Bathroom floor prep

I am about to tile my 5x8 bathroom floor. I am using Hardibacker board. Right now, I have a plywood floor that I am going to thinset and screw the hardibacker to. I laid a 4' level across the floor. In the middle of the floor (horizontally), if I press the level down on the right side of the 5' wide floor), the left side is up at least 1/4" and almost 1/2" at one point. While I have no real problem if the floor is slightly off level on the whole, I do not like this small buldge that seems to be in the middle of the floor. I tool a smaller 1' level and laid it all over the floor and it slightly rocks back and forth. If the level does this, the tile will do this too.
Will the thinset under the hardibacker board level this out? What is the best way to level this floor?
Tony
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Screed it all the way across with some dryly mixed mud bedding and a long sturdy aluminum straight edge (a piece of aluminum angle stock or something cut to room width). So that the mud brings the low spots up to the bulge peak (peak itself does not need to be buried). If you can screed the full width of the room at one pass it will be perfect. Let that dry. Now thinset the floor tile as you normally would. You may need to screed both directions the 5 foot and the 8 foot depending on how the peaks run, toilet flange in the way, etc.
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Thanks for the reply Rick. I am a tad confused. I had 18" tiles I was going to lay down diagonally until I talked to my friend yesterday, who is a builder. He told me that there is no way I can use 18" tiles over hardibacker boad and that I neeed to mud the floor. Most guys around here charge about $350 to mud the floor, plus it may not be until a few days that they can do it. I need this done NOW. So, I returned all of the 18" tile and bought 12" tile and was going to start today. Then, I checked the floor and notice a tiny slight buldge in the middle.
So, is what you described above considered "mudding" the floor? Is mud the same as the thinset that hardibacker recommends we use between the subfloor and the board? I have dur-a-flex thinset.
Tony
I wasnt going to "mud" the bathroom because most guys
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The store should know what you need, it's called mortar mix, basically a sand mix, trick is not to mix it too wet when using it to screed level. It's sold mostly for brick laying but I've used it to make a mortar bed and do leveling just like you described. Your thinset is basically portland without sand and is NOT made for leveling a floor, just sticking tile. Just dont mix the mortar too wet, a handful should stick into a ball but not be a real sloppy kind of wet almost just damp (with no dry powder pockets of course). The 12 inch tiles should do fine, he was right about the 18 inch you could easily crack a tile like that over just plywood. Good idea to transport any tiles on edge too not laying flat until you are installing them, and never step on any tile till its setting is under it.
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So, if I do the morter mix as you suggested, can I use 18" tile safely over it? I was never going to put it on the plywood. I was going to put it on top of the hardibacker board until my friend said it still wouldnt be sturdy enough to hold it without the tile cracking eventually.
I am confused about the screed process you mentioned. How do I know if the screed is level. In other words, what is to stop me from holding it on a slant, preventing me from getting a true level surface? What if I holding it higher on one end than the other as I screed it from one end to the other?
Also, is this what everyone refers to as Mudding?
Tony
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wrote:

there's level, and then there's flat. you only need flat to tile on, it doesn't have to be level, although it's nice if it is.
you prevent unlevel-ness by attaching boards to both sides of the room and having a long enough straight edge that it spans the width and rides on the boards.
it's nbd if it's a little off level. it is a bd if it is off being flat.

no. mudding is laying down a thick bed of mortar and using that as a base instead of plywood and hardibacker.

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I am not concerned about the floor being completely level. It is not flat, so I guess it is a big deal. If I lay a level across the floor, there is anywhere from 1/4 - 1/2" difference. If I lay a tile down, it rocks back and forth. Is there a way to do this with hardibacker board or is mud my only and easiest answer?
Tony
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you cannot flatten a floor with hardibacker, as it is flexible and will conform to the floor that already exists when you lay it down. you need a product that is non-flexible or will conform to the floor unevenness on one side, but will remain flat on the other side. the ways to do that are to either rip up the entire floor down to the joists and build it up again shimming the floor to make it flat, or put a moldable material on top to make it flat. THAT is what we've been trying to tell you.
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I wasnt asking if I can flatten the floor with hardibacker. I was asking if there was a way to put something under the hardibacker board (like thinset) that would make a flat surface under it. So, I have a choice of mud or rip up the floor and put another down. I am assuming that the higher part of the floor is where the joist is. Couldnt I take that one piece of plywood out and plane it down a bit. The rise is only in one section of the floor that seems to be where the joist is. Please excuse my ignorance about this. I am a computer consultant, not a builder. I have learned a lot since buying this house 3 years ago and this is an area I have never dabbled in.
Tony
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i am a computer consultant too, for about 40 years, however, i know where my library card is and am not afraid to use it. you may find that reading a book on tiling may help you better than continually asking the same question over and over.
no, you cannot plane down plywood. no, you do not need mud. there are, or should be, multiple joists under your floor. yes, you have to level the floor. yes, you have to use a cement type of product to do so. yes, there is a product you can put under the hardibacker to make it level. that is the cement type of product that we all have referred to. no, it is not mud. a mud floor would typically be approximately 1.5" of cement, screed out to be both flat and level. you only need a very thin layer of screed material, only enough to fill in the low spots. you would then put the hardibacker on top of that hardened material.
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On Thu, 9 Aug 2007 14:53:11 -0700, "charlie"

