Jointing products - don't know what base is? - What jointing product should i use?

[tillyd]

Hello, new here, DIY-er looking for help!
Have recently moved into a new house with two patios in back garden. One is concrete slabs, the other is grey slabs but I don't think they are concrete.
I need to rejoint (point?) and was looking to use Weatherpoint 365 or VDW800, because I'm not sure if the base is water permeable (which some products Easy Joint and Geofix etc say it must be).
But now reading the instructions for Weatherpoint, it says the base mustn't be a sand bed or spot bedded.
Is there any product that I can use if I don't know what the base is? Or is there a way for me to tell what the base is?? Thanks!

[seanandruby]

Yes take a slab up and look.

[blacklimestoneproblem]

Another way if you dont fancy taking a slab up, if you have any lawn or garden beds edged up to the different patio's dig down next to the different patio's until you can see the foundations and see what they are. Its easier to put mud back than a slab.