Gardenseeker

How to Build a Patio - Design and lay a patio 

This is a substantial article - It would probably be better if you print it out - DH

When you choose your paving for the patio, try to see it laid somewhere in a real life situation. Don't buy on the basis of catalogue pictures. The colours are not always true; catalogue patios are often set up in a photographic studio, where the lighting will enhance the texture of the slab.

You will rarely see a patio picture in a catalogue, without some form of planting design around the edges. The art director knows that this enhances the effect of the paving - learn from this.

There is no need to stick to one type of paving or surface in the design  - experiment. Pebbles, gravels, bricks and tiles, can all be incorporated. A contrasting brick edge can also be effective.

Generally, it is better to choose a colour that contrasts or compliments, when the patio is laid near to the house. Do not try to match the colour of the brickwork for instance. (Dark brickwork - light paving and visa versa). Dark colours are less reflective and are therefore not so much of problem in terms of `glare'.

Do not underestimate the effect of glare. Make your patio user-friendly. A darker slab will also feel much warmer (or hotter) than a lighter slab, and will retain - and radiate heat well into the evening after the sun has disappeared.

The sizes of paving slabs are usually given in `nominal' measurements. Bear this in mind when you first design your patio area. The measurement includes the pointing which you are going to have to do - usually a 10mm allowance. This is important to bear in mind if you decide for some reason to butt your slabs together instead of pointing them. A 600x600mm slab will probably be only 590x590mm in real life. If you make provision for a 12 slab run of butted slabs, you will end up 120mm short (5 inches). This can be quite upsetting.

Slate grey Patio with a surrounding border of evergreens Clematis growing out of Patio pocket

Alternatively, if your jointing/pointing is nearer to 20mm wide, then you can end up 120mm (5 inches) over your estimate on a twelve slab run. (Even more upsetting!)

With some of the riven/york finish slabs, it is virtually impossible to provide the 8-10mm joints advocated in some catalogues when laying the slabs - especially if using a combination of sizes for a random rectangular effect, unless you simply dribble sand down the gaps. (This is quite acceptable in some instances). It is a good idea to lay some of your slabs out on some level ground, to get the feel of them and assess joint width.

If using a random rectangular pattern design to lay your patio, then make sure that you choose paving which work within the pattern. The relevant sizes will have to be in multiples of the smallest dimension. For instance, 300x300mm, 600x300mm, and 600x600mm will form a `random rectangular' bond, but you will not be able to include 450x450mm. To use the 450x450mm slabs within a pattern you will have to incorporate them with 225x225mm, 225x450 and possibly 450x675.

Make a laying plan, or get a ready-made 'pattern-sheet' from your supplier which will have various random patterns printed out. I find that for laying 'three-size' patterns, a ratio of say 30:60:35 of 600x600mm : 600x300mm : 300x300 respectively, works out fine. `Random' it may look, but plan it to look that way!

If you have to cut slabs at the edges or whatever, then a diamond disc blade is best - wear ear defenders and goggles. If you just have a few cuts, then you can get away with a `stone' cutting disc at £2.oo - 3.oo each. The diamond disc is around £100.oo, but will last 40-50 times longer than a `stone' disc. You can hire them, but they are expensive. Charged at up to £60.oo per millimetre used - a big rip off!

How to build your Patio - Laying the paving

So, you have decided upon the design elements. let's get down to the easy bit - laying the patio!

The two most common construction faults which spoil patios, are uneven surfaces, and poor foundation preparation, which can result in the patio `breaking up' and sinking in sections. get this right before you start to lay your patio.

FOUNDATIONS

If the area where the patio is to go has a hard well-compacted soil base, then huge quantities of hardcore are not necessary. This type of compacted soil base is found in areas that have been well walked upon over years, or have been subject to several passes by heavy machinery. If you can dig your heel into the surface, then it will need bolstering up with a layer of MOT type 1 sub-base, compacted into the surface with a hired plate compactor.

Where the area has been used as a flower bed, or otherwise cultivated during the last few years, then it will certainly need to be prepared. A compacted base of hardcore rubble, followed by a blinding of gravel or MOT type 1 sub-base material is then laid and compacted. This can be as little as 50mm deep.

`Made-up' ground, (where soil has been deposited to raise levels) will certainly need a well prepared foundation after extensive compacting of the soil base. It would be wise to leave the area to settle before attempting to construct a patio. Regular drenches of water will accelerate the settling process.

Foundation bases are best prepared from compacted rubble and or MOT type 1 sub-base material. (Scalpings). Compact your base with a hired plate compactor. The finished base should be even without any voids between the lumps of rubble/hardcore.

The first thing to sort out before you lay your patio, is the accurate marking out of the patio shape from your design. If you want a sweeping curve, experiment with a hosepipe laid upon the ground until you get the shape you require, then put temporary canes or pegs along the curve.

If the area - or part of it - is to be based upon a right-angle, then set out by using the 3-4-5 method. Do take time to ensure that you get this set right.

