Renovate terrace on concrete slab

[cffol]

Hello,
I have a terrace on a concrete slab that I intend to renovate, and I have an idea but would like some input on possible risks and alternatives.

First, some information about the conditions:

• A concrete slab likely built in the 60s-70s, about 15 cm thick, a total of 4x5 m adjoining the house.
• The slab stands on a number of concrete pillars, and between these, walls are built up with lecablock to create an unheated storage room underneath.
• The condition of the slab is so-so - it hasn't been properly weather-protected, and the reinforcement bars at the edges have partially splintered the concrete. I have chipped away most of the loose parts at the edges, and the estimation is that it can still be repaired.

What I want to achieve:

• A patio that lasts for another 15-20 years
• Weather-resistant as we don't plan to have a roof over it (at least not entirely)

So to my proposed course of action:

1. Repair the edges with fine concrete
2. The floor level in the house is about 17 cm higher up, so I would like to raise the floor to avoid a step. At the same time, not add too much weight. Therefore, the idea is 10 cm of EPS.
3. On the EPS, I lay reinforcement mesh, electric underfloor heating (only for comfort in the evenings), and cast the thinnest possible "floating" concrete slab, about 3 cm.
4. In the casting layer, I build a slope of 1:100 away from the house.
5. On the concrete, I apply a waterproofing layer for outdoor use, like Weber Tec Superflex and finish the slope with a drip edge made of metal.
6. On the waterproofing layer, I lay outdoor tiles.

I think this should provide a not too heavy construction and be watertight - what I'm a bit worried about is the insulation and any condensation problems that could worsen in the old slab? The insulation, admittedly, is on the cold side (since the unheated storage is warmer than outside in winter), but in summer, the condensation should be even worse as it's kept quite cool in the heavy stone construction.

 

[Fjellreven]

Hello!
Reviving this question as I am facing a similar project. How did it go for you?

 

[cffol]

Hello,

It went well - did exactly as described, that is, removed all loose and ugly material, raised it with foam plastic, and then cast a new concrete slab on top with the appropriate reinforcement. It was about 5 cm thick.

I used Sopro waterproofing on top, and glued plates around the sides. Probably wouldn't use Sopro again since it was ridiculously expensive for what you get, but instead find another manufacturer. Nothing wrong with the product, easy to work with, etc., but as I said, expensive.

Laid tiles on top.

 

[Fjellreven]

Great! Thanks for the response.

I have started removing all the loose material, but along one short side, the top layer is really stubborn (see pic). Can I leave it and pour a new layer at the same level, or do I need to use the sledgehammer?

 

[Fjellreven]

 

[cffol]

What will you do then after you have leveled it up? If you are dependent on surface strength or intend for the final result to be visible, I would finish off thoroughly, but if you plan to cover everything with stone in some way, it sounds ok to just level it off.

 

[Fjellreven]

I was thinking of applying the waterproof membrane on top of this and then a thin layer that will be sanded/polished.

 

[cffol]

Sounds like it should just be a matter of casting up to level then!