Installing stack stone - How much mortar to use / how thick?

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TSHERV

New Member
Feb 28, 2019
23
Oregon, WI
Hi,

I'm in the process of installing stone veneer panels around my gas fireplace (pic below). I've used this forum and have properly prepared the wall (cement board, etc.). The fireplace is in a corner of the room, and I'm running the panels all the way to the corners, so I need to miter cut each panel that runs against the wall.

This morning I started laying out and making my cuts on the bottom row. The picture below shows my first row cut, and set against the wall (no mortar yet). I was happy that I got everything lined up when I had a realization: My miter cuts on each wall won't fit once I use mortar. If I have 1/4" or 1/2" of mortar behind each piece, I will now have a gap in my miter cut. When I did my cuts this morning, I based all of my measurements on the stone butting up directly to the cement board with no mortar. I'm a bit stumped as to how to cut each piece.

Here's a few questions:

1) What should I realistically account for in thickness of mortar when installing stackstone? I'm using a 3/8" trowel, but once I place the stone in place, I'm assuming it will squish down?

2) How can I cut my stone (corner miter cuts) in advance not really knowing how thick the mortar will be? Should I just assume it will be 1/4" or 1/2" out from the cement board?

3) Any advice on the best way to accomplish this?

Thanks!

IMG_6612.jpg
 
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TSHERV

New Member
Feb 28, 2019
23
Oregon, WI
One other thing I'm trying to figure out: do I need to put mortar on the cement board AND "back butter" the stone, or can I just "back butter" the stone?
 

mcdougy

Minister of Fire
Apr 15, 2014
647
ontario
In my experience, I would not be back buttering the tile, as it's kinda a pita. Your mitres will need to be cut a bit longer...again the pita is keeping that lined up vertically.
 

TSHERV

New Member
Feb 28, 2019
23
Oregon, WI
Thanks. If I butter the wall using a 3/8" or 1/2" trowel, once the stone is pressed into place, how thick do you think will the mortar be? I'm assuming it would compress down to under 1/4"?
 

mcdougy

Minister of Fire
Apr 15, 2014
647
ontario
3/8 trowel would be good. Try your tight cut piece and see what how it fits...it's a bit of trlal and error. The pieces are usually not exact in length, so trying to precut all your mitres may not work. If it's the type of glued together stone pieces of have worked with previously. Take your time, it will all work out.
 

TSHERV

New Member
Feb 28, 2019
23
Oregon, WI
3/8 trowel would be good. Try your tight cut piece and see what how it fits...it's a bit of trlal and error. The pieces are usually not exact in length, so trying to precut all your mitres may not work. If it's the type of glued together stone pieces of have worked with previously. Take your time, it will all work out.
Do you use a 3/8” trowel and apply mortar to the wall? Is 3/8” enough if you butter the wall and not the back of the stone?

If I use a 3/8” trowel, I’m assuming the mortar would be about 3/16” when the stone is pressed in?
 

Hogwildz

Minister of Fire
I used similar real stone veneer on my old brick fireplace, and I have installed about 400sf of cultured stone over painted superior concrete walls. Typically a scratch coat is called for on the wall side, then wet the scratch, butter the stone back, and wiggle in place for a good seal. I had better luck with a wet coat on the wall approx 1/2", then 1/2" on back of stone, then press and slightly wiggle in place. whatever you do, make sure you wet the back of the stone, either if you butter or not. Myself, I would not short cut it, and apply mortar to both surfaces.

As far as the miters, You should work from one end and across, then next course back to starting side and across. The cuts from the finish end can be cut to fit with each course, and the left over from the last pc. mitered and used as the start for the next course. Mitering each course end while actually finishing that course will save you a lot of guesswork, frustration, and cutting. 3/16" ain't much for mortar, too thin for me.

This ain't tile, and a notched trowel is not the proper trowel. You should be getting full coverage with a standard mortar trowel. There is also mortar made for stone & heavy veneer. Any bb store will have it.

mcdougy is right, take you time. & Measure twice. The patience is worth it.
 
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Hogwildz

Minister of Fire
Before, during & after
 

Attachments

TSHERV

New Member
Feb 28, 2019
23
Oregon, WI
Before, during & after
Thanks for your help Hogwildz! Thanks for the pics. That's an awesome looking fireplace!

