The Brew Cabin

Hi, I am new to this site and have a question I need answering if you can guys and gals. Im laying a patio for a friend so I need to get it right so I dont get moaned at!!!

I am going to be laying 450*450mm slabs of 30mm think. I thought the soil was quite firm until all the rain came down and although its still firm in places it a mess in other. Could you tell me what I need to do to apply a sub base and what to lay the slabs on. I was thinking of a single layer of some hardcore like scalping, pressure plated down.

What do I used aswell to lay the slabs on, Ive read so many different way and am a bit lost, I was going to use sand but I want the slabs to last years and not sink in places or anything. Please could some one give me a run through what to do and lay on

Ive also read that spot bedding is no good, is spot bedding that method of putting 5 blobs of cerment on top of a compressed sand layer and laying the slabs on to, should I not do this


Thanks all
Russ

(Edited by Rusty at 7:39 pm on May 5, 2003)

All your questions are answered on the main part of this website, Russ. Start at the Laying Flags page as that tells you all about bedding, what to use and how to place it, as well as explaining just why <spit> Spot Bedding is a crime against humanity.

If you've still got questions after reading all of that, come back and ask for guidance. :)

I have now read the topic area you said and it has helped a hell of a lot. I read that a sub base is not really required for patios, however, what is your opinion if the current soil condition is quite soft when soaking wet. Should I give it a good plate compressing down then add a small layer of hardcore just to thicken it up. I think I will also use the method of adding a bit of cerment to the bedding layer to add a bit of security

Russ

If there's a concern over the state of the sub-grade, then I'd suggest you scratch out the soft spots and fill them with sub-base material. If the sub-grade is a real mess, then perhaps a Geo-membrane will be the answer as it will help prevent the sub-base material disappearing into the mire.

Remember that a sub-base needs to be at least 75mm thick to have any inherent strength. Owt less than that is just a fill layer, which isn't a problem, but shouldn't be thought of as being load-spreading.

And the actual material used to form the sub-base is critical. Relying on brickbats and bits or rough 'hardcore' can cause more problems than it solves. It really is worth splashing out on a tonne or so of granular sub-base material, such as DTp1 and using that to form the sub-base, as that will make a dramatic improvement to the sub-grade, with or without a geo-membrane.

ok, im going to sound stupid now but whats geo-membrane, is it just the really heavy duty weed membrane you put down???

Geo-membranes and weed membranes are part of the same family known as geo-textiles, but a geo-membrane is far, far stronger, and is used to improve the strength of a pavement or other structure, whereas a weed membrane is intended to stop dandelions growing in your decorative slate mulch.

Have a read of the Geo-Fabrics page - I told you all the answers are on the site! ;)