Meaning of "flat to within 1/4" in 10 feet? - Ceramic Tile Advice Forums

LDavis · 02-11-2002, 06:36 PM

Had a frustrating discussion/arguement with a GC today about slab conditions at a job I was suppossed to start setting today. Seems we have a different understanding of hat the 1/4" in 10 feet standard means. His understanding is >>>>if the dips/valleys under a straightedge spaning 10' do not exceed 1/4", regardless of how many there are, the the slab is well within tiling tolerance as is.

My interpretation/understanding does not agree with his.

What is your definition/understanding of this standard?

John Bridge · 02-11-2002, 07:06 PM

Latney, I think the guy is right. The one-quarter inch came into being in 1999 so that our standard would agree with that of the concrete industry. Prior to 1999 the tile standard was one-eigth in ten feet. Tile contractors were getting crucified over that one on concrete slabs.

I think it means that as long as things don't deviate more than a quarter-inch anywhere along the ten foot run, it complies.

NOW ... what about level? This may be where you can nail him. The slab has to be level within 1/4 in. over the ten-foot run also.

The other rule states that the tile has to be set "to the plane." That means flat, no matter what shape the substrate is in.

LDavis · 02-11-2002, 07:32 PM

John, its been so long since I've seen a level slab, that I've gotten to the point I don't even look for that as part of the criteria anymore. However, glad you brought it up, because this same slab is "out of level" almost 3/4" in the same 10' span. That was how the "discussion" started. His response was to place a 10' 2x4 on the slab and point out that deviation beneath, from on end to the other, did not exceed the 1/4". And, he was right. Although we counted 9 locations of varying width just qualified as 1/4" or less.

I've got to set 18" porcelain tiles on this lovely, "meets the GC's specs" slab.

Bud Cline · 02-11-2002, 07:59 PM

Like tiling a washboard. What the hell did they screed it off with, a log chain?

I think 18" tile would be better than something smaller though.

Bud Cline · 02-11-2002, 08:04 PM

Oh man that reminds me.

Honest to Gods truth here. In the mid eighties I was doing some work at a manufacturing plant in Fort Worth when a guy came running into where I was working.

He was yelling and really excited..."Bud, Bud, come out here, you ain't gonna believe this one".

I dropped what I was doing and ran outside where the plant maintenance crew was pouring their own concrete slab for a metal building I had contracted to erect.

Thirty feet by forty feet. The mud was in the forms and they were dragging it off. With a fifty foot section of garden hose.

When they were done they plugged in the steel bolt templates I had fabricated and went to lunch.

02-11-2002, 10:58 PM

Isn't the tolerance also linked to the size of the tile? Larger tile needs to be flatter?

Dave Gobis · 02-12-2002, 07:00 AM

The other part of the flatness equation under American Concrete Institute Standards (ACI 302)is " no more than a 1/16" variation in 3'.

flatfloor · 02-12-2002, 03:06 PM

Geez, I assume your pissed because it was your hose?

It's getting worser and worser (or better and better) depending on how you look at it. The amount of product we are selling for remedial application on new work is increasing year by year. Stories are too long and numerous to recount here.

[Edited by flatfloor on 02-12-2002 at 04:11 PM]

John Bridge · 02-12-2002, 05:34 PM

Latney,

So the floor is off 3/4 in ten feet in that one spot. What happens if you move the 2x4 another ten feet? I'm wondering whether it corrects itself or keeps on truckin'.

What I have done on floors like that in the past is float the whole thing with latex thin set. I use a long straightedge and just hit the high spots with it. You certainly don't end up with a flat level surface, but at least you have a chance at attaining something that'll look decent with tile on it.

There is hope, by the way. A tract builder (superintendent) called me last night to get my thoughts on how to build a shower out of something other than greenboard. He said they are interested in improving the quality of their product. Encouraging, if you ask me.

LDavis · 02-12-2002, 07:32 PM

A "tract builder" called you for advice on improving shower quality. You must have been dreaming John, or you were over the "still cognitive and functioning brewski intake limit".

Otherwise I'll have to assume they are passing out the snow suits and parkas in hell.

John Bridge · 02-12-2002, 07:41 PM

There IS a god, Latney.

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