Osmotic Blisters in Urethane Cement?

Yes, it can happen.  Osmotic Blisters can occur in urethane cement applications.  But here’s how to avoid it.

Osmotic blisters are known to egregiously affect epoxy flooring applications.  They make unsightly little bumps in the finish, causing unhappy customers and project managers.

But urethane cement was invented and did a great job sealing the exposed concrete.  And for the most part, urethane cement does an excellent job stopping blisters from forming.

And that’s because it can tolerate a very high PSI.  Compared to epoxy’s 3 PSI, urethane cement can withstand up to 20 lbs per square inch, making it almost 7 times stronger.

However, even though its dominant performance against the PSI is formidable, it isn’t perfect.

But here are a few ways to avoid the unsightly blisters, that could lead to future floor failure.

Keep an Eye on Temperature

It’s generally a good idea to bring an industrial thermometer with you on any job site.  But when the product you’re installing depends on precise temperatures, a floor or painting contractor should definitely have one handy.

Urethane cement can handle more temperature variations than epoxy.  But that doesn’t dismiss it from having temperature needs.  And the general rule of thumb is that there should be more than a 15 degree difference between the concrete slab and urethane cement.

Urethane cement will cure of the bottom up.  So if the concrete slab is 15 degrees cooler, then that will retard the cooling phase from the urethane cement.  But it will not retard the curing phase in the remainder of the material.  So as the bottom stills cures and outgasses, it will start to get trapped in the material that is partially cured in the upper crust of the urethane cement.  So if you’re working with a slab that is too cold, you’ll either need to warm up the slab.  Or you’ll have to cool down the material.

But warming up the slab is going to be the best recourse.  As cooling the material can cause other problems.

Sealer Coat on the Slab

Blisters are caused by outgassing.  And outgassing occurs after the slab has been prepped, opening up the airways from the slab.  So another method to prevent blisters is to pour a thin, tight coat of urethane cement over the opened slab.

The drawback from this method is that the installer will need to spend an extra day installing flooring material.  But if by installing the first tight coat, then you’ll be able to seal the floor.   Then, install a 2nd coat, which won’t be susceptible to the outgassing, due to the now sealed concrete slab.

And although the installation now has an extra day planned into the schedule, the customer can have a must more reliable floor, that won’t have a blistering finish.


Urethane cement is the powerhouse floor material.  It has a high chemical resistance, and it tolerates more moisture transmission than epoxy.  But even though it is superior, it isn’t perfect.  But as long as the proper precautions are made, it’s reasonable to believe that your urethane cement floor can be installed flawlessly.