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Old 11-13-2006, 04:24 PM   #1
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What type of cemend on bathroom floor?


I just found out my toilet was put down on hardwood flooring and a cracked flange resulted in it rotting out. So I ripped up the hardwood, and ripped up the tounge and grove subfloor.

Now I have 3/4in plywood, tar paper, and lathe on the floor. Now I want to put down a 1/2in mud floor and level off the bathroom. I've done mud floors before. I just can't remember what kind of cement I used. I went to home depot to take a look around, the guys there wanted to sell me the self leveling stuff at $40 a bag and wonderboard (I'd rather put in cement then wonderboard). Aside from that everything else there said 2in minimum besides the sand mix, and I'd rather mix it myself.

This is going to have porcelen tiles over it.

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Old 11-13-2006, 04:56 PM   #2
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What type of cemend on bathroom floor?


Typically this is called "deck mud" and deck mud is mixed 4:1, four sharp sand to one portland cement.

You could use sandmix but it is only 3:1 in most cases. That doesn't mean it won't serve this purpose, I do it frequently.

The only problem is you only want a cement substrate of 1/2" and that isn't at all recommended. The industry recommendation is not less 1-1/4" of thickness.

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Old 11-13-2006, 05:47 PM   #3
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What type of cemend on bathroom floor?


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Typically this is called "deck mud" and deck mud is mixed 4:1, four sharp sand to one portland cement.

You could use sandmix but it is only 3:1 in most cases. That doesn't mean it won't serve this purpose, I do it frequently.

The only problem is you only want a cement substrate of 1/2" and that isn't at all recommended. The industry recommendation is not less 1-1/4" of thickness.
I guess I worked for some real hacks then. They generally did 1/2in plywood, 1/2in of mud, then tiled it. I don't think I've ever ripped up a mud floor more than 3/4in thick either.

I figured it was just portland cement but the bag says 2in minimum. So long as I mix it as you directed it should be ok to go thinner than that? The sandmix they had was the ad water and go stuff, not the kind you mix with sand.

The room had 3/4 toung and groove subfloor, 3/4in hardwood flooring, then 1/4in tile. I'd like to stay as close to that as possible which only leaves me with 3/4in for cement. If I go the extra half inch it's going to be 3/4 higher then the hallway floor and really look silly even with the saddle. Is their any trick to getting around this?

How do people get away useing 1/2in backerboard?
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Old 11-13-2006, 06:04 PM   #4
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What type of cemend on bathroom floor?


We have done it that way, 3 - 1 mix, but now, there are polymer floor compounds that "flex" and work great. However, from what you desribed, I would use the plywood and then cement board to tile to. This is an acceptable method to fix the problem.
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Old 11-14-2006, 09:12 AM   #5
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What type of cemend on bathroom floor?


The deck mud system is intended to be an isolation system so to speak. With a slip-sheet the deck mud is totally isolated from the structure and therefore movement, lateral movement, has little (if any) effect on the tile installation. With a deck mud minimum thickness of 1-1/4" the cement sort of takes on a life of it's own as there is rigidity value in the cured deck mud and the system temds to float over the structure independent of the whims of the structure.

Deck mud could be installed as thin as 3/4" thick but the rigidity is sacrificed.

Another method is to use mesh attached to the floor and the deck mud is interlaced with the mesh. Any structural movement will however be transmitted to the deck mud. The thinner the deck mud the riskier the nstallation. Deck mud only 1/2" thick offers no rigidity and becomes nothing more than a foster child of the structure.

Then there are guys that think it is OK to use the mesh and thinset (sometimes referred to as a "Jersey mud Job" or an "Oklahoma Mud Job"). This type of installation has been proven to have a very high failure rate and isn't recommended by the industry under any circumstances. Too much potential for flexibility.

Moving right along we come to CBU's (cementuous backer units) of which their are many. In my experience one is no better than the other and they all work fine. The CBU's are to be installed in a bed of unmodified thinset then fastened according to the manufacturers specifications. Not all CBU makers suggest unmodified thinset and some say modified is OK but the TCNA wants to see unmodified so that it can later seperate slightly from the substraight and some miniscule lateral movement is then allowed. I know I know, what about the fasteners? Blows my mind too!

I would do as joasis has suggested and use the CBU process, it has proven istself over the years but the structure must be in compliance first.

WHOOPS! Just noticed joasis is from Oklahoma. Have no idea where the "Oklahoma Mud Job" name comes from and no offense intended.

Last edited by Bud Cline; 11-14-2006 at 09:15 AM.
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Old 11-14-2006, 03:46 PM   #6
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What type of cemend on bathroom floor?


So in a normal instalation the mesh is not nailed to the floor? I've never seen it done that way, every installation I've seen has had it nailed down.

As far as useing a cement board the floor has at least one spot that's unlevel enough to crack the cement board trying to screw it flush with the floor. The thinset would have to be built up about half in inch in a couple spots, is that alright?
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Old 11-14-2006, 06:03 PM   #7
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What type of cemend on bathroom floor?


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So in a normal instalation the mesh is not nailed to the floor? I've never seen it done that way, every installation I've seen has had it nailed down.

