How to…

Create A Patio & Lay Slabs

building a patio base

Basic Construction — Laying Slabs & Building A Patio

  1. Existing soil or sub-base/sub-grade ideally generally level, though Type 1 will sort out any undulations further up.
  2. Type 1 MOT laid to a depth of around 100mm -150mm and compacted.
  3. Sand & cement mix, semi-dry consistency.
  4. Slabs to finish, ideally with wet mortar joints or jointing compound.

 

Tips & Tricks For Building Your Patio

Try to get your existing ground as level as possible, this will save on Type 1 MOT. You don’t normally need more than 100mm of Type 1 MOT, though you may want to put a bit more in if the ground below isn’t the best – i.e. if you’re laying the Type 1 MOT on clay or mud. Stony ground or an existing hardcore base is ideal, but you have what you have. Dig more out if it helps you get to a firmer base. You can also put a geotextile membrane between the existing ground and the Type 1 MOT if the ground isn’t the best, this will stop the Type 1 MOT from penetrating the not-so-good ground below. We sell geotextile membrane, and we also sell it ‘off the roll’ if you don’t need much of it. To find out more about our Geotextile membrane, get in touch with our friendly team today. 

Type 1 MOT should always be compacted, ideally with a flat wacker or roller. Remember that what you don’t compact at the beginning will always compact on its own over time, often with disastrous results. We hire out flat wackers and rollers. Always compact your Type 1 MOT in layers and ideally a few inches at a time. 100mm layers are too thick for compaction with a standard flat wacker.

When you’ve got your Type 1 MOT to a certain level, top it up where you need to and re-compact with your flat wacker. Now you’re ready for your screed bed. There are many variations to the make-up of a screed bed for slabs. Ask 10 builders what’s the best method and mix for a screed bed and you’ll get 10 different answers.

But here are a few examples. All of them will work to a certain extent, some of them better than others:

 

Sharp sand only, dry.

Not the best in our opinion, not unless you have extremely heavy slabs, such as 900 x 600 thick ‘council slabs’. Even then a screed mix without cement is not ideal and will increase the chances of future movement.

 

Sharp sand & cement, dry.

Much better than the above, and although dry when laid, some moisture will make its way into the mix eventually and give extra stability to the mix as the moisture reacts with the cement and hardens the mix. The mix will often be quite weak, often as weak as 6:1 or even 8:1

 

Sharp sand & cement, wet mix.

Now you’re talking! A 6:1 mix is normally sufficient, a stronger mix isn’t always best and you may even get shrinkage in a mix that is too strong and/or too wet. The mix should be dry enough that you can mould it in your hand to some extent.

 

Sharp sand, Building sand & cement mix.

Not necessarily better than the above, but a lot of people prefer this as it’s easier to work with. The sharp sand gives strength, and the building sand makes it more pliable. We can deliver sharp sand and building sand at the same time, which will be roughly mixed by the time it gets to you, will mix more when we tip it up and should be equally mixed by the time you’ve put it through your cement mixer.

Screed bed should ideally be 50mm thick, too much less will make it difficult to work with, you want to be able to push your slabs into it to get a good level. There’s no point in putting much more in and it will only cost you more money if you do. The sand & cement screed is probably twice the cost of the Type 1 MOT underneath.

Slabs should be laid soon after you have mixed up, get your slabs next to you where you want them, to reduce the amount of time that your screed mix is sat there going off slowly, particularly in the summer months.

Once you’ve laid your slabs, stay off them at least until the next day! If you walk on them too soon after you’ve laid them, you’re more likely to get some ‘rockers’. A rocker is the bane of any hard landscaper, there’s nothing worse than laying a large area of slabs and finding you have 1 or 2 the next day that is rocking slightly. There’s nothing for it, but to lift those offending slabs, dig out the screed and re-do.

 

Just with the screed bed, there are many variations when it comes to the jointing mix and method:

Dry sand-filled joints.

These are joints filled with sharp sand or ideally kiln-dried sand. We sell both types. Not the best method, but the quickest and cheapest. Sand-filled joints are only really suitable for concrete slabs with very straight edges, and where slabs have been laid very close together, a maximum of a few mm apart. As there is no cement in the sand, you’re quite likely to get small weeds growing in the sand between the slabs, and of course small weeds turn into big weeds. A membrane underneath won’t help, the weeds grow in from above not from below.

