I am planning on laying 16″ square slate tiles in the kitchen. In preparation I laid a new sub-floor using 3/4″ exterior grade ply, which I have glued and screwed every 4″.
Should I use a 1/4″ cement backerboard or lay a 1/4 – 1/2″ mortar bed with the inset plastic mesh? I want to use the option that will give me them most stable floor and that will ensure that I won’t have to re-grout every six months.
I would welcome your feedback.
Replies
There are other equally or more important issues here.
Joist sizing/span/spacing.
Personally, once I am confident with the joist issue, I would glue (yellow carpenters) 1/2" over the 3/4" and screw the heck out of it (2'' x #8) every 6" along the joists, then two rows up the bay with 1 5/8" screws.
Adding cbu's to me at least, only adds weight, not structural integrity. I have had good results in 25yrs. of using the plywood sandwich.
You could also consider a mud job.
I try to steer my clents away from those huge tiles for the reasons of cracking and that the floor must be VERY flat to provide for an easy install.
But what the heck do I know? I'm sure someone or 100 someones will come along with more answers than you are prepared to consider.
Good luck.
Eric
I Love A Hand That Meets My Own,
With A Hold That Causes Some Sensation.
[email protected]
Thank you for the feedback.
I should have mentioned that prior to laying the 3/4" ply I added new bracing bewteen the rafters, I know have support every 12" the diae being to prevent any flexing in the ply.
At the smae time I did level the floor using a laser guide so I'm pretty sure I'm flat to say ±0.050 or so which I figured the final thinset could accomodate.
The idea of using a second layer of ply is a good one, I could bond and screw this to the subfloor and then use a suitable thinset adhesive over this right?
I'm not sure what you mean by bracing.
Go back to my other post an re-read the joist SPAN/SIZE/SPACING.
If your floor joist are of insufficient size, are oer spaced or over spanned then you will have deflection in your floor system that may create problems.
There are tables in the TCA (Tile Council of America) hand book possibly their website.
Last question you had, yes.
That's my answer. Others may have their own opinions.
EricI Love A Hand That Meets My Own,
With A Hold That Causes Some Sensation.
[email protected]
What size are your floor joists and whats the span and spacing?
From memory the spacing is every 16" and they are 2"x10" beams, I have added cross braces every 12" using 2"x4"
...cross braces every 12" using 2"x4"?
Are you saying every joist bay has the cross bracing running between them and down each joist bay at 12" increments?
Sounds a bit on the overkill side of things but bet she don't bounce when you walk on 'er.
By the way Weedo, as a first time poster Welcome to Breaktime.
SanchoRon the caballero bowed low as he waved his sombrero and said goodbye.
FREE SANCHO!!!
Edited 3/2/2005 7:13 pm ET by the razzman
cross bracing will do nothing for span flex. TCA allows for no more than 1/360th of an inch flexaural deflection and that is not much!
Actually Craig, it's L/360 but with a lower case L which looks like a 1 sometimes. And for stone tiles, especially the larger ones, L/360 is inadequate. It needs to be up around L/720.
Weedo ... so you have 2x10's sppaced at 16" ... do you know how far apart tyhe supporting walls are? That's the span, and that's an important nuumber.
I'm sorry, I thought you wanted it done the right way.
wadda ya mean by "inset plastic mesh"?
the new Mapei stuff?
because for a full mudbed ... 1/4 to 1/2 inch is way too thin.
after all the structural ducks are in a row ... I'd suggest looking at Ditra as the underlay ... it'll uncouple at the same time ... which is nice for big stones.
Jeff
Buck Construction
Artistry in Carpentry
Pgh, PA