Thin Stone Veneer, Mortar and Admix Question

Old 08-10-12, 08:54 PM
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Thin Stone Veneer, Mortar and Admix Question


I have been researching and gathering supplies for an upcoming project remodeling the outside of my house. To improve the look of the front of my home, I decided to do a wainscot roughly 4' up to the bottom of my windows. Currently, I have exterior sheetrock and defective lap siding (which I assume is some type of wood product although it looks like cardboard under the paint.) That is being torn off to the studs and replaced with OSB and an engineered wood siding. The 4' wainscot is uncharted territory for me although from the research it certainly looks doable. I did however have some questions as I want to make absolutely sure this project is done right, increases the value of my home and complies with best practices.

The current plan:
- I am only doing roughly 150 sq/ft total (the front side of the home with one inside and one outside corner.)
- I purchased thin-cut stone veneer from a quarry (a sandstone in 3-6 cuts)
- The underlying construction will be wood stud with OSB sheathing unless someone strongly urges me to go with a regular plywood instead for this application
- I intend to do my water barrier with a grade D felt, doubled and overlapped
- I intend to install a galvanized foundation weep screed approximately 1 to 1.5' above grade at the base of my wainscot.
- I will have self-furred galvanized lath over that.
- I will have a casing bead around all dissimilar materials and trim.
- I will have a 1/2" scratch coat over the lath.
- I will have a 1/2" mortar joint between stones.
- Weather is variable, hot summers, cold winters.

Here are my questions:
- I purchased Quikrete brand Veneer Stone Mortar (non-polymer version), should I add an admixture to this? If yes, what is recommended? This will be used for both scratch coat, butter and the joints. Do you feel it is a suitable mortar for this? There are a ton of these and I'm uncertain which I would need. I also don't know if the Veneer Stone Mortar has anything added to it that may conflict or otherwise be a problem with an admixture. I'm not sure of what quality the Quikrete mixture is. It is listed to exceed Type S standards but does not specifically mention its composition.
- Because I am using natural stone, do I need to do any sealing or post-install treatment?
- I have read about Drainage Planes. Do I need to install a rainscreen type material between the lath and WRB? How necessary is this? Is there a recommended brand? It is generally dry here with occasionally heavy storms.
- Is there anything I have missed or any specific advice you have for this installation?

I thank you in advance for any help provided. I just want to make sure I do this absolutely right!
Old 08-11-12, 06:08 AM
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I have never used a pre-mixed mortar for veneer stones. I have always used a rich type S mortar mix (1 part type S to 2 parts sand) with no additives. Everything I've done in the past 12 years is still stuck without any issues. Unfortunately I have only applied stone to a masonry base (cement blocks, poured & pre-cast concrete...) so I did not have any experience with preparing the base like you are doing.

I have never sealed stone though I suppose you could since you are using a sandstone.

The mason that taught me to do stone used the sticky, rich mixture I mentioned. I'ts a bit counter intuitive but he taught to start at the top and work down so the wet mortar needs to be strong enough and sticky enough to support the stones. Most of the stone used around here is not cut so I pick through to find ones with straight edges and use them to form the top or border areas where a straight edge exists. Then the pattern is filled in working down and you have a jagged bottom that gets buried. In the years after I learned I've seen many masons use other mortar mixes and start at the bottom and work up placing a layer and letting the mortar harden to help support the weight of the stones going above.

With whichever method for getting the stones on the wall then I pack the joints solid with mortar. It does not have to be pretty but completely fill the joints, trying to keep the face of the stone as clean as possible. Then I wait... until the mortar is almost cured and brush it down with a stiff wire brush. If you brush too early the cement will clog the brush and smear onto the stone. Wait too late and the brush can't cut the mortar. Get it right and the mortar falls away as coarse sand with no mortar sticking to the brush or stone. You just keep brushing until you get the mortar cut back to the depth of reveal you want. Since timing is critical I only apply stones in the morning so I can brush down later in the day. During blazing hot summer it can be as soon as a couple hours but in cooler weather it can be much longer. Unfortunately, I have learned the timing the hard way a few times and was stuck at 2am with lights doing the brush down.

If you have a piece of your stone test to see how it reacts to muriatic (hydrochloric) acid. After the mortar is cured it can be used to wash off mortar that may have gotten on the face of the stones. I have only used it on non-porous stones so I don't know how sandstone will react. And, it's an extremely strong & dangerous acid in it's undiluted state so read up on safely handling it if you decide to give it a try.

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