Deck Mud vs Durock

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I recently sought tile advice at Johnbridge.com and was encouraged to consider deck mud instead of Durock or other CBU's. Anyone pour deck mud? How did it turn out? I did a search for deck mud but didn't get much.

I'm just about to install my hearth using one layer of 1/2" Micore board sandwiched between two layers of Durock. This should give me an R value of about 1.9. If I went with deck mud, since concrete doesn't have much R value, how might I achieve a comparable R value?

 

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I am not following the application for the deck mud. Latex modified thinset should work fine unless I am misunderstanding the application and hearth design. What will be the finished surface, tile?

Personally I'd put the Micore on the bottom layer, then the Durock layers. It will give you stiffer surface for the top layer.

 

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I am not following the application for the deck mud. Latex modified thinset should work fine unless I am misunderstanding the application and hearth design. What will be the finished surface, tile?

Personally I'd put the Micore on the bottom layer, then the Durock layers. It will give you stiffer surface for the top layer.

BeGreen - first, thanks for your response. From the reading I've done at Johnbridge.com, deck mud is made from 4 parts mason sand to 1 part portland cement. It is mixed and then packed into a form at least 2" thick. The top is floated flat and left to cure. When the forms are removed there is a 2" thick masonry base to bond tile. Scotty Overkill put in a similar base for his fireplace insert, though after PM'ing him, I found out that he used a concrete mix, not deck mud. Similar concept though.

The issue that I see with using deck mud is the lack of R value, since concrete (deck mud by extension) has a low R value.

I'll probably go with a Durock - Micore - Durock sandwich, because I can achieve the desire R value. I don't need the R value with my current stove, but if I were to change stoves at some point, I want to be prepared.

The finished surface will be porcelain tile.

 

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I hate to disagree, but this is total overkill. Tile sets beautifully on a solid Durock base with just thinset. However, Micore is soft. That's why I would put it on the bottom. I see no advantage to putting it in the middle of a sandwich.

 

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I hate to disagree, but this is total overkill. Tile sets beautifully on a solid Durock base with just thinset. However, Micore is soft. That's why I would put it on the bottom. I see no advantage to putting it in the middle of a sandwich.

Funny thing, BeGreen, is that I really favor Durock. I've used it before on floor tile jobs. It installs easy. Works great to bond to plywood using thinset. Then, I go to the tile forum that I mentioned previously and asked about screws. The recommendation with screwing Durock is that the screw penetrate the Durock and fully penetrate the plywood subfloor. Well my plywood subfloor is 1 3/4" thick in my hearth area. And then add 1 1/2 " of Durock/Micore. Durock screws come in max length of 2 1/4". Well you can see where I was going with this. I was looking for a tile pros perspective on being sure the top layer of my Durock was adequately held down. The next thing I know is that I'm being advised to skip Durock and put in deck mud.

As for the sandwich, my plan was to bond my first layer of Durock to plywood using modified thinset and screws as I would for a typical tile installation. Then add 3" strips of Durock on top of the first layer on the perimeter. And then set Micore within the perimeter of Durock strips. Finally, add Durock over the top. The Durock strips would give me three layers of Durock around the edges for my tile edge cap.

Putting the first layer of Durock on the bottom and bonding it to the plywood with thinset insures that there are no gaps between these two disimilar surfaces, which might ultimately result in cracked tile. That is the reason for bonding thinset to the substrate below it for regular tile installations.

Any thoughts?

 

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Really, I appreciate trying to do things right, but this is overkill. Screw down the first sheet of Durock over the micore. 1/8" thinset and put down the second sheet with longer screws. Let set and proceed with tiling on a new coat of thinset. You don't have to use the special Durock screws for the top layer. It is a totally dry area. Long drywall screws would work fine.