Patio Calculator

Calculate materials needed for your patio project including slabs, hardcore, sand, and mortar

Patio Material Calculator

How to Build a Patio

Planning Your Patio

Before starting construction, measure your intended patio area carefully and mark it out with string lines. Consider the location relative to your property, ensuring adequate drainage away from buildings. Check for underground utilities and obtain necessary permissions if required.

Essential Materials

  • Hardcore/MOT Type 1: Forms the foundation sub-base, typically 75-100mm deep
  • Sharp Sand: Mixed with cement to create mortar bedding for slabs
  • Cement: Binds the mortar mixture, usually in a 4:1 ratio with sand
  • Paving Slabs: Available in various sizes and materials including concrete, natural stone, and porcelain

Construction Steps

Excavation: Dig to accommodate the sub-base, mortar bed, and slab thickness. Include a fall of 12.5-16mm per metre away from buildings for drainage.

Sub-base Installation: Lay and compact hardcore material to create a stable foundation. This prevents settlement and provides excellent drainage.

Mortar Preparation: Mix sharp sand and cement in a 4:1 ratio. The consistency should be damp but not wet, similar to damp soil that holds together when squeezed.

Slab Installation: Lay slabs on the mortar bed, maintaining consistent gaps of 8-15mm. Use a rubber mallet and spirit level to ensure proper positioning and fall.

Top Tip: Always compact hardcore thoroughly with a plate compactor. Poor compaction can lead to uneven settlement and cracked slabs later.

Drainage Considerations

Proper drainage prevents water pooling and protects both your patio and property foundations. The minimum fall should be 12.5mm per metre for textured surfaces and 16mm per metre for smooth surfaces. Water should drain towards garden areas or suitable drainage systems, never towards buildings.

Material Specifications

Hardcore/MOT Type 1

A crushed aggregate mixture containing various sized stones from dust up to 40mm. Provides excellent compaction and drainage properties. Density is approximately 1.6 tonnes per cubic metre when compacted.

Sharp Sand

Angular sand particles that provide excellent binding properties when mixed with cement. Different from building sand, which is too fine for structural mortar applications.

Cement

Portland cement is standard for patio construction. Typically sold in 25kg bags, with approximately 40 bags per tonne. Always store in dry conditions and use within the recommended timeframe.

Important: Add approximately 10% extra materials to account for wastage, breakage, and variations in ground levels. This prevents costly delays during construction.

Frequently Asked Questions

How deep should I dig for a patio?
The total depth depends on your materials: typically 100mm for hardcore, 50mm for mortar bed, plus your slab thickness. For standard 20mm slabs, dig approximately 170mm below your finished level.
What size slabs are most popular?
600mm x 600mm slabs are the most common choice, offering a good balance between coverage and handling. Larger slabs like 900mm x 600mm reduce the number of joints but require more careful installation.
Can I lay slabs directly on sand?
For pedestrian patios, slabs can be laid on a compacted sand bed, but mortar bedding provides superior stability and longevity, especially for heavier slabs or areas with regular furniture movement.
How much fall do I need for drainage?
Minimum fall is 12.5mm per metre for textured surfaces and 16mm per metre for smooth surfaces. This equals approximately 1 in 80 gradient, ensuring water runs off effectively without being noticeable when walking.
When do I need planning permission?
Most patios fall under permitted development rights, but check with local planning authorities if your patio exceeds 5 metres from your house, covers more than half your garden, or if your property has restrictions.
How long before I can use my new patio?
Allow mortar to cure for at least 24-48 hours before walking on slabs, and 7 days before placing heavy furniture or substantial loads. Curing time may be longer in cold or wet conditions.

Cost Considerations

Material Costs

Budget approximately £15-25 per square metre for basic materials including hardcore, sand, cement, and standard concrete slabs. Natural stone or porcelain slabs increase costs significantly to £40-80+ per square metre.

Labour Costs

Professional installation typically costs £50-100 per square metre depending on complexity, access, and local rates. DIY installation can save substantially but requires proper tools and technique.

Additional Expenses

  • Waste disposal for excavated material
  • Tool hire (plate compactor, mixer, etc.)
  • Delivery charges for materials
  • Edging materials and pointing compounds
Money-Saving Tip: Order materials in bulk and coordinate delivery to minimise transport costs. Many suppliers offer discounts for larger quantities.

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