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-   -   Heavy natural stone wall tile: mastic or thinset? Is drywall adequate? (http://www.diychatroom.com/f15/heavy-natural-stone-wall-tile-mastic-thinset-drywall-adequate-131995/)

Minich 01-30-2012 05:53 PM

Heavy natural stone wall tile: mastic or thinset? Is drywall adequate?
 
Friend wants help putting up a very heavy (about 5 lbs/sheet) natural stone facade over two tall 12" square columns. The stone will be stacked about 7' high. I'm confident the columns are sturdy, 2x4 construction, feel solid when i put pressure on them from various angles and they are drywalled- 5/8". The store the stone was bought from told her: 1) drywall is fine, no cement board required; and 2) use thinset, not mastic. The columns will not be in a wet or damp location (and they are interior). The stone is the thick (maybe 1"), glued-together kind... No mesh on the back, but some natural porosity to the stone. No grout is used with this kind of stacked stone.
My questions:
1) Why thinset? Will it grip tightly enough to this heavy stone facade? The weight will be much greater than the tile I've normally worked with in my own home. Is mastic better suited for this? I've reviewed the message boards, I know there is some definite hostility towards mastic overall ;-) but I'm honestly worried that thinset would be brittle.. Wouldn't mastic provide a tiny bit of flexibility?
2) Is drywall really sufficient for this? The drywall, too, is sturdily attached, but the weight of this stone makes me nervous.
3) How high can I build the stone up before needing to let the [mastic or thinset] dry?
I really appreciate the help.

md2lgyk 01-31-2012 08:43 AM

I'm not a stonemason, just a DIYer, but I've researched this some and here's what I would do:

Wrap the columns with roofing paper (not normally required indoors but you want to protect the drywall from moisture). Then wrap them with expanded metal lath attached with plenty of galvanized nails. Apply a 1/2-inch scratch coat of mortar (Type N or S, not thinset) and let dry 48 hours. To apply the stone, completely butter the back of each one with mortar (about 1/2-inch) and press it in place with sort've a wiggling motion, enough so that some mortar oozes out around the edges. Hold in place for a few seconds. Repeat until done.

Minich 01-31-2012 08:57 AM

That's not what I expected. ;-) So, you create your own cement board in place, kind of.. Neat. Where'd you find this?

md2lgyk 01-31-2012 10:15 AM

Somewhere on the internet. I also talked to the mason who built my chimney, which will eventually be faced with veneer.

If there's a Home Depot near you, ask them for their brochure on manufactured stone veneer. There's a good description in it of how to install the stuff. Process is essentially the same for the real thing.

One thing I never knew was why the mortar you put over the lath is called a "scratch coat." The HD brochure shows a picture of what it means.

Minich 01-31-2012 08:28 PM

Thanks. Now that you've given me some of the terminology I've been able to do better research in the web, myself. It looks like a pain in the ass. :-) I'll let her know it's a weekend "plus some" kind of job! I should have known better than to promise help before I knew everything it would entail!

diyorpay 01-31-2012 10:33 PM

I agree with the lathe and scratch coat but suggest that plywood be used as the backer board, not cement board, not sheet rock. The nails work better too. Mortar mix or make your own with sand and portland cement. No mastic, no thinset.

Minich 01-31-2012 10:57 PM

I see. If using plywood, would I skip the roofing paper? Seems like I would but I'm still learning about this-

diyorpay 02-01-2012 05:51 AM

I would skip roofing paper since it's an indoor location.

md2lgyk 02-01-2012 09:27 AM

Check out www.themoldstore.info/installing_stone.html. It's a DIY guide for installing stone veneer. One thing that's sort've counterintuitive is, you should start at the top, not the bottom.


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