How to relay slabs to bed that has only been down 2 years?

[pmcx9]

I layed granite slabs (the long narrow type about 20mm deep) onto a 4" sand/cement mix last year. The screed was directly on top of a sound slab patio which had been down 30 odd years.
I have recently run a narrow channel through it and so lifted slabs as necessary whilst building an extension adjacent necessitating a drain. I have made good the channel and took a long time to ensure the surface was level and smooth with the surrounding base level. Further slabs have cement splash staining and will need changing and I also wish to widen the patio one more slab for aesthetic reasons.

I dont really want to rip up what is a perfectly good base at the moment so my question is how to relay these slabs without raising the level too much. I did drop a few slabs back to where they had been lifted but it was clear the type of slab is machined and imperfections in height are unforgiving so I suspect I will need to lift all and lay onto a thin spread of some kind of manufactured compound rather than a screed.

Any thoughts or suggestions from those with experience of this? I realise that lifting the base would be the best suggestion but I have a thousand jobs to do so have money and time constraints which dictate my need to re-lay as is.

 

[r896neo]

you need to remove the bedding mortar and relay them with new bedding. Trying to relay them on the existing bed will fail. you could use tile cement which if done very well would be 5mm or so but that will leave lots of little trip edges etc.

 

[pmcx9]

thanks neo. You prompted me to look at tile cement and it appears there are products available from this webpage extract;

"When you are ready to begin setting tiles for your new patio, that is, bonding them to theconcrete slab, you need to use the appropriate tile adhesive. With many to choose from, it is important to pick the right one. For an outdoor patio, you will almost always use a modified thinset mortar for a tile adhesive.

What is a modified thinset mortar? It is mortar made with Portland cement, fine sand, water and latex additives.


Unmodified thinset doesn't have the latex additives. We want the additives for our outdoor patio because they help reduce water absorption, improve the strength of the bond, and minimize movement due to changes in temperature."

 

[r896neo]

Any tile cement suitable for natural stone and for outdoor use will do.

The extract you posted is for laying thin tiles to a rigid concrete bed and so they must be stuck very well because they are weak and have little weight.

Your flags are very different, being heavy and strong