Wanting to put some new tiles over existing tiles. Was wondering if I'd use cement or glue? If cement is it a special mix or just a mortar type cement? The existing tiles have a textured surface so new ones should adhere well. Any advice appreciated

Scratch the existing tiles a bit, textured surface alone might not hold. Use good adhesive mortar, Crocodile brand etc. and follow instructions strictly.

professionally not acceptable but for diy with previous posters advice of correct preparation would be in my opinion suffice for a job standard of 50% its not just the adhesion aspect what about double the weight you would be placing on the original adhesive

not a great idea overall but for a make do/easier job well go for it

There is a special adhesive just for this purpose so check out the building suppliers

Just to add; the important component is the adhesive and there are many different options so first thing is to get one compatable to clay or porcelain or marble or travertine.

Then the key is key.!

I was sceptical about doing it but had it done in my shower room using Hicem excel power swimming pool cement. Seemed to work fine and made the job a lot quicker and easier.