Loose Porcelain slabs outside

[Dester]

Hi I’m a complete amateur at this apart from an afternoon spent researching the internet.
Two years ago I had porcelain slabs put down on my back garden and recently noticed a lot of them have come completely loose, as I’m not attached whatsoever I can just lift them up.
It turns out the tiles weren’t primed with a slurry so haven’t adhered to the mortar bed. I’m weighing up my options, from what I can see there’s two;
1. Remove all loose slabs, rip up the mortar bed and redo them with slurry coating the tiles a a 4:1 sand to cement mix.
2. Use an outdoor tile adhesive to secure them to the existing mortar bed.

Option 2 seems easier, the mortar bed is in pretty good shape, seems to be compacted and hard with a few gaps here and there. Can anyone advise on how to fix this issue? Is option 1 or 2 better?
Thanks in advance!

 

[Dave]

If it’s solid and not crumbling etc. then option 2 but wait till the night time temps are above 5c to avoid frost damage and correct curing temperatures.