Renewal of terrace slabs - existing substructure

Hello everyone,

I want to renovate my terrace. Currently, there are concrete slabs (50x50x5 cm) laid in a sand bed (approx. 25 cm). I don't know how the entire substructure is constructed since it was done before I owned the house. However, it has lasted 25 years, so I assume the substructure is reasonable.

I want to replace the concrete slabs with 60x60x2 cm porcelain stoneware slabs. I will lay these loosely on gravel. Now the main question is: can I leave the sand as it is?

That means the substructure would look like this:
- Sand (approx. 20-25 cm)
- Geotextile fabric, drainage fleece, or similar (to properly separate the sand from the gravel)
- Gravel (4-5 cm)
- Porcelain stoneware

I am aware of the special requirements for the loose laying of porcelain stoneware slabs. I also have experience with this because the adjacent area of the terrace was constructed in the same way. However, there I completely renewed everything (gravel + gravel). The question came up about the existing sand with the renovation of the old terrace section.

Thank you very much for your advice in advance!
Alex

Allow me to intervene, Alex: and the 20 mm plates can withstand that? I would be afraid they would break... because it definitely looks better and we have that coming up as well...

It will probably hold; on pedestals, they are sometimes laid with 20mm as well. But I would definitely not lay them loose in that format; it quickly starts to wobble. I would consider the time too precious for that.

As for the sand... according to the textbook, one would use gravel because of the load-bearing capacity. But for light loads, sand is basically sufficient; as mentioned, it has already lasted 25 years. You don't have a warranty on your own work anyway.

Thank you for the quick responses!

Allow me to butt in, Alex: and the 20 mm slabs hold up? I would be afraid they would break... but it definitely looks nicer and we have that planned too...

They hold up without any problems, those are by now almost the most common terrace slabs. I have absolutely no concerns. As WilderSueden already mentioned, people often worry that the slabs will start to wobble. I took this "risk" and realized a new terrace 5 x 4.5 m in this way (loose laying in split). So far not a single slab wobbles. Of course, you must not just lay the slabs in split, but tap them properly with a rubber mallet so that they sit firmly. I'm not the only one for whom it works.

WilderSueden, thanks for your assessment regarding the existing sand base. I just feel it’s a pity to take all the sand away, get gravel and fill it back in, compact it, etc.

By the way, do you have to compact the sand with the vibrating plate?

But when renewing the old terrace section, the question arose about the existing sand.

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

By the way, do you have to compact the sand with the vibrating plate?

Actually, it should have been compacted 25 years ago. However, it certainly doesn't hurt to go over it again.