A couple followup questions to your post:

1) Do I need a scratch coat being I used concrete board? Would it work if I used a 1/2" mason trowel and either butter the stone OR butter the wall? With concrete board, I don't need to butter BOTH with a 1/2", correct?

2) When you talk about wetting the scratch and wetting the back of the stone, do you use something like a spray bottle just to get it damp? If I'm buttering the back of the stone, do I wet the back of the stone first?

Thanks!
 

mcdougy

Minister of Fire
Apr 15, 2014
647
ontario
With a tight fitting stone like you are using I feel you don't need to scratch coat the cement board. I would just butter the wall. A good mix on your mortar is essential, follow the mixing instructions. With larger stone than you have...I use a fast set mortar. With your smaller size stone I would just use standard mortar. 3/8 or 1/2 Square notch is fine. No need to stress over the stick, as you will find out, with proper mixed mortar there will be a lot of stick. The only time you will have trouble is if your mortar dries out on you. Wiping the back of the stone with clean water and sponge is a good idea to remove any dust, especially on the stones you cut which will have alot of dust from cutting them. Relax and take your time. You won't want to go all the way to the top in one session as your stone won't handle the weight until set. Probably 36" is as much vertical height in one session with standard mortar. You will be fine, just go for it.
 

zrock

Minister of Fire
Dec 2, 2017
1,064
bc
As stated above backbutter your pc do not try to save time or money in this area... I have pulled many of surfaces where you can tell they did not backbutter the pc and things were falling off and extremely easy to remove.. Doing this gives you 100% adhesion
 

Hogwildz

Minister of Fire
Thanks for your help Hogwildz! Thanks for the pics. That's an awesome looking fireplace!

A couple followup questions to your post:

1) Do I need a scratch coat being I used concrete board? Would it work if I used a 1/2" mason trowel and either butter the stone OR butter the wall? With concrete board, I don't need to butter BOTH with a 1/2", correct?


2) When you talk about wetting the scratch and wetting the back of the stone, do you use something like a spray bottle just to get it damp? If I'm buttering the back of the stone, do I wet the back of the stone first?

Thanks!
Not sure what product you are using, but per MSI real veneer panels, the product I used, and also did same for Corning Cultures stone, I coated the wall with 1/2" of mortar, (always covering a few more inches than the actual stone size will be on the wall, then buttered the back of each stone, about same 1/2" full coverage (no notched trowel), then set & pressed the stones in place which will give you approx 1/2" to 3/4" of mortar thickness after pressed into place. When you butter the back of the stones, around the perimeter of the stones, you will trowel off the mortar at a 45 degree angle around the perimeter of the stone to the edge of the stone. This helps keep too much mortar from oozing our from behind the stone when you install it to the wall. You def want some ooze which shows you 100% full coverage. Any additional mortar the oozes out, you can trowel over to the area of the wall you will cover with the next stone. Repeat for each stone. Tedious process, but I guarantee the stone will set in place solid. They recommend tapping on the stone with a rubber mallet, I just used the butt end of the trowel handle. Also, slightly wiggling the stone back & forth will help set it in full coverage of mortar, and also creates a vacuum to help hold the stone in place till it dries.
See link for typical install directions:
https://images.homedepot-static.com/catalog/pdfImages/fa/fac62032-3e32-416f-8152-32c248ca0ad6.pdf

As far as mortar goes, I used Mason's Mix Type S on the cultured stone:
https://www.homedepot.com/p/Quikrete-80-lb-Type-S-Mason-Mix-113680/100318510

and Natural stone & large tile mortar for the real stone veneer panels:
https://www.homedepot.com/p/Custom-Building-Products-Natural-Stone-and-Large-Tile-50-lb-White-Premium-Mortar-MGMM50/100154560

I didn't like the results of letting the scratch coat dry, and I set into a wet bed instead, along with buttered stone back also. I wet the back of the stones with a elcheapo 3" paint brush dipped in a bucket of water. You don't want the stone soaked, just wet so it doesn't absorb the moisture from the mortar too fast. Too wet, and the mortar will slide off. Creates a great bond.

