12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?

 
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Old 09-03-2016, 02:00 PM   #1
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12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


Im just in the process of installing a natural Stone Veneer on our house and I have a few concerns about the objective hazards of rock fall.

Here is some specs.



1. Fastened metal lathe to ICF with stainless steal screws 6-8" on center both vertically and horizontally. Large overlap with metal lathing. The top 14" is cedar 3x14" with 2 layers of tar paper.

2. Put scratch coat over the lathe using type N mortar. Aimed for about 1/2 thick but total thickness on average including the Lathe is about 3/8"- 1/2". Scratched with scarifier and have been spraying water on the scratch coat for the last couple days its cool and damp out side.

3. Rocks vary in size the largest are about 6 ft x4 ft and 1-2" thick. The shale is fairly smooth and one could say "greasy". I plan to back butter them with Type N mortar and possibly drill through the scratch coat into the ICF a try to put in some brick ties.

What I'm worried about is what are the chances of a rock coming off the wall. The area below is relatively high traffic.

I know with tile and such the backs are pretty rough. Im curious if it would be a waste of my time to "scarify" the backs of the rock with heavy grit sand paper or a tile saw ect///

Any insight or advice much appreciated. I will get more photos of the rock and wall.
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Old 09-03-2016, 06:04 PM   #2
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


I would not use Type N. I would use a polymer modified Type S, and make sure the back of the stone is free of dust or dirt. The polymer should alleviate most of the bond issue with a slick back. If I was doing it for someone, I would use the appropriate Laticrete thinset product.

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Old 09-03-2016, 07:02 PM   #3
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


I wouldn't worry too much about it as well following the advice above, i would also make sure the scratch coat is damp when installing the stone to keep the mortar from drying out... I usually keep the mortar a little on the wet side so when you put the stone on you can you can shimmy it on and you can feel the mortar squeezing behind the stone and creating a suction til its dry.

I have had to remove/demo stone that was installed this way and cannot believe how strong the bond is. I would never think twice about it falling off
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Old 09-03-2016, 07:10 PM   #4
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


Thanks for the replys guys reassuring and makes sense to use a polymer additive.

I went with type N mortar because the stone I have is soft and I was thinking that the Type S would be hard on the stone. That being said the only reason I did the scratch coat in Type N was to keep it all the same. Looking back it might have been better to do the scratch in type S as long as the bond between different mortars remains the same.

Is there any reason to not do the scratch coat in type N butter the backs of the stone in type S with a polymer and then do the joints in type N? I know some people say to do it all the same but never understood the reason behind it.

Here is some pics of the rock and wall,



Not sure why the photo came out so weird but the actual lines are horizontal.

Last edited by RedBaronww1; 09-03-2016 at 07:20 PM.
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Old 09-03-2016, 07:16 PM   #5
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


Quote:
Originally Posted by RedBaronww1 View Post
Thanks for the replys guys reassuring and makes sense to use a polymer additive.

I went with type N mortar because the stone I have is soft and I was thinking that the Type S would be hard on the stone. That being said the only reason I did the scratch coat in Type N was to keep it all the same. Looking back it might have been better to do the scratch in type S as long as the bond between different mortars remains the same.

Is there any reason to not do the scratch coat in type N butter the backs of the stone in type S with a polymer and then do the joints in type N?

Here is some pics of the rock and wall,

I always use type n
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Old 09-03-2016, 07:20 PM   #6
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


I'm with Tscar ,Laticrete is the way to go !
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Old 09-03-2016, 10:25 PM   #7
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


Skip type n. Its designed to keep bricks apart. Laticrtete, thin stone mud, even bonding agent on the stones and possibly a modified type S. Shim the stones and point up later.
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Old 09-03-2016, 10:29 PM   #8
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


The window detail looks concerning from a quick picture.
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Old 09-03-2016, 11:28 PM   #9
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


I will look into Laticrete.

So its ok for me to use type S with additives after I have put up the scratch coat with type N? No bonding issues?

JMB The window detail isnt finished still need to cut flush some of the metal lathe and install flashing and trim. Only have typar on there right now that didnt bond to well. Its ok for now the roof overhang is 10ft so it doesnt see much water unless the wind is really hammering.

Last edited by RedBaronww1; 09-03-2016 at 11:32 PM.
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Old 09-04-2016, 11:08 AM   #10
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


Quote:
Originally Posted by RedBaronww1 View Post

JMB The window detail isnt finished still need to cut flush some of the metal lathe and install flashing and trim. Only have typar on there right now that didnt bond to well. Its ok for now the roof overhang is 10ft so it doesnt see much water unless the wind is really hammering.
How is it flashed on top of the veneer?
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Old 09-04-2016, 12:26 PM   #11
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


Taped 10 mil poly on the inside of the EPS foam before concrete was poured that will be taped to the window then trim around it. I know most people typar to the outside but from what i understand EPS foam is permeable to moisture. We have resito moisture barrier up around the outside of the eps on everything below grade.
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Old 09-04-2016, 03:18 PM   #12
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


Talked to a friend and he recommended using weld bond in the mortar. Any one tried it?
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Old 09-04-2016, 04:19 PM   #13
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


You can use S over N or vice-versa. There is absolutely no reason why you can't. When laying brick/block/stone, you want the mortar to be softer than the material being laid.

