Hi all. We’re planning on building a 3m x 5.5m timber garage and they recommend a concrete slab 6ins thick. That’s 4ins below ground and 2ins above to let the rain drain off the side. What depth of hardcore do you reckon I need below the concrete?

150mm min, but will depend on thickness of topsoil and ground conditions

Strip off the topsoil and then make up the level to where you want to be and you should be good, if you can easily dig your heel into what’s below the topsoil (say soft clay) then maybe go a little deeper. Make sure you compact it well. Also, try and time this all to be complete just before concrete is booked in, so you don’t have a gravel filled pit full of rainwater…

Used this site when I did some block paving and had no problems

http://www.pavingexpert.com/concrete.htm

Looking at the diagram, would you suggest a DPM between the hardcore and the concrete? Will damp really get through a 6ins slab of concrete?

Will damp really get through a 6ins slab of concrete?

I suspect it all depends on the soil type, what level the water table sits at, is there obvious drainage from rain water run off away from your property or does other properties rain water run-off drain towards yours, etc, etc.

As a child I lived in an old house with no damp proofing etc, and in the winter damp would wick up the outside toilet wall by about 1 1/2 feet

For the price of the DPC and the little hassle of installing it you’d be silly not to. If a car is going on the slab then wack in some A193 mesh for extra oompah.

From memory you need 18″ of concrete to form a waterproof barrier
The slab is bigger than the garage so it will wick in from the sides anyway to some extent. But I’d put a membrane in, it’s good practice and will stop the concrete draining into the hard-core when you pour it

Sounds good advice then. Won’t be parking a car in there so doubt I’d need the mesh but you’re right……for the cost it sounds worth putting in the DPM. I need to calculate costs of hardcore, concrete and skip/grab loader hire now. I presume for the amount of effort it’ll take, no one would bother mixing the concrete themselves in a mixer?

Use as much hardcore as you can get, proper stuff mind, no soft hedge-pron…………

Nooo, don’t mix yourself, it’ll be setting before you finish!!! Ready mix is the way to go. Make sure you have wellies, gloves, eyewear and rakes. Set your framework up prior and skim off the top to level. You can hire a gadget that will give you a nice smooth level finish for little effort.

Not worth mixing yourself that’s for sure 🙂
You wouldn’t get it consistent enough and you’d be hard pressed to mix it fast enough anyway in Belle
If you’re laying 6″ I don’t think you’ll need mesh but if you were going for 4″ put some in