Grout Strength... Should I Be Concerned? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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04-23-2008, 08:09 AM
Hi there,

I'm laying some slate in my bathroom, and on Saturday (5 days ago) I grouted it. Yesterday, I cleaned the slate/grout with fresh water to prepare it for sealing. Out of curiosity, I tested the strength of the grout with my fingernail. To my surprise, I was able to stratch some of the grout out with my fingernail. It was definitely hard to do, but it was not rock hard like I expected it to be. Is this normal?

I know too much water when you mix the grout, and too much water when you sponge the grout off can weaken the finished product and even cause the grout's color to run (my grout is black). I mixed the grout to a consistency where it was still thick enough that when I dragged my grout float through it the grout would stay where I pushed it and not slump back to the bottom of the pail. When I sponged the grout off, I ensured my sponge was as wrung out as possible and made sure there was no sitting water on the grout lines or slate. In my opinion, the finished grout job looked terrific. Even color and very little "valley effect" in the grout which I've heard can indicate your grout was mixed too thin.

Should I be concerned about the strength of the grout, or is this normal prior to sealing?

The bag it came in indicated that foot traffic should be avoided for 12 hours and that immersion should be avoided for 72 hours. Given this, I'd imagine the grout should be pretty close to finished strength right now.

As it is now 5 days after I grouted, is there any reason I couldn't seal it tonight? The grout bag said nothing about how long to wait until sealing, and my sealer (SBS Sealer from Aldon) just says "Surface must be absolutely dry and clean" prior to sealing.

Thanks for your help,


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04-23-2008, 09:16 AM
I think you'll be OK. It will get harder as the cure progresses over the next several weeks.

I've not used Aldon's SBS (Solvent Based Sealer) so can't help you much with the wait-time question.

04-23-2008, 05:52 PM
While cement products are fairly hard in a week, their specification is measured after 28-days, and it continues to get stronger and harder for years.