Replies

1. 
   Billy | Oct 25, 2006 07:47pm | #1

   Normally I would say to put Ditra underneath for freeze/thaw protection, but it's probably unnecessary where you are in Calfornia.

   Why not use a medium bed thinset mortar that can go up to 3/4" thick?  Here's one from Laticrete.  Better yet, call your local Laticrete rep and discuss the best product for your application.  Make sure the substrate and the slate are clean, etc.

   http://www.laticrete.com/sellSheets/A1198255.pdf
   http://www.laticrete.com/prodsheets/datashts/LDS2550.pdf

   Billy

1. 
   stombler | Oct 26, 2006 10:00am | #2

   thanks for the suggestion.  we set a few stones one day with some extra mortar from bricklaying, but they "popped" easily two days later.  clearly the smooth surface of the slate leads to minimal adhesion.  i will contact the links you provided.   spoke to my local brick/stone supplier about the issue.  they told me that there are numerous masons who do mix thinsets with mortar and claim success, but their recommendation is replacing water in the mortar mix with latex bonding agents.

   my experience with repairs down the road is that they aren't worth it at any price!  i think we will segregate stone by thickness, use thinset alone where possible and float a higher bed of mortar where necessary then use thinset for the other stones.

    

    thanks,

    

   steve

1. 
   Billy | Oct 26, 2006 05:06pm | #3

   The other thing you can do that is fairly common is to level the slate in the mudbed, pull it out, and back-butter it with thinset before laying it in for good.  This saves on material costs but it will save on labor.  Note that you should back-butter the slate even when using medium bed thinset.

   Billy

1. 
   stombler | Oct 27, 2006 07:07am | #4

   clever idea.  is the bed mortar and the back butter thinset?  the mortar bed  would have the consistency to resist settling at those thicknesses .   would the wet thinset backbutter to wet mortar bond be strong ?

1. 
   Billy | Oct 27, 2006 04:44pm | #5

   You asked:

   is the bed mortar and the back butter thinset?  

   >>>>>Yes.  By mortar I mean a dry-pack mortar or "mud bed."

   would the wet thinset backbutter to wet mortar bond be strong ?

   >>>>>Yes, very strong. 

   Billy

2. 
   DoRight | Oct 27, 2006 07:39pm | #6

   What is Ditra?

1. 
   Billy | Oct 27, 2006 07:46pm | #7

   Ditra is a de-coupling membrane for use between a substrate and tile or stone surfaces.  Outdoors it can help with freeze-thaw issues.  Here's the website:

   http://www.schluter.com/english/products/2002/sectionf/ditra/601-index.html

   I suggest that you search on this site for "Ditra" and you'll find a lot of discussion.

   Billy

    

2. 
   Piffin | Oct 27, 2006 11:42pm | #8

   Is this exterior?

    

    

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1. 
   stombler | Oct 28, 2006 11:25am | #9

   yes, exterior stonework inlaid in a front walkway.  we are underway and are using latex fortified thinset called flexbond.  in those places where bed was too deep we brought the level up with mortar then when dry set the stone on thinset.    

1. 
   Piffin | Oct 28, 2006 04:20pm | #10

   Around here, we would not use less tan 1-1/2" slate for exterior pathways and most masons are leary of that without great adhesion and sealing against water penetration at the grout lines. We have frost here though that is harder on such things. The oils in slate make it hard to get a good bond in the first place. But I see now thaat you are in California, so this frost issue is probably not pertinent for you 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

1. 
   stombler | Oct 28, 2006 08:07pm | #11

   i grew up in the east and i know you're right about the frost.  here the problem is flexing of the bond by soil lifting and settling as we have very expansive clay soils.  i'm not worried about that as we construct super footings and my foreman usually fortifies them to withstand 8.0 earthquakes!   

   the stone is very slick, but maybe the problem i will eventually see is seperation along a cleavage line within the slate itself... something the bond between bottom of stone and bed wouldn't address anyway.