We built a new home in Orange County, CA, about six years ago. For our patio, we used a concrete slab and then covered that with porcelain tile with a 1/2" wide grout joint. All over the patio, what I have been told is "calcium" deposits have oozed up through the grout, creating rock hard, very unsightly deposits on the grout. As I understand it, to have avoided this, the contractor should have put down a "moisture barrier," commonly referred to as a simple sheet of visqueen plastic, before the slab was poured. Is this correct? Is there anything I can do after the fact to remedy this? Any help would be much appreciated. Thank you.

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Originally Posted by MrAllied

We built a new home in Orange County, CA, about six years ago. For our patio, we used a concrete slab and then covered that with porcelain tile with a 1/2" wide grout joint. All over the patio, what I have been told is "calcium" deposits have oozed up through the grout, creating rock hard, very unsightly deposits on the grout. As I understand it, to have avoided this, the contractor should have put down a "moisture barrier," commonly referred to as a simple sheet of visqueen plastic, before the slab was poured. Is this correct? Is there anything I can do after the fact to remedy this? Any help would be much appreciated. Thank you.

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Well, you need to remove the moisture build up underneath the slab. Not only could the visqueen have helped minimize the water vapor transmission if a cure sealer was used on the finish product it will trap the remaining moisture between two sealed surafces reducing unrestrained oxidation. Concrete cures continuously. To minimize oxidation from below place visqueen. Allow the concrete to cure by oxidation before using sealant. The best method to cure concrete is to allow to cure over several days applying water as required to maintain a moist surface continuously. Remember to protect against flying particals. This link may help a little What is a Calcium Deposit?

Seems a little late in the process to talk about what to do under the slab.

You could try sealing the existing grout, but it won't last long and will come back, as you have to make the sealer soak into (or thru) the grout. The seal needs to be on the underneath side of the grout.

However, I would try regrouting with an epoxy-based grout, which will seal the grout lines. Involves removing the old grout, YUK. But, what do you have to loose? If you do it yourself, it won't cost much to give this a try.

You'll need to get that calcuim off... maybe muriatic acid will clean it off. Test in an inconspicuous area, first. Long rubber gloves, safety glasses and/or face shield is a must.

If that doesn't work, I think you'll have to start over.