How are 60cm x 60cm porcelain tiles (9mm thickness) best laid outdoors?

You need 20mm for exterior use , 9 mm wont stand up to the frost

These should be suitable to lay out doors. You must make sure the concrete is flat and level,and totally dry and dust free. I would suggest sealing prior to tiling with good quality sealer, ie SBR bond, or similar. You must also use flexible adhesive and grout,suitable for outside use and vitrified tiles. Hope this helps

I wouldn't lay 9mm tiles outside the frost would wreck them

Make sure the concrete slab is solid and not moving then lay porcelain tiles using a 10mm notch trowel and making sure the adhesive is suitable for exterior use. Bobh