The Brew Cabin

Posted: **Tue Nov 07, 2006 11:22 pm**

Having used this site before to good use I thought you may be able to help a guy at work.

It appears that he had a section of tarmac drive laid aprox 12 months ago.

Straight away he noticed that rainwater seemed to drain away correctly (towards the falls), but when he washed his car on the drive (ie water containing a detergent) this wash water seemed to penetrate the tarmac as if it was porous.

He contacted the contractors but they just didn't believe what he was saying, and never came back to check.

What would you suggest he could "coat" the surface with to prevent this water penetration - as presumably over time the current situation would lead to settlement of the sub-base.

Thanks in advance

Chris B

Posted: **Tue Nov 07, 2006 11:59 pm**

all bitumen/macadams or "tarmac" are porous to a degree. compared with hot rolled asphalt which is a denser mix and is not porous. the former is cheaper but is fine for a surface which is not heavily trafficed or gets heavy turning.if the sub-base is laid correctly and you have enough depth of tar,this porosity shouldnt be a problem and you should get at least 10-15 yrs out of it.

for a driveway surface i would recommend a 6mm (stone size) tarmac.some contractors may use a 14mm or 20mm tarmac,which will obviously be more porous than the 6mm,while not as pleasing to the eye as a denser mix,they should still be strong enough for the intended use.

Posted: **Wed Nov 08, 2006 6:06 pm**

Agree - it all depends upon the tarmc specification as bobbi o has said.

A 6mm SMA surface will drain very little water, most of it will simply run off whereas a coarser surface will drain far more freely. A 10mm SMA will behave in a very similar manner.

Posted: **Sat Nov 11, 2006 9:26 pm**

Hi Chris,

porous tarmac is not a problem if it meant to be so. Modern tennis courts are porous to make them playable straight after rain. If it's not meant to be porous then he might experience water damage to the base course. Macadams can be sealed with bitumen-based sealers, that give water-proof, hard wearing surface that will also extend the useful life of the surface. The Americans do it all the time - known as sealcoating over there.

Geoff

The Brew Cabin

Porous tarmac