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Thread: Installing anchors in a flagstone deck

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    Installing anchors in a flagstone deck

    Hi! We recently revamped the 12 year old pool in the backyard of the house we bought 3 years ago, including plumbing repair, liner replacement, conversion to salt water, and replacement of the aggregate concrete deck (which we had to tear up to fix the plumbing) with a tiled flagstone deck. In our area, the pool builders with experience laying stone decks were more high-end and therefore not interested/experienced with vinyl pools, and so we ended up going with a highly recommended vinyl pool builder with little stone experience, and having him do all the liner/repair work and laying the concrete base for the deck, and then bringing in an experienced stone guy to lay the flagstone tile on top.

    The pool came with an Anchor safety mesh cover, and now we'd like to set anchors so that we can use it when we close the pool this fall. During construction, some of the guys on the stone crew said that they should do it, so that they would be around to replace any tiles that cracked during drilling and placement, and since our PB doesn't have much experience working with stone, using him seems like a disaster waiting to happen But, I believe this is the first pool deck the stone crew has done; they are more experienced with patios, etc, so they haven't set anchors before and NONE of us are interested in screwing up the $$$ stone we just laid. The stone guy seems a little hesitant since he is inexperienced with this task and I told him I would find out what I could. The folks at Anchor covers were totally useless when I called for their advice, so I thought I'd turn here.

    The stone is square and rectangular Pennsylvania bluestone, average thickness 1.5", on top of a ~ 1" base of mud, and mortared in between, all set on top of a solid concrete base. Will it be sufficient to drill into the stone and set the anchors there? Do they need to be epoxied? Do we need to use the 9" metal sleeves recommended for unmortared flagstone (I did read one horror story in this case on this forum) or will the mud and stone be enough to hold it down? It is an approx 18'x35' Grecian pool with a total of 41 anchor points. I am in Northwest Arkansas, if that is relevant.

    Thanks for any advice! We're first time pool owners so I have learned a lot from this forum!


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    Re: Installing anchors in a flagstone deck

    I would use a diamond core drill, as a hammer drill will likely crack the stones. As long as the stones are properly mortared down to a solid concrete base and mortared in between, then you probably don't need the anchor pipes.

    Although, it would be stronger with the pipes. The pipes do require a slightly larger hole and are therefore more conspicuous. The pipes and anchors don't blend in as well as just using the anchors.

    I would also recommend slightly sanding down the ridges of the anchors as they can be a bit aggressive and cause chipping and spalling when inserted.

    Slightly sanding down the edges of the hole before inserting the anchor can help reduce spalling and chipping.

    Note 1: Don't oversand the ridges of the anchors or edges of the holes as that would cause the anchor to be too loose. Do a little bit and then test for fit. The anchor should fit snug, but should not need to be hammered in with great force.

    Note 2: You should make sure that the cover is not put on with too much tension in the springs/straps and that the cover does not get overloaded with water, snow, ice or other debris.

    Note 3: Most stones eventually become unbonded from the underlying base. This is due to factors such as:

    A) Heating and cooling causing expansion and contraction of the stones and base at different rates.
    B) Groundwater dissolving the mortar.
    C) Water freezing in the area between the stones and the base.

    Stress from the straps pulling on the anchors can accelerate this process. Therefore, using the pipes can help reduce the frequency of having to remortar and regrout the stones. Once the stones become unbonded, then the anchors will not hold properly without pipes.

    Is the cover mesh or solid?

    Do you usually get a lot of snow?

    If you expect snow loading, then using the pipes wouldl probably be a good idea.
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    duraleigh's Avatar
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    Apr 2007
    Sebring, Florida

    Re: Installing anchors in a flagstone deck

    Excellent post, JamesW.

    Repeating what he said for emphasis, anchoring into just the flagstone will probably fail. I would use the pipes and drill down well into the concrete. No easy task but I think it is probably necessary.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Installing anchors in a flagstone deck

    If you are considering replacing the cover any time soon, a solid cover generally is a better choice. However, the anchor spacing is different. Therefore, it might be better replace the cover before doing the anchors.

    Another option is to keep the pool open. If your maintenance is minimal, then it might be a good choice.
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    Re: Installing anchors in a flagstone deck

    Ok, Thanks guys.

    Our winter weather is pretty variable, but we don't often get more than a few inches of snow at a time. The dumber of our two retrievers has been known to walk across a corner of the cover, but otherwise the load would be really minimal.

    I'm not sure I'd be 100% comfortable keeping the pool open through the winter, as we are in a rural area and do get the occasional ice storm which could cut off power and keep us from running the pump when it gets below freezing. After the plumbing nightmare that we've dealt with since moving into the house, I want to be extra careful to avoid busting it up again. Also, with little kids I like the idea of a cover to provide an extra degree of safety (not an adequate safety measure on its own, I know, but prevents a fall from the edge into 8' water).

    I guess we will need to probably use ~5" pipes to get down through the mud and into the concrete and set the anchors down into these. Sigh, won't look as nice, but better than a torn up deck!

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