poolnerd

An all-too-common problem with pools is tiles that are loose or falling off. People often ask, “How much would it cost to put these tiles back on?” Well, sticking tile back on is pretty cheap, but it doesn’t address the underlying problem. They’ll just keep coming off.

The problem isn’t with the tile. The problem is with the expansion joint, which is supposed to isolate the pool from the deck. If this expansion joint is missing or isn’t done properly, the usual result is dislodged tile.

Here’s what’s happening: As the deck heats up, it expands. Mainly laterally. As it expands, it starts pushing on the back of the coping (brick, flagstone, cast concrete, whatever). Since the force of the deck expansion is much greater than the strength of the bond between coping and bond beam, the coping is dislodged and pushed out toward the pool. Often it takes the underlying mortar bed with it. The result is that the top inch or so of tile is dislodged.

I’ve seen this occur when the deck is laid between the house and the pool. It’s fairly common, and is easy to understand why this happening: the deck’s got to expand, and it sure as heck isn’t going to move the house foundation much. So the pool’s got to give. But, on the other extreme, I’ve witnessed three-foot wide sidewalks that have knocked tiles off, too. It seems as if the sidewalk would just expand into the grass behind it and leave the pool alone. But let’s not try to out-think expanding concrete. Let’s try to remedy the situation so that we don’t have to worry about what the concrete will do.

An expansion joint between the coping and the concrete will take care of this problem, no matter what the darn deck decides to do.

But it must be done the right way. And often it isn’t. (But that’s OK … I’ll put my kids through college by fixing pools where things weren’t done the right way.) For the inside info on how to construct this little detail properly, read on.

The Secret Life of an Expansion Joint

The purpose of an expansion joint is to isolate two things so one’s expansion has no effect on the other. In pools, this is usually accomplished by laying a flexible strip of foam between the deck and the pool, specifically the pool’s coping. The foam is usually about a half-inch thick and three to four inches high and comes in rolls of up to 100 feet in length.

The top half-inch is usually detachable, so that a mastic sealant can be applied over the top of the foam. This mastic, usually a two-part polysulfide (Deck-O-Seal is the most common brand around here), is supposed to bond to the coping on one side and the deck on the other, and is meant to provide a flexible, water-tight joint.

Now you know what an expansion joint is and how it’s supposed to work. Simple, huh? But, in the real world, things are seldom that easy.

Do It Right the First Time

Often, expansion joints are constructed improperly. Sometimes, for instance, the decking subcontractor will nail the foam to the back of the coping before pouring concrete. Bad move. I have remodeled pools where things were done this way, and, guess what? Loose coping, tile falling off. Those stout little concrete nails they use to attach the foam are transferring the force of the expanding deck into the back of the coping, and from there to the tile. Not all of the coping stones were loose, but enough were that the client asked for a proper fix.

What should be done instead of nailing up the foam? Some people recommend using a spray adhesive instead, but I haven’t had real good luck with that. I lay the foam against the coping as the concrete is placed against it, moving slowly around the pool with the concrete pumper. This is hard, dirty work (which, in the interest of truth and full disclosure, I usually watch a laborer do — the older I get the more I dislike sweating and getting dirty), but I can ensure that the top of the foam is flush with the deck and that the bottom of it is contact with the soil.

Which brings us to another common installation problem: concrete placed under the bottom of the foam strip. Concrete that is in contact with the pool’s structure. Heck, you may as well have saved the twenty bucks on the foam, ’cause it’s not doing anything. Not expanding, not contracting, nothing. The foam strip is just attached to the deck, along for the ride as the concrete slowly but inevitably breaks the top portion of the bond beam.

Yeah, I’ve seen that, too: The irresistible push of the expanding deck sheering off the top inch or so of the pool structure. Sure, the bond beam is reinforced concrete, but the steel is three inches down from the top face. And often the gunite finishers “hand pack” gunite to get that last little bit of bond beam. Contrary to what those rascally gunite guys say, this hand-packed (or more accurately, flung-and-trimmed) stuff doesn’t have much structural value. The expanding deck is going to sheer that crummy gunite loose every time. But the result is the same to the homeowner: loose tiles … but with an added twist — the possibility of water seeping through that crack behind the tile. Seen that, too, but that’s another can of worms we won’t open right now.

If your foam isn’t tall enough to back the coping properly, backfill with a little ramp of sand or dirt to at least the bottom of the foam. Do what it takes to isolate pool from deck.

