Tiling Over Old Mortar Bed

278 Views 7 Replies 5 Participants Last post by AustinDB, 4 d ago

LovinItAll

Discussion Starter · 19 d ago

Hi,

I’ve just removed tiles from an old mortar bed and am preparing to lay new tiles. It’s a dry area (bathroom floor). The old mortar bed is in good shape except for a few small divots. Removing the mortar bed isn’t an option.

I would like something smoother to set the tile on. Apparently self-leveling compound isn’t supposed to be used on mortar beds. I’ve consisted Ditra, but I’ve also thought about 1/4” cement board. Not sure exactly what fasteners to use for the cement board, though. I’d put thinset under either Ditra or the cement board. It’s a small area (~25sf).

Suggestions?

Thanks in advance.
__
Ray

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3rd4thGEN

· #2 · 19 d ago

Diamond surface grinder on high spots, vac and a light acid wash? then screed a layer of thinset/tile mortar with an accelerator, maybe a little bonding agent? then as normal thinset tile next day?
Maybe dampen entire surface so the thinset doesn't DRY out too fast during tiling....

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tjbnwi

· #3 · 19 d ago

Bostik SL-Gyp.

Tom

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LovinItAll

Discussion Starter · #4 · 18 d ago

3rd4thGEN said:
Diamond surface grinder on high spots, vac and a light acid wash? then screed a layer of thinset/tile mortar with an accelerator, maybe a little bonding agent? then as normal thinset tile next day?
Maybe dampen entire surface so the thinset doesn't DRY out too fast during tiling....

Any particular bonding agent you’d recommend?

Someone else mentioned using an acrylic primer and then a floor leveling product. Not really sure about that. My original thought was pretty much what you suggested: Level with thinset, then lay tile. I wish I had been allowed to remove the mortar bed, but the client was adamant about leaving it.

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G&Co.

· #5 · 18 d ago

tjbnwi said:
Bostik SL-Gyp.

Tom, what makes a gyp-based self leveler better than the common variety?

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tjbnwi

· #6 · 18 d ago

G&Co. said:
Tom, what makes a gyp-based self leveler better than the common variety?

I don’t know what makes it work, it is the only SLC I know of that listed mud beds as an approved substrate. Two primer coats are required.

Normally I use the “common variety” SLC, heard about the Bostik at one of the Schluter classes. Don’t know if it’s still the case, Bostik made/makes the Schluter mortars.

Tom

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LovinItAll

Discussion Starter · #7 · 18 d ago

tjbnwi said:
Bostik SL-Gyp.

Tom

I’m sorry, I didn’t know what you were talking about. Bostik SLC for gypsum…found it. Any particular primer recommendation? SLC is really the way I wanted to go. Thank you.

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AustinDB

· #8 · 4 d ago

the tech sheet has details on the primer to use. it indicated after the second coat of primer you have between 2-24hrs to apply the SL-Gyp.

should Ditra or an equivalent decoupling membrane be used or can you tile directly to the SL-Gyp?

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