Epoxy Grout Failure


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Old 07-20-22, 11:09 AM
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Epoxy Grout Failure

Was wondering if anyone has experienced epoxy grout failure in a shower. We had our shower retiled in early 2020 and have recently noticed the grout getting soft and coming out on the walls. I can scrape it out with my fingernail and it is worse when the grout is wet. The floor of the shower seems to be okay.

Some details:
  • Shower is tiled in 6 inch subway tiles on the walls
  • grout lines are 1/8" or smaller on the walls
  • Schluter waterproofing underneath
Is it possible that the thin grout lines could have created the problem and if this is the case it looks like the shower will probably have to be retiled? If that is the case is there any way to save the expensive Schluter system underneath? We have someone coming tomorrow to try to remove as much of the soft grout as possible and regrout. We spent several thousand on the shower and I am not ashamed to say I would like to find the cheapest fix and am considering a bath fitter type option over the tile as the simplest solution.
 
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Old 07-20-22, 12:10 PM
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I have a lot of epoxy grout in my house and not had any of it go bad and much of it is outside. So, when done sorta right it can last a very long time. But, the epoxies I used 20 years ago may be very different than what's available in most home centers today. Back when I did it epoxies were only starting to be used residentially with most going to things like fast food restaurant floors.
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My first thought was the sides of the tiles where the grout must stick were dirty. I've seen this when cutting with a diamond blade. The super fine dust needs to be rinsed off before setting the tile. The dust on the sides of the tile can prevent any grout from properly sticking. That doesn't explain why your grout is "soft" though. If this were the problem I would expect cracking or chunks of hard grout to pop out.

Epoxy is a perishable product so it needs to be reasonably fresh. I have seen old epoxies that simply don't harden properly. I suppose the base chemicals break down over time or heat/freezing so they no longer work properly.

Epoxy MUST be thoroughly mixed. Some accustomed to regular cement based grout may not mix nearly enough. You can get away with minimal mixing of cement based grouts as the water will wick through the product and eventually harden it all. Epoxy MUST be mixed beyond the point where it looks mixed, essentially to the molecular level so every bit of the epoxy can properly harden.

Epoxy is sensitive to temperature. Make sure to follow the manufacturers recommendations. This probably wasn't an issue if it was inside a finished home where the heat and AC are running. If applied in colder temperatures it takes longer to harden. If applied when too hot the epoxy hardens in the pot. Some will still try to apply it or will stir to try and keep it flowing as it jells. Unfortunately with epoxy once it starts to kick... it's over. The batch needs to be thrown out. Stirring as it tries to harden just breaks whatever bonds it's forming and they can never reform so it severely weakens it and it may never fully harden. This is a surprisingly common problem especially when mixing larger batches (I've had it melt plastic mixing buckets). Epoxy makes heat when it cures. A large pot or bucket of it can have a runaway chemical reaction where it's heat makes it kick faster, producing more heat... that makes it kick faster.

Grout joints 1/8" or smaller generally use unsanded grout. I can't imagine how a narrower spacing can cause the grout to go "soft". I suspect if the space is really small there isn't enough room for the epoxy to encapsulate and make the sand grains stick. I think this would take a really narrow gap though so I doubt it's a major issue.
 
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Old 07-21-22, 10:17 AM
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Thanks for the info. Here's hoping the 2nd tile job this installer did 18 months later doesn't have the same problem.
 
 

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