I am doing a 350 sq. ft. ceramic tile floor...after reading many posts in this forum, I have found out that the people I received my info from to do my first tile floor job a year ago were no experts (HDepot folks said to add a layer of 1/4" thk. ply then teh lath & scratch coat, then thin-set, tile & grout)...although it is still holding up well, I guess i got luckey!!

my qusestion is this: I have read in the forum that 2"x10" joist @ 16" o.c (approx 10' span) with 5/8" thk. subfloor is a solid enough floor system & need not add extra layers of ply to stiffen. I can use modified thin-set mortar directly on ply, followed by a layer of "Ditra", followd by unmodified thin-set, then the tile then grout? Is there a cheaper alternative to teh "ditra" or any other sugestions?
Thank you for any help.
Brad H

H Brad,

Your joists size and span are more than adequate for tiles. The joists deflection rating is over L800, you need L360 for tile and L720 for natural stone. If your 5/8 subfloor is ext. grade t&g plywood (exposure 1), it is also technically ok. I say that because it is the very minimum if every thing was done right. I would not consider 5/8 plywood as a good subfloor. Too much deflection in this system between the joists. I recommend an additional layer of min. 3/8. Then Ditra or cement backer board over that.

In researching whether 5/8 plywood is good enough, you will read that most CBU manufacturers say that it is. However they always add those disclaimers which many people do not pay attention to. Their approval is always followed by something like this: ...and subfloor to also meets L360 when measured using a 300 lb.load. Again this is where your 5/8" plywood is likely to fail.

A cheaper alternative to Ditra would be almost anything else...cement backer board I mean. Depending on where you are and if anyone stocks Ditra, you could save 40-70 cents per sq. ft.? But Ditra is better, thinner and much easier to install.

Jaz

Just curious why you are slamming Home Depot associates who gave you sound advice that obviously worked..

1/4" ply with lath and a scratch coat is not sound advise!

Thanks for the sound advice Jaz, & your support Randall...I am putting this forum in "my favorites"...I know i will be back for more very soon!!
ps: I am in Brampton, can i find "Ditra" in the area?
Brad H

Home Depot must carry it. Look at the end of the isle with tiling supplies (e.g. OCB, thinsets, etc.) It's sold in rolls 5mX1m or 10mX1m ($130 and $270 respectively-- about CAD2.50 per sq.foot).

It Worked!!

its only been a year TIMSTER

Timmer,

Please try to understand to concept of receiving approval of an installation method by professionals or trade associations.

The method has to be proven to work as designed as close to 100% as possible. Even approved method have a small failure rate, usually due to not following every step as written.

The 'scratch-coat' 'jersey-mud' or what ever you wanna call it, has proven that it cannot pass any long term test. Sure...it might work at least 50% of the time, maybe even 75%? Not good enough. I have found that even when the homeowner thinks that it has held up fine, when inspected closely, I could find areas that are loose and with hairline cracks in the grout.

This method should be avoided.

Jaz

I agree with Jaz.Here,in the Toronto area probably 90% of tile installations over wood floor construction are set over the "scratchcoat" system.A lot of misguided contractors...since this method has been the standard here for over 2 decades.It's used because it's easy and cheap...and I suppose it "seems" the thing to do because it's a cement based material with metal reinforcement.Although really there is no reinforcement of anything with that system.

Most of my work is renovation and usually when preparing a floor I have to remove the old tile installation.Usually it is tile over "scratchcoat" and most of them show signs of failure.Not always,but it's just not a good way to do it especially with what we have available to us now in this industry.