Best seal for flagstone/brick patio?

I did a google search on this topic and didn't find an answer, so apologies if this question has been asked a million times before.
We recently had some brick and flagstone patio installed in addition to our existing flagstone patio. The brick near the firepit and built in BBQ that were installed at the same time has some efflorescence, presumably from the concrete leaching into it (from the BBQ/firepit installs). The mason tried to clean it with muriatic acid, but it didn't work. I know about the efflorescence treatments and plan to try that. Is that the best way to deal with this problem?
After getting the brick clean, we want to seal the brick and flagstone. What is a good brand of sealer? I know to avoid Thompson's. We would like the wet look. Will this make the surface slippery to walk on?
Also, one of the newly installed flagstones is flaking. Is this a problem that requires the piece to be replaced? None of the others are doing this, including the already existing ones.
Thanks a million for any advice.
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I too have had efflorescence on a brick path where ground water from a nearby bank has seeped under the brick, through the crushed rock underlay, then up thru the brick, evaporating and leaving a calcium crust. Part of the problem is near surface ground water, which you may have, and part could be due to the material he used to place the flags on. The crust may or may not be due to other installs nearby. Might want to check your drainage, as this kind of deposit may be difficult to control with sealers, as it is only symtomatic solution, not root cause. Re the flaking flagstone, I wonder whether the contractor bought real flagstone, which is usually extremely hard quartzite or meta-sandstone, that shoud literally ring when hit with a hammer. Flaking, or a sort of thump/thud sound when you tap it, could be a softer rock, like shale or siltstone, which is prone to quick weathering and crumbling. Check out where he got the material, and inquire of the supplier what it actually is.
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primarily sand. We are in the desert, and managed to avoid getting the caliche soils (not that sand is great, but better than caliche). I don't think surface groundwater is a problem either. The landscaping contractor was pretty sure that the brick being laid right along with the construction of the bbq, firepit, and a bench, was the source of the effervescence. He also said it would go away over time, which seems to be in line with some other stuff I've read. The effervescence is in the brick only, btw, not the flagstone.
As far as whether it is real flagstone, that's a good question. It is exactly the same stuff that was already here, and that is used in abundance here in Arizona. However, maybe what they call "flagstone" here is really not. I'll give it the hammer test. I know it tends to flake and chip a fair amount, as I've seen this problem just about everywhere I see the flagstone.
Well, we'll try to clean it with the stuff I mentioned and see how that goes.
Any recommendations for a sealer?
Dawn
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stepdawn wrote:

walkway last year and it is still working. Don't know about the flagstone chipping.
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Thanks! I will look into that sealer.
Dawn
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