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

Hello everyone,
we renewed our terrace. We compacted the gravel, leveled the aggregate, and laid the slabs on top using a floating method.

Is there a way to finish the joints so that they allow hardly any water to pass through during a heavy rain? We designed the terrace with a slope away from the house. However, if all the water seeps into the joints, this slope won't be effective.

Are there flexible joint mortars that are also nearly waterproof?

That doesn’t work. “Floating” and “waterproof” cannot be combined… (not even with firmly glued tiles…).

Nightfil schrieb:

Hello everyone,
we have renovated our terrace. We compacted gravel, leveled crushed stone, and installed the slabs on top as a floating layer.

Is there a way to fill the joints so that they hardly let any water through in case of heavy rain? We designed the terrace with a slope away from the house. But if all the water goes into the joints, the slope doesn’t help us.

Are there flexible joint mortars that are almost waterproof at the same time?

Why do you need waterproof joints when you have created the perfect permeable base with gravel? We also use gravel, crushed stone, and floating installation. Even during heavy rainfall, the water drains very well through the joints.

I am also not entirely sure what the exact problem is. In light rain, water seeps through the joints and then into the ground. In heavy rain, the infiltration may sometimes be insufficient, so the slope directs water away from the house. The foundation should be designed to be frost-resistant anyway, and a small amount of seepage water should not cause any issues.

Aloha_Lars schrieb:

Why do you need a waterproof joint when you have created the perfect substrate for infiltration with gravel? We also have gravel, crushed stone, and floating installation. Even during heavy rain, the water infiltrates very well through the joints.

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 permeable soil beneath the gravel (gray clay/loam).
If water infiltrates there, I am concerned that the precipitation might then flow back toward the house.
Normal rainfall probably won’t affect the house, but heavy rain for 2-3 days?…

That’s why I’m asking if it is possible to fill the joints in a way that prevents or significantly reduces water penetration.

What would happen if I simply filled the joints with joint mortar (quartz sand + cement)? Would this damage the slabs?

Nightfil schrieb:

Normal rainfall probably won’t damage the house. But heavy rain for 2-3 days?....

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

A little help: The joints make up about 1% of the surface area (roughly estimated with 60x60cm (24x24 inches) tiles), just to give you a reference size. There’s also a slope installed.
What do you think will actually come through the joints during two days of continuous heavy rain? More than 35 liters (9 gallons) per square meter in 6 hours is considered a severe storm. Most of the water runs off directly. So, the amount of water entering through the joints will really be in the milliliter range. Even after two days of severe continuous rain, essentially nothing gets through (at least no relevant amount).