Tarmac thickness? - Tarmac guidelines

[eltommos]

Having drive laid with red tarmac. Contractor has quoted to lay 6mm red colour tarmac 50mm thick on stone base. Question - should the tarmac be laid in two stages with a base course and wearing course or is it ok just to lay one 50mm thick course?

[Tony McC]

Should be two layers: base and surface. Read the Tarmac Layers page.

Also, with red macadam, it's critical you check what type of red macadam is being proposed. Is this just any old aggregate in a red binder or is it a red agg (eg: Mountsorrel granite or a quartzite) in a red binder?

[Dave_L]

6mm Redpave SMA - my fave!

[eltommos]

Many thanks for the advice. I've since spoken with the contracor who is willing to use two layers (no extra cost) as recommended on the website, but he says that the wearing layer will over time begin to wear away and break up. In his 40 years experience he says it's much better to have one well compressed 50mm layer and will be more durable. He has done may jobs in the local area and has a good reputation. Can I trust him?

[Tony McC]

Based on that bollocks:no!

If a surface is going to wear, and all trafficked surfaces will, then the number of layers cannot possibly affect the wear.

What is it about single layer construction that prevents it wearing away and breaking up as your man says happens with a double layer construction? Is the bitmac used any better? How does having a single 50mm surface course avoid the type of abrasion to which a 20+40mm double layer construction is subjected?

If, however, his argument is that the surface course can break away from a base/binder course in a multi-layer construction, then he's not prepping his layers effectively. He should be tack-coating or over-laying while the base/binder course is still fresh (ie: within 12 hours).

He would never, ever get away with single layer construction on a commercial project, so I'd suspect his 40 years of experience have been spent doing driveways only. In my paltry 30 years on site with the black stuff, I've never known a (decent) job where a single layer was deemed satisfactory.



Edited By Tony McC on 1171729045

[Dave_L]

Sounds very fishy to me!

Next housing development we surface, I'll suggest we do the roads in one nice thick layer! :p

Never have done single layer construction, even on a residential driveway.

Is he willing to offer a decent guarantee on his proposed works?

[eltommos]

Yes, he says work is guaranteed. I will ask for two layers as advised. Thanks all for your help.