Mortar / Grout / Cement / ?? - Need to fill joints Flagstone coping

troye

Silver Supporter
Apr 10, 2013
61
I reset all of our flagstone coping. It is time now to tuck in material into the joints. On our flagstone retaining walls and previously in the coping joints the material there is texture / looks like there is some aggregate maybe? I did a test with some type s mortar and its not the same and definitely not what I want, it is very plain with no texture.

Any idea what products I need to use ?
 

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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,481
Tucson, AZ
I was just in Home Depot and noticed they do sell a specific stone/rock mortar mix. It’s not Type S cement. Different package. Says it’s specifically design for cut stones and natural rocks/boulders. Perhaps check that out.
 

MinerJason

Bronze Supporter
Jan 29, 2018
256
Tucson, AZ
Assuming first pic is existing mortar? In the second pic, the left is obviously a test with the mix you bought, but is the right side of that photo also a test with that mix, or the previous/existing mortar?

The first thing that jumps out about the textures is that the previous mortar used a poorly graded sand, which is to say it has a wide distribution of particle sizes. This is part of what gives it more texture (and also makes it a bit stronger). The bagged pre-mix mortars typically use a more well graded sand because it's easier for them to control consistency and quality using sand with even particle sizes. Mixing your own with some locally sourced masonry sand might get you something closer to the existing mortar.

If the right side of the second photo is the existing mortar, then a large part of your problem is that your test was smoothed over with a float or trowel covering all the sand particles with cement cream, whereas the existing mortar was likely shaped/wiped with a wet sponge or rag to clean the joints and remove excess mortar, which removed the cement cream on the surface and exposed the sand particles. If this is the case, you didn't really make an apples to apples comparison.
 

troye

Silver Supporter
Apr 10, 2013
61
Hello
I was just in Home Depot and noticed they do sell a specific stone/rock mortar mix. It’s not Type S cement. Different package. Says it’s specifically design for cut stones and natural rocks/boulders. Perhaps check that out.
Sounds good! I will go to home depot tomorrow
 

troye

Silver Supporter
Apr 10, 2013
61
Assuming first pic is existing mortar? In the second pic, the left is obviously a test with the mix you bought, but is the right side of that photo also a test with that mix, or the previous/existing mortar?

you are correct on all points. I should have used a sponge so it would be a fair comparison, that makes sense. In the test pic (Second pic) the material to the right is the existing mortar, so is the first pic.

I will give it a try tomorrow and see what happens