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

Allow me to step in, Alex: and the 20mm (0.8 inch) panels can handle that? I would be worried they might break... but it definitely looks better, and we are planning to do the same...

It will probably hold up; sometimes they are even installed on pedestals with 20mm (0.8 inches) spacing. But with a size like that, I definitely wouldn’t lay them loose, as they tend to wobble quickly. That would be a waste of time for me.

Regarding the sand... according to standard practice, gravel would be used because of its load-bearing capacity. However, for light loads, sand is basically sufficient; as mentioned, it has already lasted 25 years. In any case, you don’t have a warranty on your own work.

Thank you for the quick responses!

Jesse Custer schrieb:

Allow me to jump in, Alex: will the 20 mm (0.8 inch) slabs hold up? I would be worried about them breaking... although they definitely look better, and we are planning something similar here...

They hold up without any problems; these are now almost the most common patio slabs. I have absolutely no concerns. As WilderSueden already mentioned, people often worry that the slabs might start to rock. I took that “risk” and built a new 5 x 4.5 m (16.4 x 14.8 ft) patio this way (loose installation on crushed stone). So far, not a single slab rocks. Of course, you shouldn’t just lay the slabs loosely on the crushed stone—you need to tap them firmly into place with a rubber mallet so they sit properly. I am not the only one for whom this method works.

WilderSueden, thanks for your input regarding the existing sand base. I’m just a bit reluctant to spend the time and effort removing all the sand, obtaining gravel, replacing it, compacting it, etc.

By the way, does the sand need to be compacted with a plate compactor?

AlexBau24 schrieb:

When renewing the old terrace section, the question about the existing sand came up.

Then just leave everything as it is. Just because installation on sand is considered "old-fashioned" doesn't mean it's wrong.

AlexBau24 schrieb:

By the way, does the sand need to be compacted with a plate compactor?

Actually, it should have been compacted already 25 years ago. However, it certainly won’t hurt to run over it again.