 

Semi-dry or dry sand-filled joints with limited added cement.

Same as above, still not ideal, but if you mix a bit of cement into your sand you’ll reduce the likelihood of weeds. Again, okay for concrete slabs with very straight edges and only if your gaps are very tight.

 

Wet mortar mix.

One of the best ways to point between slabs is basically a mix of building sand and cement, normally mixed to a ratio of between 6:1 and 4:1 and mixed wetter than the screed bed mix, but not too wet that it stains your slabs. This will normally be trowelled in and finished with a bricklayer’s jointer. More skill and experience required, but a better job all around! Some people mix a bit of sharp sand with building sand for extra strength and a bit more texture, but you should ideally have a lot more building sand in the mix than sharp sand.

 

Jointing compound.

One of the best ways to point slabs, but check with the manufacturer or supplier of the slabs first. This is a pre-mixed compound in plastic tubs that is basically swept in between the slabs, and then jointed whilst still ‘wet’, full instructions will always come with the product. The best method of jointing most types of slabs in our opinion. And although the most expensive method by far, you’ll save time when compared to the traditional wet mortar mix method. We sell this.


Frequently Asked Questions (and some silly ones)

Can I just lay slabs on mud, or lay the screed bed on mud?

No! Well you can if you want but you’ll be taking it up within a year, probably before. The screed is just the sticky stuff that binds the slabs and cements them in to a certain level. But without the Type 1 MOT on the bottom, things are bound to move. One reason is that the existing soil or sub base will expand and contract with the different seasons and varying temperatures throughout the year, especially if it is clay. Type 1 MOT will not. The only time you can do away with the Type 1 MOT is if you already have an existing stone or hardcore subbase.

Always on a slight slope, and with natural stone or ‘riven’ slabs you may want to increase the fall a bit to reduce ‘puddling’. Aim for a gradient of 1:80 for concrete slabs, and 1:60 for natural stone or ‘riven’. To lay to a 1:80 gradient, have a fall of 1 inch for every 80 inches of patio. Or 1cm for every 80cm of patio, and so on.

It’s best to fall the patio away from the house, but if the ‘lay of the land’ is towards the house then you may sometimes have to fall the patio towards the house In which case you will need a gravel trap (ideally 100mm – 50mm in width) at the house, or an ACO drain. We sell materials for both.

No, this will fall foul of Building Regulations and will likely cause you issues with damp where the patio meets the house. Always have 150mm between the dpc or floor level on the house, and the patio level.

It depends what you want to achieve, if it’s a path down the side of a house which is not on display, then why not use concrete slabs? If it’s a patio that you are going to spend a lot of time sitting on and looking at, then natural stone would be better. But you may prefer concrete slabs, of course cost comes into it. Concrete slabs are normally cheaper, and they do the job. The main difference is that concrete slabs will discolour more than natural stone slabs.

It depends on your experience, if you are a practical person who can turn his or her hand to most DIY jobs then you are going to get on better than somebody who is not very practical and who never undertakes any DIY themselves. If it’s your first time, then you are probably going to see a bit of imperfection in the job as opposed to, say, the 5th or 6th time you do it. So it’s a bit of trial and error at the beginning, but it depends on the standard of job you want doing, and of course if you can’t afford to get somebody in, then you may only have the option of doing it yourself. If you do need us to recommend somebody then please ask us, but bear in mind that most good hard landscapers are booked up many months in advance. If you want a new patio laying for the summer, you need to be getting quotes and getting organised in the new year, not around May/June!

We supply sand, cement, Type 1 MOT, all other aggregates and we also sell the jointing compound, and we deliver most items >>. We don’t supply slabs, but all the local builders’ merchants do. And we do plant hire , Click here >> We can also remove all of the material you excavate on our grab lorries >>

Maybe, it depends on how much needs digging out. If you can’t drive a digger or you don’t need much digging out to get to the required level, then you’ll most likely have to dig it out by hand. Click here for digger hire >>

Yes. Advice should be available from the manufacturer and/or supplier. Concrete slabs are more likely to discolour over time, natural stone slabs are more likely to retain their appearance. Wet mortar joints and joints filled with jointing compound are the most maintenance-free, but joint may need attention and may need re-doing after 5 years or more. Nothing lasts forever.

For calculating Type 1 MOT and sand, click here for our helpful online calculators >>

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