Planning a Patio in Swindon: How to Choose, Measure and Lay Paving Slabs

A good patio is mostly hidden. What you see is the surface, but what makes it last is everything underneath: the levels, the drainage, the base and the way the slabs are bedded. Patios that look wonderful in year one and sink, rock or grow weeds in year three almost always failed below the surface.

This guide walks through the whole process for a garden in Swindon or the surrounding area, from deciding where the patio goes to ordering the right amount of material. It covers the choice between porcelain and natural stone, sizes, layout, planning rules, the base, laying, jointing and aftercare. You will also see the points where it pays to get a professional involved. Where laying methods differ between products, always follow the manufacturer’s instructions for the slabs you choose.

Decide what the patio is for

Before you look at a single slab, think about how you will use the space. This sounds obvious, but it shapes almost every later decision.

• Dining and entertaining. You need room for a table, chairs and enough space to push chairs back. A table for six needs more space than people expect.
• A quiet seating corner. Smaller, but still needs a view and some shelter.
• A barbecue or outdoor kitchen. Needs a very solid, easy-to-clean surface and space around the cooker.
• A path or connecting area. Width, grip and drainage matter most.
• A base for a hot tub, shed or summerhouse. These need a stronger base than a normal patio, and you should check the weight and the supplier’s instructions.

Draw it on paper. Then mark it out on the ground with string, canes or a hosepipe and live with the outline for a few days. Move a chair and table into the space. It is much cheaper to move a line on the lawn than to move a finished patio.

Where to put it: sun, shade, shelter and access

A patio should be where you will actually sit. Think about:

Sun. Which parts of the garden get sun in the morning, afternoon and evening? A patio against the house may be in shade for much of the day, so some people build a second seating area further down the garden.

Shelter. Wind can ruin an exposed patio. A fence, hedge or the house wall can help.

Views and privacy. Look at the space from your windows and from where you will sit.

Access. Is there a clear route from the house, from the side gate and for deliveries? Bulk bags and pallets of slabs have to be moved somewhere, so think about how materials will get to the work area.

Underground services. Before digging, check for drains, pipes and cables. If you are unsure, ask the water company or use a cable detector, and if anything looks unusual, stop and take advice.

Planning permission and drainage rules

Most patios do not need planning permission, but there are rules about paving over front gardens that catch people out. In England, if you pave more than five square metres of a front garden with a surface that does not let water drain away, you generally need planning permission, unless the surface is permeable or the rainwater runs onto a lawn or border within the property. Rules also differ for listed buildings, conservation areas and flats, and your property may have its own restrictions.

If you are unsure, check with Swindon Borough Council or a planning professional before you start. It is a simple check that can save a very expensive correction.

Building regulations can also apply where a patio is next to the house, because of how it affects damp and drainage, which brings us to levels.

Levels, falls and damp proofing

Two rules matter more than any other when building a patio next to the house.

Keep the surface below the damp proof course. The finished patio level should be at least 150mm below the damp proof course (the visible plastic or slate layer in the wall, or the height of the airbricks). If the patio is too high, water can bridge the damp proof course and get into the walls. If the existing ground is higher than this, you may need to lower it or take advice.

Give the surface a slight fall away from the house. Water must run off rather than collect. A common guide is a fall of about 1 in 80, which is around 12mm of drop for every metre of width. That is hardly visible but it is enough to move water. Mark the levels with pegs and a string line before you dig.

On heavy clay soils, which are found across much of the Swindon area, water drains away slowly, and a patio without a proper fall or drainage can stay wet and green. If standing water is a problem, think about drainage channels, a soakaway or permeable paving with the right base.

Porcelain or natural stone: the main choice

Most patio slabs fall into two broad groups, and the choice between them affects the look, the laying method and the maintenance.

Porcelain paving is a manufactured product made from clay and minerals and fired at high temperature. It is dense, with a very low rate of water absorption. It is consistent in colour from slab to slab, comes in many styles and is generally easy to keep clean. The paving and patio slabs range at Sansums includes slabs in a 900 x 600 x 20mm size, as well as 150 x 900 x 20mm porcelain border tiles.

Natural stone, such as sandstone, has natural variation in colour and surface. Each slab is slightly different, which gives a patio character, but it also means you need to mix slabs from several packs to get a good spread of tone. Some stones are more porous and benefit from sealing, and some can be marked by oil and food if they are not looked after.

