The Brew Cabin

I am planning to put in a concrete patio beside our deck, and we are considering using the "Odjob pathmate (random stone - http://www.scepter.com/gc....)"
concrete mold to fill up the space with a cheap but attractive alternative to paving stones. Could I use a exposed aggregate finish?? Or should I just color the concrete?

1) Any ideas / comments / ideas?
2) Anyone every tried this?

We plan to put the stone mold up to the edge of the large garage door, then put in a regular driveway. Any help / advice would be appreciated. Thanks!

Cory Lechner
Regina, Saskatchewan, Canada

You could use an exposed aggregate finish, and you could colour the concrete - you could even do both, but I often wonder whether these 'home-made mouldings' are actually a cost-saver.

By the time you've bought the mould, bought the aggregates, the cement, the dyes and/or retarders, and then invested the time mixing, placing, vibrating and finishing, it seems to me that it works out more expensive than using pre-cast pavings. I know from feedback sent in by others who have used similar systems that, although they had good fun doing the work, they were often disappointed at the results and that, on refelection, about two-thirds of them wouldn't bother with it again.

Maybe this is because they had impossibly high expectations of just what is acheivable by the average diy'er using these moulds, or perhaps the amount of effort and time required was far greater than anticipated, but only about one in three (admittedly, I've only had 11 correspendents recount their experiences to me) were happy with the results.

Have you costed it out, and compared it against buying-in pre-cast pavings, Cory? I onbly know a couple of manufacturters ovver there in Canada, but prices are roughly similar to those in the UK/RoI, and, as such, the potential savings offered by a home casting system are very limited.

I can get cementing gravel, pea gravel (for the exposed aggregate) and a small cement mixer for nothing, all I need is about &#3650 of cement and &#3650 for concrete pigment. I checked out pavers and it wil cost &#36300 plus taxes. I think that it would have a neat random stone look that you cannot get with paving stones. My wife is also thinking that the spaces between the stones could eventually fill in with grass or moss to give them color.

I need to have a straight edge along the entire exterior of the patio - any ideas on how to accomplish it?

Any other ideas / advice / comments are appreciated.

Cory

Mmmmm....the 'random stone look' doesn't last, though. Getting the concrete properly vibrated and acheiving a consistent mix is always a problem with these jobs. However, as we say in my country, "Whoever pays the fiddler, calls the tune" :)

For your straight edge, you'll need some form of shuttering or formwork. Have a look at the Formwork page.

Good luck!

Tony - thanks for all the input, you are very knowledgeable.

1) I plan on using the higher strength concrete (is it called psi 4000?). Should I use this type of concrete?

2) My thoughts . . . the nice thing is in time, if one of the stones needs replacement, I should be able to pry it out and use the mold again can't I?

3) You talk about having to vibrate in the concrete mix - should I use something to tamp the concrete so it packs well?

4) What material should I use as a base for the concrete? Clay? gravel? sand? fill dirt?

5) any advice on sloping / drainage of this project?

6) what do you mean by the comment that the random stone look doesn't last? Do the stones breakdown? I do have our Canadian winter to contend with.

Thanks again!

Cory
PS - I plan on replacing our driveway as well, so I might be asking more advice on this as well.

1 - In the UK and the rest of Europe, concrete isn't measured in p.s.i. - it's 28-day strength can be assessed in Newtons per square millimetre (N/mm²) and, via empirical observations, mixes can be designed to achieve the required 28 day strength. What you need is a C30 or above equivalent concrete and the mix proportions for such a concrete is given on the Concrete Mixes page.

2 - yes, but it's still a lot of work!

3 - tamping just packs down the concrete, as you say, but you need vibration to shake out the air pockets and get a solid concrete, not one that's riddled with holes like a honeycomb, which, obviously, has a deleterious effect on end strength. Wet-cast manufacturers use a vibrating table - you'll have to come up with something more domestic!

4 - Base? Where? In the moulds or on the ground?

5 - Depending on the texture of the finished 'stones' I'd suggest a fall of not less than 1:60, with a figure of between 1:40 and 1:60 being ideal.

6 - Because you are doing this as a home project and don't have access to all the fancy admixtures, curing chambers and special kit that is used to manufacture high-quality paving units, the 'stones' you're going to produce will be softer and will deteriorate relatively quickly, compared to professionally moulded products. What looks like a good quality casting this year will begin to look like haphazard concrete after a couple of years of weathering.

It's an interesting project, but I wouldn't want to raise your expectations as to just what is possible with these home moulding systems. If they were as good as the sellers would have you believe, we'd all be using them. The fact that we don't, tells its own story.

Base - Yes I mean the material that the concrete will be set on top of. What should I use?

I'd use a sub-base of compacted crushed rock (whatever you have in your part of the world - over here we'd use DTp 1) and then overlay that with an impermeable membrane (damp proof membrane) of 1200 gauge polythene. That helps prevent the sub-base parching the concrete when it's first placed, and also helps protect it against aggressive ground water in the years to come.

There's a sketch of a typical cross-section for cast in-situ concrete on the Concrete Hardstanding page.