Cleaning and Sealing Flagstone

Old 06-13-03, 07:57 AM
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Cleaning and Sealing Flagstone

I've had a FLagstone patio for about 2 years now, and never got around to sealing it. Well now I have a green moss/milde/mold growing over it and it's time to take some action. Is their any products out there for this, or is using a mild detergent, scrub brush and hands and knees the best way. I thought about pressure washing but my Flagstone is "dryset" and I think I would ruin the gavel/grout, or at least make a big mess.

Also after the cleaning process is done what is the best sealer for flagstone that will retaing it's natural color? And I would like to redo the grout lines(so maybe I will pressure wash after all) but I can't use pure concrete because of the cold weather. Because it heaves and cracks in the winter...what is a good alternative? i've seen a show were they used a mortar mix with a much heavier ratio of sand. Thanks

BTW this is in Maryland if you're wondering.


Old 06-13-03, 02:28 PM
Join Date: Feb 2003
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I've pressure washed a flagstone (mortar set) patio recently. It worked very well. You shouldn't have a problem if you only wash the stones and don't hit your gravel joints. Be careful not to use to much pressure, because you run the danger of flaking off a layer of the stone. You could do a pre-wash with TSP (tri-sodium phosphate) or similar "grime" cleaner...but I think you'll find the pressure wash does it all. Easy does it.

Unfortunately, I can't help you too much with your joint re-do.

Good luck with the cleaning.
Old 06-16-03, 03:09 AM
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Find an oxygenated bleach (sodium percarbonate) in crystal form.
It's made for cleaning/brightening wood decks and is basically harmless to grass and plants. It will kill algae, moss, and mildew.
Look for it in the better paint stores.


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