Installing stone veneer - having trouble getting mortar to right consistency


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Old 08-16-21, 07:48 PM
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Installing stone veneer - having trouble getting mortar to right consistency

I'm installing thin rock (real stone, approx 3/4"-1.25" thick) using CSC-4. The bag says to mix in a certain amount of water for every 80lb bag, let it rest for 10-15 minutes, then add additional water as necessary.

When I do this the mix seems very hard to move with the trowel - but I can never seem to get it to a point where it will stay on my trowel - either it's too loose, or too thick. I've watched countless YouTube videos but I'm at a loss.

I've installed about 20 sq ft, but am concerned I'll run into issues with stones falling off years from now...

Any advice?
 
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Old 08-16-21, 07:53 PM
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Oh - two other tangentially-related questions.

1) For layout, I have a board setup with a line and board along the top so I can pre-plan my rock position (the rocks are randomly sized - see https://www.instagram.com/p/CSnNoC4sXnV/). However, it never seems to work out. I've started marking my scratch coat with a sharpie so I know exactly where to position them, but it wears the tip down. Any marking options that would work better?

2) When pressing the stone into the scratch coat, how much mortar should remain between the stone and scratch coat? Should it be touching, or should I leave a little bit of mortar (ie, 1/4", 1/2")?
 
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Old 08-17-21, 06:10 AM
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I have never used that mortar. When setting a stone veneer I usually mix my own and make it a very rich mixture. Initially it's the suction formed on the back of the stone that holds it in place until the mortar hardens. I always do a butter coat on the back of the stone, then a thorough buttering of the wall with a thick bonding coat or big blob of mortar on top. Place the stone on the wall and tap it into position with a rubber mallet. Large stones may sag down slightly under their weight but if you don't break the suction on the back side they will stick.

1. I lay my stones out on the ground. I start with the edges picking stones with straight edges. Then I fill in the field with other stones as needed.

2. I do my butter/scratch coats right before attaching the stone so none of it is very cured. I just hold the stone in place and tap it in with a rubber mallet. How much it moves into the wall and it's sag will tell you if it's stuck enough. As for how far in to drive the stone that is up to you. I go for aesthetics trying to get the face flat even though the stones vary in thickness so some are hard against the scratch coats while others have a thicker mortar layer in between.
 
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Old 08-17-21, 06:34 AM
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Two important tips - first, the stone and wall should be wet when you apply the mortar so keep a spray bottle of water around to soak the stones- if you apply mortar to dry surface it doesn't stick nearly as well.
Second, if the mortar isn't 'gluey' enough, you can add some lime and stone dust to the mix- a lime/stone dust mortar can be almost as clingy as toothpaste- but you have to color match it to the old mortar, and you want to add stone dust so that adding the white lime doesn't change the color mix.

Question - are you on chlorinated city water, well water (usually hard water) or surface water (usually soft water)?
 
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Old 08-17-21, 07:02 AM
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When I did my stone work on my shed last summer the product recommended was Custom builders LFT, it's a latex fortified material and it was very easy to work with.

https://www.homedepot.com/p/Custom-B...MG50/205789819

Small batches, peanut butter consistence, no back butter needed, once it was installed it wasn't coming off.

Thickness of mortar, after some trial and error a 1" thick layer on the back, with the edges tapered inward gave the correct amount.

 
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Old 08-17-21, 08:42 AM
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Marq1 - oh, wish I had done durock. I ended up using spiderlath+scratch coat (fiberglass)... which worked but overall probably took me longer what with the scratch coat... then I could have used a mortar like you did. However, mine isn't a dry stack - I'll be grouting this afterwards, though that probably doesn't matter much.

Hal_s - I did that at first but it seemed to make the mortar too runny when I pressed it in (granted I was using my garden hose). I use a wet sponge to wet the back of the stone, though don't wet the scratch coat. I'll pick up a spray bottle for the scratch coat going forward.

As for the water - well water. I can use softened, but presume that would be a bad choice? No city water available, though I could get some from a family member if that's necessary.
 
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Old 08-17-21, 10:06 AM
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Correct, you do not want to use softened water because of the salt (sodium).
 
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Old 08-17-21, 02:04 PM
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As for the water
Unless your in 100 plus heat or in direct sun where it's sucking and drying the water out of your mortar you really dont need any supplemental water.

Ive never heard any comment about the difference between well or city water, for that matter I guess your mortar would see a greater effect, as long as it's potable your good!

I did that shed in normal summer weather, 80 ish, but did sides that were in the shade at different times of the day, no issues!
 
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Old 08-29-21, 05:54 PM
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Quick update, I'll know more later this week...

I originally bought 12 bags from the company - after using them all up I had a lot of issues with the mortar:

1) I could never get it to the sweet spot - either had to make it too runny so I could work it, or if I got it "perfect" by the time I waited ten minutes it was very difficult to spread, and adding water made it too runny.

2) Most of the bags had small chunks of hardened mortar - well the powder was hard and bag-shaped. The last two bags I went through had so many little balls of mortar that I got my soil screener out

3) I picked up another four bags last week, and used one of them today... I was able to mix it to a perfect consistency, it held as expected on my trowel, and the bag was clean.

I'm a little bummed - if the next three bags are like this I kind of want to complain to the company but I don't know what to say. It feels like I got old/defective/damaged product. I was able to use it, but I suspect I wasted at least a bag due to a combination of clumps and inability to mix properly.
 
 

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