I could tell you more stories, like the one where the deck guy cut the foam strip in half, so it was only two inches tall, then peeled it back out after the concrete was done. He then filled the gap with Deck-O-Seal. Solid. That’s a lot of mastic, which ain’t cheap. The end result was, of course, deck in contact with pool (and some more money in my pocket). Or the one where they used plastic sheeting as the expansion joint. WTF!?! Or the guy who, for some unknown reason, thickened the concrete around the entire pool, installing a footing of sorts. Or all of the jobs I’ve seen where the expansion joint was omitted entirely (after all, it saves the builder a couple of hundred bucks).

I’ve got a bunch of stories like that, but it grows old after a few. The sorrow of others is not very funny.

The point of all this stuff is simple: don’t let the deck touch the pool at any point.

No how. Never.

Gotta Fill the Voids

After the foam and deck are laid, the top half inch or so of foam is removed to make way for a flexible water-proof joint. But before laying that stuff, we have to fill any empty pockets around the foam so that the gooey mastic won’t sag into these voids, which makes for an ugly installation.

Most of the guys I know who do this use sand to fill in. It’s cheap, easy to pour (if dry), and is readily available. Just be careful not to pack the sand in: we just want it to loosely fill in those spaces, we don’t want it packed in. It doesn’t have a lot of give to it then, so our expansion joint won’t be as flexible.

After things are leveled out and filled in, we’re ready for the next step. This part is real messy though, so don’t wear you’re Sunday best, or anything you care about.

Mastic

Not all pools are engineered for wet soil right behind the pool wall, so this step is essential. This top element of our expansion joint is a mastic. Like I said before, it’s supposed to adhere to both deck and coping and move with them, providing a flexible. water-tight joint. It’s often a two-part kit, mixed just before application. It comes in many colors to match lots of different deck or coping finishes. Gray is the most common, but other colors are tan, redwood, white, and black.

This stuff initially has the consistency of tar (and the aroma of rotten eggs), but slowly sets up to become something more akin to soft rubber. How fast it cures depends on the temperature: on hot days it may be a matter of a few hours; if it’s real cold, we may be talking in terms of days.

And whatever you do, don’t step in it before it has dried. If you do, you’ll track it around on your new deck, and it’ll be there pretty much forever. Don’t let the dog or kids come anywhere near it. Put some sort of notice on doors and gates into the pool area, warning others (start-up guys, inspectors, nosy neighbors, etc.) to stay away. It is possible to clean it up if something does happen, but it can be messy and difficult — which often means $$$.

Sometimes a sprinkling of silica sand is added as the mastic is setting up. This helps it blend in well with mortar made from silica sand, and helps camouflage any imperfections. But what does the manufacturer say of this practice? One guy told me that they don’t recommend it because it makes the mastic less flexible. But it would also help it last longer. If, you know, someone actually did something unapproved like that. Wink, wink.

A Special Case

Cantilever pools were popular in Southern California back in the seventies and early eighties. Many are in need of remodeling and renovation now: the tiles have been falling off for years and homeowners are getting tired of sticking them back on, sick of their shabby-looking pools. I understand that this type of decking is becoming again in certain parts of the country, especially in the booming markets around Phoenix and Las Vegas.

If you plan on having a cantilever concrete deck, you run the risk of tiles getting knocked off by the deck, too; discuss this detail with your pool builder or decking subcontractor. There is no expansion joint between the pool and deck, but another type of joint instead: a slip joint. It is still meant to isolate one from the other, but the idea in this situation is to allow the expanding deck to slide over the top of the pool without impacting it.

That’s the idea, but the way things were done back then allowed the deck to be in contact with the tile. Inevitably, the poor tile lost the battle with the mighty concrete deck.

This situation, cantilever concrete decks and tile problems associated with them, is beyond what I set out to cover in this post. To explain things properly, I need to use some illustrations, and the technical aspects of attaching those to the accompanying text have not been mastered yet. Perhaps soon.

As Time Goes By

After a few years, your once-pretty mastic will become cracked and ugly, sometimes even separating from the deck and/or coping. Time to peel out the old stuff and put in the new.

That sounds easy, but it isn’t. It involves a lot of crawling around, cutting and scraping with a utility knife. I’ve done it many times, but at this point in my life I’d hire someone else to do it. Believe me, even if they’re charging six or seven hundred bucks, and only using $150 in materials, it’s well worth it.

The underlying foam doesn’t need any ongoing maintenance. If it’s done right, it should keep doing it’s job for decades.

Then, eventually, years down the road, some pool contractor like me will come in to remodel the pool. He’ll see the beautiful work you’ve done on the expansion joint — I see them done right occasionally, too — and he’ll pause to inspect and admire the craftsmanship of a job done well.

This entry was posted on Wednesday, February 7th, 2007 at 12:40 pm and is filed under Uncategorized, Constuction, For Homeowners, For Contractors. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.