I just started making a raised bed with flagstones that are relatively smooth. After using nearly 160 lbs. of mortar, I find that more flagstones are not adhered together than are. I paid attention to directions, particularly not doing the job when night temps would go below 40 degrees. What can I do to make my project work? I am thoroughly frustrated, but really want this to work. Please help me figure this out!

  • How clean (no dust) were the flagstones before you mortared them? You could clean an awful lot of dust off with a garden hose and spray nozel. What kind of mortar did you use? There's a binding agent you can (must with cheaper mortar) put into the mortar to make it "stickier." Is there any chance the mortar was mixed too dry, or dried out too much before you were able to use it all? You might find the smartest tile & stone person where you bought the mortar and get them talking. Mar 29, 2015 at 22:19
  • A picture of the project would be good. I have only seen flagstone laid on sidewalks and patios. Never seen them used to make a raised bed... Are you just stacking/piling them up to make a bit of a wall all around?
    – Jack
    Mar 30, 2015 at 2:00
  • I will put a picture in here tomorrow. Yes, I am stacking them up to make a wall around. I used concrete rubble in the middle to make the deep bed not only drain but not be so hard to fill with soil.
    – Adriana
    Mar 30, 2015 at 4:50
  • Craig---yes they probably were dusty. I will have to look at the name of the mortar, but it had a "type S" thing on it. I am not a construction person, just a fly by the seat of my pants DIYer. I will definitely go back for the binder. I may also have not made the mortar wet enough. I didn't mix up a lot at once, but made it more frequently. Thank you so much!
    – Adriana
    Mar 30, 2015 at 4:54
  • Dirty is also my first choice. I have been known to use construction adhesive, as well as drilling small hole in the center using a bit of drill rod to keep them in line.
    – Some Guy
    Mar 30, 2015 at 12:14

2 Answers 2


Sorry but Tyler Durden is talking pure imaginative theory with no practical substance. Install drainage, which drains to where exactly. Install gravel and sand and put walls on it? Gravel, the roll around stuff? And sand the soft stuff?

Still sound like something you want under your walls? No.

Sure dry stone walling stands the test of time, provided there are zero, and I mean zero side thrust loads applied to the wall, ever. And definitely means no soil.

Mortar helps the wall absorb loads by simultaneously sticking the units together AND holding them apart. Probably the reason the mortar didn't stick (assuming you have proper/suitable mortar) is that your slabs were dusty/dry and the mortar was probably too dry.

To cure: Wash all dust off the slabs with a hosepipe and allow the surface water to soak in (the slab will still look dark/wet). Mix the mortar using enough water to make a smooth, creamy mix that doesn't crumble.

Lay slabs using the nice and creamy mortar and tap into place, remove excess that squeezes out with a trowel and once the mortar has hardened off a little, tool it off with whatever finish you want (half round, struck with a trowel etc). Joint thickness shouldn't be too thin, aim for 10mm, give or take a few mm's either way.

At the end of the days work, cover down with fleece (or old blankets) and a layer of polythene. Keep 'green' mortar covered thus for a week or so.

At least thats how we lay brick/block/concrete stuff in the UK/EU...

  • Thank you! I didn't think what he said was going to work after I thought about it. I appreciate your help!
    – Adriana
    Apr 5, 2015 at 3:18

I will tell you a mason's secret: mortar is not cement.

Without a proper foundation below the frost line any structure will move.

For a small wall the best procedure is to first bury drainage pipes to make sure the area is fully and completely drained, then lay 8-12 inches of gravel, then put sand on top of the gravel, then set the wall in the sand, the deeper the better.

The key thing to remember is that the purpose of the mortar is to set the stones, that just means keep them in position while they are laid, not glue them together. If the stones do not fit together naturally and apply equal force to each other, no amount of mortar will keep them together. A really well made wall will use almost no mortar at all.

  • It wasn't anything below the frost line, and is not a foot path. It is a raised flower bed.
    – Adriana
    Mar 30, 2015 at 4:48
  • @Adriana I have updated my answer. Mar 30, 2015 at 5:27
  • @TylerDurden I agree with not using mortar on stone walls. there are many old stone walls near my home that are all dry laid (no mortar) and still standing. These date to before the days of barbed wire fence which is going back quite a bit. Some of these may even go back to the colonial era. Mar 30, 2015 at 19:18
  • Okay, so I guess it would be better to just stack them differently, staggering them like bricks. Admittedly, the mortar just doesn't look great. Thanks for your help. I thought that using the mortar would keep it together, but apparently stacking them would do the same and be more economical too. Plus, I won't have to wait for the right temps to finish it. I appreciate your input!
    – Adriana
    Mar 31, 2015 at 6:43

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