The Brew Cabin

We have recently moved to a bungalow which is built below where water drains from a stream, through the house next to ours and then on to our drive and garden. We have had quotes for block paving and imprinted concrete both of which are going to lay drainage to the site to help alleviate the water problem. We would like advice on whether block paving would be likely to be unsettled by movement from below caused by any constant water problems? Is Imprinted concrete likely to be any better? Help and advice please

The short answer is that both surfaces are more than capable of surviving minor groundwater movements, with the standard pavingexpert.com proviso...all together now..."As long as they have been laid properly".

I assume your chosen contractor will install some form of interceptor drain to collect the groundwater before it gets to the driveway. This being the case, then as long as a decent sub-base is laid, incorporating a geo-membrane if there's any concern regarding high water table level or iffy ground, then either blocks or PIC will be fine. If there's a risk of inundation or excessive amounts of water running across the surface (known as 'scour' in the paving trade), then it might be a good idea to use a decent sealant if you opt for blocks, more to protect the sand jointing than to protect the blocks themselves.

It's also worth considering what happen if it does go wrong. PIC cannot be repaired. If it cracks; it's cracked. If there's any significant ground movement, it will crack and/or settle. Meanwhile, flexible block paving (assuming that's the type under consideration) will move with the ground, but can be lifted and relaid if the worst happens.

Proper design is going to be essential, whichever surface you go with. While PIC might be able to bridge any minor settlement, it will suffer badly if there was to be any significant movement within the ground unless it was full reinforced with steel, which is not the norm for PIC. Conversely, flexible block paving could reflect every little movement in the ground, but such movement won't be catastrophic and, as I said, can be rectified quite easily. The use of a geo-membrane around the sub-base of either surface will reduce the risk to the pavement by 'containing' the load-bearing layer, and preventing it being washed away or having the fines removed by the natural flow of groundwater, which would seriously compromise its effectiveness.

So, it comes down to personal taste and, I suppose, cost. I make no secret of my preference for block paving to PIC in 99 scenarios out of 100, which reflects my personal taste as well as professional judgement, but it's you that has to live with the driveway, and so the choice should be yours.

I hope that helps, but I suspect I've just confused you even more! Have you asked each of the contractors to explain why they think their preferred surface is better than the opposition for your project?

Thanks very much for for very prompt reply. Everything you say is useful. Just to let you know that contractors are going to put in interceptor drainage. However, the site is fairly level with not much drain off and is clay which since we have been here becomes completely waterlogged and in some areas underwater within a short time of any rain. Does the membrane youmention, which has been specified by the block paving contractor deal with this. Also we are concerned about weeds growing through block paving especially in these damp conditions. Is there any permanent treatment to prevent this or are we faced with a constant application of weedkiller?

Thanks again

There are dozens, possibly hundreds (I've not counted recently!), of different membranes and it's important that the right one is used for your application. The crappy stuff sold at B&Q and Garden Centres is not going to be the right one, but I imagine one of the higher strength Terram series (Terram 2000, f'rinstrance) might well be the stuff to use. However, I can't specify or recommend a particular membrane for your job, as I haven't seen it or surveyed the site, but you should make sure that your eventual contractor does specify a particular membrane, and justifies its selection. Plantex, Mypex or a 'weed control fabric' is not up to the job.

Weeds will not grow through block paving that has been properly laid. They will, however, settle onto the surface and grow into the pavement, but this can be drastically reduced or even eliminated by use of a decent sealant which should keep you more or less weed-free (which is not the same as maintenance-free) for 4 or 5 years at least.

Thanks again for more prompt advice. You have cleared up quite a few points for us. We will definitely recommend your site to others.