"What's with this joint"?

[Bud Cline]

OK Guys.....Learn me somtin'.

With all the talk of "joints" in floors (and even some walls) that comes up time after time, and now joints in a steam shower and so on and so on. I'm sure we all agree that most joints (expansion, control, juncture) must be honored in some fashion. I don't want to rehash all that. Then there is the matter of leaving a "perimeter gap" (for expansion) at all walls and floor penetrations.

Finally here's the question (I think).

What about all these terrazzo jobs you see? The floors appear to be continuous. Some floors abut a terrazzo cove feature that turns and climbs the wall a little. I don't recall seeing any soft or expansion joints here. These jobs are huge. In years past I have been involved in some terrazzo jobs but never fully understood the overall principals and none of them I was involved in included coves and base.

Have I simply been overlooking were the joints are placed or waht?

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[Rob Z]

Bud

Good observation. Are you like me, when you walk into a resturant or bar or mall or what ever, and point out tile stuff to your wife? I think she ACTS like she's interested...

Our local supermarket has terazzo, and has cracks all through it. The cracks continue through into the quarry tile around the salad bar.

Is terazzo bonded to the concrete below? Where's Bri? Doesn't he do terazzo work?

[kalford]

I'm glad to hear someone else dose that! I must bore my wife to tears with......."see how they let the joints get out of line......."

[Bud Cline]

I'm afraid my wife also just humors me. I see some jobs (tile) that really piss me off.

So what about the terrazzo? What is done to allow for expansion?

[Bri]

Don't you know? There's Ditra underneath!(Just kidding) Depending on the job, most Terrazzo floors are floating on a mortar bed...so it's not really attached to the slab underneath...unless it's epoxy terrazzo...and of course, there are the jobs where you just stick it down and go home. The metal strips between the panels are control joints...hopefully any movement will run down the weakest point which is the strip..and on larger areas there are flexable expansion joints. The cove base is attached to the floor and the walls, so it does crack a lot, but I don't know what choice there is. it's kinda hard to put a expansion joint through the cove. And like any job, if the slab moves a lot, then it's going to crack what's on top of it. Considering some floors are 50-60 year old and still look pretty good, a few cracks here and there are acceptable.

[John Bridge]

Well, I know I'll catch it, but I've argued the value of perimeter spaces on other forums. I've been chewed by the best of them, including Dave G.

Usually the problem is one of "tenting," and someone asks, "Well, were there movement joints at the perimeter? No? Well, there's your problem."

But it's really not that simple. Tenting as you all know hardly ever occurs anywhere near the perimeter. The tiles there are often well bonded, while the interior sections have delaminated. I can't see that in these situations the lack of caulking at the baseboards has contrubuted to the problem.

Also, baseboards are rather loosly attached near the floor, and there is usually a space at the bottom of the drywall that the base covers. I am convinced that this space, coupled with the softness of the base itself, will accommodate any slight movement that might occur in the tile plane. Especially when you consider that the field can't move even a mm independent of the substrate. Running tight against a baseboard, then, is simply not the same as running tight against a brick wall.

I continue to cut and grout tight to existing baseboards to this day, and I'm not the least bit worried about it. I have, however, become a believer in the use of interior movement joints when large floor areas are bonded to concrete slabs. I also use modified thin set on each and every job I do (except Saltillo).

[Dave Gobis]

John,
Take two sticks of equal length. Hold one in an 1/8" from the other. Whats it look like? Pressure from the side walls, racking, or torqued. Your the only one I know of as smart as you that just plan refuses to believe. I have 100's of field examples. That you changed to latex modified and it stopped only confirms it by the increased shear strength. You knew this was coming!
Dave

[Derek & Jacqui]

Bud,
The firm I apprenticed with considered terrazzo to be a seperate trade but I worked alongside terrazzo layers and saw what it involved. As you stated, it was squared with brass strips every six? foot and at eighteen foot intervals there was inlaid a strip of ebonite to act as an expansion joint. (This was pre-plastic era)
I have laid a few terrazzo tile floors 12x12 already polished.
Derek

[Rob Z]

John

Is the tenting that you describe occurring on slab-on-grade concrete? Tensioned slabs? Old concrete? Green concrete? Residential and commercial?

I have never personally witnessed it, but I do all residential stuff, 99% is over wood subfloors. Very few houses around here are on slabs.

Rob

[John Bridge]

All,

All of the "tenting" around here occurs over concrete slabs (slab-on-grade). I had problems years ago at about the 5-year point after installation. Sections of floors would delaminate, usually toward the middle of the installation. This takes us back about ten years, and at that time I was still using "regular" thin set.

Corrected the problem jobs and went to using latex. Finally graduated to modified. No problems since.

Of course I asked for it, Dave. I said as much at the onset. Who would keep your ancient blood moving if it weren't for me? The part about the two sticks left me guessing, though. Jack and Coke?

Delamination does happen over a concrete slab. There are a number of reasons for it, including hydrostatic pressure and incompatible coefficients of expansion between super hard tiles and super soft concrete. There is also improper installation, of course. And failure to use the best adhesive available.

I have stated for years that applying tiles directly to a concrete slab is not the best possible thing one can do. It happens to be the only practical thing one can do in a retrofit situation in a house built with the slab-on-grade method. If anything, the use of interior movement joints and, possibly, applied membranes, will alleviate the problem. Nothing is going to cure it, though.

Trying to run caulking all the way around a retrofit kitchen/breakfast area floor makes one godawful mess. You're going to have to show me it's worth it. Saying there are hundreds of examples in the field, simply states there have been hundreds of failures (thousands even) for various reasons. It doesn't point to a specific cause or a cure.

Tell me why the delamination seldom occurs near the perimeter if the base is the cause. And tell me why, when there is a definite tent "ridge" apparent, that the ridge is almost always at a perpendicular angle to the long run of the room. Is it that the walls at those extremes are exerting more pressure than those at the lesser extremes? Or is it possible that the mass of tile itself is blocking the movement?

[Edited by John Bridge on 06-17-2001 at 10:21 PM]

[chip]

I believe you have actually answered your own question.

The tenting, caused by no expansion on the perimeter walls. Happens because of movement one wall against the other, creating shear pressures on the tiles that is compounded by the distance and should accure near the middle grout joint.

If you don't tile or grout up to the wall and put your base over the gap and not down to the floor, you don't need to caulk as the gap will be covered with the base.

[John Bridge]

I know that, Art. We never abut base in the new homes I work on. The base is always installed over the flooring. Of course, we don't install tile directly to slabs in the new homes I work on, either.

But we are talking about retrofiting here. It would break the budget, usually, to have to re-do the base (and the paint, and maybe the wallpaper).

Art, have you ever examined a tile floor over a concrete slab that has delaminated?

[chip]

As you know I am new to this market, and I have yet to actually see a delaminated floor. Although in my old territory I did see a few over wood.

Although I have heard the horror stories down here.

Wouldn't an undercut saw do the trick?

The painting? Sounds like a job for a painter.

Have you ever had a floor delaminate in the new houses that you do with mud? Once again you may have answered your own question.