Fact Checked

What is Polyurethane Sealant?

Eric Tallberg
Eric Tallberg

Manufactured through the reaction of glycol and an isocyanate, polyurethane is an organic compound with particularly good moisture- and corrosion-resistance characteristics. Polyurethane sealant is useful in both industrial and commercial applications. Additionally, polyurethane is often used as a heavy-duty adhesive, as well as a coating.

A polyurethane sealant may be pressed, layered, sprayed, or brushed onto joints, but the most common method of application is with a caulk gun. Most sealants are sold in 10-ounce (295.74 ml) tubes that will fit the common caulking gun.

A caulk gun is used to apply polyurethane sealant.
A caulk gun is used to apply polyurethane sealant.

As well as being resistant to moisture, chemicals, and corrosion, polyurethane sealant is noted for its flexibility. A common problem with joints is the expansion and contraction of the joint. Polyurethane, with its inherent resiliency, is particularly resistant to cracking due to movement of the joint materials.

These sealants are available as either one- or two-component compounds. Since the typical residential user is typically looking for one that is easy to use, the basic residential product has only one component. This means there is no need to mix ingredients before they can be used.

Polyurethane sealant.
Polyurethane sealant.

The typical polyurethane sealant is hydrocarbon-based. With the advances in water-based polyurethane technology, however, effective water-based, or latex, sealants and coatings are now available. These products are noted for their low-odor, low-variable organic compound (VOC) content, and ease of application and cleanup.

In addition to producing an excellent sealing compound, polyurethane is often used as a wood coating. The same factors that make it a good sealant contribute to its effectiveness as a coating. Polyurethane’s resistance to abrasion, its scuff resistance, makes the product a superior wood-floor coating.

Polyurethane sealant can be used to adhere various building materials like steel, wood, concrete, vinyl or even aluminum.
Polyurethane sealant can be used to adhere various building materials like steel, wood, concrete, vinyl or even aluminum.

A quality sealant will adhere to masonry, wood, concrete, steel, aluminum, vinyl, and most plastics. Its flexible, yet durable finish not only protects these vulnerable materials, but, when used as a coating, provides a gleaming, blemish-free finish, as well. Obviously, proper application methods must be used to achieve the desired results. Polyurethane coatings work especially well as an anti-corrosive on metal products. Some experts even recommend using it over powder coating for protecting metal, though a textured finish, which many people require, is difficult to achieve.

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Discussion Comments


@andrearaerae: You might ask at your local home store if there is something you can put on the countertops to seal the paint better.

For a cheaper, fast solution, go to Target or somewhere similar and pick up a set of plastic cutting mats. They're cheap, flexible and you can stick them in a drawer when you're not using them. Chefmate makes a nice set.

They're not bulky like a wood or hard plastic board, and they're big enough to accommodate your food preparation. And since they're plastic, nothing will bleed through on to your food. I really like mine and I use them frequently. They're also easy to clean.

It could be a short-term solution, anyway.


My countertops were painted with latex paint and sealed with some sort of urethane sealant. My landlord "renewed" our countertops in this fashion.

We have been here for two months and the paint is streaky in many areas. Every time I clean you can see the paint come up. Is this safe for food preparation?

My landlord suggested putting down a cloth before preparing food, but if the cloth gets wet, anything beneath it will eventually find its way through the cloth. Is there a way to seal it so that it does not come off into my food? Is it safe to prepare food on it?


Does polyurethane sealant react chemically with modified asphalt products?


I have developed a PU Sealer which having less than three hours pot life even though all other performances are excellent. Kindly suggest to me how I can improve it up to six hours.


I have a narrow (small) reticulation pipe of copper in which copper and plastic hosing is inserted at regular intervals. These insertions require a sealant fix strong enough to support the water pressure for reticulation purposes. I have two questions:

1) does copper react adversely to a polyurethane sealant?

2) is this sealant appropriate for the above purpose? Many thanks.


What is the toxicity of the off gases after applying to large surfaces such as log home?


Is Polyurethane Sealant good enough to use in joints and approved by the Aust std 3740 for the use in wet areas before a weather proof membrane is applied?


Ref using polyurethane to coat pine flower boxes; it will work, but several coats - at least five - are required to effectively protect the wood. It's also adviseable to use an oil-based polyurethane. Recoating every three or four years is a good idea, as well.


Is it advisable to use polyurethane on pine wood for garden boxes? Will it protect from weather and animals?


It's my experience that polyurethane will chip, peel, and break down if not applied correctly. Even if poly-u. is applied correctly with the proper surface preparation, some erosion will occur over time. Granted, this erosion, peeling, chipping, etc. will likely be in minute amounts, however, it's also my experience that any contamination of a vintage wine is not so good!

In any case, there are latex - water-based - polyurethanes available that, if nothing else, will be somewhat less toxic than oil- based poly-u.

There are a vast number of websites dedicated to wine-making. It might be a good idea to consult these before coating your feeder box.


I was given a grape crusher for making wine that has been stored in a barn or basement for many years. I unbolted the feeder box and sanded away many years of dust and grime.

I would like to know if it is safe to Polyurethane it inside and out and use it to crush the grapes.

My concerns are for there to be no contaminants from the Polyurethane to leach into the grapes and wine?

I won't be making the wine until late September or early October.

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    • A caulk gun is used to apply polyurethane sealant.
      By: andersphoto
      A caulk gun is used to apply polyurethane sealant.
    • Polyurethane sealant.
      By: PiLensPhoto
      Polyurethane sealant.
    • Polyurethane sealant can be used to adhere various building materials like steel, wood, concrete, vinyl or even aluminum.
      By: SeanPavonePhoto
      Polyurethane sealant can be used to adhere various building materials like steel, wood, concrete, vinyl or even aluminum.