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Making a Gunite Pool Shallower

Posted by Brian McGarry, CBP on November 14, 2008 at 10:53am in Pool Service Topics
I realize that some of you have done renovations to pools to raise the depth from 8 to 5 feet. I was wondering if any of you have had success with any particular method of doing this to ensure integrity of the final plaster and eliminate cracking in gunite installations?

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Tags: gunite, remodel, renovation
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  • Rob Lane March 4, 2009 at 6:08pm
    First, it is important to break out a 4'x4' area around the main drain. Haul the concrete out. Fill the hole and the deep end with gravel in 6" lifts. The gravel will allow the ground water to get to your new pots and hydrostats. Use a vib. plate compactor on every lift. Most VPC will pound thru 12" of gravel. That is why we use six inch lifts of gravel. Run the gravel up to finish minus 8"-12". Set up a pair of VGB compliant md's at 4' apart. Concrete and steel must be able to go under and around the pots. Go large on the plumbing between the pots.
    How to get at the existing steel? One way is to jackhammer up the sides and expose the steel. This steel can be bent up into your new structure, the new pool bottom. When we are just installing new pots, we save all of the existing steel by breaking the old concrete off of it. It is important to leave the old steel attached into the old shell, at one end at least. This means that you are not totally relying on the doweled steel. We then dowel the old shell and double the amount of steel in the hole. Don't be shy, use lots of concrete(8" min.)and steel, (6"x 6" o.c.e.w.).
    I would shotcrete or gunite the bottom back in place, using plenty of bonding agent against the old cleaned concrete surfaces, just prior to hitting it with the new concrete. It is a good thing to pound the concrete under, around and behind the surfaces that you wish to bond to. This takes a lot of digging prior to concrete day.The concrete needs to be very tight.
    This is a hard and complex project. I am sure I've left out a lot of issues and problems. You can email me prior to bidding, if you wish. I also like Rex's bentonite idea, however I've never used it.
  • 3t94l0x1hbw8f March 3, 2009 at 3:02pm
    Sorry, I did not mean to copy the previous reply in my earlier comment. My computer blinked just at that point in time. Or maybe it was a hicup.

    Good information - keep it coming. With the emphasis on reducing energy costs I expect to get more requests for making pools shallower. In some jurisdictions it can change the code requirement for having a lifeguard on duty at commercial pools.

    Paul
  • 3t94l0x1hbw8f March 3, 2009 at 11:54am
    Has anyone seen the new APSP Builders Manual? There is a unit on concrete construction with information about keyways and Bentonite waterstops. I am not a Builder or an Engineer or a lawyer (thank God) but the Builder's Manual seem to be very authoritative; although not specifically for this type of renovation.

    I certainly understand the need for 100% compaction but I have never heard of "Flowable fill". Can you give me a little more information about that?

    Remember, anything that is less than 100% compaction will eventually be at 100%... it's just a matter of time.

    My Engineer recommends Flowable fill for our construction. We have used this in the past and have been very successful. Flowable fill, when ordered properly, can test at 100% compaction and this is what you want in a case like this. . this is my input. An Engineer should always be involved in a project like this and always demand a copy of his current "Errors and Omissions" insurance for you and your clients peace of mind. This is our ounce of prevention weather doing an all-tile or pebble sheen pool. Mistakes are never cheap...

    Hope this helps.

    Nathan
  • N. McCartney March 2, 2009 at 4:41pm
    This is a topic I have discussed with other builders for years and Rex is spot on with what we practice.

    Usually, in Texas, the standard practice also includes some sort of flex fill from your cement supplier. The justification I have heard for this is that it is used under highways for support. If it is good for supporting 18 wheelers and high traffic then it must be good for a pool right?

    Wrong.

    Avoid using this as part of your plan if offered. Flex fill can come in at 90% compaction. This may be fine for a 6 inch fill base which may need some give say .5 of an inch or so. But filling a 48 inch void can allow for up to a full 5 inch variance in final fill leaving a potential nasty cleanup after a few years. Remember, anything that is less than 100% compaction will eventually be at 100%... it's just a matter of time.

    My Engineer recommends Flowable fill for our construction. We have used this in the past and have been very successful. Flowable fill, when ordered properly, can test at 100% compaction and this is what you want in a case like this. . this is my input. An Engineer should always be involved in a project like this and always demand a copy of his current "Errors and Omissions" insurance for you and your clients peace of mind. This is our ounce of prevention weather doing an all-tile or pebble sheen pool. Mistakes are never cheap...

    Hope this helps.

    Nathan
  • Jeffrey Kohlhas March 2, 2009 at 6:16am
    I have had success using two different methods. The first is filling the pool with flowable fly-ash fill and then pouring an 8" rebar reinforced floor over the top. The other is using Self Compacting Concrete to fill the pool to the desired depth. Both strategies work very well, you just have to consider the pool, access, labor, etc. You can pump flowable fill with a trash pump so that method is better for a job with poor access, although it is more labor intensive in the end; tying steel, multiple steps... Pouring the floor monolithically is much less labor, but the materials are more expensive. If the slab is properly tied to the existing shell I don't see the need for a waterstop.
  • This reply was deleted.
    • Brian McGarry, CBP November 16, 2008 at 1:09pm
      Thanks Rex, we were planning to approach the solution exactly as you explained with the exception of the bentonite strip. I see where that would prevent future cracking as a result of the expansion & contraction of the independent slabs..
      • This reply was deleted.
        • David Bauer November 19, 2008 at 9:00am
          You know, Rex....I've sold Bentonite for years to the well industry for lining wells drilled through multiple layers of aquifer. Never have I sold it to a pool builder or contractor for this purpose. Some concrete / shot-crete companies will buy quickgel for lining their hoses and equipment, though. Comes from the same source.
        • Joe Dethloff November 17, 2008 at 4:06pm
          Rex do you have some photos of the keyway with the Bentonite strip? Also some pics of the fountains, pipe penetrations or light niche applications you are talking about for some visual clarification?
          • Brian McGarry, CBP > Joe Dethloff November 18, 2008 at 9:57am
            Rex, I've been looking on line for the bentonite in the rope style as you suggested and can't seem to nail down a source for it. Can it be bought through distribution? Also looking forward to seeing the pics Joe is talking about....
This reply was deleted.

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