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Old 09-13-2011, 05:19 PM   #1
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tiling over painted T&G


I have a small tiling job (65 ft sq) over painted hardwood tongue and groove that sits on a rough assemblage of 1x6 plank subfloor. Do I need to remove the paint to accomodate the Thinset, or can it serve as a decoupling layer? I plan to install an EastMat product.

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Old 09-13-2011, 05:41 PM   #2
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You can not use Easy Mat over a wood substrate such as that. The wood needs to be either removed or covered with a minimum of 3/8" plywood.

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Old 09-13-2011, 08:39 PM   #3
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How about Ditra over T&G then?
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Old 09-13-2011, 09:12 PM   #4
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No!
You ain't gettin' it are ya.
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Old 09-14-2011, 05:57 AM   #5
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No tile can go over t&g wood---remove the wood and add plywood then backer board set in thinset.

T&g wood moved to much and the tile will come loose.
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Old 09-14-2011, 08:43 AM   #6
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I thought the decoupling membrane would fix the t&g wood movement problem. I suppose there are different types of movements going on.
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Old 09-14-2011, 09:18 AM   #7
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The decoupling membrane just means that if the floor shifts the tile does not shift with it, but it still must have a stong supporting backing. The tile and grout will not flex well. The T&G will flext...it just can't support the tile floor the way it needs to. This is why you put down backer board. Even a plywood subflor will flex a little. Just things I have learned over the years...sometimes the hard way!
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Old 09-14-2011, 10:04 AM   #8
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Okay I'm going to do this one more time.

Any dimensional lumber (wood) will expand and contract. Plywood is not considered a dimensional lumber and is kept in check (in and of itself) because it is engineered and laminated with wood grains of each layer opposing one another thereby inhibiting the possibility of movement.

Raw lumber on the other hand can and will move in all directions, both laterally and up and down.

DITRA will isolate lateral movement due to its design but it can not isolate or reduce upward or downward movement taking place below. Therein lies the problem with using DITRA over dimensional lumber.

Dimensional lumber (as in this case) will naturally try to cup and curl and expand and contract with climatic changes as well as invasions of moisture and dryness from other sources. Tongue and groove dimensional lumber would help to contain some of the upward and downward movement but won't stop it.

In the case of treated dimensional lumber the fibers of the wood are expanded during the impregnation of the wood process. This expansion obviously opens the cells of the wood to allow-in the liquid treatment chemicals. Over time the treated wood will dry. As it dries it basically allows the expanded cells to remain open making them even more susceptible to future moisture invasions.

Treated materials of this nature are never used in a rigid tile installation. That is an understanding of the installation industry and has been forever.

When one buys treated goods, just because the goods aren't weeping chemical moisture doesn't mean the moisture content isn't high. The moisture content is high and must remain so so as not to prematurely cause warping of the product and rejection by a potential customer.

Treated materials are available kiln-dried (KD) but they cost more and aren't readily found on a store shelf. KD materials are generally a special order product.

The tile installation industry would rather no tile be installed over any dimensional lumber product anywhere in the mix but also recognizes that many sub-floors were constructed with dimensional lumber in years past and and that material is a force that must be reckoned with. Therefore the use of plywood over a dimensional lumber subfloor has become the standard. Not just any plywood is recommended however. The only acceptable plywood is underlayment grade, exterior grade, Exposure 1, plywood but that product wears more than one label around the country.

The "exterior grade" nomenclature means the plywood has been constructed with water resistant adhesives. This product is recommended and used in tile installations because of the water that is used to mix the thinset mortar adhesives used in tile installations. This product is not to be confused with CDX plywood or treated plywood, they are not the same product and will not qualify for various reasons.
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Old 09-14-2011, 10:23 AM   #9
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Thanks Bud for the thorough explanation, parts of which I have seen in other threads. Looks like I will be ripping up painted T&G.

However to keep those nasty PT chemicals completly out of the interior space, I may follow the Hardiboard recommendation. This would probably then warrant keeping the T&G for the stiffness it offers.
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Old 09-14-2011, 03:47 PM   #10
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Quote:
However to keep those nasty PT chemicals completly out of the interior space, I may follow the Hardiboard recommendation. This would probably then warrant keeping the T&G for the stiffness it offers.
Please xplain.

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Old 09-14-2011, 04:39 PM   #11
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Most plywood adhesive will gas off with formaldehyde unless it is soy based or otherwise proven "inert". Exterior grade is treated with additional chemicals and probably has a higher threshold for exposure due to its placement. I could either analyze the products available, or special order them. See pharosproject.net for the effort to assess many building materials. I purchased formaldehyde-free insulation with the info they posted. The smallest traces of chemicals has been proven to have biological effects.

If you are referring to the cementatious backer, that is stable and inert in many ways. I figure it would "stabilize" the dimensional instability of the T&G, while leveraging its stiffness. This may be my most practical route due to its availablity and effort savings.

I would rather tolerate a hairline crack on my floor than endocrine disruption or some other effect.
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Old 09-14-2011, 05:23 PM   #12
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HOLY SCHIT !

This thread has just hit the scrap pile for me. Someone hasn't been taking their meds.
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Old 09-14-2011, 06:53 PM   #13
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Does that scooter have a back seat?

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Old 09-14-2011, 06:58 PM   #14
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A complete solution needs to consider all facets, otherwise aesthetics is just window dressing, with no basis for value.
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Old 09-14-2011, 07:05 PM   #15
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Well, This certainly went in a new direction----You are on your own---Mike---

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