When you are using the mortar as a backing (scratchcoat) or adhesive (sticking the stones), you want as strong a material as possible.

Some Laticrete thinsets achieve over 10,000 PSI, AND have a high flexural strength, which is one of the things the polymer additive increases. Weld Bond is a polymer additive.
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Old 09-04-2016, 06:16 PM   #14
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


Just an afterthought,I would have liked to see the second floor timbers project beyond the veneer finish. The principle is like the lap pf roof shingles. I suppose you can rig something up,but the ship already sailed IMHO.
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Old 09-04-2016, 08:04 PM   #15
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


At FJN: a metal "zee" flashing above the stone thin veneer to deflect any rain water runoff...

The compression strength of the various materials is rather meaningless in this application, IT is THE tensile BOND between the scratch coat and the units... The bond is mostly created by the cement paste, and some additives flowing into the two materials pores being conjoined.... Don't pre wet either the scratch coat or the stones, too maximize the "suck" of the dry wall and stone... Use as 'wet' mortar as possible to maximize the bond/capillary action.

Clean and DRY, especially any cuts.

During warm and dry summertime, I never had any issues sticking stones on day old scratch coats, 2-3 days in colder weather. Keeping the wall damp/moist for a week to a month after installation of the stone of course would increase the structural strength some what...

If you are nervous, build a mock up using the various suggested methods and materials, and perform a "pull' test with some epoxy "nails" glue to the stone pieces, fish scales of the correct size and a come- a -long winch...

I have questions about foam holding the weight of the entire panel of stone... with out enough fasteners that actually penetrate into the concrete portion of the foundation instead of the ICF bead board. Maybe a 1/4"diameter tapcon every sq. ft or more? between the scratch coat and concrete.

Last edited by Fouthgeneration; 09-04-2016 at 08:07 PM.
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Old 09-04-2016, 08:21 PM   #16
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


Fourthgen,I agree but it is one more thing too add,flash and counter flash. Not to mention,aesthetically with the wood projecting, it would be unnecessary and more pleasing to the eye.
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Old 09-04-2016, 10:17 PM   #17
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


Thanks Tscarborough nice to clear that up.

Fouthgeneration thank you I'm defiantly interested in getting the best bond possible so I will look more into setting the rock on there dry with wet mortar and adding more cement to the mix maybe 1:2 cement sand? Would adding lime be of any benefit?

As for the ICF holding the weight (Im on the same page as you) I called the manufacture and they said to space the screws 8-16" apart depending on fastener size for 2" stone veneer and dont worry about a ledger. I went with #10 stainless steal mixed with decking screws and doubled up the washers spaced them 6-8".

That being said I'm still not confident if just the plastic webbing can support 1/2 scratch coat plus the weight of the veneer, down the road when the plastic starts to deteriorate even if its 60-100 years I would hate to see it fall on someone. I'm looking at splitting the bigger stones and using stuff around 1" or thinner to at least minimize the weight. Using Tapco screws would help although the concrete is 3" in so there would be allot of leverage on the screws. The plastic strapping comes out to around 1".

As for the timber overhang above the veneer I completely agree fjn. We went out as far as we could and managed to get it flush on the front of the building only the sides where there is going to be a covered deck attached has a 1 1/2" lip. We simply couldn't go out anymore or the buildings weight would have been supported by 3" of EPS foam, we needed it transferred to the foundation.

We went with 8" wide timbers. Some are 14" tall but we just didnt have big enough trees or enough $$ or lift to get big enough timbers for an over hang.

As Fouthgeneration said we will be running flashing out over the veneer where there isnt a covered deck.

hers a pic to see the building. We will have a covered deck wraping around 6 of the 9 sides and a overhang on the front. Very little water should hit the wall.

Photo from afar you can see where the deck will come out.



Also photo of us putting up the logs, you will see how we would need much bigger timbers to get an overhang, if we went with bigger timber I suppose we could have beefed up our timber crane and added more blocks and tackle but were pretty tight on cash.


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Old 09-06-2016, 03:41 PM   #18
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


Quote:
Originally Posted by RedBaronww1 View Post
Talked to a friend and he recommended using weld bond in the mortar. Any one tried it?
Weld o bond is meant to be pasted on the backs. C21 is what you add to the mud.
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Old 09-06-2016, 06:33 PM   #19
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


I thought Weld bond was both integral and as a surface bond? Not all are, but most are.
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Old 09-06-2016, 07:07 PM   #20
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Re: 12ft High 2" Stone (slate/shale) Veneer. Rock Fall Hazard?


I never heard of weld o bond being used like that, didnt look like any mention of it here http://www.silpro.com/datasheets/Silpro_Weldobond.pdf

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