installing porcelain tile over concrete subfloor

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  #1  
Old 12-12-03, 12:30 PM
JSV909
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installing porcelain tile over concrete subfloor

I am getting ready to install 18" X 18" porcelain tile over a concrete subfloor. The subfloor is in good condition (no cracks and about a year old). There are two bathrooms and a laundry room totaling about 225 sq. ft. Currently the floors are covered with vinyl. I plan on removing the vinyl before I install the tile.

Any other tips or suggestions concerning:

best type of thinset?
trowel size?
do I need to back butter the tile?
additional subfloor prep?
any other potential problems?

Thanks in advance for your time and expertise.

jsv
 
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  #2  
Old 12-12-03, 05:32 PM
floorman
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i was going to suggest a mat test to check for moisture but,if you are not having problems with the vinyl then no need for the mat test.Any tile 16" and over you need to use a 1/2x 1/2 notch trowel no need to back butter unless you are having to build the tile up for one reason or another.Make sure you get as much of the backing off as possible,glue as well.If there are any cracks in the slab you will need to put a membrane on the cracks to isolate them schluter kerdi works well for that as well as blue 92 a roll on membrane.The saw cuts (if any) will need a membrane too,blue 92 will work for that also.
Latex modified thinset will work nicely there.

Other than that just remember the smooth side goes up

Oh if there are any drains that you need to address cut the tile to conform to the drain,you'll need to cut the tile where the concrete starts to taper towards the drain
 
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Old 12-13-03, 03:38 PM
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There is no set trowel-to-tile size guideline. The best method would be to test out the coverage you'll get with a few sizes of trowels and determine which gives you the best coverage.

There is a method for trowelling the thinset which will improve coverage over traditional methods. There are also trowels which have a notch pattern which will also improve coverage.

If you were to use a 1/2" notched trowel with your tile, you'd likely be spending more time cleaning mortar out of the joints than laying tile. You would also be going through a lot of thinset, with no guarantee of proper coverage. Keep in mind the thinset between tiles should not come up more than 1/3 of the joint height.

That being said, once you've found the trowel size and style that will give you an acceptable level of coverage (95% or more), you should still take up the occasional tile to check coverage as you are laying the floor.

I'll go through the trowelling method on another thread.

Good luck!

David
 
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Old 12-14-03, 10:43 AM
floorman
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no,there are no guidlines on this in writing that i know of,however the rule of thumb is that the larger format tile have a concave back on them for whatever reason,maybe to add strength i do'nt know,so we ,when seeing the larger tile automatically grab a 1/2 notch trowel and move on.Then there are no questions of wether or not there is eneough thin set under the tile or not.

Same goes for marble or limestone 1/2 notch automatically.
 
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Old 12-15-03, 03:44 PM
JSV909
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Thanks guys for the help. Any restrictions to the width of the joints. I was thinking narrow joints, like 1/8".

Thanks Again,

jsv
 
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Old 12-16-03, 05:36 AM
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I agree, on the " notching!

Bigger format tiles need more mortar, that or that subfloor better be flat!

I suggest finding the high spots!! Big tiles don't like high spots!!!
Screed the low spots and let it set up, prior to setting the tile.

If you don't, proud edges and lipping are going to be throughout the installation.
 
  #7  
Old 12-18-03, 12:41 AM
marcovit
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ANSI A108.5

A-4.3.3 INSTALLATION OF TILE FOR FLOORS
A-4.3.3.1 General
A-4.3.3.1.1 Installation of floor shall be over concrete slabs, cement motar base, or glass mesh mortar units.
A-4.3.3.2.1 Applying dry set portland cement or latex modified thinset.
A-4.3.3.2.1 Clean surface thoroughly. Dampen if very dry, but do not saturate.
A-4.3.3.2.2 Apply mortar with flat side of trowel over an area no greater than can be covered with tile while mortar remains plastic. Withen ten minutes before applying tile and using notched trowel of type recommended by mortar manufacturer, comb mortar to obtain even setting bed without scraping backing material. Cover surface uniformly with no bare spots, with sufficiant mortar to insure a minimum mortar thickness of 3/32 inch between tile and backing after tile has been beaten into place. Tile shall not be applied to skinned over mortar.
A-4.3.3.3.1 Press tile into freshly combed mortar, insuring mortar contact with tile while maintaining accurate joint alignment and spaceing. Keep a minimum of 2/3 of joint depth open for grouting.
A-4.3.3.3.2 thoroughly beat beat all tile or tile assemblies into place with a beating block ( on larger tiles I use a rubber malet) to obtain maximum contact of thin-set mortar on the back of each tile, or back of each tile and back mounting material. Average contact area shall be not less then 80% except on exterior or shower installations where contact area shall be be 95% when no less then three tiles or assemblies are removed for inspection.


This was all taken from CTA ( tile councel of america)
CTI ( ceramic tile institute)
SNSI ( American National Standard Specificaton for installation for ceramic tile)
 
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Old 12-18-03, 12:52 AM
marcovit
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Average contact area shall be not less then 80% except on exterior or shower installations where contact area shall be be 95% when no less then three tiles or assemblies are removed for inspection.

One would asume if they recomend no less the 80% coverage in the interior floor area then 80 to 90 % would be more then sufficent for interior floor installation. Am i wrong?
 
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Old 12-18-03, 10:52 AM
JSV909
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just wondering...

Why is there no mention of a "membrane" in the installation specs that marvocit posted?
 
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Old 12-18-03, 11:17 AM
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Installing a membrane on a floor is still considered to be an optional move, depending what backer unit or underlayment you are going with for the substrate. There's always a need for one in the shower.

These specs are a little out-dated, but current. The TCA publishes their Handbook every two years. ANSI's last one was 1999. So much has changed, it's time for another ANSI one, at least.

David
 
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Old 12-18-03, 12:49 PM
JSV909
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Thanks to everyone for their help!

jsv909
 
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