Neither is better in every case. Think about:

• The look you want. Uniform and contemporary, or varied and traditional?
• How the garden is used. A barbecue patio near children and food may favour a surface that wipes clean easily.
• Maintenance. Be honest about how much cleaning and sealing you are willing to do.
• The house. Many people choose a stone or colour that matches the brick or render.
• Budget. Ask for prices on the specific products you like, because costs vary between products.

A useful trick: ask for samples and look at them outside, next to your house wall, in both sun and shade, wet and dry.

Slab sizes and laying patterns

Slabs come in many sizes, and the size you choose affects the look and the number of cuts.

Large format slabs such as 900 x 600mm give a clean, modern look with fewer joints. They are heavy and need to be handled carefully, usually by two people, and they need a very flat base. Large slabs make a small patio look bigger.

Smaller slabs and setts, such as 100 x 100 setts, give a more traditional, detailed look. Setts are good for borders, edges, circles and decorative panels.

Border tiles such as 150 x 900mm are used to frame a patio, or to make a path or a feature edge.

Laying patterns include:

• Stack bond: slabs in a grid with joints lining up. Simple and modern, but you need a very accurate base.
• Brick or running bond: each row offset by half a slab. Looks natural and hides small errors.
• Random or mixed size: a traditional look using several sizes together. Needs careful planning so the pattern works out, and the supplier usually provides a pattern.

Draw the layout on paper first. Starting from a straight edge, such as the house wall, and working outwards helps you keep the lines true. Think about where the cuts fall. Cuts against the house or boundary are less noticeable than cuts in the middle of the patio.

Measuring and working out how many slabs you need

1. Measure the area in square metres. For a rectangle, length x width. For other shapes, split into rectangles and add them up.
2. Check the coverage of the slab. Each pack or pallet usually covers a stated area, depending on the size and number of slabs. Ask the supplier for the coverage per pack. The team at Sansums can help you work out quantities if you give them your measurements.
3. Allow for joints. If you are using wide joints, take that into account when you work out the area.
4. Add extra for cuts and breakages. A normal allowance is 5% to 10%, more if the layout has curves or lots of angles. Slabs can break during handling and cutting, and it is far easier to have a few spare than to find a matching batch later.
5. Keep a few spare. Buy everything in one go if you can, because colour and shade can vary between batches, especially with natural stone.

Example: a 4m x 5m patio is 20 m2. With 10% extra, order enough slabs to cover 22 m2, and round up to the next full pack.

Also order what goes under and around the slabs, such as the sub-base material, sharp sand or bedding mortar, jointing material and edging.

Building the base

The base is where most failures begin. A typical domestic patio build-up looks like this, from the bottom:

1. Compacted ground. Excavate to the right depth and compact the soil.
2. Sub-base. A layer of compacted crushed stone or similar, usually 100mm for a normal patio, deeper where the ground is soft or the load is heavy. Compact it in layers of no more than about 50mm using a plate compactor.
3. Bedding layer. A layer of sharp sand and cement or a mortar bed, usually about 30mm to 40mm thick.
4. Slabs. Typically 20mm thick for porcelain and varying thickness for stone.

Added together, that is roughly 150mm to 200mm, so you need to dig down deeper than the finished level. Do not forget that your finished level has to stay below the damp proof course.

Use a weed membrane under the sub-base only if you have a particular weed problem, and check the base type recommended by the slab manufacturer.

Laying methods

Different slabs call for different methods, and there is no single right way. Common approaches include:

Full mortar bed. The slab is laid on a continuous bed of mortar. This gives good support and is commonly used for natural stone and for porcelain. Many porcelain manufacturers also recommend a bonding or priming slurry on the back of the slab so it bonds to the mortar.

Spot bedding (five-spot). Dabs of mortar at the corners and middle. This is quick but leaves voids under the slab, and is generally not recommended for porcelain or for areas that take heavy loads.

Sand and cement bed. A semi-dry mix of sharp sand and cement, often used for sandstone and for concrete slabs.

Dry laying. Some systems let slabs sit on grit, sand or pedestals. Used on roofs, decks and some porcelain systems. Only use this approach where the manufacturer’s instructions allow it.

Whichever method you use, check the product’s installation guidance, and follow it for thickness, bonding and the jointing material. Poor laying is the usual reason for cracked or rocking slabs.

