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Old 11-03-2010, 04:53 AM   #1
infogeek
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modified or unmodified thinset

I am going to be installing porcelain 12 x 12 tiles to the floor and in a shower in a bathroom. In the past I have used modified thinset to install porcelain and ceramic tiles...for this install I am using some products for the first time and wanted to be sure of the proper use of materials.

I am about to use ditra for the first time and the instructions are instructing to use unmodified thinset to set the tile so the mortar can cure properly with the impermeable ditra layer.

I will also be building a shower where I will be installing a traditional mud bed and then using 1/2 hardi for the shower walls. I am going to red guard the hardi on the walls. I am wondering since the red guard is also an impermeable membrane should I use an unmodified thinset to set the 12 x 12 porcelain tiles on the shower walls over the red guard?
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Old 11-03-2010, 05:03 AM   #2
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Welcome to the forum, Tom.
You do want to follow Schluter's recommendation to use an unmodified mortar over the Ditra if you'd like them to honor their warranty, though some of the Pro's here endorse using a slightly modified mortar found at HD, namely Versabond, and warranty the work themselves. Under the Ditra, when applying to wood, you do want to use a modified thinset. 12x12's at one time were considered "big", but today it common to see 18's, 20's, and 24's, where the issue of trapped uncured latex would be a huge issue. I'd use Versabond on both sides of the Ditra in your case and feel good about it, but wouldn't have Schluter backing the system. For your walls, Custom Building Products, to my knowledge, has no restrictions on what is used to bond to Redguard. It may be due to a high perm rating, which would allow vapor to escape. Be sure to check the wet film thickness on the Redguard, and allow it to dry thoroughly. With Hardi being as thirsty as it is, it might be suggested by the Technical folks to thin out the RG with water and "pretreat" the walls before rolling on your membrane. They are usually helpful, I'd give 'em a call to find out.
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Old 11-03-2010, 06:12 AM   #3
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Welcome, Tom

Whatever you decide, don't get roped into buying Home Depot's "CustomBlend" unmodified. It is not a premium unmodified thinset mortar, and is widely regarded as unsatisfactory for Ditra installs.

Over the Hardie+RedGard walls, plain ol' Versabond will do you right

Enjoy!
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Old 11-03-2010, 07:28 AM   #4
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add one more vote for versabond.
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Old 11-07-2010, 03:26 AM   #5
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leveling subfloor under ditra

I need to level a subfloor before the ditra goes down. There are a few low spots here in there from crowned joists. Can anyone recommend a product? What is the maximum tolerance for low spots and high spots for ditra and a 12 x 12 tile install....for example 1/8" in 6 feet,etc?
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Old 11-07-2010, 06:10 AM   #6
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Sometimes just sanding the high spots with a belt sander will suffice. How big an area are we talking? How high are the high spots?
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Old 11-07-2010, 06:48 AM   #7
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Welcome, Tom.

It's helpful if you'll keep all your project questions on one thread so folks can see what you're working on and what's been previously asked and answered. We can give it a more generic title any time you'd like to suggest one.

The industry standard for flatness is no deviation of more than 1/4" in ten feet and no more than 1/16th" in any one foot. Flatter is better.

My opinion; worth price charged.
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Old 11-07-2010, 08:41 AM   #8
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Thanks for the responses! It's actually a different job....I usually use 1/4 cbu but I will have almost a full roll of ditra left over from the other job so I am planning to burn the rest of it on this job, but as long as I am getting these real time responses I don't care where you put my posts

This bathroom is about 6 feet wide and 7 feet long. The variances are 1/8"-3/16" in a couple places.

1/4" seems like a lot for variance, and seems like once the ditra is adhered it is going telegraph any ups and downs a lot more then 1/4 cbu...but I have never used ditra before. I know the ditra install instructions did say to take care of the flattness issues in subfloor before the ditra layer. In the practical world of construction, can you make up any inconsistencies in the flatness on top of the ditra layer...if so how much?

What about a SLC before the thinset and ditra layer?
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Old 11-07-2010, 08:44 AM   #9
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SLC would be just fine to use, as long as you follow the manufacturer's instructions to the letter. Personally, on such a small area, I would just level it while setting the tile.
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Old 11-07-2010, 09:11 AM   #10
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Sorry about that, Tom. Looked like same project from over here.

When considering doing your flattening while setting your tiles, consider also that people like Greg have likely done it a couple times before.

Nothing quite like having a flat substrate before you start setting tiles for those of us who don't do it on a daily basis.

My opinion; worth price charged.
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Old 11-07-2010, 02:35 PM   #11
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I bought some of the Custom Blend unmodified thinset from HD so I will take it back.How does one know if its slightly modified? What are sone good brands of unmodified thin set?

Thanks Glenn
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Old 11-07-2010, 02:39 PM   #12
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Hi Glenn,

Unmodified thinsets that I would use:

DitraSet (by Bostik I think)
Laticrete 317
Mapei Kerabond

As for a "slightly modified" thinset - Versabond, available at HD.
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Old 11-07-2010, 02:48 PM   #13
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Quote:
Originally Posted by Glenn
How does one know if its slightly modified?
One guesses, Glenn, best I can tell. But the price tag is gonna give a fella some hints, too.

I very much like Joe's list above.
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