ᐅ Experience with 3 cm thick patio slabs – do they break easily?

Hello, yesterday we talked with a mason / all-rounder about our terrace. We are planning to use slabs measuring 60 x 120cm (24 x 48 inches) with a thickness of 3cm (1.2 inches). He advised against this. According to him, because of the thickness, the slabs cannot be compacted with a plate compactor without breaking. He also said that the base would gradually settle over time (even if it was compacted without the slabs beforehand), creating voids that would cause the slabs to become loose.

Does anyone have experience with this? Specifically, have such “thin” slabs been installed for a longer period, and can confirm or deny this?

Thank you!

You either need to use mortar or thicker panels.

Yes, exactly, it occurs at the edge, and you notice that it gives way slightly (millimeters?). This is because the gravel has settled there. The problem is that it cannot be properly compacted. With your large panels, there is also a risk of breakage. So either mortar it immediately to make it stable, or use thicker panels. This was recommended by a professional on site (to put it mildly).

Dealing with thicker slabs is not that simple. To be able to vibrate them properly, they need to be 6cm, ideally 8cm (2.4 inches, preferably 3.1 inches) thick. There are no (affordable) slabs available in that thickness and size. Even 60 x 60cm (24 x 24 inches) slabs are either unaffordable or nearly impossible to lift. That means you would have to use smaller paving stones for the terrace, which is exactly what we actually want to avoid...

When using mortar, there is also a risk that it could freeze and deteriorate from underneath during winter.

For this reason, when building the house, we had a slab foundation poured for the terrace right away.

Then at least use slightly smaller panels and create wider joints so that you can remove and repair any loose sections individually.