As far as useing a cement board the floor has at least one spot that's unlevel enough to crack the cement board trying to screw it flush with the floor. The thinset would have to be built up about half in inch in a couple spots, is that alright?
No, if the floor isn't level, adding thinset under the CBU won't help and shouldn't be tried, once screwed down, it will still be uneven, if CBU can't be installed and the floor leveled after, then use a SLC and tile on that or Mud the floor.
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Old 11-14-2006, 06:42 PM   #8
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What type of cemend on bathroom floor?


I would do as joasis has suggested and use the CBU process, it has proven istself over the years but the structure must be in compliance first.

WHOOPS! Just noticed joasis is from Oklahoma. Have no idea where the "Oklahoma Mud Job" name comes from and no offense intended.[/quote]

Uh huh! I saw that!
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Old 11-14-2006, 07:24 PM   #9
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What type of cemend on bathroom floor?


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So in a normal instalation the mesh is not nailed to the floor?
Not what I said.I said: "Another method is to use mesh attached to the floor and the deck mud is interlaced with the mesh."
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Old 11-15-2006, 07:09 AM   #10
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What type of cemend on bathroom floor?


Wet bedding anything is an old school way to do this stuff...why put yourself through it when you can use a good cement board that works fine, plus save the weight of a mortar set?
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Old 11-15-2006, 08:16 AM   #11
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What type of cemend on bathroom floor?


My only cencern with cement board is the level of the floor. This is a very small bathroom, 49*39 with a 24*39 space for the toilet. In the space for the toilet it is half an inch lower in the middle then around the edges. It seems to me that cement board is simply going to crack and that's if the screws even hold it down in an area that unlevel. In another spot it peaks then goes right back down creating a perfect spot for the board to crack over. I'd have to level the floor with somthing first, then put down the cement board.

I'm not too concerned about weight. The bathroom is pretty small, and it's an old house with actaul 2*8 beams a little closer than 16in on center.
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Old 11-15-2006, 08:45 AM   #12
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What type of cemend on bathroom floor?


The first thing to do is to see if the saucer in the floor at the toilet area can be repaired from below structuraly. Obviously the toilet over the years has stressed the structural members of the floor and it may continue to do so depending on exactly what the problem is down below.

The next thing is to install the cement board over a fresh bed of thinset as recommended by the manufacturer. Draw it down with fasteners as recommended.

THEN (and only then) is when you would fill the low spots and level the floor with either a portland cement patching compound or a Self Levelling Compound. YOU CAN NOT level the floor by filling the low spots and then install the cement board, it doesn't work like that. Cement board cracking isn't the issue and it's nothing to worry about.

The deck mud system is age-old and proven and it is still the best way to do a tile substrate but not if you are going to shave the specifications of the technique. A proper mudbed will add something like twelve pounds per square foot to your structure and we can all easily see your structure won't take it. It is already wavy from stress and strain and age.

I'll bet you are some kind of an engineer in your day-job, huh? You're beatin' this thing to death.
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Old 11-15-2006, 12:04 PM   #13
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What type of cemend on bathroom floor?


As far as the floor being so off level. This bathroom is right up against a very large chimney. I guess in 1915 it was legal to have a structural chimney because the joists are nailed to a board fixed to the chimney. As the bricks got old the floor started to move. The joists have since been supported by columns, so while the floor isn't getting any better it's not getting any worse either.

The deck mud option is definatly out the window here due largly to how high it would have to be built up around the door to level with the highest part of the floor if built up to a minimum of 1-1/4in. The only way to really do this now would be rip out the new subfloor and re-install it between the beams to get the extra height which I really don't want to do..

On to the cement board. If I use 1/2in CBU and level from the highest point some areas need to be brought up an inch and a quarter. Can cement patch or self leveling compount be installed that thick? As I understand it, it goes plywood, unmodified thinset, CBU screwed to the subfloor, tape over the seams, self leveling compound or portland cement patch. Is this correct or should their be a vapor barrier? Do I have to thinset the seams so long as they're taped and covered with the leveling compound or patch?



As far as my day job, I go to college full time two days a week, and do trim work or automotive work the rest of the week.

Last edited by Tmb9862; 11-15-2006 at 12:11 PM.
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Old 11-15-2006, 02:03 PM   #14
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What type of cemend on bathroom floor?


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On to the cement board. If I use 1/2in CBU and level from the highest point some areas need to be brought up an inch and a quarter. Can cement patch or self leveling compount be installed that thick? As I understand it, it goes plywood, unmodified thinset, CBU screwed to the subfloor, tape over the seams, self leveling compound or portland cement patch. Is this correct or should their be a vapor barrier? Do I have to thinset the seams so long as they're taped and covered with the leveling compound or patch?
Finally we have agreed on a sequence of events. Any portland patch or SLC can be installed as thick as you need but some SLC's require this be done with maximum pours per episode, so read the instructions on the SLC you choose and follow those instructions to the letter.

If you choose not to embed the seam tape in thinset and simply pour SLC over it so be it, probably not a big deal.

I can't imagine why a vapor barrier would be needed at this point or where it could be installed to be effective. If there were a crawl space then a vapor barrier would be needed over the dirt and venting of the crawl space would be reqired.

I think I have been of all the help I can be.
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Old 11-15-2006, 02:46 PM   #15
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What type of cemend on bathroom floor?


Thank you to all who helped me with this, it is greatly appreciated.

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