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Old 10-05-2018, 09:56 AM   #1
joeconroy3
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Test for hardness of grout

Please point me to credible standards and documentation for testing the hardness of non-sanded grout. Polyblend tech guy mentioned the fingernail and credit card scraping test but that seems like lore, not documented anywhere by "authorities" such as TCNA or NTCA. And yes, my Prism non-sanded 1/8" floor grout, put down 3 mo ago by an $80/hr guy, does scrape up into powder by scraping with a credit card drawn length-wise down the grout line with the edge of card perpendicular to the line.
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Old 10-05-2018, 11:17 AM   #2
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Welcome, Joe.

Closest you'll get is the ANSI Standard for Standard Cement Grouts (A118.6) and High Performance Cement Grouts (A118.7) where the compressive strength is listed. For both categories and for both sanded and unsanded cementitious grouts, the compressive strength at 28 days is a minimum of 3,000 psi.

An installed grout meeting that standard would not yield to the edge of a credit card.

An installed grout that can be scraped out with a credit card was likely mixed with too much water or too much water was used in the clean-up, or both. Or perhaps the grout had passed its expiration date before it was used.

And 80-dollar-per-hour tile installer should recognize that.

How long had your grout cured when you "tested" it?

What grout did you use? Please be specific: Name brand, make and model.

My opinion; worth price charged.
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Old 10-05-2018, 12:59 PM   #3
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There is no such test, and I do a lot of testing. I agree with CX, it should be nearly as hard as concrete. Closest thing you could come up with to answer the question is it any good would be a petrographic analysis using thin slides and someone that knows how to read it all. That is not inexpensive as you might imagine. The floor would have to be cored and the core seperated and prepped in the lab.
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Old 10-05-2018, 05:27 PM   #4
joeconroy3
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Durometer readings

CX and Dave, thanks much for your help. What about using the specs of the manufacturer - Custom Building Products - who told me a reading of at least 50 on a durometer is ok for the Prism grout that was used, anything less was not mixed correctly. The result is not psi as stated in this Wikipedia description: "The Vickers test can be used for all metals and has one of the widest scales among hardness tests. The unit of hardness given by the test is known as the Vickers Pyramid Number (HV) or Diamond Pyramid Hardness (DPH). The hardness number can be converted into units of pascals, but should not be confused with pressure, which uses the same units. The hardness number is determined by the load over the surface area of the indentation and not the area normal to the force, and is therefore not pressure."

I think this is the same measurement used to gauge the hardness of woods and other materials.
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Old 10-05-2018, 06:47 PM   #5
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Quote:
Originally Posted by Joe
Custom Building Products - who told me a reading of at least 50 on a durometer is ok for the Prism grout that was used
50 what, Joe? On what scale? A reading of 50 on a durometer doesn't mean much without knowing the scale, at least.

Again, the tile industry has no test or standard for the hardness of cementitious grout. If the manufacturer specifies, in writing, a particular test and an acceptable hardness, that would be the best you could hope for.

My opinion; worth price charged.
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Old 10-05-2018, 07:49 PM   #6
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Durometers tend to be used on softer things like rubber and plastics. There are multiple scales and the resulting shape of the test probe.

Not sure if it's really applicable to something like a cement based grout. It would work on epoxy based or one-part plastic based ones, though.

https://en.wikipedia.org/wiki/Shore_durometer

FWIW, 50, depending on the scale, isn't really all that hard.
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