Question For The Schluter-savvy.

 
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Old 05-28-2010, 01:35 AM   #1
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Question For The Schluter-savvy.


I have tiled probably 15-20 showers/tub surrounds. The last two that I did, I used Kerdi over Hardi Backer and it worked great. I have some Kerdi left over, that I want to use to tile the existing plaster tub surround in my rental property that used to be covered by very thin, very crappy fiberglass sheets (3 separate sheets with plastic corner moldings in the corners). After tearing out the fiberglass I see that the wall behind the fiberglass was painted before the fiberglass sheets were installed. I see that Schluter specifies unmodified thinset behind the Kerdi, but I'm not sure if unmodified will stick to painted plaster.

My first question is will unmodified stick to a painted surface?

If not, my second question is can modified be used instead?
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Old 05-28-2010, 01:37 AM   #2
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Re: Question For The Schluter-savvy.


ANGUS!!

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Old 05-28-2010, 01:49 AM   #3
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Re: Question For The Schluter-savvy.


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ANGUS!!
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Old 05-28-2010, 02:11 AM   #4
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Re: Question For The Schluter-savvy.


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I have tiled probably 15-20 showers/tub surrounds. The last two that I did, I used Kerdi over Hardi Backer and it worked great. I have some Kerdi left over, that I want to use to tile the existing plaster tub surround in my rental property that used to be covered by very thin, very crappy fiberglass sheets (3 separate sheets with plastic corner moldings in the corners). After tearing out the fiberglass I see that the wall behind the fiberglass was painted before the fiberglass sheets were installed. I see that Schluter specifies unmodified thinset behind the Kerdi, but I'm not sure if unmodified will stick to painted plaster.

My first question is will unmodified stick to a painted surface?

If not, my second question is can modified be used instead?
I guess I'm a bit confused by the 2 statements I highlighted above.

Would the Kerdi be going over plaster or painted drywall?

If it's only painted drywall, maybe scuff the paint and use a quality unmodified like Kerabond. When I do a shower area, I use DensArmor fiberglass wallboard & use Kerabond directly over it when installing Kerdi. No issues!

If it's plaster, that's a different story....
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Old 05-28-2010, 03:23 AM   #5
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Re: Question For The Schluter-savvy.


The original wall is plaster. It had been painted for whatever reason, and then a cheap fiberglass panel was glued onto the painted wall. I removed the fiberglass panels, and what is left is a painted plaster wall with a small amount of glue residue on it. I scraped the glue residue as smooth as possible, and now I want to apply Kerdi to the wall and then tile over it. Schluter obviously recommends unmodified thinset, but I'm not sure if unmodified will stick to a painted surface. I feel pretty confident that modified would stick to the painted wall, but I'm guessing the Kerdi won't bond to the modified thinset very well. I don't see why it wouldn't, but they specify unmodified on their web site.
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Old 05-29-2010, 02:41 PM   #6
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Re: Question For The Schluter-savvy.


The unmodified requirement is a CYA for Schluter... I use Versabond behind Kerdi regularly without issues. I wouldnt use a heavily modified like Flexbond though...

The weak point in the sandwich you have is the paint's bond to the plaster. How will you know if the moisture in the thinset didnt affect the paints bond? Can you grind the paint off, prime with an oil sealer like CoverStain, and then Kerdi? How about mechanically fasten 1/4 cement board OVER the plaster and then Kerdi?

How about just do it right and rip the plaster to the studs and put up some fresh wallboard?
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Old 06-02-2010, 11:29 AM   #7
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Re: Question For The Schluter-savvy.


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How about just do it right and rip the plaster to the studs and put up some fresh wallboard?
BINGO!

The plaster walls would steer me clear of going directly over with Kerdi.

The issue is not whether the thinset will stick to the paint, it's if the moisture in any kind of thinset you use will deteriorate the plaster. Have you seen plaster walls start peeling and/or crumbling? Do you want to use that type of a material for a tile substrate?
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Old 06-02-2010, 06:15 PM   #8
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Re: Question For The Schluter-savvy.


I'm with Angus on this - I wouldn't trust going over plaster

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