ᐅ Grouting Loose-Laid Patio Slabs to Make Them "Waterproof"

SaniererNRW123 schrieb:

Just think about how much water can pass through the joints. Once you’ve thought it through, you’ll realize your question doesn’t really make sense 😉 .

Helpful info:
The joints make up about 1% of the surface area (rough estimate with 60x60cm (24x24 inches) tiles), just to give you a rough idea. There is also a slope installed.
What do you think will actually pass through the joints during continuous rainfall over two days? More than 35 liters (9 gallons) per square meter in 6 hours of rain counts as a heavy storm. Most of the water runs off directly. So, the actual water ingress through the joints will be in the milliliter range. Even after two days of constant heavy rain, practically no significant amount gets through.

Many have told me that already.
But if I turn on the garden hose full blast and place it at the top of my terrace, the water doesn’t go past joint 2. All the water flows down joints 1 and 2… And that is with a 3.5% slope.
The joints are about 1mm (0.04 inches) wide.

SaniererNRW123 schrieb:

Just think about how much water actually gets through the joints. Once you’ve thought it through, you’ll realize your question doesn’t make much sense 😉 .

Helpful hint:
The joints account for about 1% of the surface area (rough estimate with 60x60cm (24x24 inch) tiles), just to give you a figure to work with. There is also a slope incorporated.
What do you think will actually come through the joints during a continuous two-day rain? More than 35 liters (9 gallons) per square meter in 6 hours of rain is considered a severe storm. Most of the water runs off directly. So in reality, you’d only get a water ingress in the range of milliliters through the joints. Even after two days of continuous heavy rain, almost nothing gets through (at least not a relevant amount).

That is not correct, of course. Where does the water from the tiles go? Exactly, into the joints.

driver55 schrieb:

That’s not correct, of course. Where does the water from the panels go? Exactly, into the joints.

In heavy rain, with a 3.5% slope and 1mm (0.04 inches) joints, not really.

Nightfil schrieb:

The joints are about 1mm (0.04 inches) wide.

That’s not a drainage joint. We’re talking at least 5mm (0.2 inches), often 8mm (0.3 inches) or even wider. Over time, fine particles will wash into the joints, making them less permeable.

Nightfil schrieb:

Although the slabs, as well as the gravel and crushed stone, have a slope away from the house, this does not apply to the poorly water-permeable soil beneath the gravel (grey clay).

That’s the real problem. The slope needs to be present at all levels: the subsoil, the gravel, the crushed stone, and the paving. A 3.5% slope is actually quite steep for a patio—you’d risk water running over like a soup plate. Did you do the work yourselves or hire someone?

P.S. I quickly checked some tables – keyword runoff coefficient (of course, there is a relevant DIN standard for this). Under heavy rain and with a sealed asphalt surface, it is 1.0, meaning all water runs off. For patio slabs, it is 0.90, only slightly lower than the sealed asphalt. Under normal rain, the numbers are 0.9 versus 0.7 (the remainder up to 1.0 infiltrates or evaporates). Unfortunately, there are no exact figures for large slabs with very narrow joints (calculated with 5–8mm (0.2–0.3 inches)), so the value is generally higher. In both of my cases, it is significantly higher.