Can't get dtp1 - best alternative? - Crusher (25mm-dust), dolomite, hardcore

[InfAddict]

I'm going to be putting down a subbase for my patio shortly and I've been getting quotes for the material. My local BM's don't seem to stock DTP1 (in fact most requests for DTP1 seem to result in confused silence, as if they don't know what I'm talking about!). This usually happens again when I then ask what other granular subbase materials they stock ???

Anyway, I can choose from the following :

- Crusher Run (1 inch to dust)
- Dolomite
- Hardcore

I've found information on Crusher Run (50mm) and Hardcore on this site, but I'd like other peoples opinions on what I should go for in the absence on DTP1.

The patio will be light use only but I'm putting a subbase down to fill some depressions and to get a nice level starting point on my heavy clay soil.

Thanks in advance.

[steve r]

If you really want DTp1 have a look in yellow pages under sand and gravel merchants.
I bet there's a page full of entries all willing to take a few quid from your wallet.

regards Steve

[Tony McC]

They must be real numpties is that don't understand the term DTp1 or Type 1 - it's a very, very standard term used throughout the construction industry in Britain and Ireland (although in Ireland it's often known as "804" as the actual 'recipe' for the material is contained within clause 804 of the Specification for Highway Works, a document used in both Britain and Ireland, and many other countries around the world).

Inch to dust crusher run is too fine. If thye can get inch-and-a-half or 40mm to dust, that would be better, as they are usually quite similar to Type 1 or type 2 specification. Dolomite is a type of limestone and so it tells us nothing about the size of the stone - it could be 150mm down or it could be 6mm chippings! Hardcore, as I've said many times before, is a sloppy non-specific term that really shouldn't be used by any BM with pretensions to professionalism, as it can be anything from reasonable quality crushed stone to owld knackered bricks, broken concrete, and muddy crap dug from some godforsaken hole in the ground.

[InfAddict]

Thanks for the replies guys.

I've been through all local BM's in the Yellow Pages and only a couple can get hold of MOT1 and this comes loose (direct from the quarry) rather than in dump bags - ideally I wanted it in tonne bags as I don't want 5 tonnes dumped on the road.

Tony, you mention that inch to dust is too fine. I'm guessing this is due to the rule of thumb mentioned on the sub-base page to do with the depth of sub-base and max particle size (e.g. 50mm particle = 100mm depth).

Firstly, remember this is for a light use patio and my main reasons for using a sub-base is to fill some depressions and to raise the level slightly on a clay soil.

Also, my subbase will be maximum of 75mm and in places less than this (maybe 40-50mm or less). Therefore, would 50mm particles not be too big for these depths? With this extra information, would you still say that 25mm is too fine?

Finally, I have a question about how to achieve the correct fall and transverse level when laying the subbase. The area is fairly small (40m2) so running down the area I have 3 string lines which have been adjusted to provide the correct fall towards the garden and away from the house. Whats the best approach to use when laying the subbase? Should I spread and rake the material, compact it and then check for an equal vertical distance to these string lines (which are currently at finished patio height) and then also use a long spirit level for transverse level?

Thanks again for the continued help and sorry if I'm being an eejit ???

[steve r]

I'll leave the stone question to Tony.

If you run a line between the outer 3 pegs, that will give you your level, you can check it with a spirit level.
Pegs can be driven in along your 3 lines at intervals and a pencil mark made where the line touches them.
You can now put a string line between any of the pegs, and measure down from it to get the sub base level.
Put a pencil line on a piece of batten at a distance equal to the thickness of the flags + bedding up from the bottom, and that will give you the height of the sub base from the string line.

[InfAddict]

Thanks very much for the reply Steve - I will put your procedure into action sometime this week!

Tony, when you get back and have time, I'd appreciate your comments on the choice of subbase as per above. Ta.

[InfAddict]

Quick update : after finalising levels the subbase will be maximum of 95mm and in places will only be 40-50mm. With these depths and variances can anyone tell me if 25mm or 50mm crusher run is best? I'm ordering on Thursday so if anyone can help before then that would be great.

Oh also, with regard to the calculators on this site, does anyone know :

1) What compaction rates does the subbase calculator assume? Will this be fairly accurate for both 25mm and 50mm crusher run or only for DTP1?

2) What depth does the bedding calculator assume? I'm planning to use approx 40mm bedding (min 30mm max 50mm) - does the calculator do the same?

Cheers and Beers

[Tony McC]

I've spent most of today catching up with posts to the Brew Cabin and I'm sure I wrote summat about 20mm to dust earlier - too dusty to form a truly competent sub-base, but better than nowt, I suppose. You'll probably get away with it for a patio but I couldn't and wouldn't sanction its use on a driveway.

Turning to the calculators, the coverage rates are based on the density of a typical limestone material ciompacted to refusal. There is some variation if you're using, say, a gritstone or a gran ite, and if you use a depth of material significantly different to the 100-150mm standard, but you'd have to be working on a project of 100m² or more for it to make any real difference.

The bedding mix calculator assumes a 50mm bed and gaian, you'd need to be doing 100m² or more before there was any real impact on calculated quantities.

[InfAddict]

Thanks very much for the reply Tony - I appreciate what it must be like to return and not only miss the Guiness, but also have to reply to hundreds of forum posts

Anyway, 5 tonne of 40mm crusher run has now been ordered and will arrive Saturday morning. Whacker has been reserved so I'm all set for a fun weekend of barrowing 5 tonne from the front drive to the back of the house :O

I'm in a good mood anyhow cos I've just knocked £200 off the price of my flags by ringing round a few other places!

P.S. I'm taking photos of the site from before I started, thru digging out, sub-base and then onto finished patio. I'll forward them on at the end of the project and you can rate my efforts!

[Tony McC]

There's a special section of the website for the DIY jobs - I'll add your piccies when you're ready.