Stone Capping Not Adhering To Mortar?

Foresty Forest · 30 May 2021

Most of these stone cappings were loose, so I relaid them all last year. But quite a lot of them are loose again. I think the pointing is all that's holding a lot in place.

I used a bed of 6:1 (I think?) mortar , and was careful that it wasn't too dry or too wet. I also used mortar tone, about 40:1.

Is this one of those things that's just tricky? Is there something I should have done differently? And is there a quick fix for the ones that are loose?

^woody^ · 30 May 2021

It should be a 3:1 mix and the important thing is for the cappings to be squeezed down, slid or tapped into wet but not soaking mortar to form some suction and get a good bond.

The joints should be put on the capping stone and compressed likewise, not put in afterwards.

catlad · 31 May 2021

A slurry mix on the stone to be layed will help bonding.

mrrusty · 1 Jun 2021

add some sbr to some cement to make a slurry. Paint the back of the copings. They won't shift then. wash off any splashes immediately or they'll set solid.

Foresty Forest · 4 Jun 2021

catlad said:
A slurry mix on the stone to be layed will help bonding.

Thanks. What's a slurry mix? And is this something I can use on the loose stones now?

Btw. I did use 3:1 in the first place, so has anyone got an idea what went wrong? Is it that stone is just non-absorbent and repels mortar?

mikeey84 · 4 Jun 2021

Mix pure cement with enough water to make a consistency like double cream. SBR can also be added.

Foresty Forest · 4 Jun 2021

I have some ready mix acrylic wall tile adhesive - would that work to quickly reattach the loose stones?

Or would the slurry mix be a quick fix?

bsr · 4 Jun 2021

I would use powdered tile adhesive but not ready mixed.

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Stone Capping Not Adhering To Mortar?

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