Thursday, 30 May 2013

Garden Design Ideas - How to Lay Garden Paving

Paving is one of the most expensive parts of any garden construction project.  You can calculate the likely cost of laying a patio by working out the square metrage of the area to be paved.  Then use a ‘laid’ or ‘all in’ cost of £100 per square metre to work out how much it will cost to get a landscape contractor to lay the patio.  So, if you want a patio that measures 5m x 7m the total area will be 35 square metres which will cost £3500 if you use a medium priced paving slab.

 Random Indian Sandstone Paving - Berkshire Garden Design

If the site is open and flat, laying paving is not too difficult for someone with good DIY skills who is not averse to hard physical work. So, if you decide to do the work yourself here are some basic instructions on how to lay a patio.

Start by measuring out the area to be paved and marking it clearly.  Aerosol cans of spray line marker are available from builders merchants and area ideal for this purpose.  Next dig out the area to a deep enough for the sub-base, which needs to be 75mm deep for foot traffic, or at least 150mm deep if vehicles are to be driven over the surface, plus the height of the paving slabs and a mortar bed of 30mm – 50mm. 

The top of the paved area must finish two brickwork courses below the damp proof course at any point where it touches the house. Paving must have a fall of around 1:80 towards an area of lawn or planting or a drain to enable surface water to drain from the surface.

Construction detail - cross section of paving

The commonest sub-base material is MOT Type 1 hardcore often referred to as scalpings.  This material is tipped into the excavated area, roughly leveled then compressed to a hard surface using a vibrating plate, often called a whacker plate. This surface should be flat, but don’t worry if it is not absolutely level as the difference can be adjusted with the mortar bed.

The best way to lay the paving slabs is to use a full mortar bed.  If you don’t use a full mortar bed there will be gaps under the paving which can cause it to sink and crack over time.  A mortar mix is placed on top of the sub-base to fix each slab securely to the sub-base.  A suitable mortar mix is 1:5, which means 1 part cement to 1 part sharp sand.

 Sandstone Paved Circle - Windsor Courtyard Garden Design

Start laying the paving in one corner of the marked out area.  If the paving is being laid by the house start at the house wall and work out.  Put down enough mortar mix to create a bed for one slab.  Level it out so that it is covering the area where you want to lay each slab and rough up the surface with the spade to ensure the slab will stick to the mortar.  It is important to create a mortar bed for each slab separately to cater for varying slab thicknesses.  Use a string line to keep lines straight and a spirit level to check the falls as you work across the area.  Use an angle grinder to cut slabs where necessary.  After the paving is laid do not walk on it for 24 hours to allow the mortar to set hard.

 Granite Paved Terrace - Buckinghamshire Garden Design

Most paving is laid with a gap in between each slab of around 10-15mm.  This is later filled with mortar.  This gap is called a pointing gap and should be measured (keep a small piece of wood of the correct width in your pocket to check) to ensure it is uniform for each slab.  When the surface is finished and the mortar bed is set you can fill the pointing gaps with a mortar mix.  Use a fairly dry mortar mix, drop it into the gaps and push it in with a pointing trowel and smooth the top.  Remove any loose mortar from the surface to stop it staining the paving.

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