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#5274 - 09/07/07 11:08 PM Will Thinset stick to old glue?
lien Offline
Junior Member

Registered: 06/15/07
Posts: 19
Loc: newmarket
I have a subfloor with old glue (dried up but very hard to get all residue of plywood) stuck to it from the old linoleum floor I ripped up. I was wondering if thinset will stick to it so I can put down my hardi-backer board down on top of it.
Also should it modified or unmodified thinset??

Thanks!!

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#5275 - 09/07/07 11:48 PM Re: Will Thinset stick to old glue?
Jaz Online   content
Senior Member

Registered: 03/11/02
Posts: 626
Loc: Troy, Michigan U.S.A.
Hi Lien,

Usually sheet vinyl is glued to some type of 1/4" underlayment of some type. If that is what you're now looking at, you need to remove it. Try to figure out what you've got and also the type and thickness of the subfloor. The 1/4" underlayment should have been stapled to the subfloor.

While you're at it you may as well measure the size of the joists, their spacing and also measure the unsupported span. This is to make sure the house can handle tile. Let us know those numbers.

If by chance your house is older, and has a double subfloor, the top sheet being 1/2" or 5/8", then it would be fine to spread thinset and install Hardi over it. You see, the thinset is there to support..."push" the board up, while the fasteners push the board down. The board doesn't even have to bond to the subfloor. That is why Hardi recommends either modified or unmodified thinset to set their backer. Unmodified of course does not bond the plywood. You must us modified thinset to install the tiles however. I usually recommend modified for both steps so I only buy one type.

Jaz
_________________________
Tile 4 You..Troy,Michigan U.S.A.
www.tile4you.com
KERDI Shower Specialist-DITRA Installs-Containers of TRAVERTINE direct, ship anywhere. SAVE 40-70%
I've NEVER made a mistake, I thought I did once...but I was wrong!

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#5276 - 09/08/07 09:33 AM Re: Will Thinset stick to old glue?
lien Offline
Junior Member

Registered: 06/15/07
Posts: 19
Loc: newmarket
Thanks Jaz!
My subfloor is 5/8 plywood 16 inchs on center.(6x5 bathroom floor)
There is no 1/4 underlayment! So the thinset doesn't have to stick to the old glue because it is acting more like a gasket than a adhesive??
I am also adding the nuheat electric floor and wanted to put Ditra on top of the nuheat mat. My problem is that nuheat says its mats should be installed with modified thinset and then Ditra suggest a unmodified thinset below and above the Ditra so it can work properly. I am confused! I called them and they said set the nuheat mat in modified and then let it dry and then on top dried modified spread the unmodified and set the ditra in it!
My question is how do I get the modified thinset to dry at a even height across the room? Won't that be difficult especially since the mat doesn't extend across the whole room??

Thanks again!!

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#5277 - 09/08/07 12:24 PM Re: Will Thinset stick to old glue?
Rob Z Offline
Senior Member

Registered: 09/16/01
Posts: 905
Loc: Loudoun County, VA USA
Hi Lien,

It can be problematic trying to skim out a floor around the perimeter of a NuHeat mat. Whenver possbile, we skim coat the NuHeat mat, prime it with SLC primer, and then mix and our SLC over the entire floor.

Whether you skim coat the Nuheat mat and go with the Ditra, or skim coat the mat and go with SLC, I suggest adding a layer of plywood over the existing 5/8" in order to beef it up.

Also, once you have skimmed completely over the NuHeat mat with thinset and the thinset is hardened, Ditra will install with no problem as long as you use a quality un-modified thinset.
_________________________
Kitchen & Bath Renovations (VA USA)

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#5278 - 09/08/07 06:51 PM Re: Will Thinset stick to old glue?
lien Offline
Junior Member

Registered: 06/15/07
Posts: 19
Loc: newmarket
Thanks for the info! What exactly is SLC primer??

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#5279 - 09/08/07 07:43 PM Re: Will Thinset stick to old glue?
Jaz Online   content
Senior Member

Registered: 03/11/02
Posts: 626
Loc: Troy, Michigan U.S.A.
SLC= Self-Leveling-Cement, and so SLC primer is the primer used with it.

I agree with Rob on the installation, and yes, you need more plywood over that 5/8" (minimum standards) subfloor.

Just remember when installing Ditra to the floor, use a thinset type that is appropriate for the substrate. So, if the substrate is cementitious, use unmodified, if it's plywood or OSB, you need to use modified. Use unmodified to set tile onto Ditra as always.

Jaz
_________________________
Tile 4 You..Troy,Michigan U.S.A.
www.tile4you.com
KERDI Shower Specialist-DITRA Installs-Containers of TRAVERTINE direct, ship anywhere. SAVE 40-70%
I've NEVER made a mistake, I thought I did once...but I was wrong!

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#5280 - 09/08/07 11:38 PM Re: Will Thinset stick to old glue?
lien Offline
Junior Member

Registered: 06/15/07
Posts: 19
Loc: newmarket
Thanks Jaz!
Is this a really stupid idea?? To create a smooth floor of equal height, I thought I might use the nothced trowel to comb in lines of modified thinset over the nuheat and the part of the floor that isn't heated. Then let that dry and come back and fill in the valleys of the dried thinset with more thinset to create a smooth even base of equal height, or is this a waste of time?????

Comments???

Thanks!!

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