ᐅ Replacement of Terrace Paving Slabs – Existing Substructure

Hello everyone,

I want to renovate my terrace. Currently, there are concrete slabs (50x50x5 cm (20x20x2 inches)) laid on a sand bed (about 25 cm (10 inches)). I don’t know the exact structure of the subbase since it was done before I moved in. However, it has lasted 25 years, so I assume the subbase is solid.

I want to replace the concrete slabs with 60x60x2 cm (24x24x1 inch) porcelain tiles. These will be laid loose on gravel. My main question is: can I keep the existing sand layer?

In other words, the subbase would be as follows:
- Sand (about 20-25 cm (8-10 inches))
- Geotextile fabric, drainage fleece, or similar (to properly separate the sand from the gravel)
- Gravel (4-5 cm (1.5-2 inches))
- Porcelain tiles

I am aware of the particular requirements for loose laying of porcelain tiles. I have some experience since the adjacent terrace area was installed the same way, but there I completely installed a new base (crushed stone + gravel). For renewing the old part of the terrace, the question now is about the existing sand.

Thanks in advance for your advice!
AlexBau24