# do i need to use a scratch coat and wire mesh on cement board(floor)



## JazMan (Feb 17, 2007)

Steve,

Tumbled marble for a bathroom floor eh? OK :no: it's your home.

Irrespective of the possible maintenance problems you're likely to have, stone tiles require a much stiffer subfloor system than ceramic or porcelain tile need. It sounds to me that your floor is likely to not meet those minimums. 

Your joists are probably too bouncy for stone. You probably only have one layer of subfloor. It's possible what you think is the subfloor is actually a layer of 1/4" ply or ? that should have also been removed. 

Will you check and measure; the type and size of the joists, their species and grade, spacing, unsupported span. All this is done from under the floor. Also verify the type of subfloor sheet, thickness and if it's only one layer.

To your original q about scratch coat, NO, that systems is junk. Once the floor meets specs, you tile on the backer board.

Jaz


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## Limit54 (Nov 6, 2009)

ok it might not matter to much but my house was built in the 1950's.
My joists are 2x8's and spaced 16" from the center. The main support joits are about 5 2x8's(maybe a little thicker) bolted together. The type of wood i don't know?? the wood that was on the floor before I put on the cement board was not plywood. I don't know what it was but it had a grid pattern on it like this:

+ + + + + 
+ + + + +
+ + + + +
+ + + + +

This was printed on the full floor/wood
I'm not sure if there was plywood under this? The only thing I know is that my hardwood floors that are in my hallway are flush with this wood subfloor.

Anyway, No matter what I have to use this tile and my cement board is down. I'll have to do the best i can. Before I put down teh cement baord I fired a ****load of drywall screws into the so called subfloor. Then I put some leveling compound and then the cement board. After this I used galvanized screws and used meshtape and joint compound on the cementbaord. this might not be enough but at the time I figured it was ok.


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## JazMan (Feb 17, 2007)

Well, you provided answers to 2 of the 6 questions I asked.:whistling2: As I suspected what you describe with those +'s is not your subfloor. It's probably 1/4" underlayment which was installed for the old vinyl tiles you removed. 

I still don't know, if this + + + underlayment is still in place since you said "was" and not "is". I also don't know if the subfloor is plywood or something else, and how thick. I also don't know the unsupported span of the 2x8 joists. 

Chances are 95% that your joists system does NOT meet any standards for stone tile. And if your subfloor is only one sheet of say 3/4" ply, I can tell you that I am 100% sure that also falls way short of standards for stone tiles. And if you did not set your cement board into fresh thin set mortar, that too is fatal. 

A few other things were done wrong, like you said you mesh taped the cement board and used "joint compound", do you mean drywall joint compound or something else? Well....no matter, if there is no thin set under the board you have cracks soon enough anyway. 

I recommend you spend a few hours to remove the board, install more plywood and possibly sister those joists, so this project will last a long time.:thumbsup:

Jaz


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## Limit54 (Nov 6, 2009)

ok so I dug into a little of this wood. I found that this top sheet is 1/4" and then there is 1/2" plywood under that. I did leave that ++++ board on the floor. I also used mortar under the cement board. When I said I used mesh tape and joint compound I ment galvanized mesh tape and joint compound for cement board(looks like thinset but is freaking rock hard when it dries).

Also thanks for the help Jaz. I really appreciate it.


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## JazMan (Feb 17, 2007)

Not good.

Please check the thickness of your ply subfloor again. Measure carefully and/or the bottom may be marked with type and thickness. If it's 1/2", you've got big problems. The minimum subfloor thickness for 16" o.c. is 5/8" t&g in perfect condition. To me, 5/8" is way too flimsy and I would never guarantee any tile over that. Remember the CBU you installed adds almost no structural strength. Plus again, you have stone, not ceramic.

A bit of building history. Years ago, until the mid 70's here, floors were built with 1/2" over the joists, then a good quality 5/8" over that as the layer sheet vinyl was installed over. That required the flooring people to do an undetermined amount of prep to get the ply smooth enough. This obviously caused many problems in pricing and since rough carpenters are called that by the kind of work some of them do, the method was changed. Since the mid '70's it has been common to use a single sheet of subfloor, usually it was plywood and 3/4" t&g. As time went on, some "cheap-ass" builders started using 5/8" subs and others went to 19.2" and 24" o.c. systems. Anything to save a few hundred $$$ while still meeting minimum code. I don't think it's very smart to strive to meet minimum standards.

If your sub is 1/2", it's possible someone removed the top layer of ply at some time in the past. Half inch with 1/4" may be ok with vinyl, but that floor must feel kinda bouncy eh?


I guess it's too late to do it by the book now? Maybe you've already installed the tumbled marble tiles. 

What is this galvanized mesh seam tape, never seen it. Use thin set mortar, which is Portland based, many patching compounds are gypsum based and Portland and gyp do not like each other.

Jaz


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## MI-Roger (Aug 8, 2009)

*Can you see the bottom side of the floor?*

You said your house was built in the 1950's. You said you have hardwood floors that are flush with the underlayment. You said you have 1/2-inch ply beneath the underlayment.

Homes in the 1950's were still commonly built with 1x8 pine boards laid diagonally atop the floor joists with 1/4-inch gaps between the boards. Hardwood flors in the 1950's were commonly 3/4 inch thick. A layer of 1/2-inch ply covered with 1/4-inch underlayment will equal the thickness of a 3/4-inch hardwood floor.

You may have a floor comprised of 1x8 pine covered with 1/2-inch ply and 1/4-inch underlayment. I will let the floor pros determine if the 1x8's and 1/2-inch ply is strong enough to support the cement board and finsh tiles. The tile underlayment should have been removed prior to installing the cement board.

What color are the floor joists? Are they sort of a deep reddish brown? My parent's home was bult in the 1950's and had reddish-brown supporting joists which my dad called Red Fir. Red Fir is another name for Douglas Fir, one of the strongest woods used in rough construction and no longer available at affordable prices.


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## Limit54 (Nov 6, 2009)

yep they are reddish brown. Also when I did my kitchen we removed 3 layers of vinyl tiles and went right to the the diagonally laid wood on the floor. So I'm sure this is the one you are talking about. I've been thinking about ripping out the cement board and the ply. I'm not sure what i should do yet? I'll let you guys tell me whats best.


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## Limit54 (Nov 6, 2009)

so I'm going to do the floor properly. Can you give me some guidance as to what I should do step by step?

Thanks guys.


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## JazMan (Feb 17, 2007)

What's best is if you could accurately tell us how your floor is built. You haven't done very well yet.:whistling2:

You first said you removed the old flooring down to the subfloor. This "subfloor" ended up being 1/4" underlayment. Then you said you uncovered 1/2" plywood. So now I think this 1/2" is the subfloor. Now we find you have 1 x diagonal boards on the joists. This is the subfloor. 

Please verify if the above is correct.

Jaz


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## Limit54 (Nov 6, 2009)

ok JazMan I'll do my best to tell you what I can. I haven't ripped out the floor yet so I'll have to wait. What I do know for sure is that I have a section near the toilet flange that sweeks(the floor) so my guess is that no matter what i need to get down there and fix this. One thing that is for sure is that the floor is solid as hell. No movement at all just one small section. I know one section is not good. So I'm gonna rip it all out. I'll let you know what I find. I'm just hoping that I'm not going lay down the same stuff that is already there and do all of this in vein. 

Thanks I'll let you know.


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