Seal the deal on construction

Polyurethane sealants: Professional grade, for professional results

Wondering what kind of polyurethane sealant is right for your project? We’ll explain the difference between sealant and adhesive, how to apply it and direct you to the best polyurethane caulk for heavy-duty structural jobs.

What is polyurethane sealant?

Polyurethane sealers are flexible and versatile construction sealants appropriate for a number of surfaces like wood, metal, plastic, masonry, aluminum, stucco and much more. They’re water tight and flexible under any weather condition, making them perfect for sealing gaps and joints on the exterior of structures.

Are polyurethane sealants the same as PL adhesives?

While polyurethane sealants have some of the same properties as their adhesive counterpart, they are not the same and shouldn’t be used for the same applications. Polyurethane adhesives are specifically designed to provide load bearing strength to structures. Whereas polyurethane sealants are very flexible and intended to provide air and water-tight seals.

How to apply polyurethane sealant.

Applying polyurethane sealant is simple with the right tools. Here’s what you’ll need, and how to do it.

You’ll need:

  • A caulk gun
  • Utility knife
  • Polyurethane sealant cartridge
  • A compatible smoothing agent


  1. Cut the application tip to the desired bead size.
  2. Puncture the cartridge and insert it into the caulk gun.
  3. Prime the cartridge and do a test stream on a disposable surface to make sure the bead size is correct.
  4. Apply sealant according to the manufacturer’s instructions. 
  5. Apply smoothing agent according to the manufacturer's instructions.

Prepare your surfaces: For achieving the strongest seal, surfaces will need to be free from dust, grime, grease, rust and brittle paint. Concrete should be scrubbed with a wire brush, and rust should be removed from metals. Joints deeper than 0.5 inches might need a backer rod. Different surfaces will require different preparation such as using a primer, so check individual product instructions for details.

The best polyurethane caulk for structural applications.

Loctite has designed a number of polyurethane sealants that are suited for any outdoor structural application.

If you’re sealing gaps around windows, doors, siding, garage framing, fascia and sill plates, pick up Loctite PL S40 Polyurethane Window, Door & Siding Sealant. This permanent and flexible polyurethane caulk sealant is tear-resistant and will not lose its function when exposed to UV rays. It’s water proof, paintable and compatible with all common construction materials.

If you’re working on a roof, reach for Loctite PL S30 Roof & Flashing Polyurethane Sealant. This professional grade sealant complies with Federal & State Regulatory Requirements, and provides extra protection against corrosion. Its non-sag formula makes it perfect for sealing flashing around roof edging and chimneys, and is perfect for shingle tabbing.