Patio base.

[Nicksun]

Hi all. I'm building a raised patio, 4 course high, with hardcore and approx 100mm of reinforced concrete fill. The concrete will be contained between the house and wall. Do I need to put any expansion gaps in? I've hopefully uploaded a pic with sizes etc.
Thanks. Nick

 

[Ian H]

I'm not sure about expansion gaps but the reinforcement is unusual, you might want to check/replace any drains you might be covering.

 

[Nicksun]

Perhaps I should've given more detail. The concrete will be a level slab for me to lay Indian sandstone with the recommended fall away from the house. Reinforcement may be overkill, but I'm doing it myself, a bit belt n braces perhaps?
There are no drains underneath.

 

[Ian H]

Normal thing would be hardcore then a full layer (rather than spotting) of sand and cement mix about 50mm think.

 

[^woody^]

The reinforcement is a complete waste of time, and the concrete a waste of time.

If you put a movement joint in to the concrete then potentially any movement will show through to the slabs on top. If you dont and it cracks, then so will that.

 

[Nicksun]

Cheers both. So, fill it with hardcore and type 1, both wacked? any other suggestions?

 

[Ian H]

If your hardcore wacks well I'd just have that then bed your slabs straight onto 50mm of wet sand/cement mix.

Point up with a wet mix too.

 

[Nicksun]

Cheers Ian.

 

[^woody^]

Whack the hardcore in 75mm layers or so.

 

[oldbutnotdead]

4 courses? So bang on the 300mm limit under PD for raised platforms? Be careful with your finished height- wouldn't want your neighbours kicking off and some clever sod appearing with a tape measure to tell you the concrete is fine but the slabs on top need to go

 

[eddiewakey]

Similar question from me. I need to lay some Slabs for a sloping path down to bottom of garden
Do I need concrete or can I just use sand ?

Also, should the slabs be butted up close or should they have an equal gap and then pointed ?

If I need concrete, what's the best mix?

 

[oldbutnotdead]

Very rude hijacking the thread, especially when its well off topic. If you're laying slabs then you don't need concrete. If the ground is firm and you're using beefy (50mm) slabs then sand will be fine, put some anti weed fabric down as well so the dandelions don't grow between the slabs. Butt the slabs together, wouldn't bother pointing unless you're OCD and can't tolerate 5mm height differences after a couple of years. Concrete- 3 2 1 (gravel/sharp sand/cement).Which you don't need to know cos you don't need concrete.

 

[r896neo]

A deep fill of compactible hard-core like that is a bad idea. As long as its restrained on all sides by masonary fill the lot with clean rubble and clean stone. It does not need compacted and will not settle. Lay slabs on a good full wet 50mm bed of 5:1 grit sand:cement.

Unless you can get a vibrating roller on it you will never compact that much to refusal and it will settle fractionally in a year or two.