The Brew Cabin

Using soil excavated from the footings of a huge extension and double garage we had built, I am in the process of landscaping a large rear garden (about 400m2) which lies on a medium gradient slope away from the house. The main feature is that the garden is to be terraced, with a pergola walkway down one side of the upper garden, and over part of the across the middle of the garden. The flagstone path will continue round the outer edge of the whole of the upper garden. The terracing process involves shifting large amounts of topsoil and heavy clay subsoil to create the necessary changes of level. The work has been going on for the best part of a year now, as I am barrowing it all. (Don't ask!) Do you have any advice on the length of time I'd be advised to leave the shifted material to settle naturally, what's the best way of compacting it - if that's what should be done - and the kind of base I'd be best advised to have before I pave it with flags? At its deepest point the difference between the new level and the old level is about a metre; at its shallowest it's about 300mm.

I've read with interest all your stuff on this site and found it extremely helpful and informative, I could just do with some clarification on this particular issue.

Good to see you made it into the forum at last, Roger! :)

It could take anything from 12 months to 12 years for your re-grading to settle and compact. It all depends on soil type, particle sizes, weather (honest!), traffic, and probably the winner of the Grand National on Saturday!

What you could do is get yourself a wacker plate and run that over the planned pathway a dozen or so times. Allow at least 450mm spread each side, so, f'rinstance, if you want a 1200mm wide path, wacker it 1200+450+450=2100mm wide.

You will find that the wacker plate sticks to the clay, but by spreading grit sand or scattering a sprinkling of DTp1 over the semi-compacted earth, you should be able to manage.

There are a couple of tools that are specially designed to compact earth/soil/clay. The first is a Trench compactor, which is similar to a wacker plate but has a much more powerful engine and a wider plate. Secondly, there is a Rammer - a sort of motorised leg that bounces up and down and litterally hammers the ground solid. You should be able to hire these via somewhere like Hewden Hire. The Rammer (aka Rampactor or Jumping Jack) is a bit of an experience the first time you use one, but they're great fun once you've learned to control them. :)

And, of course, you could always use a roller. A single drum might be a bit like hard work, but a double drum, something like a Bomag 75 walk-behind, might do the job, but be wary of getting it bogged down.


Let us know how you get on! :)

First of all, great site Tony, it's very rare to find this sort of in-depth info to help DIYer's make the most of expert experience to do projects like patio laying the right way.

I'm building a raised patio using a three course brick wall around the perimeter, infilled with a 150mm layer of compacted hardcore, 40mm layer of semi dry bedding mix and then Bradstone slabs on top. I'm doing a raised patio because my patio doors are 6 courses of brick high off the ground. The DPC is right under the patio doors so the raised patio surface will be 150mm below the DPC.

Once the wall is built, can I load my hardcore layer directly onto the top soil, then use a wacker to compact it, or do I need to excavate the top soil first ? It would be a right pain in the a**e to move all that top soil only to fill the space with more hardcore. I'm thinking of using crusher run as the hardcore.

Also, if I butt the patio onto the back of the house, it will cover a number of air bricks which are positioned low down on the back wall. To get round this, I'm going to leave a 150mm gap between the back wall of the house and the patio to allow air to get to the air bricks. Although the patio will slope away from the house, I'm worried about any water which might collect in this "gully". I'm thinking about putting a 4m run of linear drain into this "gully" which will sit below the level of the air bricks, and hence about 100mm below the patio surface. As I'm not expecting too much water to get into this drain, can I just leave both ends of the drain blocked and let any water to just evaporate away or do I need to run some drain piping to feed the water into the rainwater system ?

Thanks in advance

Hi Jonny, you sweet talking sod! ;)

You should be ok laying the sub-base over the topsoil, but strip off any vegetation first, along with the top 25-50mm or so, as this tends to be soft or improperly compacted. Further, if you have soft, made-up or iffy ground of any sort, it might be worth putting down a separation membrane forst - something like Patio Partner from Terram, or Terram 1000, if you have a lrrge enough area.

As for the airbricks, one way of resolving this common problem is to build a small retainer around the airbricks, using bricks or concrete edgings. If the retainer is kept 150mm or so clear of the airbrick, this will ensure adequate ventilation, and, by raising the retainer by 25mm or more above the paving level, you can prevent almost all water (other than a few drips of rain) from getting anywhere near the airbricks.

As I said, this is a common pronblem and I've been building a page dealing with the most common solutions, but, it's not ready for upload just yet. However, if you can't understand what I'm wittering on about in the paragraph above, I'll sketch it out and upload a drawing for you.

Your solution using a linear drain is another oft-quoted solution, but, you really do need to have an outfall at one or both ends, even if it's only to a mini-soakaway. Without an outfall, you're more or less inviting trouble and you can almost guarantee the damned thing will fill with water! The best solution, of course, is to connect the lin drain to the existing SW system, if at all possible.

Cheers Tony. I've gone for the Linear drain option and it's worked a treat. I'm now about to lay the slabs. I've dry laid them out onto the compacted hardcore sub base. How do you recommend laying the slabs onto bedding mix...lifting them one at a time, adding bedding mix and bedding in before moving on to the next slab, or lifting all the dry laid slabs, putting bedding mix down over whole area and then bedding the slabs in ? The area to lay is about 20 m2.

Thanks,

Jonny

For me (before I was knackered), I would have cleared out the flags, spread the bedding material, then laid all the flags and been in the alehouse by dinner time. ;)

However, if you're going to be working slower than that, it may be worth doing half at a time, spreading around 10m2 of bedding and getting that area flagged before deciding if you want to do any more that day.

I'd still get all the flags out of the way, first, though. Lifting one at a time and adding bedding will be a nightmare - you'll be tripping up over the unlaid flag, losing your tools, struggling to bring in the bedding material. It's always better to work in a cleared area. :)