concrete base for jacuzzi

Hi I have to help a friend who is buying a jacuzzi which he is putting on the lawn area. The size of it is 2.2x2.2m and 98cm high. I spoke to the supplier and they recommended a concrete slab with a mesh for strength. They said they would advise making the slab 2.1m square so that you don't see it. They said his is the most common way to do it.

I have made a concrete base before but it was donkies years ago and I can't remember much so need some guidance please.

Considering what it is for , does it need a membrane?

Do I need any fall on it, I would have thought it best in this case to make it totally flat as it wont get any rain hiting it and the base of the tub is a flat sheet of some kind, do you aggree?

How thick does the hard core need to be?

How thick does the concrete need to be, bearing in mind the size of the tub and the weight of the water and people in it?

What mix would I need for the concrete, when I did mine years ago for a big shed I used about 3.5 or 4 to 1 which seems a bit strong when I read some of the other posts here now, what do you think? Is strong not better within reason?

As this is quite a samll base do I need to go to the trouble of hiring a compactor for the hardcore or is there a hand tool I can use, I seem to remember seeing some handheld ramming tool?

Also I have not properly worked out materials yet, but assuming I do not need a huge delivery of hardcore maybe I can go to DIY store and buy bags of something which I can use as hardcore, any suggestions what I could use?

Lastly can anyone give me a simple way to calculate what quantities of ballast and bags of cement I will need please?

a 4" concrete slab will deal with a lot of weight. my fully loaded van can't crack a 4" slab anyhow, with or without reinforcing mesh.


dig out 200-250mm of earth.

lay and compact 100mm m.o.t. stone.

blind with sand at 25-50mm thick

lay 100mm deep shutter boards, lay 1200 gauge polythene and lay 100mm concrete slab.

make sure the slab is well tamped before trowelling. mix the concrete at 6 parts ballast to 1 cement. don't skimp on the cement.

a 2.1m square, 100mm thick slab will require a tonne of ballast (sand and gravel mixed) and 7 bags of dust.

3/4 tonne of mot will probably be ok. polythene is optional.

Sorry need some explaining please, what is m.o.t stone?

What sand do I blind with, is it sharp sand?

What do those big bags hold that they deliver ie will one bag contain a tonne of ballast?

Considering it is a jucuzzi, would you recommend I blind the hardcore and use a polythene sheet or will it serve no purpose in this instance?

Also can you confirm that I make it flat with no fall in this situation?

Sorry for all the questions.

happyhero said:

Sorry need some explaining please, what is m.o.t stone?

What sand do I blind with, is it sharp sand?

What do those big bags hold that they deliver ie will one bag contain a tonne of ballast?

Considering it is a jucuzzi, would you recommend I blind the hardcore and use a polythene sheet or will it serve no purpose in this instance?

Also can you confirm that I make it flat with no fall in this situation?

Sorry for all the questions.

Click to expand...

m.o.t. is a ubiquitous graded (30mm-dust) limestone sold at builders merchants

any soft sand.

those big bags hold a tonne.

if the jacuzzi ever becomes 'indoors', you're covered.

flat, no fall.