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Thread: Replacing mastic around flagstone

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    Replacing mastic around flagstone

    Hi Folks,

    Attached are rare photos of how mastic can look when someone does not take care of it
    I just took over this pool after we purchased the home few months ago. So this is not reflection of how I like my pool to look.
    I got some crazy estimates ranging from $300-$1,200 to replace is it. So, I think I will try to do this myself.

    Based on the old threads I identified few products but the jury is still out on which are actually good.

    http://www.ultimatepoolseal.com/
    http://santasticpoolmastic.com/index.html

    Per my research there seems to be confusion on the best approach.
    I heard some people mention that you need to back-fill the gap with sand while others swear by using foam strips.
    If you look at the photos the back of the pool has a .5in drop between concrete and the flagstone.
    I need to think of some creative mason work to cover that up. Ideas?

    Folks, please advise on the product and how to back-fill the hole.
    Attached Images Attached Images
    ~14,000K avg 5.5ft deep kidney shaped pool + Waterfall.
    Challenger 2.2hp pump, Pentair 48sf DE filter.

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    Qwaxalot's Avatar
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    Jun 2012
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    Re: Replacing mastic around flagstone

    You might want to look into the deck settling issue. That caulking has failed because of the settling.

    If you're convinced the deck is done settling; you'll need to remove all the old material (a challenge in itself); If there's a large void, fill it with sand to within a 1/4 inch of the deck. If there's no giant void use closed cell foam backer rod.

    The caulk I prefer to use is DOW 790 (UV resistant with a high modulus of elasticity, and toolable) You won't be able to use self leveling (because of the disparity between the height of the deck and the coping).

    You'll have to mask off the coping and the deck to about 1/4 inch from the edge, then apply the caulking, and "tool" it in to create an attractive and smooth finish.

    Be advised, this is a job that makes grown men cry, and, around here, goes for $8.00 to $10.00 per lineal foot.
    In the industry, CSP (Certified Service Professional) by the NSPI and it's successor the APSP. My company services over 600 pools every year. I think the practices regularly espoused on this forum (especially the BBB method) are outstanding; however my comments will be often oriented towards the goal of getting it done, and getting it done right now!

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    Re: Replacing mastic around flagstone

    Quote Originally Posted by Qwaxalot
    You might want to look into the deck settling issue. That caulking has failed because of the settling.

    If you're convinced the deck is done settling; you'll need to remove all the old material (a challenge in itself); If there's a large void, fill it with sand to within a 1/4 inch of the deck. If there's no giant void use closed cell foam backer rod.

    The caulk I prefer to use is DOW 790 (UV resistant with a high modulus of elasticity, and toolable) You won't be able to use self leveling (because of the disparity between the height of the deck and the coping).

    You'll have to mask off the coping and the deck to about 1/4 inch from the edge, then apply the caulking, and "tool" it in to create an attractive and smooth finish.

    Be advised, this is a job that makes grown men cry, and, around here, goes for $8.00 to $10.00 per lineal foot.
    Thanks. i cry just by looking at it. The deck should have settled by now. The gap (in the pic) is only about 2ft-3ft long and @ the back of the bool. The rest of the perimeter is leveled. Should I still use caulk and not mastic? If I use caulk can I still sprinkle some sand on top for a nice finish?
    ~14,000K avg 5.5ft deep kidney shaped pool + Waterfall.
    Challenger 2.2hp pump, Pentair 48sf DE filter.

  4. Back To Top    #4
    XsAllOverIt's Avatar
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    Dec 2010
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    Mount Airy, Maryland
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    Re: Replacing mastic around flagstone

    That looks quite like mine did after one year. I had a concrete deck around the pool and it is about 1/2 higher in some areas. I used the self-leveling caulk with foam backers. I think you need to simply insure that you seal off everything so the caulk can't escape is the main reason behind filling and also using less material because the caulk is expensive. After it was completed, I still have a 1/4-1/2" height difference between the coping and the deck, but I've got to tell you, you quickly don't pay attention to it and NOONE notices but you. If it doesn't heave anymore than what it did that first winter, I'll be happy for quite some time.
    18 x 36 Inground Gunnite, White Plaster 21K gallon
    18" raised spa, 8' Diameter (620 gallon)
    Triton II Sand filter, Intellichlor IC40 SWG
    Pentair Pump, Max-E-Therm 400 BTU
    Lamotte ColorQ PRO 7-Plus test kit
    TFT-100 test kit

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