ᐅ Substructure for Terrace / Patio

Created on: 21 Jun 2016 22:05
A
Andreas2001
Hello everyone,

Our house is now 6 years old, and we want to replace the patio slabs (at the time, we installed plain concrete slabs for cost reasons). Now, we want to install porcelain tiles on top. A landscaper inspected the area and looked underneath the slabs. He found that the layer of grit is quite thick, around 8-10 cm (3-4 inches) at the spot he checked. Below that is the crushed stone layer, but we don’t know its thickness; it might be thinner.

The landscaper recommends removing and rebuilding the base because there is too much grit used. Since the new tiles are about 2 cm (1 inch) thinner, adding 2 cm (1 inch) of grit on top would mean a total of about 10-12 cm (4-5 inches).

Is that really too much? Why would this be a problem?
C
costa
22 Jun 2016 16:47
One00 schrieb:
Then you could also remove the gravel, add some crushed stone on top, compact it again, and then put a bit more gravel over that. I would also consider completely rebuilding it pointless, at least based on the information we have.

That is exactly how the landscape gardener wants to do it as well.
A
Andreas2001
22 Jun 2016 17:13
Yes, okay. But why is the maximum allowed 50mm (2 inches)? What happens if it is more? Sorry, I just want to understand.
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Payday
22 Jun 2016 18:24
Crushed stone is basically “large” stones that offer little vertical give but can shift relatively easily sideways. The thicker the layer, the easier it is for the material to move laterally. If the slabs are fully encased in concrete on all four sides, you can probably do it similarly to that.

As I mentioned on page 1: either use slabs of the same height, consider whether a 2cm (0.8 inch) difference in depth is an issue, or do it properly by lifting the slabs, underpinning them, and then putting crushed stone back on top.
Mycraft22 Jun 2016 19:00
It’s the other way around. "Splitt" is the finer material... Gravel, on the other hand, refers to the larger stones that Payday is talking about.