The Brew Cabin

Hi
I am getting some estimates for a block pave driveway along with our neighbour. She has had one quoting for dolomite for the sub base. I am not a builder but as far as I am aware this is something like crushed limestone. How does this compare to "DTp1" or "50mm Crusher run". Is it just another name used for the same material? Just want to get my facts right in advance.

This driveway will be replacing a tarmac drive which has been down since the house was built 12 years ago. Overall it is basically sound apart from a long crack running parallel 9" from one edge and the surface is now getting pitted and grotty looking. Also, it appears to have settled down about 0.5" relative to a drain in the centre. From what I read, I belive it is possible to retain this sub base. This may be dolomite. When the house was being built I remember the site foreman talking about a delivery of the stuff for drives and pathways.

Malcolm

Hi Malcolm,

dolomite is just another rock type and should be fine as a sub-base material. It may actually be classed as a DTp1, depending on its source. Whereabouts are you? Most of the dolomite is found/used in the east and SE.

As fopr the existing sub-base, after 12 years, it's probably settled as much as it is going to settle. A bit of re-grading to the top 25mm or swo, and re-compacting should be all that's needed.

Hi Tony
I am in the North East, Newcastle / Sunderland area. I've heard quite a few people talk about putting down the "Dolomite layer". So if the dolomite contains all sizes "down to dust", or I find out its the stuff they use on public roads, it could be DTp1 or as good as?

I thought you might be somewhere around there, as the biggest source of dolomite is them hills near Middlesborough (I can't recall the name now!!)

It probably is a DTp1. At worst, it would be a DTp2, but it should be fine for your driveway. DTp1 *is* the stuff they use on public roads - it refers to a distribution of grain sizes and rock hardness, not to a specific rock type. So, f'rinstance, over here in the NW, we get a DTp1 that's gritsone from the pennines, limestone from the Peak District, hardstone from N.Wales or even a granite shipped into Liverpool from some island they are quarrying of the W coast of Scotland. All very different rock types but all qualifying as a DTp1. :~)

As long as there is the right balance of fines and lumps, it will be ideal. :~)

Cleveland hills?

Thanks Tony. At least I won't tell a contractor his dolomite is rubbish, rather confirm that it has the right mix of sizes.

Just out of interest, what is DTp2 ? Is that the 50mm crusher run stuff?

Cleveland hills?

That's 'em! It's a few years since I last had a trudge around those parts! :~)

Thanks Tony. At least I won't tell a contractor his dolomite is rubbish, rather confirm that it has the right mix of sizes.

Just out of interest, what is DTp2 ? Is that the 50mm crusher run stuff?

Not quite. DTp2 has a slightly different 'grading envelope' to DTp1. I can't fiond the spec just at the mo', but if memory serves me well, it has more 'dust' than DTp1. It's a minoor diff, and not one that would make a masive difference to a residential drivewa\y, but, seeing as it's the same price (to withing pennies!) as DTp1, you might as well have the best stuff! :)

50mm crusher run is a very loose term that would probably be classed as a "Selected Fill Type 1 (SF1)". There's no grading envelope for 50mm C/run - it's all, more or less, passed through a 50mm sieve, so, theoretically, you can end up with all lumps or all fines, but, generally, it's a rough mix of lumps and fines.

Aren't you glad you asked! ;)

Yes. It's been very enlightening.

Thanks
Malcolm