Replies

1. 
   John_Arteaga | Apr 25, 1999 11:54am | #1

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   Folks, I'm about to do a 17'by25' wire and mortar float over an OSB subfloor. It should be fairly thick (3/4-1") and it's going to be set with green slate 6by6s. I don't think that dare do this without some kind of crack control joints, which should line up with grout joints. One way I thought might work would be to double up the 1" chicken wire except whee I want to have cracks form, where there would be just 1 layer of wire.Anybody out there have any other ideas? Thanks, John

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   Guest_ | Apr 25, 1999 06:43pm | #2

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   Hi John,

   As an alternative to consider, why not save yourself a little money and simply install a 3/4" plywood over the OSB, that will stiffen it enough for your slate and with modern polymar grouts and thinset you should be fine without the control joints.

   Gabe

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   Guest_ | Apr 25, 1999 07:11pm | #3

   *1" mortar float is best, You do mean tile lath by (Chicken wire), much thicker. The tiles will bond much better to the mortar than plywood regardless of additives. You will likely find it is cheaper to go this method also...3/4" ply aint cheap. You may also wish to check the spans to make sure the joists are not undersized, if so west system epoxy and screws every 12" and another 2x2 underneath should do it.

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   Guest_ | Apr 25, 1999 07:12pm | #4

   *I would use cement board. 1) screw down subfloor. 2)use thin set to laminate cement board to subfloor (Also screw this down) 3)they make a special fiber glass tape for this, use thin set to tape the joints like you would drywall.4) tile with thin set. Hard as rock, no cracks in several floors for over 5 years.

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   Guest_ | Apr 25, 1999 08:04pm | #5

   *Hi Lawrence,Just a note, when I threw in an alternative and indicated that it would be probably less expensive, I was taking into account all aspects. Labour and material. Your material costs are less, maybe, but your labour is much higher, for sure.With 3/4" ply, the entire project, with the exception of the grouting, can be done in one day and easily by a DIY.With regards to the tiles bonding better to mortar than plywood, you must not have had to remove any tiles off plywood before, it sticks very well, you have to smash the tiles into pieces to remove them and then sand down the thinset afterwards.Also with the 3/4" plywood the weight on the floor is less.Gabe

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   Guest_ | Apr 26, 1999 07:56am | #6

   *I'm not sure about green slate, but green marble requires epoxy thinset. I'd check it out if I were you.

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   John_Arteaga | Apr 26, 1999 10:40am | #7

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   Thanks for the responses so far, but firstly, I NEVER adhere tile to plywood. It seems to me that they are incompatible materials; the tile has no expansion/contraction and the plywood does. I believe that it is only a matter of time before tiles break underfoot or loosen, though I'm sure that the price of 3/4 ply is less than the labor to make a proper float. It is the integrity of the float, due to the wire in it that makes floated tile jobs last virtually forever. As for my joist sizing, they are well under alowable span. I have been planning to put a rather heavy floor down and have taken care to frame the floor accordingly. I hope that there's SOMEONE out there in our vast virtual community who has experience with the problem of allowing for expansion and contraction of the wooden structure under a large float.

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   Guest_ | Apr 26, 1999 02:38pm | #8

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   This won't be much help because I never paid much attention to them when I saw them going in, but it seems to me that there are rubber mats/barriers you can install betweeen a wood subfloor and tile or mortar bed. It is suppose to be for the expansion thing. I was always a little suspicious of these and my method seems to be fine for me. Maybe you could check at a real tile supply house. (NOT the Depot)

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   Guest_ | Apr 26, 1999 08:40pm | #9

   *Morning John,A quick check this morning with my supliers and any good quality product like Proflex Polymar Modified thinset will most certainly adhere slate to plywood.The area you indicated does not require control joints over plywood or any solid surface if indoors.All recommend glue and screws for the plywood and all indicate that it is the easier and cheaper method for your project.It was only a suggestion as an alternative to your proposed method of installation.Still hope I was of some help,Gabe.

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   G.LaLonde | Apr 26, 1999 08:57pm | #10

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   Gabe, I agree with you about the plywood. I have heard this subject of tile floor underlayment debated on and on and it basically comes down to what you are used to doing and are successful with. Performance is the bottom line. I think the mortar bed process is a regional thing. Around here everyone uses plywood or cement board. The big advantage to plywood is that it is easy to work with and when glued and screwed to the other subfloor, adds a tremendous amount of strength to the floor system. A 1 1/4" or 1 1/2" plywood floor is like walking on a concrete slab.

   I have installed over 50,000 sq. ft. of all kinds of tile over laminated ply and have Never-Ever had a problem with a tile coming loose. On the contrary, when I've had to go in and remove some of it for remodeling work, it is impossible to break the bond between the thinset and the plywood. The outer layer of plywood will rip off first.

   I think any problem with poor performance is a direct result of either using the wrong kind of thinset or not applying it properly. You have to really lean on the flat side of the trowel and apply a thin bonding coat and then use the notches to apply the working coat.

   In the end everyone will use the technique they feel comfortable with, and we shouldn't just dismiss certain methods just because we don't do it that way. It's like everything else, there's usually many ways to do the same job!

6. 
   John_Arteaga | Apr 26, 1999 08:57pm | #11

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   dealing with crack control in large mortar floats over plywood subfloor