DPC - Damp Proof Course

Decide where the finished level of the patio is to be in relation to surrounding ground levels and damp-proof course on buildings. It should be at least 150mm below the DPC. In deciding the finished levels, you will have to allow for a `fall' across the patio, to allow rainwater to run off. (Where is it going to go?) You may need a drainage channel for the surface water to run into in some circumstances. (In theory, water will actually run off a perfectly level surface, but your laying technique will have to be spot on to ensure no puddling. The patio will also have to be above the surrounding ground levels.)

A normal `fall' of around 50mm over 2.4 metres is quite adequate. (This will give you a 2inch fall over the length of an 8 foot long `straightedge' in old money, and will not have people toppling off chairs.)

If the patio is going next to the house, then the fall must be away from the house. If it is absolutely impossible to fall away from the house, then surface water must be intercepted by a suitable drainage channel with adequate collection pit/soak-away. This is best incorporated when you lay your patio.

You should start laying your paving from a straight base line and work from that. Do not try to work from two fronts when using regular patterned slabs, for a slight discrepancy in your right-angle will be magnified as you progress and you could end up with widening or narrowing joints .

It is possible to lay some slabs onto a sand/cement mortar mix that has simply been screeded, but more often than not it will be better to lay each slab individually from a `trowelled bed'. Commonly, five dabs of mortar are put down - one for each corner and one in the middle. Alternatively, a shovel of mortar can be dumped where the slab is to be laid, and then trowelled out.

The mortar mix should not be too wet. Unlike bricks, paving stones are made from concrete; which does not soak up moisture. A wet mix will have your paving slabs `floating' and as you tap one down, an adjoining one will rise - leaving you with an uneven surface. The mortar will need to be firm enough to allow the slabs to be bedded down firmly into place.

Coarse sharp sand is normally used for the mix in preference to the softer `building sand'. I often use a 50/50 mixture of coarse and building sand. It works out at half bag of each in the mix, with one and a half shovels of cement. You will need to determine the volumes of the bags of aggregate in your own area. The coarse sand gives the strength, whilst the building sand makes the mortar just a little more pliable - easier to tap the slab down into position. This mix also seems to adhere to the slabs better than a sharp sand mix. A bedding mix of 5 aggregate (sand) to 1 of cement is usually sufficient. Perhaps a slightly stronger mix of 4 to 1 in less stable soils.

If the slab you are positioning does not want to `sit down', take it back up, remove the mortar mix from slab and base and start again. Likewise, if the slab is too eager to `sit down' do not be tempted to raise it up and ram mortar under the edge. Take it up; start again. Check in all directions with your straightedge.

For tapping the slab into position, I tend to use a pickaxe. A 1 metre length of 100x100mm (4x4inch) fence post will also act as a good punner - especially when it has been used a few times to soften the end.

(If the slab is just a little stubborn, try tapping your punner - on top - from side to side. This slight sideways movement can often drop your slab a further centimetre.)

If the slabs have a flat un-patterned surface then the levelling process - using a straight edge - is reasonably basic. However, remember to set the slab to levels from two ways. With artificial stone patterning, laying true to levels is usually a little more difficult. There can be as much a cm difference in levels from centre to edge one way or the other. This is where the ` eye' comes into its own. A good practice in the case of uneven slabs, is to run the straight-edge along the edge, rather than across the middle. Alternatively, use the high spots of the slab as your level line, and ignore any dips towards the edges. This gives it a more realistic effect anyway. It may be better to increase the fall with this type of slab to prevent any rainwater lingering. Say 75mm (3 inches) over 2.4 metres (8 feet).

Jointing/Pointing

The mixture for jointing your slabs will depend to a certain extent on the type of paving that you use. If you use a `pressed' slab - these are normally cheaper and have very square edges, with both faces of the slab very similar in appearance - then a rather dry pointing mix is best. It is more difficult to remove cement mortar stains from this type of paving. For the moulded slabs - a smoother finish, bevelled edges with the reverse different to the face side - then a normal mortar mix will be in order. It is much easier to remove mortar stains from the surface of this type of slab.

The mixture should be of the ratio 1 part (by volume) cement to 3.5 - 4 parts building sand. Coarse sharp sand can also be used where preferable, and gives a more durable joint in areas of heavy wear.

The jointing/pointing of the paving is very important to the success and longevity of your work. It is not simply a cosmetic exercise. Make sure that the pointing mortar goes right down into the joints. It is far better to have a slightly messy slab, which can be easily cleaned, but with a total bond between joint and mortar base.

Use a complementary or contrasting colour pigment in the mortar. Brown, black or buff are usually all right - not red. All coloured mixes tone down considerably upon drying. Experiment if unsure.

The newly laid and pointed patio, should be allowed time to `cure' before using. This should be for at least three days in the spring/summer months. Cover with a polythene sheet and sprinkle with water during this time if necessary. Do not allow to dry out too quickly.

Joints can either be recessed by raking out partially dry mortar with a trowel or other metal `scraper', or they can be trowelled to a range of shapes. The final cleaning of `grogs' should be carried out when the mortar is near to dry - anything from 6 to 48 hours depending upon the temperature. I usually carry this out on the following day.

Does your patio resemble the original design?   Let me know when the grand opening is to be.....

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By David Hughes - info@gardenseeker.com