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Category: Adhesives Product: Polyurethane Construction Adhesive
Temperature Limitations: Above +5 C (+40 F) and below +30 C (+86 F)
Rain Limitations: No rain for 1 hour
Wind Limitations: n/a
Humidity Limitations: Very low humidity will prevent curing
Continuous Conditions: Keep free of freezing for 24 hours
Comments: Polyurethane adhesive is the strongest of the construction adhesives and cures rock hard. It requires moisture to cure, but has difficulty sticking to wet surfaces. It sticks well to both wood and concrete/masonry. It has very low shrinkage and can fill gaps. For use on a roof, see Polyurethane Caulking for roofs, which cures flexible.
Weather limitations on most renovation products can be located on the WEATHER tab above.
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APPLICATION / INSTALLATION DETAILS
Polyurethane adhesive is the strongest of the construction adhesives.
It contains no solvents and cures by exposure to moisture, so it actually takes longer to cure under very dry conditions.
Because of it curing by chemical reaction rather than by evaporation, it has a very low level of shrinkage and it cures to a rock hard state -- permitting it to be used as both an adhesive and filler -- a perfect joint fit is not necessary.
It adheres especially well to both concrete and wood. It is the adhesive of choice for attaching the top row of a concrete tile retaining wall -- or for repairing a bird bath.
Most versions of it will not stick well to asphalt products -- but there are specially formulated polyurethane sealants that make the best of the adhesives for loose shingles.
Although best applied to a clean dry surface, it can be applied to a moist surface but not a wet surface or under standing water as it simply can't push the water away in order to stick to the surface.
For wet surfaces some thermal plastic adhesives are made for the task.
For underwater jobs there is are special epoxies that can do the task.
Polyurethane adhesive will stain skin, even after the adhesive is cleaned off, although it is not toxic.
Construction adhesives generally are applied with a caulking gun and one of the tricks to working well in any cool to very cold weather is to keep the cartridges indoors and warm until they will be used. Cold adhesive is very difficult to "gun" -- to get to flow properly out of the gun and spread properly on the job.
Polyurethane is temperature sensitive and must be kept from freezing for 24 hours. If your cartridge of polyurethane adhesive is warm but will not flow easily, it is either old or has been left open and the chemical reaction initiated by moist air has begun to harden the cartridge. Unlike solvent based adhesives it is not simply a question of removing the dry plug -- the hardening is happening inside and could be all the way through the product. Don't fight it -- buy a new cartridge. It has about a 1 year shelf life so don't buy too much extra.
For more details check out: What is an outdoor adhesive?
And if you are trying to apply a straight bead of adhesive along the narrow edge of a floor joist, check out this adhesive guiding tip.