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Unread 07-08-2004, 11:01 AM   #1
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Unhappy Pre-mixed thinset on CBU - opps

Just read all the advice regarding pre-mixed thinset. Wish I read it earlier.

Just completed my shower base and seat (haven't tiled the walls/floor yet) but unfurtunately used pre-mixed mortar I got from HD to join all my CBU. I can still get at most of the CBU joints but have buried some of the joints behind the shower seat.

How bad is it? I obviously dont want to rip down all the work I've done but is there something I can do to minimize the damage?

Can I apply thin set over the pre-mixed stuff? Will that help? Can I apply some waterproofing over it?

Do I need to worry about the CBU joints behind the seat?

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Unread 07-08-2004, 11:07 AM   #2
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You need to be concerned about any place that will see water. The pre-mixed stuff is water soluble and will degrade if it is exposed to moisture.

I say tear out what ever you can get to...

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Unread 07-08-2004, 12:00 PM   #3
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Can I apply anthing over the premixed stuff?
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Unread 07-08-2004, 01:25 PM   #4
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At this point I would buy some Laticrete 9235 or any of its clones out there. I use one made by ThoroughSeal. I would strongly recommend this system for you because it will keep water off that CBU and keep that pre-mixed thinset from re-emulsifying. Dave Gobis at the Tile Council once showed me premixed thinset that had fully cured and was then exposed to water. It re-emulsified and looked like snot.

It is a two part water proofing system. Black Latex like rubber liquid and a fiberglass mat. 5 Galls is about $250 at my supplier. Worth every penny. For the average shower, you will use about 2-3 gallons. I use the extra as waterproofing for fence posts or planter boxes. Or the neighbor's cat.

One applies the latex then smooshes in the fiberglass mat while wet, then top coat the mess with more latex.

If you go with the Laticrete 9235, I have a couple of tips:

1. Wear clothing that you want to throw away. I have been known to wear shirts that I find in Dumpsters for applying 9235. Every surface will be covered with this black sticky latex which will not wash off. Of course, wear a hat. You shoes will be trashed. I cover them with blue masking tape. This is an awfull messy job. After you are through, you'll be able to audition for the part of a mistral singer, should you care to do so.

2. I use a roller to apply the first coat. The stuff sets up fairly quickly (about 5 minutes) so if you think you'll be able to paint the whole inside of the shower, think heavy thoughts, drink a cup o joe, and stand around, forget it. You might have to split the area into thirds or quarters. I think about 32 sq feet is about the limit that a DIY without help can do in one setting. without it setting up on you. That is about 1 wall.

3. Pre cut the fabric. I measure and pre cut the fabric before rolling out the latex, allowing for a 2 inch overlap. Butt joint the corners (don't fold them through the corner) and then go over the corner with a 4" strip, 2 inches on each side of the corner. You don't have to be exact, with a 2 inch overlap you can be fairly inexact. If there is a section that has a quarter inch overlap and another that has 3 inches, it is no big deal. The latex does most of the work anyway. I like to cut off large hunks of the stuff (they give you way too much) and tape and drape it around the shower with blue tape, then razor knife the stuff down to a manageable size. Lotsa 4 inch corner strips. Carrry a sharp pair of scissors and a sharp razor knife in your back pocket. Label the pieces with a Black Sharpie if you drink on the job like I like to do.

4. Once the bottom coat is on, just lay the matting onto the black latex and sorta poke it into place with your fingers. I can't wear gloves for this, maybe you can. I am way too clumsy. Once it is in place, sorta tacked in, I go over it with a plastic putty knife or gently with a roller or brush to smooosh it into the latex.

5. Apply the top coat with a stiff brush or trowel. You again want to smoosh the fabric into wet latex and add some depth to the membrane with the top coat so a wide brush or flat trowel works well. But I've used a roller too, so it is no big deal. Trim off the excess with your razor knife being carefull not to puncture the shower membrane of course.

Once it is dry, you'll have to go to Office Depot or Staples and get a "white out" correction pen, which spurts out white ink correction fluid to do your layout. It is impossible to see chaulk lines over 9235, but that is another story for another day.

Have fun. Don't forget the blue tape.

Anyway, those are my tips. File it under "Laticrete 9235 for Dummies".
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Unread 07-08-2004, 01:36 PM   #5
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or instead of all that goo...you could use a sheet membrane like Nobleseal from Noble Co. or Kerdi from Schluter Systems.
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Unread 07-08-2004, 01:44 PM   #6
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Scooter's jits spoofin' ya about the cat.

You can't really waterproof a cat even if you pewt on two coats of 9235, and there ain't no way to git the fabric to go around the leg joints.

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Unread 07-08-2004, 06:27 PM   #7
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