# Taping and mudding cement board



## ToolSeeker

jonhayden said:


> Hey all,
> 
> Thanks in advance for the help. I'm surprised I'm having such a hard time finding instructions on this. I couldn't even find any videos on youtube. I just finished adding a bedroom to the basement and now I'm adding an adjoining bathroom. I'll be using the moisture resistant drywall everywhere except in the shower area. I'll be using Durock from Home Depot. I've researched and understand I need to use fiberglass mesh tape for the joints. And I've read that I use thinset for the mud.
> 
> By thinset, is that just the same mortar that I use for hanging tiles? Or should I use something different?
> 
> Does it sand like drywall compound? For example, do I have to do several layers of mudding and sanding like with regular drywall? I did a level 5 finish on the drywall in the bedroom, but do I need to do the same for the cement backerboard? I'm assuming no since it's going to be tiled.
> 
> What kind of mud do I use where the green board meets the cement board? Thinset there too? And again, does it sand and feather like drywall compound?
> 
> Occasionally someone mentions they use Redgard. Do I care about this?
> 
> I'm also installing a Tile Redi Niche. The instructions just say, "Take 100% waterproofing silicone and seal the gap between the wall board and the REDI NICHE®." Is that sufficient or should I also use some thinset over the gap? Or Redgard? I'm guessing I should stick with the manufacturers instructions.
> 
> Sorry for all the questions.
> 
> Thanks,
> Jon


Thinset is the same as you set your tile. No it does not sand and there should be no place you need to sand it. You put it on run your notched trowel thru it to give you the right amount (thickness) then set your tile in it. Use the thin set to the end of the tile, then while still wet wipe off the excess and use joint compound from that point. NO it does't sand and feather it is basically concrete. Redguard will work as it waterproofer roll it over the board not over the thin set.


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## jonhayden

ToolSeeker said:


> Thinset is the same as you set your tile. No it does not sand and there should be no place you need to sand it. You put it on run your notched trowel thru it to give you the right amount (thickness) then set your tile in it. Use the thin set to the end of the tile, then while still wet wipe off the excess and use joint compound from that point. NO it does't sand and feather it is basically concrete. Redguard will work as it waterproofer roll it over the board not over the thin set.


Thanks for the reply. So are you saying that I do the joint mudding the same time I do the tiling? I don't have to do the taping and mudding at the same time? I can put on the mesh tape one day (without adding thinset) and then do tiling the next day and fill in the mesh tape with thinset as I get to that spot with my tiling?

I should place my last row of tiles over the drywall/cement board joint, right? And I use thinset for that even though it will get on the drywall? At that point, I wouldn't need drywall compound since the joint is already covered I'm guessing.

Is Regard necessary if I'm using a 4-mil moisture barrier behind the cement board?


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## Jb1234

If you do vapor barrier then don't Redgard. Google Redgard with vapor barrier to read all the results. I didn't want to hotlink other forums.


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## joecaption

You should not be using vapor barrier behind the cement board!
Only need the Red Guard on the surface of the cement board.
Grout and tile board are not water proof. Why would you want the water to go through all the layers and get trapped behind the wall? 
I install the tape with the thin set then waterproof everything. The seams are the most likely place it's going to leak why not waterproof them?


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## Jb1234

Joe I completely agree with you. Here's a little story of when I did my bathroom down to the studs. House is almost 30 years old and the tile was originally thinset to drywall and no vapor barrier. I went down to the studs for fear of mold, etc. behind it. Guess what I found? 100% mold free and clean as could be! This was a pleasant surprise. When I did the remodel I used cement board and Hydro Ban (like Redgard) and installed the tile. Now my point is, I would always install to spec and go above and beyond. But just because something might not have been done to the ideal doesn't mean you are living in a disaster either. Now I'm not recommending that, but this isn't rocket surgery either.


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## jonhayden

Quick question about mudding than. If I tape and then mud the joints with thinset, do I just apply the thinset like I would with drywall compound? Just use a taping knife to apply it smooth? Since it can't be sanded, how do you get it smooth before you redgard and tile?


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## ToolSeeker

Why do you want it smooth? Forget drywall compound it is not even close to the same and neither is the procedure.


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## djlandkpl

jonhayden said:


> Quick question about mudding than. If I tape and then mud the joints with thinset, do I just apply the thinset like I would with drywall compound? Just use a taping knife to apply it smooth? Since it can't be sanded, how do you get it smooth before you redgard and tile?


Apply the tape and then cover the tape and seam with thinset. It does not have to be smooth like drywall compound. It should be flat with no ridges. Ridges can affect your tile depending upon the trowel depth.


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## Jb1234

I agree with the above. You're over thinking it a bit. Imbed the tape and you're set, it's getting covered, doesn't have to be pretty.


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## jonhayden

Thanks all! I think I have it figured out now.

Oh, one last question, can the redgard get put over the silicon that is going to be used between the Redi Niche and cement board? Just want to make sure there's no bad chemical reaction between the 2 products.


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## ToolSeeker

Why would there be silicone between the board and the tile?


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## jonhayden

ToolSeeker said:


> Why would there be silicone between the board and the tile?


Instructions say:

"Take 100% waterproofing silicone and seal the gap between the wall board and the REDI NICHE®."


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