Sealing Arizona Flagstone

We received this question from a reader concerning sealers and Arizona Flagstone:

Q: Please advise us as to sealing Rosa Az. Flagstone from the Tucson area. We live in Sacramento, CA. We are installing a small patio of this material on 2″ of crushed rock, then 2″ of sand. We are putting polymeric sand in the joints. 2 people have advised us that it is not necessary to seal the flagstone. They advised that, because the flagstone is so porous, it would use too much sealer. Also, they said that leaving it in it’s porous state would help keep it more breathable for less algae growth. We are a little worried that, without a sealer, it will stain too much, as it is so porous.

Thank you so much for your help!!! My husband is a Tucson native, and we are really excited about this flagstone.

Pat Witzens

A: Pat,

We typically don’t seal Arizona flagstone, as far as the amount of sealer necessary, I wouldn’t doubt the advise you have received. As far as algae comment, we don’t have any experience with sealed vs. unsealed- algae is typical in Arizona because of its porosity, and is best removed with a pressure washer and/or push broom with diluted acid wash (Muriatic pool acid), although in some rare cases this can cause efflorescence in the stone. We have not been impressed with the weathering of some of the stone sealers out there. If you are looking for particular brands, Aldon is one we have used in the past, or you can visit your local stone/masonry supply yard or tile dealer. There are some high end (expensive) sealers out there for stones tiles like travertine, that seem to be better. Remember with any sealer or stain used outdoors, it is exposed to lots of moisture, heat, and sunlight, especially in the hot valley summers, so expect results accordingly.

Good luck with the new stone.