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4just1don 09-23-2011 11:32 PM

install of underlayment
putting down 'green e' underlayment to install ceramic tile for small bathroom

16" 2 bye 8" with old style 1 bye sheathing on the angle,,,topped by full thick old time oak floors. took masonite underlayment and last vinyl up...floor joists span 12' or so. floor is 5 foot by 6 foot plus new closet getting tiled also .

have read my new underlayment needs to be installed in thinset base,,,why is that??/

JazMan 09-24-2011 10:08 AM


I'm sure you meant to say planks on an angle and not sheathing. :thumbsup:

2x8 spanning 12 ft. is very marginal for tile, but might work for you. Are they exposed from below?

You've got a little more work to do than you thought. The 3/4" oak floor has to go. You will then install new 1/2" underlayment grade plywood, then the tile backer into fresh thin set mortar. All tile backers must be installed this way when used on floors and counters. Did you read the Green E-Board installation directions?


Bud Cline 09-24-2011 10:47 AM

Green-E is a good product but it can not be installed directly over any dimensional lumber (which is what you have) without first installing underlayment plywood.:) The hardwood should be removed first.:yes:

4just1don 09-25-2011 05:10 AM

i dont understand . why would you take off one kind of wood and replace with another. What happens if the oak floor stays under there? just wondering? oak seems much more solid than ply,especially 1/2"

And still wondering,,,what does thinset do under backer board? what happens when it is NOT there?

didnt get any install directions with green E, where would I find them?

oh'mike 09-25-2011 06:13 AM

Plywood is much more dimensionally stable than oak strips--oak expands and contracts a lot big gaps in winter--tight in summer --and it cups and flattens with the seasons. This is to much movement for brittle tile.

The thin set under the board is to fill any voids and keep the backer as stiff and inflexible as possible.

Backer board has no structural strength to speak of----its purpose id to provide an ideal bond between the tile and the plywood---

so the thickness of the backer doesn't matter -----1/4" wonderboard is a fine product.

JazMan 09-25-2011 11:32 AM

In addition to what Mike said................


didnt get any install directions with green E, where would I find them?
I suggest their website.


4just1don 09-25-2011 02:41 PM

Thanks guys!!I get ti now!! I am such a slow learner. Would have had it all screwed up without you!!!!

Says need 2 inch fiberglass tape for seams,,,is that same tape as cement board tape,,,that is gray,,,I also have fiberglass mesh drywall tape, regular stuff guessing cement board tape better. Right?

Guy at apron store said I needed type 3 thinset (fast setting for walls and big tile. Then another said no type 2 is all I need. This was for 4 bye 4 tile on shower surround of tub. Reason I find is type 3 is 10 bucks higher.

So for floor tile 12 inch square what thinset do I really need? for under e board and setting tile?

Then doing 6 bye 6 wainscoat on walls,,,what thinset there??

And lastly(arent you glad?) it says for wet locations do a vapor barrier. Is a bath floor or general walls not the shower of course,,,considered a wet area?? Hope its not wet but anything can happen, shower spill,,,stool leak sink leak etc. Whats the best vapor barrier if needed??? (used red guard in shower)

Bud Cline 09-25-2011 03:37 PM

There is no such thing as "Type 2" thinset or "Type 3" thinset. [Type I and Type II are designations for mastic tile adhesive and you shouldn't be using that stuff for your project at all] You must be dealing with the morons at a Home Depot. Those numbers on the bags are put there by the thinset maker at the request of HD and they are "step" numbers not type numbers. Forget about all those numbers that is nonsense.

Yes you should use the alkali resistant seam tape for all cement board seams. You can use the lower cost "unmodified thinset" for under the cement board and the higher priced "modified thinset" for the tile installation.

A moisture barrier is recommended in showers but not bathroom floors. A moisture barrier on the studs can be roofing felt type paper or plastic sheeting.

Or, you can forgo the moisture barrier on the studs if you use liquid waterproofing on the surface of the wallboard.

Please stop asking those guys at the home center diss-count stores how to do things. They will get you into a world of trouble needlessly.:)

Bud Cline 09-25-2011 04:04 PM

Something has just occurred to me...

Are you talking about Mapei's Ultraflex 2 and Ultraflex 3 when you call them "type 2 thinset" and "type 3 thinset"?

If you guys would use brand names here it would make this a lot easier. You mention Redgard but fail to mention thinset brands.:)

JazMan 09-25-2011 07:48 PM

Bud, you may be right about it being Ultraflex 2 or 3. In which case he may have spoken to the nice morons at Lowe's? In any case, please give brands and specific item names


4just1don 09-25-2011 08:22 PM

Bud was right, cept it wasnt Loewes but their direct comprtitor,,,Me-nards,,,same brand of stuff the Mapeii stuff,,,my old age shows thru and cant member.

thanks for all the info

I did get the redguard fromhome depot tho since other stores dont have

JazMan 09-25-2011 08:32 PM

OK Menards. There isn't one within 50 miles of here, but I wish they'd open one soon. Someone told me Menards is actually a better big box than the others. We'll see.

So have your Q's been answered?


4just1don 09-25-2011 08:45 PM

thanks,,,seems so,,,you guys make this look so easy,,,maybe after I do about 25 jobs like this I my know 'something'...dont worry,,I am not for hire just doing my own house,,,at my age no chance of getting to 25,,,so therefore I know nothing!!!!

Bud Cline 09-26-2011 07:12 AM

Menard's stores here do a good job overall. They don't train their tile people any better for the most part but at least they will listen and aren't so eager to act as if they know it all.:) The young man that heads up the flooring department at my local store does a good job and is somewhat knowledgeable.:)

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