Laying paving stones the right way

I had an email from a friend of mine who is in a quandary and has asked for some help.

Paul has laid a patio in his back garden outside a shed/chalet where he has a little workshop. Half of the building forms the shed and the chalet part is a sort of outside kitchen come family room for the summer where they eat regularly when the weather is nice.

Until now the lawn used to go right up to a wooden deck which is integral to the chalet.

He dug out an area that he wanted to pave to a depth of 75mm and in-filled the base area with course sharp sand. The sand was consolidated and graded off level.

The slabs were then laid directly onto the sand and pointed in with a 4:1 sand cement semi-dry-mix mortar but just three weeks later he noticed movement in the slabs with considerable movement when he walked on them.

Paul tells me that he was given advice on what to do at the local builders merchants. Advice I consider to be incorrect.

The slabs Paul used were 37mm thick and 450mm x 450mm square. It is my view that these are far too thin for bedding down directly onto sand, especially on a bed of 38mm. I have always been an advocate of using 5:1 sharp sand and OPC (Ordinary Portland Cement) mixed to a fairly wet consistency so it runs quite freely from the mixer. Do not worry that it is wet because once the mortar comes into contact with the paving it will very quickly firm up as the water is 'pulled' from the mixture onto the stone.

It is quite acceptable for pedestrian use only to lay the slabs directly onto the mortar which in turn is directly on the soil providing the soil is firm, but make sure you have a depth of mortar of at least 50mm. However, it is always advisable to provide a consolidated sub-base of type 2 limestone scalpings so that the chances of movement are diminished.

I like to level out the mortar with an ordinary trowel and then fluff it up using the point. When you present the slab, the air is pushed out and the water is absorbed into the slab. You should not have to tap hard, just enough for it to locate your pre-set levels.

If the traffic is to be heavier with say a garden tractor or perhaps a car then it is essential to use 75-100mm of limestone scalpings compacted using a vibrating plate or roller and then at least 50mm of mortar to bed the slabs onto - assess your base depending on the type and regularity of any traffic.

Use a rubber mallet to tap down the paving; it is easy to damage a club hammer handle if you use it constantly. After 24 hours the mortar mix should be as hard as nails and the joints can be pointed in. Be careful as the cement is still green. If you are able to leave for a week then even better.

As far as just sand bases are concerned, it is best to do this only if you have a heavy flag stone like York paving. Heavy stones and interlocking paviors will hold in place quiet easily on a consolidated as sand base.

There are also a number of ways of using a sub base support system that acts as a profile which is set in place beneath your paving stones. It is very interesting way to fix your slabs but you must ensure the metal bars are well fixed and cannot move otherwise the problems described above will occur again.

You must also make sure that the thickness of the paving is consistent. Some manufacturers, especially the cheap 99p type of slab will often vary so be careful.

Edited 9th May 2008

Comments

[andy]

I've gone with a 10:1 ratio of sharp sand and cement using a dry mix amd that seems to do the job for low use area.

[D&S Services]

I also went with a 10:1 of sharp sand and cement dry mix and sets really well.. i left it for 3 days to go off and on the second day just lightly sprayed with hose. I pointed the joints on 3rd day and even sealed it all with sealer.. to be honest its spot on.. but on bigger areas like one ive just done which was 64m2 i used 5:1 sand and cement wet mix which works good, but i do always seal it where the client doesnt mind that kind of finish.

Hi

My neighbour is having her garden flagged. The guy has laid a plastic membrane over the grass and up to now poured in 4 tons of sand and tamped it down. He's started at one side of the garden laying stone flags and up to the gate, across which he has placed a plastic kick board (which isn't high enough) the level is currently running at 8 and a half inches. Beyond this he needs another couple of tons of sand we reckon to finish the job. This seems excessively high to pave a lawned area. Her other neighbour has a wooden fence with a small concrete kick board (sorry I don't know the technical terms for these) at the bottom and we have a brick wall. We reckon the floor level could hit a foot by the time she reaches us and her back door step will probably just about be level if now lower... She's probably done it so that she can see over our 5ft8" wall but obviously when she's finished, we'll be raising that. Just a bit worried about the weight of all that sand/stone on the structures around it.

[Philip Voice]

Hi

Can you send a photo of the work? [email protected]

[William Smith]

Great article! Keep up the excellent work.

[installation of pavers backyard in los angeles]

Great post, everybody is interested in getting the knowledge of paving stones and this can be a great guide for the people.

[Evie W]

Interesting read!

[Landscaping Company North London]

Very well detailed job spec, really enjoyed to read, great work. I totally agree with the section regarding slab thickness, and it boils down to you pay cheap you get cheap

[Stuart]

Nice article! Very detailed and unlike other paving articles emphasised the difference in compaction required for foot traffic vs vehicular traffic.

[Joe Bloggs]

Not done a lot of this stuff but over here in wet Wales I always want a good layer of hardcore going down first (minimum of 4-8inches depending on the nature of where it is going) and then impacting down to form a solid base. Then you can go on with a wet mix of sand / concrete. Again that would be a depth of about 4xinches minimum...

[Derek Dewitt]

My wife and I are thinking about installing a new concrete driveway but don't know where to start. I like that you talk about using a rubber mallet instead of a metal hammer for tapping down the pavement. I was wondering what we were going to use instead to avoid damaging the concrete so this was perfect. Thanks for the help!