Laying Natural Stone

Top Tips for laying Sandstone and other paving slabs

 

IMPORTANT INFORMATION

Slate, granite ice and granite frost

These products sometimes absorb colour impurities from ordinary Portland cement (OPC). We strongly recommend substituting white cement in the mortar to reduce colour leeching and staining and adding an SBR or other bonding agents. Lay granite with the textured slip-resistant face upwards.

Granite - all colours

Depending on site conditions, moisture coming through from the mortar bed below can create moisture transparency (dark/damp patchiness on the installed product) which is a natural drying process that can affect all slabs (particularly granite). This is completely normal and should dry out over time.

Veining in granite products

Our granite products (particularly Dusk) may display natural veins which may not be visible when the product is dry. It is advised that when the stone is dry laid before fixing you should wet the stone to ensure you are happy with the appearance, as veins become more apparent when wet. Veins are a natural feature of the product and are often mistaken as cracks - veins should not be considered a defect as they will not affect the durability of the product.

 

Step by Step Laying Guide

1. Before any work is carried out, each piece of natural stone should be inspected prior to laying as pieces will vary. No returns can be accepted once the product is installed, so it is important to confirm you are happy with your product before proceeding. When work begins, ensure the area is cleared of all vegetation and debris. Then, ideally using a scaled drawing of your planned area, you can start plot pointing by marking out the space using pegs and a string line.

 

2. Dig the ground to a depth of approximately 150mm below the finished patio level (or 200mm deep below the finished driveway level), making sure the soil is compact.

 

3. In the now excavated area spread a layer approximately 100mm deep of hardcore (or 150mm deep for driveways). Remember to leave room for the thickness of the flags and 30-50mm of mortar. Compact the layer of hardcore thoroughly, ideally using a plate compactor. Foundations must not be laid on water-saturated ground as they may sink in time, creating uneven paving. Extra drainage may be required.

4. Once happy with the layout, using your line and pegs as a reference you can start laying your flags down on a full bed of slightly wet mortar mix 30-50mm deep. For the mortar mix we advise 1 part cement to 5 parts sharp sand (some contractors use a 50/50 mixture of building and sharp sand). All products must be laid on a full bed of mortar, especially when laying a driveway. A full bed of mortar is key to help reduce moisture transparency or discolouration, as well as to provide a solid base for the patio. A bonding agent should be used to help the slabs adhere to the mortar bed. An SBR bonding agent should be painted on to the back of each slab before laying when using natural stone. Use a rubber mallet to gently tap down the flags and a spirit level to check the patio is uniformly level, being careful to check you follow your slope level as you go along. To provide suitable run-off during wet weather a fall angle must be considered. Falls must be angled away from buildings or structures at an incline of 1:60 or steeper. An adequate drainage outlet source should be present at the end of the patio’s runoff edge. A planning officer may need to be consulted for further advice. It is important to note that Digby Stone products are not designed to be butt jointed, and a suggested joint of approx 10mm should be used. For products with an aged finish, we suggest increasing the joint size accordingly in order to accommodate for any potential variations in edges (between 15 - 20mm approx).

 

5. Once the main area of the patio is laid down and there are slabs that need cutting, in the case of natural stone a disc cutter with a suitable attachment or a hammer and chisel is needed to shape your flags effectively (please see our porcelain laying advice overleaf for specific guidance on cutting porcelain tiles). Once happy with the shapes of the now cut flags you may lay them down (refer to step 4) on a full bed of slightly wet mortar mix. Using a rubber mallet, gently tap down the flags and use a spirit level to check for a uniform flatness (taking into account a fall).

 

6. Once the patio has been fully laid, ideally allow a few days for the mortar to set. There are several ways of sealing the joints between paving slabs - the installer must determine the most appropriate method to use. Some use a cement based mortar mix and so create a solid, inflexible joint. Others use a modern jointing compound that brushes in and hardens with contact with the air, commonly known as paving jointing compound. When using any jointing products always follow manufacturer’s instructions.

When laying a driveway

A minimum of 150mm compressed hardcore foundation must be used before laying products for a driveway (only suitable products to be used).It is essential that products are laid on a full bed of wet mortar for driveways.

Circle features

These should be dry laid before final positioning on a full bed of mortar, starting from the centre of the circle outward.

Calibrated products are subject to a minimum of +/-3mm variation. Due to the composition of natural stone, colour variations may occur after installation.

Some delamination (when riven parts of the stone flake off) may occur after laying - this is perfectly normal and tends to happen near the riven part of the slab.

As with all Sandstone products, the spot-laying method is not suitable - always use a full bed of mortar.

Natural Paving Info

All dimensions given are nominal and subject to manufacturing tolerances.

The quoted sizes and coverage of our paving ranges are for the overall areas including appropriate joints, making it easier for you to plan a project and order the right quantities. For precise dimensions, measure several product samples at a stockist. We are continually making innovations and improving products so we reserve the right to vary designs and specifications without notice.

Variations in colour shade occur in all natural stone products.

While the colours shown in this brochure are as accurate as reprographic processes allow, it is essential that you see actual materials at your local stockist before choosing. This is particularly important with natural stone products where considerable variation occurs. Our reconstituted stone products contain natural aggregates so we cannot guarantee that products made at different times will have identical shades. When using several packs, mix products from each pack to achieve a blended overall appearance.

Weathering and site conditions can cause variations in shade to appear on individual units.

These will not affect performance in any way and will diminish over time. Both natural and reconstituted stone products are affected by sunlight and rainfall. Natural stone may develop brown markings as its iron content oxidises. Stonemarket cannot accept a for efflorescence which may occur as a deposit and/or apparent colour fading in the form of patches or drip staining.