cemenet mix for paving slabs

[eskymo]

I want to make my own paving slabs and want to know the best mix/ratio of sand/cement/aggregate/water.

The slab moulds are 450x450x38 in size.

I've bought blue circle cement, some builders sand and some 10mm aggregate - not sure whether to use the aggregate or not as I'm worried about not getting a smooth finish.

Can anyone help?

 

[JohnD]

You want to make concrete, not mortar, so you should be using a concreting mix - (sharp/concreting sand, not building/bricklayers/soft sand) and aggregate. The mould will give a smooth finish to the face of the slabs when you turn them out. You can probably buy an all-in ballast mix for fine concrete in bags if you do not need a load delivered. The bags will probably be marked with the aggregate size and suitable concrete thickness. 10mm sounds OK.

In one of the other posts today I saw the tip of putting a layer of chicken wire half-way through the depth of concrete as you place it, to reduce the chance of cracking. Compress it well and use as little water as you need to make a workable mix - water will dry out and leave air pores in the concrete, and air has no strength

 

[WabbitPoo]

I want to make my own paving slabs and want to know the best mix/ratio of sand/cement/aggregate/water.

The slab moulds are 450x450x38 in size.

I've bought blue circle cement, some builders sand and some 10mm aggregate - not sure whether to use the aggregate or not as I'm worried about not getting a smooth finish.

Can anyone help?

OK, I am dying to ask - WHY are you casting your own? For fun or is some old mold that you cant buy any more?

 

[eskymo]

We're casting them ourselves mostly because we can't stand the colours of the bog standard slabs you get in the likes of B&Q. they're either too bright yellow or red or plain grey. So we've got some pigment and mixing our own colour. But also it's alot of fun.

Getting a lot of air bubbles though, which we don't mind so much but does anyone know of a way of minismising them - we don't have a vibrating table or anything like that so it would have to be a back to basics option.

 

[JohnD]

If you have an orbital sander you can press that against the side of your table to make it vibrate. Bubbles should be on the top surface so will not show when the slabs are laid right-way-up.

 

[eskymo]

Thanks for the tip, but we've managed to do a couple of tests and the last one was the best. We used a flat rectangular trowel - the type you use to plaster walls and pummelled each addition of concrete into the mould to knock the air bubble out. My other half did a very good job and we got a slab that has only got tiny air bubbles around the edges which we're not bothered about. The main expanse of the slab in bubble free.

If anyone out there is interested in making slabs - these are the quantities we used.For one slab we mixed:

7 parts sand
2 parts aggregate
1.5 parts cements


We also mixed in a small amount of colouring - 3 film canisters full to be exact.

 

[arapototo]

for a slab/paving stone i would use 1prt grit sand 1prt aggregate and 2 prt cement. plus your colouring powder.

thats if you don't want it to crack if something falls on it.

your mix sounds pretty scary,,,,it WILL crack eventually.

sure it will have been a nice manageable smooth mix with ALL the sand you used

 

[joe-90]

The thread is six years old.