Bonding mix - Lack of bonding

[Caspurs]

Hi all, I hope i'm posting in the right area, apologies if not.
I've laid a sandstone patio using a moist (not overly wet) 5-1 sharp sand mix. I have found that a large proportion of the stones haven't bonded, even though I got good contact with the stone.
Can someone please help me understand why, and where I must have gone wrong. Am now in the process of lifting stones and relaying them next week.
Any help fankfully excepted.

[exoticpete]

Make sure the flags are damp also you can use a SBR cement bond bridge they wont go anywhere after that

[Caspurs]

Is there anyway I can use a product such as SBR cement bond without removing the now cured concrete mix, or any other technique to bond the stones without digging up the base, as the client/friend is reluctant to do so at the moment?

[Tony McC]

It's not a good idea to use a SBR slurry as a 'glue' to re-seat flagstones.

I've seen it done, and sometimes it works, but most times it just makes a mess or the flag won't quite sit flush. In theory, you need at lest 3mm of a slurry to ensure ample adhesion to the existing bed and the underside of the flag. That means the flag will be 3mm proud which, in most cases, is just a bit too much.

The 'best practice' method is to lift out the loose flagstones, break out the existing bedding, put in a new bed of mortar and then re-lay the flag with a bond bridge applied to its underside.

I know it can seem a lot of work but it's the only way certain to work without leading to further problems.