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Unread 06-17-2003, 05:55 PM   #1
H1ckory
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tiles rock when dry fit

After installing plywood, then cementboard, and finally taping the cementboard joints, I dry-laid the 12" square porcelain tiles to check the layout. Gently walking over the tiles, I noticed a tiny bit of rocking (perhaps 1/16" or 1/8"), over the cementboard joints and also perhaps where some of the "rock-on" screws are slightly above the cementboard. Most of the tiles do not rock at all.

The last time I tiled, I just used plywood and had no rocking, so I don't know whether this is a real problem, or whether I am being too timid. Will the mortar make up the difference? If not, do you recommend a self-levelling compound?

Thanks in advance!

-- Bob Cole
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Unread 06-17-2003, 06:20 PM   #2
bbcamp
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Hey, Bob, don't walk on the tile until the thinset sets! Which kinda means don't walk on then without the thinset, too!


The screws need to be driven flush, or you will hear a tile crack. You may have to back out some and re-set them. Or use ring-shanked, hot dip galvanized roofing nails. Just don't drive them in with a hammer! Or pound on your floor after 10:00 PM, unless you live far, far away from other folks.

Other non-uniformity will be absorbed by the thinset.

Bob
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Unread 06-17-2003, 06:22 PM   #3
Jason_Butler
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Hi Bob,

Depends on the size trowel you use. A 1/2 " notch trowel will most likely compensate for the screws.

This is precisely why I use the galvanized roofing nails. I have had problems in the past with the screws not countersinking.

You can use an SLC but it's really not necessary..

Jason
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Unread 06-17-2003, 08:09 PM   #4
H1ckory
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Thanks -- great advice. I almost think throwing an SLC on would be easier than dealing with all of those screws.... Any advice on specific SLC or type of SLC? I bought an Armstrong product but didn't use it bec. it seemed to be oriented toward sheet flooring preparation.

The bit about not hammering the roofing nails was a joke, right?

Another issue, please: this is for a summer cabin which is not heated during the winter, which made me a bit afraid of expansion/contraction tile cracking issues. I decided to pretend it was an outdoor patio (though it's an indoor bathroom) and chose porcelain floor tiles and a premium-priced "Flex-bond" Custom mortar which requires water instead of a latex mix. Any opinions on those choices? Or was I nuts to tile a summer cabin's bathroom? I haven't chosen wall tiles yet, but would ceramic be okay?

Thanks so much for your help!

-- Bob C
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Unread 06-18-2003, 05:54 AM   #5
John Bridge
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Hi Bob, Welcome.

I don't think you need SLC. In fact, I know you don't. If the screws are up no more than a sixteenth, you should be able to accommodate them with the thin set as you go. Same with the taped joints.

Besides that, many 12 inch tiles are not completely flat. It's not unusual to get a batch that is slightly warped. It keeps us on our toes.
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Unread 06-20-2003, 07:14 AM   #6
bmiller
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this questions brings up one that bothers, confuses,etc. me - I couldn't find the thread, but I'm almost certain I have read that 1/4" dips in a floor can be accomodated with thinset. But how do you pros do that? Do you dry-lay tiles in your grid first and check for low areas, and then just know you gotta put extra thinset down? I'm doing a smalll laundry room in my house and I keep pulling up tile to add thinset. I tend to be too much of a perfectionist, but my method seems very much trial and error. You guys must do it infinitely more effecient? Is it just practice?

thanks,
Brian:
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Unread 06-20-2003, 12:02 PM   #7
Art in Stone
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Brian,
When I first started at this, I use to walk through a job site with my ex-boss, and he use to make marks here and there on the slab. Sure'nough, all the marks were high and low spots. I couldn't see a thing. He told me, " When you spend a few years down on the ground you'll be able to see it also", sure'nough, it was true.
When we go into a job we usually take a Large Level, or a 15' aluminum straight edge(Big Bertha)or some string, and we go over the slab looking for highs and lows. We don't go over every inch, but you get the idea.
When you spend some time becoming good friends with the slab, you kinda get a better idea of what the slab is doing up ahead. You always want to be able to add a little thinset, never take all of it away. Having to chip at a slab after you began tiling really stinks.
Brian, if you're lifting the tile to add thinset to make it flat, you're going to make a hell of a TileSetter. It's going to be trial and error until you gain more experience. Make sure you always have a level handy to make sure it's the slab and not your eyes, or you might end up with a ramp on one side of the room.
Those grout lines have been known to Hypnotize.
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Unread 06-20-2003, 03:07 PM   #8
tileguytodd
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And by all means, Clean up as you go.Your Thinset(Flexbond) Has the polymer addative already included in the mix.You could use a 16" flat trowel and feather the edges of those CBU seams in the spots that are the worst.Let it dry overnight and then set your tile the next day.You may find it easier to do this then lift and add thinset.
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Unread 06-22-2003, 06:47 PM   #9
bmiller
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Ramon,
thanks for the input...i guess i'm glad it takes practice and nothing specifically wrong with my technique...just sort drives me nuts to feel a high spot ever so often between tiles? this is called lippage??
i gotta find a real expert to go on a few jobs with to get a better feel for this..maybe
i like the string idea...seems easy and reasonably straight forward, plus you always have the right length

thanks,
Brian
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Unread 06-22-2003, 07:29 PM   #10
Jason_Butler
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Hey Brian,

I support all the previous comments...

Once you know how the slab is poured, you'll know where your problem spots are. Grade stakes are often placed about midpint of a large pour. These are usually high points

Basically any place where an object protrudes up through the slab will be a high point. This includes toilets, floor outlets, sleeving for gas piping, downdraft vents for grills, etc.

As a general rule, I don't like to use anything less than a 1/2" notch trowel for tiles over 12". You get one of those 18" tiles on a high spot and you're up that famous creek

I sometimes sprinkle large areas with water to see the surface imperfections. It's so damn hot here in Texas the water is gone by the tile I start tilin'

Water will pool up in the low spots and run off the high spots.

For smaller areas, use a good level or straightedge

Jason
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