Charlie,
I have a library card and I took out a book just last week (Home Depot tile book). It doesnt mean I understood everything I read. I also get tons of contradicting answers from everyone I ask. That is why I ask here. And you misunderstood what I said. I never suggested that one could plane plywood. I asked if I can plane the joist (whatever it is made of, 2x4?). That is what I asked. I already have the jardibacker in my house and I really do not want to use cement board on the floor, so I dont think I will go that way. I will probably go for the mud. Does it have to be 1.5" thick? Can it b 1"? I ask because I do not want the bathroom floor to be higher than the hallway.
Tony
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Tony wrote:

Let me offer a *possible* methodology. Others will comment on its possible efficacy, I am sure... ________________
All you really need is to get more thinset under the side edges of the cement board so as to get the board level edge<>center<>edge. Your room is 5'X8'. Cut your cement board into three approximately egual pieces each 5' by whatever (cut them a bit less than 5' too...1/2" - 1" less). They need to be sufficiently narrow so that you can reach from one long edge to another without having to lean on the board when it is on the floor.
Now generously slop out thinset in an area to accomodate one piece of cement board. Mix the thinset a bit on the runny side - use enough water so that peaks collapse slowly. Slop out additional along the low edges. The goal is to have more than enough and for it to be runny enough to flow a bit under moderate pressure.
Now stand one piece of board on edge and let it fall onto the thinset. Before dropping it, assure that the edge is resting on the floor so the cement board will fall where you want it. For example, if there is a tub at the end of the room butt the edge against it. If all goes well, the excess thinset at the sides should ooze out. Assure that the cement board is flat and level by using a board & level across it, pressing down on the leveling board as necessary.
Clean up excess thinset and repeat the above for the other pieces of cement board. On those, be sure to also check for flat and level relative to already laid pieces.
Let it sit for a while before walking on it - 24 hours absolute minimum, a week is better. ________________
All the above does is use the thinset to level the plywood relative to the cement board. Net effect should be the same as screeing a layer of material onto the floor and then laying the cement board on that.
I see no need for mechanical fasteners...it can't move laterally as the gaps at the wall should be filled with mortar. It can't rock as you have removed the height differential. It isn't going to lift up as it is heavy and will be heavier still after you lay the tile.
AFAIK, there is no reason you couldn't lay your tile - even the 18" - in the same way; i.e., no cement board, leveling tiles one to another with extra thinset.
--

dadiOH
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In lieu of a mud bed some will screed it flat, let dry (as discussed) AND thinset with wide notched trowel DuRock backer board rough side down (which is just a 1/2 inch cement board), let dry. Tile it.
I think Hardiboard is a fiber/cement product and IMO probably not good for 18 inch tile backer on floor, I dont know.
Assuming you have no flex at all in the plywood, especially that high spot, the DuRock over thinset job might be good enough. But you are taking chances any time 18 inch is going over something other than a concrete slab or mud base.
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Tony wrote:

Step #1 would be to bounce up and down on the plywood and see if it flexes in the middle. If it does, fasten it down better.
--

dadiOH
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wrote:

We had our bathroom floor retiled last year. Though we're pretty handy around the house -- for example, we did 90% of our kitchen renovation -- we hired someone to do it.
We realized quickly that if we did it, it would cost more to fix our mistakes than to simply pay someone to do it right the first time.
Tile isn't easy to fix, especially if there are already some problems with the floor.
--Nan
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I want to thank everyone for their suggestions. In the end, I spoke to my friend (a builder) and he gave me the phone number of a tile guy he swears by. For $2000, he will mud and tile the entire bathroom, not matter what patterns or sized tile I want to use. He said he takes so much pride in his work that he will not tile over walls that arent plumb and will make them if needed. He also bevels tile instead of using bullnose, etc. So, even though I could use the money, I think that it will be wisely spent by getting a professional. I know if I do it myself, I am going to run into problems like the walls not being plumb and all that. This will add a few years of life .
Thanks again, I have saved all of these posts in case I ever decide to re-do my smaller bathroom in the basement (sink, toilet shower - no bathtub).
Tony
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Tony wrote:

What a bargain...only <gasp> $50 per square foot.
--

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From what I understand, here on Long Island, that is a bargain. I had another guy here who said he would charge $2400 and he flat out told me that if the wall isnt plumb, it isnt going to look any better after he installs the tile. This new guy will make the walls perfect before he tiles.
Aside from that, there wasnt anyone that would mud my 5x8 floor for less than $300. So, since that is included, the tile job is only $1700 to me. My wife's cousin is a tile installer and does great work and when I was originally only going to tile the floor (40 sq/ft) and the shower area (50sq/ft), his great family discount price was $1400 and that did not include the mud floor. So, this new guy is charging $300 more to tile another 180 sq/ft than my wife's cousin.
Labor rates vary by geographical location. My buddy has houses in Delaware and they charge less than half to do anything over there. So, you are probably in one of those areas where it doesnt cost much to live. I just bought a small ranch (1000 sq/ft witha full finished basement, but you dont count the 1000 sq/ft down there because it's a basement) and I paid $350,000. That was a major bargan. I couldnt find a crappy fixer upper for less than $450,000 30 miles closer to NYC where I was originally brought up. Prices are all relative. $50 sq/ft is a good deal by me and, the guy is great. he wont do the shoddy work like the guy who came here a few months back (from the major tile store) and I banned them from ever coming back in my house again. You get what you pay for.
Tony
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