The underside of the tiles look like the picture shown. So you will see that they are about 80 small 'feet' which distribute the load onto the surface on which you are laying the tiles. And there are 16 stainless steel screws which attached the plastic base to the wood pieces.

Do you sell the plastic substrate separately?

Sorry we don't offer the plastic base separately but if you just want an interlocking plastic base without anything on top, there are other companies in the US who sell such items

can we use this tile for decorative wall?

If you had some means of fixing them to the wall you could certainly use the tiles in this application. Some people have indeed used

them in such a way but it's not very common.

I see the picture of the bottom. I’ve got a roof deck with dechtech polyvinyl surface that I don’t want to damage or penetrate, however I’d like to be able to have something like these over it and still allow drainage. Any recommendations for what to put between these and the roof deck so that there is no damage to the surface below as we walk on them over time?