If you do a dry scratch coat, you'll have to wet the scratch coat similarly. Either way, when you are done for the day, you want a thin layer of mortar protruding a few inches around the perimeter of the stone that has been installed, scratch the mortar that is on the wall surrounding the installed stones, which is just making some horizontal grooves in it with anything pointy. When you come back the next day or later to start installing more, just wet the scratch area, apply more wet coat on the area you will be installing on, butter the stones and go. You can get an idea of what I am talking about in the photos I posted.

As you can see in the previous photos, thew results speak for themselves.

No sense skimping, take your time, do it right, and enjoy the fruits of your labor when finished.
Good luck, it is pretty easy. Just go with patience.
 
Last edited:

TSHERV

New Member
Feb 28, 2019
23
Oregon, WI
Not sure what product you are using, but per MSI real veneer panels, the product I used, and also did same for Corning Cultures stone, I coated the wall with 1/2" of mortar, (always covering a few more inches than the actual stone size will be on the wall, then buttered the back of each stone, about same 1/2" full coverage (no notched trowel), then set & pressed the stones in place which will give you approx 1/2" to 3/4" of mortar thickness after pressed into place. When you butter the back of the stones, around the perimeter of the stones, you will trowel off the mortar at a 45 degree angle around the perimeter of the stone to the edge of the stone. This helps keep too much mortar from oozing our from behind the stone when you install it to the wall. You def want some ooze which shows you 100% full coverage. Any additional mortar the oozes out, you can trowel over to the area of the wall you will cover with the next stone. Repeat for each stone. Tedious process, but I guarantee the stone will set in place solid. They recommend tapping on the stone with a rubber mallet, I just used the butt end of the trowel handle. Also, slightly wiggling the stone back & forth will help set it in full coverage of mortar, and also creates a vacuum to help hold the stone in place till it dries.
See link for typical install directions:
https://images.homedepot-static.com/catalog/pdfImages/fa/fac62032-3e32-416f-8152-32c248ca0ad6.pdf

As far as mortar goes, I used Mason's Mix Type S on the cultured stone:
https://www.homedepot.com/p/Quikrete-80-lb-Type-S-Mason-Mix-113680/100318510

and Natural stone & large tile mortar for the real stone veneer panels:
https://www.homedepot.com/p/Custom-Building-Products-Natural-Stone-and-Large-Tile-50-lb-White-Premium-Mortar-MGMM50/100154560

I didn't like the results of letting the scratch coat dry, and I set into a wet bed instead, along with buttered stone back also. I wet the back of the stones with a elcheapo 3" paint brush dipped in a bucket of water. You don't want the stone soaked, just wet so it doesn't absorb the moisture from the mortar too fast. Too wet, and the mortar will slide off. Creates a great bond.

If you do a dry scratch coat, you'll have to wet the scratch coat similarly. Either way, when you are done for the day, you want a thin layer of mortar protruding a few inches around the perimeter of the stone that has been installed, scratch the mortar that is on the wall surrounding the installed stones, which is just making some horizontal grooves in it with anything pointy. When you come back the next day or later to start installing more, just wet the scratch area, apply more wet coat on the area you will be installing on, butter the stones and go. You can get an idea of what I am talking about in the photos I posted.

As you can see in the previous photos, thew results speak for themselves.

No sense skimping, take your time, do it right, and enjoy the fruits of your labor when finished.
Good luck, it is pretty easy. Just go with patience.

Thanks for the responses! I could use some really quick advice. I started on my first row, and I think I may not have the mortar mixed right. It has the consistency of peanut butter, but it feels sandy. I use the flat edge of my trowel and put a layer on the wall (kind of pressing it in). Once I have an even coat, I use my 1/2" notched trowel at a 45 degree angle. I cannot get good grooves in the mortar. Does that mean it's not wet enough? the trowel seems to just remove all of the mortar. Does that mean I need more water? I'm using Mastercraft Stone Mortar mix in a 60LB bag.

Thanks!
 

Hogwildz

Minister of Fire
Thanks for the responses! I could use some really quick advice. I started on my first row, and I think I may not have the mortar mixed right. It has the consistency of peanut butter, but it feels sandy. I use the flat edge of my trowel and put a layer on the wall (kind of pressing it in). Once I have an even coat, I use my 1/2" notched trowel at a 45 degree angle. I cannot get good grooves in the mortar. Does that mean it's not wet enough? the trowel seems to just remove all of the mortar. Does that mean I need more water? I'm using Mastercraft Stone Mortar mix in a 60LB bag.