Laying the slabs

1. Set the first slab accurately. Lay it against a line or edge, tap it down to the correct level and check with a spirit level, remembering the fall.
2. Work in rows. Lay slabs to a string line, using spacers to keep the joints even.
3. Check levels often. Use a long straight edge across several slabs. It is easier to adjust at once than after the mortar has set.
4. Keep the surface clean. Wipe off mortar quickly, especially on porcelain and light stone.
5. Use pieces from several packs. Mixing stone from different packs avoids patchy blocks of colour.
6. Do not walk on it too soon. Leave it for the time the mortar manufacturer recommends before heavy use.

Cutting slabs safely

Most patios need some cutting, and it is the stage with the biggest safety risks. Use a diamond blade suitable for the material, ideally with water suppression or a wet cutter, to reduce dust. Wear eye protection, hearing protection, gloves and a proper dust mask, because dust from cutting stone and porcelain contains fine silica particles that should not be breathed in. Cut outdoors, away from other people, and use a stable cutting table. Porcelain is hard, and a blade not designed for it will wear quickly or chip the edge.

Jointing and finishing

Once the slabs are laid and set, joints need filling so the patio is stable and tidy.

• Mortar or pointing mix. A cement-based pointing mix is commonly used, particularly for natural stone. Press it into the joints and finish neatly. Avoid smearing it across the surface.
• Resin or specialist jointing compounds. Used for porcelain and areas where weeds and ants are a problem. Follow the manufacturer’s weather and drying guidance.
• Kiln dried sand. Used in block paving and for some slab systems that allow sand-filled joints. It is brushed in and the surface swept clean.

Make sure joints are fully filled and compacted. Gaps encourage weeds, trap dirt and let water get into the base.

Edging, steps and finishing details

The edge of a patio takes a lot of stress. Without proper edging, slabs can loosen and spread.

• Haunching. A strip of concrete or mortar at the back of the edge slabs or edging keeps them in place.
• Edging stones or setts. A row of setts or border tiles creates a neat finish and can define curves.
• Steps and level changes. Each step needs a stable base, and a consistent rise and depth. This is an area where getting professional help makes sense.
• Lighting and services. If you want lighting or power outside, plan the ducting before the slabs go down, and use a qualified electrician for any electrical work.

Aftercare: cleaning and sealing

How you look after a patio depends on the material.

Porcelain is generally easy to clean with water, a brush and a suitable cleaner, and it does not normally need sealing. Always check the manufacturer’s advice.

Natural stone may need sealing, especially around cooking and dining areas. A sealer can help reduce staining, but it can also change the look of the stone, so test on a spare piece first.

For both: brush regularly to remove leaves and grit, clean spills quickly, and avoid harsh acids or strong chemicals unless the manufacturer says they are suitable. Be careful with pressure washers, which can blow the jointing material out of the joints or damage the surface if used too close. In winter, remove leaves and moss to reduce slipperiness, and be cautious with de-icing products.

Mistakes to avoid

• No fall. Water sits on the surface and algae follow.
• Too high against the house. The damp proof course is bridged.
• A thin or poorly compacted base. The slabs sink and rock.
• Wrong laying method for the slab. Especially spot bedding with porcelain.
• Not allowing for cuts and breakages. You run out, and the new batch does not match.
• Skipping the layout plan. You end up with awkward slivers at the edges.
• Ignoring the manufacturer’s guidance. It exists for a reason.
• Forgetting access. Pallets and bulk materials need to get to the work area.

Frequently asked questions

How thick should patio slabs be? 

Porcelain patio slabs are commonly 20mm thick. Natural stone varies, so check the specification and the laying method for the product you choose.

How deep do I need to dig for a patio? 

Often around 150mm to 200mm below the finished level, which allows for the sub-base, bedding layer and slab. The depth depends on your ground and the product, and the finished level must stay below the damp proof course.

Do I need planning permission for a patio? 

Usually not for a back garden, but paving more than five square metres of a front garden with a non-permeable surface generally does. Check with Swindon Borough Council if you are unsure.

Is porcelain better than sandstone? 

Neither is better overall. Porcelain is uniform and easy to maintain, while natural stone has character and variation. The right choice depends on the look you want and how much upkeep you accept.

How many spare slabs should I buy? 

Allow 5% to 10% extra for cuts and breakages, and keep any left over for repairs.

Can I lay a patio myself? 

Many people do, particularly smaller areas. It is physical work and the base has to be done properly. For large areas, steps, complex layouts or anything near drainage and services, consider a professional.