the temperature, go with either Flex Seal or Leak Seal. But if it’s outdoors, go the safe way with Leak Seal. And remember, don’t apply any to the surfaces that are in direct contact with what you eat or drink.

Application Method: Leak Seal vs. Flex Seal

The best thing about using the liquid rubber sealant to fix your leakage is that you can do it yourself, and quite easily. However, you should follow the instructions carefully to get the best possible results.

When the application method is concerned, there are no significant differences between Leak Seal and Flex Seal. The process for applying those is basically the same, and it consists of the steps listed below.

First, you should prepare the surface. Although you can skip this step, the results would be much better if you didn’t. Make sure that the surface is as smooth as possible. You might need to do some sanding to smooth it out. Then, you should dry the surface and make sure it is clean — there shouldn’t be any remains of oil, grease or dirt.

After you’ve cleaned and dried the surface, you should mark it up, so you can do the coating with a high level of precision. You can use painter’s tape for this. Also, make sure you cover the rest of the surface so you don’t accidentally spray over it.

Next, you should make sure that the place you’re doing the coating on is well-ventilated. The time needed for the seal to dry will depend greatly on the ventilation conditions.

Now that you’ve prepared everything, you can start the spraying. The recommendation is to keep the spray can 8–12 inches from the surface and to try to do the spraying with an even sweeping motion. Even if it appears that some sections weren’t well covered, don’t worry — you’ll get back to that later. It is better to have several thin, evenly distributed layers than one clumsy thick layer. Just make sure not to spray a new coat before the first one completely dries.

Finally, be patient and let the sealant dry. Depending on the ventilation, it can dry in a couple of hours, but to be sure — we recommend leaving the sealant for 24–48 hours. Afterwards, you can paint over it — with oil based or latex-based paints.

It is clear from the above mentioned that the application method isn’t something you should base your Rust-Oleum Leak Seal vs. Flex Seal decision on. They are both equally easy and convenient to use.

To sum up this section and answer the related questions we didn’t cover, let’s take a look at frequently asked questions related to the application of Flex Seal and Leak Seal.

How much Flex Seal do I need?

This will depend on the surface you want to cover and the number of layers you need. But to give you a rough idea on this, here are some estimates. You can cover up to 8 ft with one Large 10-oz can, and with one Jumbo 14-oz. can, you should be able to cover up to 12 ft.

Can Rust-Oleum Leak Seal be used on wet surfaces? And what about Flex Seal — does Flex Seal work on wet surfaces?

People often ask these questions. The answer is the same for both sealants: yes, you can use them on wet surfaces, but try to avoid that. What does this mean? It means that in the case of an emergency, you can apply sealants on wet surfaces or in moist environments. It will do the trick, but since those adhere better on clean and dry surfaces, you should make sure to re-apply the coating after the treated area dries.

How long does Flex Seal take to dry? How long does Rust-Oleum Leak Seal take to dry?

It will depend on the weather and ventilation conditions. Both Flex Seal and Leak Seal approximately take 3–4 hours to dry, and you could probably touch them after this time period. However, we recommend you leave them for 24–48 hours.

How long before Flex Seal can get wet?

It would be best if it would dry completely before getting in touch with water. However, it would be OK if it got wet immediately after you put it on. We’ve already mentioned that Flex Seal, the same as Leak Seal, can both be applied even to already wet surfaces. They can both be applied during a light rain, but strong downpour may wash them away. In any case, make sure to re-apply the coating once the area gets completely dry.

How to paint Flex Seal?

Flex Seal can be painted with oil-based or latex-based paint. You should wait for the sealant to dry completely and then apply the paint. What we would recommend is to choose the color of the sealant that is close to the color of your surface. That way, you wouldn’t need to spend much time painting.

How to remove Flex Seal?

It depends on where you’ve sprayed it. If you sprayed it on metal, acetone should remove it just fine — you just need to put a bit more effort into scrubbing. For cars, apply toluene, which is, basically, an acetone too. Apply a small amount and rub. For other materials, like carpet, fabric, tiles — go with a mineral spirit.

How do I remove Flex Seal from my hands?


To remove flex seal from your hands, you can use some mild citrus-based cleaner, or you can even use baby oil and rub it off with a towel.

Durability: Rustoleum Rubber Sealant vs. Flex Seal

The question of durability is one of the most important to consider when Rust-Oleum Leak Seal vs. Flex Seal dilemma is considered. Here, we have a clear winner — it’s Rust-Oleum Leak Seal. Even though Flex Seal won’t dry out, crack or peel, sag or drip in the summer heat, it is quite vulnerable to temperatures. On the other hand, rustoleum rubber sealant is quite resistant to temperatures, and thus a better choice for the longevity of your sealant.

Let’s get more specific with a couple of frequently asked questions on the topic:

How long does Rust-Oleum Leak Seal last?

Due to its high resistance to temperatures, it can last for years before you need to re-apply it. However, you should check up on your sealant once in a while to make sure it didn’t start to deteriorate and prevent problems.

How long does Flex Seal last on a roof?

As already elaborated, it will depend on the weather conditions. Flex Seal is quite sensitive to very high and very low temperatures. In mild climates, it could probably last for years. However, we recommend you use Leak Seal anyway, as it is a clear winner when it comes to sealing something outdoors.

How good is Flex Seal?

It is very good! Easy to apply, strong and flexible, its only downside is temperature vulnerability. But if you need to seal something indoors, then Flex Seal is the right choice. Also, it is a great choice for surfaces that move (slide, open and close, etc.) as it has the needed flexibility and won’t crack from frequent pressure.


Now that you have the full information on all important aspects of Rust-Oleum Leak Seal vs. Flex Seal dilemma, are you ready to make the decision?

Whatever you decide, you can’t go wrong. These are both great sealants, and which one you choose should depend on your specific situation and preferences. Need a more flexible sealant? Go with Flex Seal! Need a sealant that you can use outdoors without worrying it will deteriorate quickly due to extreme climate conditions? Go with Leak Seal!

Whichever you choose, just make sure to follow the instructions and our advice closely! Good luck, and happy sealing!

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