What mortar for sandstone crazy paving?

BEALE

We are about to retry mortaring our sandstone pavers at the bottom of our stairs.

Attempt one was a dry mortar with fine mist to bed it in; however, once set, it crumbled in places.  We ended up removing the mortar with a Karcher - not a nice job.

Seeking some advice and experience on what others have used as mortar for sandstone crazy pave?

Thanks in advance for any ideas/suggestions.

MitchellMc

Grouting sandstone crazy paving is, unfortunately, more difficult than standard tile crazy paving @BEALE, where wide joint grout can simply be applied and then wiped off the surface of the glazed tile. Because sandstone is very porous, any grout or mortar that gets onto the surface tends to soak in, making clean-up extremely difficult and often leaving permanent staining. This is why wet grouting methods are rarely successful with natural sandstone unless the surface has been heavily sealed beforehand.

Given that, I can understand why you tried the dry-set method. While that approach can work, it is very sensitive to mix ratios and curing conditions, and if the mortar is too dry or not compacted enough it can crumble, which sounds like what you have experienced.

Realistically, the most reliable method is to use a standard mortar and pack the joints by hand using a small tuckpointing trowel. It is slow, detailed work, but it allows you to control exactly where the mortar goes and minimise contact with the surface of the stone. Working in small sections and cleaning as you go is important. Avoid flooding the area with water during clean-up, as this can draw cement fines into the stone and cause staining.

It is not the fastest or easiest option, but it tends to give the best long-term result with sandstone. Taking your time now will save you from having to remove and redo joints again later.

Let me tag @EleventhCoastal to see if she has any thoughts.

Please let me know if you have any questions.

Mitchell