How to Lay a Patio
A solid, well-draining patio built right the first time - the foundation work is everything.
Difficulty
Hard
Time
2-3 days
Cost
£200 - £1,000
Before You Start
Check for underground services before digging - gas, electric, water and drainage pipes may be just below the surface. Use a CAT scanner or request utility plans. Paving slabs are heavy - lift with your legs, not your back, or use a slab lifter. Wear steel-toe boots, gloves and safety goggles when cutting slabs. Wet cutting creates less dust than dry cutting.
A well-laid patio transforms your outdoor space and lasts for decades with minimal maintenance. The secret is entirely in the preparation - a patio is only as good as what is underneath it. Skimp on the sub-base and you will have sinking, rocking slabs within a year. Take the time to excavate properly, compact thoroughly, and get the levels right before you lay a single slab. The laying itself is the easy part.
What You Will Need
Tools
- - Spade and shovel
- - Wheelbarrow
- - Spirit level (long) and straight-edge timber
- - String line, pegs and tape measure
- - Rubber mallet
- - Plate compactor (hire) or hand tamper
- - Angle grinder or slab cutter (hire)
- - Pointing trowel
- - Rake
Materials
- - Paving slabs (measure area and add 5% for cuts)
- - MOT Type 1 sub-base aggregate
- - Sharp sand
- - Cement (for mortar bed and pointing)
- - Soft sand (for pointing mix)
- - Weed membrane
- - Haunching concrete (for edging)
Step-by-Step Instructions
Plan the Layout
Mark out the patio area with string lines and pegs. Make the patio slightly larger than you think you need - you always wish you had gone bigger. Ensure the patio falls away from the house at a gradient of 1 in 60 (roughly a 25mm drop per 1.5 metres). This is essential for drainage.
Excavate
Dig out the marked area to a depth of about 200mm (150mm sub-base + 30mm mortar bed + slab thickness - any amount you want above ground level). Keep the base roughly level. Remove any tree roots as they will grow back and disrupt the patio.
Lay the Sub-Base
Spread MOT Type 1 aggregate (crushed stone) over the excavated area to a depth of 100-150mm. Compact it with a plate compactor (available from any tool hire shop) making at least two passes in different directions. The surface should be firm enough that you leave no footprints.
Set the Level
Lay a screed of sharp sand and cement (4:1 mix, just damp) about 30mm thick over the sub-base. Use timber rails and a straight-edge to screed it level, maintaining the drainage fall. Check levels constantly with a spirit level.
Lay the Slabs
Start at the corner nearest the house and work outward. Lay each slab onto the mortar bed and tap down with a rubber mallet until it is level. Leave a 10mm gap between slabs for pointing. Check each slab is level with its neighbours and that the drainage fall is maintained.
Cut Edge Slabs
Measure and mark slabs that need cutting to fit at the edges. Score a line on the surface with an angle grinder and diamond blade, then either snap along the score or cut all the way through. Always cut with the good face up.
Point the Joints
Wait 24 hours for the mortar bed to set. Mix pointing mortar (4 parts soft sand to 1 part cement, fairly dry). Press it firmly into the joints with a pointing trowel. Smooth the surface of the pointing with a rounded tool. Brush off excess from the slab faces before it dries.
Edge Restraint
Apply a haunching of concrete (a triangular bead) along all outside edges of the patio. This stops the edge slabs from creeping outward over time. The haunching should come halfway up the side of the slabs but not be visible from above.
Pro Tip: Dry-Lay First
Before mixing any mortar, dry-lay slabs across the whole area. Adjust the layout to minimise cuts and ensure cut slabs at the edges are at least half a slab wide. This saves huge amounts of time and cutting.
Pro Tip: The Drainage Fall
A fall of 1 in 60 away from the house is critical. Place a 25mm thick piece of wood under one end of a 1.5 metre spirit level. When the bubble reads level, you have the correct fall. Check this on every row.
Common Mistakes to Avoid
- - Insufficient sub-base depth - slabs sink and rock within months
- - Not compacting the sub-base - same result, uneven settling and rocking slabs
- - Patio sloping toward the house - rainwater runs into the building and causes damp
- - Pointing with too-wet mortar - it stains the slab faces and is very difficult to remove
- - Not leaving expansion gaps between the patio and house wall - the slabs push against the wall as they expand
- - Laying on sand only (without cement) - slabs shift and weeds grow through quickly
When to Call a Professional
If your patio area has complex drainage requirements, needs to tie into existing soakaways, or covers areas where services run, get a professional landscaper. Also if you are laying natural stone (which varies in thickness and needs more skill to level) or if the area requires significant level changes and retaining walls.