Thanks!
NO NOTCHED TROWEL NEEDED! Use a standard mason trowel you would use for brickwork etc.
The mortar should be a firm consistency, is should not fall or run off the trowel when the trowel is tilted. Firm not super wet. Too wet weakens the mortar, too dry won't get the best adhesion.

I used the following types:
For wall coat: flat no notch finish trowel
https://www.homedepot.com/p/Husky-14-in-x-4-in-Pro-Finishing-Trowel-57496/300976862

For buttering back of stone:
https://www.homedepot.com/p/10-in-x-4-5-8-in-Brick-Trowel-57491/300960820?MERCH=REC-_-SearchPLPHorizontal1_rr-_-NA-_-300960820-_-N

For cleaning up cracks, gaps & some ooze:
https://www.homedepot.com/p/Husky-3-8-in-Pro-Tuck-Pointing-Trowel-57509/300976858

And general purpose for smoothing ooze from around set stones & applying mortar around finished stones when quitting for the day:
https://www.homedepot.com/p/Husky-6-in-x-2-in-Pro-Margin-Trowel-57506/303744805?MERCH=REC-_-SearchPLPHorizontal1_rr-_-NA-_-303744805-_-N

When you get ooze between the set stones, don't try and wipe it, you can try and knock some off with a trowel, but best bet is to let it set a bit and knock it off whole as a piece. If you get some on the face, don't touch it, let it dry and clean it off when dry and use a tooth brush to wisp any remainder it off.

The only scratch or grooves you want in any mortar is when you are done for the day, and the remaining mortar protruding away from the set stones. Look at my photos of the partially done wall, and you can see the mortar on the wall at sides and top of the stones that were set, and you can faintly see the scratch in the mortar I left on wall for when I started up to set more stones another day. The grooves give the wet mortar a place to grab into when restarting another day.
 
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Dobish

Minister of Fire
Oct 26, 2015
2,024
Golden CO
Thanks for the responses! I could use some really quick advice. I started on my first row, and I think I may not have the mortar mixed right. It has the consistency of peanut butter, but it feels sandy. I use the flat edge of my trowel and put a layer on the wall (kind of pressing it in). Once I have an even coat, I use my 1/2" notched trowel at a 45 degree angle. I cannot get good grooves in the mortar. Does that mean it's not wet enough? the trowel seems to just remove all of the mortar. Does that mean I need more water? I'm using Mastercraft Stone Mortar mix in a 60LB bag.

Thanks!
mortar is a bit too dry. i did a similar stacked stone, laid up the wall with mortar and also the back of the stone. I sort of wish I had just bought the precut corner pieces for mine, as I am still working on cleaning up the edges (its hidden by a curtain). i ended up leaving the corners a little short and then cut individual pieces of the stone for them instead of trying to cut the whole tile down.
 

TSHERV

New Member
Feb 28, 2019
23
Oregon, WI
Thank you all so much for your help. I'm mostly complete with my project (still have some cleanup to do, redo the mantle, etc.). With all of your help, you made the project MUCH easier.

Thanks again!!

Before and after pics:

IMG_6526.jpg IMG_6646.jpg
 
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Dobish

Minister of Fire
Oct 26, 2015
2,024
Golden CO
Where in Colorado are you... ?
 

Dobish

Minister of Fire
Oct 26, 2015
2,024
Golden CO
I'm down the road in golden
 

clancey

Minister of Fire
Feb 26, 2021
708
Colorado
Yea I know and that's a pretty little town with its address going across the street and on the way to red rocks as well----I love Golden..Been here in Denver over 40 years I think--lol..I transplanted from the east coast and lived down South for many years and the West is very different from the Southern living and I miss the south a whole lot but I am cemented here now and just waiting for the Lord to call me..but in the meanwhile I am going to have a emergency stove just to be able to keep warm if everything goes to ----.Its nice to have someone from my state here now--feels like old times...lol lol..Bless you...clancey
 

begreen

Mooderator
Staff member
Nov 18, 2005
87,729
South Puget Sound, WA
I'm down the road in golden
Golden was my introduction to CO. I stayed at a friend's house there many years ago on my first cross-country sojourn.