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Soft patches or "hot spots"

By Jack Josephsen

Have you ever seen a solventless, two-pack epoxy floor coating cure hard except for a couple of soft patches, or “hot spots” as they’re sometimes called?

Do you know why something like this might happen? There are a few reasons, however one of the most common causes for mistakes like this is simply a failure to mix the coating correctly.

Mixing well isn’t enough

OK, you may have beaten the product with a drill mixer for five minutes, but unfortunately that doesn’t mean you mixed it well. The fact is you will always have areas within your bucket that do not mix well naturally - namely, the sides - and if you don’t pay attention to these then hot spots can occur.

I see and hear about it all the time; a contractor has mixed the product in a bucket and scraped the sides or left the bucket sitting upside down to get as much out as possible. There’s nothing wrong with trying to minimise losses this way, however to avoid soft epoxy patches you must be sure these regions are mixed properly as well. The only way to do this is to scrape the sides of the bucket during the mixing process to lift the stagnant product and draw it into the middle. It becomes even more important during cooler temperatures or if using a thicker product that doesn’t flow as easily.   

Soft spots, or soft patches, creating a dirty looking floor.

What about larger soft spots?

The hot spots created by poor mixing practices with solventless epoxies are usually small in size, so what might be the cause of larger soft spots?  If you have large soft spots, i.e. covering a full kit or more, then I would be asking questions about the mix ratio or, heaven forbid, forgetting to add the curing agent at all. Don't laugh, it does happen! If the coating was a solvent-borne or water-borne product (or even if solvent was added to a solventless product) then something called solvent entrapment might be in play and I’ll get around to that in another post.

How can I fix soft spots?

Unfortunately there are no quick fixes for soft spots. You can’t simply roll some curing agent into the mix and hope it magically hardens into the perfect film you originally intended. Instead, you have to take your medicine, so to speak, look to remove the defective film and go again. On most occasions this will involve scraping up the soft epoxy and solvent wiping away any residue. Once the solvent has evaporated you can patch the area or overcoat it. Be aware though, if you go back to bare concrete with your solvent wipe then you should patch that immediate area first before over-coating otherwise you could end up seeing it through the topcoat.

Take care and keep smiling,

Jack Josephsen
Real World Epoxies

Jack has spent over 15 years formulating, manufacturing and helping epoxy users learn about epoxies. His company prides itself on epoxy products that perform in the field and is passionate about linking industry know how.

In 2010, Jack started Epoxy School and a couple of years ago he published his first book “Finally, real answers for real contractors – Industrial Flooring”, which is available through NACE and Amazon. 


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Steven Owen wrote:
7 Nov '18 2:39am
Interesting article Jack...

I agree with you comments about scraping the sides of the bucket but from experience, I'm not convinced that is enough. What I have always taught my lab people and we are now pushing it into the real world is to actually pour the mixed product into a second bucket, scrape the sides of the first bucket into the second and mix again.

This is a technique I was taught as a young Chemist and have found it invaluable...extra step but I've never had an issue with a floor when mixing is done this way