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Thread: Coping / Tile issues

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    Default Coping / Tile issues

    New to the forum

    On a Sylvan IGP [~24k gal] from the mid 1980's we continue to have tile that pops off with residual loose concrete. I've replaced a great deal of the tile but it happens again. When tapping on some of the coping it sounds as if it's hollow which tells me that perhaps the coping bed has been eroded allowing water to freeze / thaw and pop the tile?? Is this correct? plausible? make sense? The coping is a bull-nosed open-faced rough concrete aggregate in about 2 ft lengths and mortar is used to fill the joint between the coping stones as well. The current plan is to use a chisel and carefully remove the coping and re-mortar in place and reseal the gap at the decking. The question is about the mortar. Is there a special type to use specifically for pool coping? Will any Quickcrete mortar mix do the job? is this truly a DIY job or should I be looking for a contractor? Any insight would be greatly appreciated!!

    sorry for the lengthy description but wanted to provide as many details as possible.


    thank you
    Rob

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    Default Re: Coping / Tile issues

    running out the door, so can't spend much time . . . but I think I know what it is.

    Take some digital pictures of BOTH the tile and popped-off areas from near pool level AND the coping deck edge from above. Send them to me (poolforum AT gmail DOT com) and I'll edit and post them and then answer as best I can.
    (Restricted Users can't post pics or links).

    Ben

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    Default Re: Coping / Tile issues

    Ok. Here we go.

    At least in my own area, horizontal tile line cracking is extremely common. And, it almost always results from a single problem: poor construction technique.

    But, before you run go find your builder and proceed to commit murder, you need to understand that he probably didn't make THIS error on purpose.

    I don't know as much about pool construction as I do about pool chemistry. But, what I do know makes me suspect that there are at least as many dumb things "everybody knows" in pool construction as there are in pool chemistry.

    On to the cause, and solution.

    There are some facts you need to understand:
    • Concrete is NOT elastic -- if you force it to move, it cracks.
    • Concrete, like most things, shrinks when it gets cold, and expands when it gets hot.
    • As they shrink and expand, pool decks move parallel to the ground.
    • Because pool shell temperatures are moderated by the presence of water, pool shells don't move as much as decks.
    • But, when they DO move, they move up and down or perpendicular to the ground.
    • When hard concrete moving in one direction meets other hard concrete not moving, or moving differently, bad things happen.
    • Control cracks in pool decks are designed, not to AVOID cracks, but to 'specify' where they appear.
    • On the other hand, expansion joints are placed in PRE-FORMED cracks, and are designed to allow different pieces of concrete to move in different directions without breaking each other.
    • None of the pool builders I've ever talked to understand the difference between a "control joint" and an "expansion joint".
    • Nor, do they understand what an "expansion joint" is supposed to be doing.
    • Most pool decks are poured by 'concrete finishers' who are subcontracted to the pool builder.
    • Most concrete finishers get paid by the square foot finished.
    • Good concrete has little water, lots of aggregate, is quickly finished and not overworked, and is wet cured for 3 days or more.
    • Poor concrete has lots of water, less aggregate (or poorly graded aggregate), is slowly finished by a small crew, and is not wet cured.
    • Good concrete is MUCH harder to finish, and takes a larger crew, than poor concrete.
    • Proper, full depth expansion joints are a pain to set up (by the builder) and a pain to pour and finish (for the finisher).
    • During the first year, poor concrete and good concrete often look the same.

    Ok,so far?

    Here's a picture of how a possible valid pool bond beam, coping, and deck edge configuration:

    (from http://www.ebuild.com/articles/145359.hwx)

    Now, that's not usually how they actually look.

    For one thing, it's hard to pour the bond beam perfectly level, so that the coping can be set right on top of it. So what often happens is a layer of mush, low grade gunite or mortar is used to level out the bond beam. Then, a thick layer of mortar is used to finish the job, and set the coping stones.

    So . . . you end up with a weak layer between the gunite bond beam and the coping. (The details are different with the more modern style "cantilevered deck", but the same things happen).

    Also, because the "expansion joint" is a pain, and the need and function is not really understood, expansion joints get omitted, turned into control joints, or not made FULL DEPTH.

    Remember, the purpose of the expansion joint is to LOOSELY connect to hunks of concrete that are moving in different directions. But, when the joint is not done correctly, the concrete moving in one direction, tears up (cracks, breaks) the other concrete. Now, the strongest breaks the weakest, and what's usually weakest, along the line where the stresses occur is under the coping, and behind the tile.

    So, here's the first picture "RAchenb" sent me:


    And, voila' ! A crack right in the mush, behind the tile.

    But, why did it happen?

    Well, location of the crack tells us that it was pressure from the deck pushing against the mush under the tile. So let's look at the deck:


    Now, it looks like an attempt was made to create a sort of expansion joint. And, though you can't see it in this picture, the deck is so narrow that 1/2" wide FULL DEPTH expansion joint would have done the trick. But, it looks like the expansion joint may not have been full depth.

    I can't tell for sure, without removing coping, but the crack itself identifies the problem.

    Here's a drawing that may help make things clearer:



    So, what's the solution?

    Well, you have to replace the tile, of course. But FIRST you have to install a full depth expansion joint!

    There may be other ways, but the only method I know involves using a diamond blade saw to saw ALL the way through the deck, down to dirt, to create a FULL (no contact!!) 1/2" to 3/4" gap between the leading edge of the deck, and all parts of the coping / mortar / bond beam arrangement. Then, you install "backer rod" or other filler to retain the sealant, and cover it with a pourable rubber expansion joint material. It's a messy, somewhat difficult job.

    But, if you don't do, and do it right any tile repairs made won't last.

    Sorry for the bad news. Hope this at least helps make things clearer!

    Ben
    "PoolDoc"

    poolchron
    Last edited by PoolDoc; 09-10-2010 at 06:54 PM.

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    Default Re: Coping / Tile issues

    Ben,

    Thanks for the detailed explanation and description.

    2 questions then:

    1] After removing the coping and in the process of resetting it in place, would it be feasible to artificially widen the expansion joint by not quite placing the coping back in the original position but rather say 1/4- 3/8" more so in toward the pool and away from the deck? [yes it make appear a bit off overhanging the tile but if it can help eliminate the problem from reoccurring..]

    2] Would you know if there is a specific type of mortar used for resetting the coping?

    Thanks again for all your help

    Rob

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    Default Re: Coping / Tile issues

    1) Yes, it's possible that would work. But it's not likely. What's more likely is that the deck is impinging on the concrete mess UNDER the coping, instead of the coping itself. However, you can do whatever isolates the coping and bond beam from the movement of the deck.

    2) I don't know. Probably any mortar that's mixed to be relatively impervious to water would be OK. (Mortar that's highly absorbent, due to low cement or high water content, is likely to suffer from freezing, if you are in a area that's (a) wet and (b) cold in winter.

    PoolDoc

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