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Thread: Flagstone flakes and rust

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    Flagstone flakes and rust

    I have a pool under construction and the rock guys are going to have to come back to replace some rocks in my coping and water feature wall because I found saw cuts in them. While I previously did not think it was a big deal, I now also now wonder if I should have several pieces replaced that are flaking and have a surface that appears rusty.

    Previously I had assumed that once things were done they would power wash the stone to get all that off but after flaking some of it off by hand, it is rusty underneath as well. While it is a pretty color I don't want rust getting in the pool or on swimsuits/feet etc.

    Can anyone speak to whether this is an issue with the rock or if it is just a matter of cleaning the rock? We have only 2 of them like this and the fact that the others don't look like this has me thinking more and more those stones need to be swapped out.

    Is rust an issue for flagstone in general?

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    pragmatic's Avatar
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    Re: Flagstone flakes and rust

    Whether it’s rust or not is unimportant. Metal oxides (rust) are just part of the make-up of some rock. The key is choosing a rock with higher density. Flagstone and moss-rock are affordable but not the best choices for pools (low density type rocks); some worse than others. It appears they sourced a very "soft" batch and I don't think any cleaning will help. A sealer can help in some cases. But, it’s really hard to fix rock that is so soft / porous. If changing it out completely is not an option, I’d suggest finding a good sealer, re-seal annually and keep your pool chemistry in close check (mainly pH).
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    Re: Flagstone flakes and rust

    Quote Originally Posted by pragmatic View Post
    Whether its rust or not is unimportant. Metal oxides (rust) are just part of the make-up of some rock. The key is choosing a rock with higher density. Flagstone and moss-rock are affordable but not the best choices for pools (low density type rocks); some worse than others. It appears they sourced a very "soft" batch and I don't think any cleaning will help. A sealer can help in some cases. But, its really hard to fix rock that is so soft / porous. If changing it out completely is not an option, Id suggest finding a good sealer, re-seal annually and keep your pool chemistry in close check (mainly pH).
    Thanks for confirming. I will have them swap out those rocks. The others look much more dense and solid, and all very beautiful. This is Oklahoma flagstone if that makes any difference. We don't want to swap out for a different type of rock at this point but it would appear those two pieces are not up to snuff.

    We have not considered sealing the flagstone, but I had heard something about sealing it making it rather slippery. Do you have any recommendations on a good sealer?

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    Divin Dave's Avatar
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    Re: Flagstone flakes and rust

    If your pool is saltwater, it's generally a good idea to seal the flagstone as the salt will have a tendency to eat away at it over time. The softer the stone, the quicker it will deteriorate. Prolly should re-seal every couple of years or so to make the stone last as long as you can and keep looking sharp.

    Also a sealer will prevent stains from penetrating into the stone or concrete permenantly, so as far as maintaining deck, a sealer makes that much easier. It also help in retarding mold and algae growth in those moist shady areas. So there are lots of reasons to seal a deck.

    Depending on if you want a natural dry appearance or the glossy wet appearance or somewhere in between should the the 1st thing to consider when selecting a sealer, then go from there.
    Non Slip additives can be mixed in to almost any sealer to make it less slippery.

    Generally speaking, sealers are oil / solvent based or water based. In some states, the oil or solvent based ones are a no no because of the high VOC's.
    Oil based sealers with high solid contenct generally last longer and are easier to touch up.

    You can read all sorts of more stuff about sealers by googling it and then decide which works best for you.

    I orderd a glossy oil based sealer from Home Depot online to seal my exposed aggragate with, so far all I can say is it rocks! Its only been on for a month or so, so the jury is out for the long term, but it still looks like it was put on this morning!

    hope this helps get you started.
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    pragmatic's Avatar
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    Re: Flagstone flakes and rust

    Quote Originally Posted by zimm27 View Post
    We have not considered sealing the flagstone, but I had heard something about sealing it making it rather slippery. Do you have any recommendations on a good sealer?
    Sealing is a good alternative. Here is an old thread about sealing concrete http://www.troublefreepool.com/threa...oncrete-Sealer
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    Re: Flagstone flakes and rust

    Talked to a rock guy I know, he said that some rust and flaking was normal and the surface of the rock needs to wear down a bit, ideally 6 months or so before sealing. He typically does non-wet area work though. With a good sealer I should be fine. Talked with the pool builder when he was out this morning and he said once the work is done they power wash the heck out of the flagstone to get chips and rust etc off and then they seal it with a transparent sealer. That sounds good to me. The power washer will simulate extended rain and foot traffic so all should be good.

    My upper patio area flagstone will not be sealed, but looking at having them do it or doing it myself.

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    Re: Flagstone flakes and rust

    Quote Originally Posted by zimm27 View Post
    Talked to a rock guy I know, he said that some rust and flaking was normal and the surface of the rock needs to wear down a bit, ideally 6 months or so before sealing. He typically does non-wet area work though. With a good sealer I should be fine. Talked with the pool builder when he was out this morning and he said once the work is done they power wash the heck out of the flagstone to get chips and rust etc off and then they seal it with a transparent sealer. That sounds good to me. The power washer will simulate extended rain and foot traffic so all should be good.

    My upper patio area flagstone will not be sealed, but looking at having them do it or doing it myself.
    I went round mine with a hose and sprayed off the flaky areas. Any that continued flaking rather than just chipping off with the initial spray then being fine, I had replaced.
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