Sub-base - Not level

[slovak]

OK, I am a female novice so be easy on me. I have a freind that is helping me do my drive which is around 55sqmt. He has dug the concrete drive out to a level of 200mm. We put a geo-membrane down and then 11 tonnes of MOT. The problem is, he has wacked it down and it is really firm now but in places it is higher than other places. I know the problem is my drive as it is on a gradient going towards the house. I am getting the grit sand delivered tomorrow but I am not happy with the un even level. My freind wants to proceed as it is as he thinks when we put the sand down the level will correct itself. Obviuosly I think that this a receipe for disaster as I beleive your sub-base is the part that needs to be the most important part of the whole project. Please help as I need him to get this right. Thanks

[Tony McC]

No: the sub-base has to be more or less 'even' on the surface because you MUST have a laying course of regular depth. If you rely on a laying course of variable depth to make up the difference, then you get differential settlement in the completed pavement. This is because 80mm of sand will compact to agreater dgree than would 40mm.

The BS for block laying (BS7533 Part 3) requires the sub-base to have a tolerance of +20mm to -15mm but most site engineers (and many contractors) will work to a tolerance of ±15mm for the sub-base