Polyurethane Caulk – Possibly the Best Sealant

The ultimate sealant could possibly be polyurethane caulk. This is a bold claim, especially with so many types of sealants on the market. This sealant has taken all the best attributes of all other sealant types and put it into a convenient, single component cartridge ready to tackle your most difficult, or even impossible, caulking requirements.

Urethane caulk can be difficult to apply. It has a sticky, putty like, consistency and requires mineral spirits for both tooling and clean up. But, it will cure into a paintable rubber capable of stretching 300% or more. Some manufactures boast as much as 1200% elongation. Plus, it has very high tensile strength. Can adhere to almost all types of surfaces. Including concrete, wood, glass, plastic and metal.

This incredible ability to adhere to so many dissimilar materials is just one of its features. Very important when trying to create a seal between various materials that expand or contract at different rates. Plus, urethane caulk has excellent chemical resistance.


No Mixing or Special Equipment Required

Available in single component cartridges are designed for both standard 10 ounce and 1-quart caulking guns. You have a choice of non-sagging or self-leveling formulas.

  • Use the non-sagging formula for expansion joints in concrete block, gaps in wood siding and around windows or doors.
  • Self-leveling formulas have a very high resistance to abrasion. A perfect match for control joints in concrete floors, especially garage floors prior to the application of epoxy.


Polyurethane caulk can be applied to very large gaps, 1 inch or more, and not loose its ability to create a perfect seal. I have used Sonneborn NP-1 for years on commercial buildings and garage floors prior to the application of a high performance finish, with perfect results.

Although this sealant is difficult to use and will cost considerably more than standard caulking, the benefits will be worth it in the long run. It’s possible this type of caulking could outlast the paint job and the person who applied it.

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  1. George Kenter

    I used self-leveling caulk, a premium-grade polyurethane sealant, on expansion joints on my concrete parking pad, with poor results, even using baker rods, due to wide variation in depth and width. Some parts of the job are quite low, giving an uneven up and down look. Other than attempting to finish with more of the same (I found the product hard to use), is there another type of caulk I can apply in about a week to even the appearance?

  2. J L MacDougall

    What type of paint is recommended for polyurethane caulk? I tried a water-based one and that doesn’t work.

    • Polyurethane sealants require priming before painting with normal house paints. Try a good universal oil base primer, like Zinsser Cover Stain. Allow to dry then paint as normal.

      Recommended coatings without primer can include epoxies and elastomerics. Always consult the product label or with the manufacture for more info.

  3. Daniel

    Can I use a form of eurethane finish over the top of np1 filled joints. not sure if there will be any reactions since they are both forms of eurethane. thanks.

  4. Duncan Hoge

    We had some damage to a masonry chimney and needed to put polyurethane caulk in the mortar joints. Looks it will do the trick, but our repairs stand out, since the color of the caulk does not match the original mortar. Can the caulk be stained or is paint the only choice? Thank you for your answer….

    • The caulk can’t be stained. If painting, make sure to prime the caulking first with an oil based primer (some poly sealants don’t take paint well). Read the tube for painting instructions.

  5. Rob Nuckols

    Question: Where can I buy Polyurethane Caulk that come in an orange caulking tube and is called M-1 or NP-1 ??

    • Here in Colorado Springs I find it at a local concrete finishing store. They rent/sell forms, stamps, stains, finishing tools, stuff like that. You will have to call around. Also, your local paint could order it in for you.

  6. Newlook Painting

    You can’t beat this stuff, It’s possible that the Caulk will outlive the house you put it on. I use this stuff all the time. It is a bit tricky, But use it enough and you become a pro.. I found that a cordless caulk gun works best when temps are cooler. It’s very versatile, I use it to seal gutters, , leaky roofs, seams on metal buildings, metal building screws. I even use it to bond retaining wall blocks and CMU’s. If you do use a primer, Use one that flexes such as XIM bonding primer or Bonding Primer RX By Sherwin Williams .. Standard primers wont flex with it and will crack, make sure you wait until it’s dry before you paint

  7. Eddie

    I am using the Loctite Concrete polyurethane (non Sag) for my exterior porch steps. I cleaned the entire area first and then after with a wire brush and vacuumed the crack/gap and placed backer rod before using the caulking. I will give it a week to cure fully but should I use an Oil Based Primer? over this before top coating everything right. I will top coat with a ( Behr Concrete Floor- Water Based Paint).

    Please advise, thank you!

  8. V

    Can I use a sanded acrylic caulk over this to get the color and texture I need?

  9. Jeff

    Just put down NP-1 in 3/4″ wide driveway expansion joints, located in central Texas with ambient temperatures reaching the low 90s, and it almost all blistered. Going to remove it and start over. Any suggestions how to remove it? Any polyurethane caulk you like in particular (except NP-1)?

    • Sikaflex is another brand that works well. Did you use self-leveling sealant? Horizontal cracks, like your expansion joints, should have the self-leveling type.

      Blistering is a bit odd, I suppose the heat could have something to do with it. Cutting it out completely isn’t possible, I don’t think it is. Use a razor knife with sharp blades and cut at a parallel angle to remove the top and blistered areas, this will leave a ‘V’ shape depression to fill later.

  10. Craig

    Should you prime raw wood before applying urethane caulk or does it bond well directly to wood?

  11. Tony Z

    I put PVC trim moulding around my tub and old tub surround and where the top of the tub and bottom of the tub surround meet, it’s replacing caulking tape that would never adhere for very long.

    The manufacturer of the PVC trim moulding does not recommend using silicone sealants, instead the manufacturer recommends using acrylic, urethane, or polyurethane caulking.

    Which of the three is more user friendly and would be the easiest to seal around the tub and tub surround? Also, I’ve looked at Home Depots website and any acrylic caulking I’ve seen includes silicone, is there acrylic caulk that contains zero silicone?

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