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Old 08-06-2005, 12:05 PM   #1
dbenoit
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What thinset to use for Durock?

I'd like to put my Durock down today... The guy from HD has given me a product called Flexbond. Is this what I want to use? There is a difference between unmodified and modified I imagine, but what are the differences and where should you be using what where?

Thanks.

Dan
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Old 08-06-2005, 12:22 PM   #2
Tool Guy - Kg
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Hi Dan,
I wouldn't spend that much money on Flexbond under the Durock. To install the Durock down to the floor, use an unmodified thinset (cheap) under it and you'll be perfectly fine.

The difference is this:
Unmodified mortars don't have latex added to them and have little "grab" to the materials they are sticking to.

Modified mortars have latax in them and have a stronger "grab" to them. Often times used to set tiles...especially with porcelain tiles that are non-porous and are hard to bond to.

To get a modified mortar, you either buy a bag of modified thinset that has the dry additves already in the bag and you simply mix the powder with water, OR you buy unmodifed thinset and mix the liquid latex additive to the powder.

There is much to learn on when and where to use them, so come back and ask specific questions along the way to keep yourself on the right track. If you tell us what type of tile you are installing on top of the Durock, we can chime in on what you need. Most likely you'll be using a modified thinset like Versbond, or Flexbond to set the tile. It isn't rocket science, but your projects will last a long time if the proper materials are chosen for setting materials.
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Last edited by Tool Guy - Kg; 08-06-2005 at 12:30 PM.
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Old 08-06-2005, 12:29 PM   #3
dbenoit
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So Flexbond is ok then to use under Durock, it's just that it's more $$$ than unmodified. I figure I've got it now... so I may as well use it.

What type of thinset do I use between the tile and Durock?

Dan
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Old 08-06-2005, 12:30 PM   #4
jadnashua
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What kind of tile?
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Old 08-06-2005, 12:34 PM   #5
Tool Guy - Kg
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Yep, it is ok, but you'll be spending a lot more for it than a cheap $5-$8 bag that will do the same job.

When you thinset the Durock down, the idea is to get rid of all the little voids under it. You want to support the cement board so that there is no flex or give to it. Up and down flexing is the kiss of death to any tile job.

It sounds like you are going to need more thinset, so you might want to get some cheap stuff for the Durock and save the expensive Flexbond for where it counts.....the setting of the tile.

Before we go any further, tell me what kind of floor you are going over. Floors need to be strong enough to prevent undue flexing. Take a look at the deflecto calculator. It'll tell you if the joists under your room are strong enough to handle your tile job.
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Old 08-06-2005, 12:39 PM   #6
dbenoit
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Tile is ceramic... nothin' expensive.

Okay... so I'll go back and buy any kind of unmodified thinset then? I thought that Flexbond was the best for adhering anything to plywood?

So flexbond for tile is good?

Dan
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Old 08-06-2005, 12:44 PM   #7
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Sorry... the floor is 2x10's 16"oc, middle 2x10's are doubled. 3/4" plywood subfloor. New 2x10's have been shimmed from underneath using plywood on the sill and steel beam they rest on so they're level with originals. Original 2x10's acually measured anywhere from 9-1'2" - 9-3/4" inches.

Dan
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Old 08-06-2005, 01:00 PM   #8
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Okay, you are good to go with your understructure. Just checking. Hate to see this project go forward and have discovered later that the floor was too weak. The 3/4" ply is ok for using 1/2" cement board. Some may say you could use 1/4" cement board, but I don't like skirting the minimums for a floor that should last generations.

You can use unmodifed under lots of the cement boards in many occasions. There are times when the floor thickness is running at a minimum, or the joists are spaced out further that using modified is required. There is nothing wrong with using modified in this case, it just cost a few bucks more. If you want to use modified under there......go ahead.....but I think I'd use Versabond to still save you some dough.

Dan, because open bags of thinset start collecting moisture right after they are opened, they don't last long (30 days opened). If I use 2 types of mortar on a job, the chances of having open bags when I'm done is twice as great as if I use one type of mortar. I do complete kitchen and bath remodeling so there is always weeks between tiling projects. For this reason, I use a modified for everything....less open bags that want to go bad on me and less mess in the truck.

Hope that sheds more light on the subject.
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Old 08-06-2005, 02:19 PM   #9
dbenoit
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Thanks Kurt!!! Your help and opinion are greatly valued and appreciated.

Thanks again.

Dan
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