As a customer how do you decide whether to buy calibrated paving slabs or invest in thicker slabs which will cost slightly more?
Over the last decade natural sandstone paving has become increasingly popular as a landscaping material in the UK, and there seems to be a lot of choice out there.
Indian Sandstone Paving
Most of sandstone paving for sale in the UK comes from India. There are now thousands of different suppliers across the UK, and to most consumers they all appear to be selling a very similar product. The most popular products you will be offered are Raj Green and Fossil Mint Sandstone, plus there are a number of other colours less well known such as Kandla Grey, Modak, Cathedral, Mellow Yellow, Buff and Black (They are known by various different names given to them by different retailers). However, not many of these stone suppliers have any control over the quality or ethicality of their supplies.
How do you choose the right stone for your project?
One of the ways you can ensure you are buying a quality product is to purchase your natural stone paving from a retailer that is sourcing directly from the quarry in India. When a business has a direct relationship with the source of the product they can ensure that codes of practise are followed. An example would be adhering to the Ethical Trading Policy or the Modern Slavery Act, which safeguards the welfare of workers in the trade. Direct sourcing from a regular supplier also enables a solid trading relationship to build which enables the stone retailer to dictate what quality and production standards are required. As these procedures take a greater commitment by the retailer, there are fewer of these types of stone retailing businesses around.
What are Calibrated Paving Slabs?
Calibrated slabs have been cut to a specific thickness. Today the majority of stone paving slabs produced are calibrated (depth measurement) at 18-22mm thick, whereas the norm 10 years ago used to be 25-35mm thick which some businesses still prefer.
Calibrating the slabs to 18-22mm thick has not been introduced for the benefit of the customer. No, it has benefitted the producer, as they can pack more, thinner slabs in a crate for export, enabling them to sell more product at a cheaper price.
You may wonder why thinner slabs are a problem, or if calibration of slabs is a good thing…
The answer is no. Unfortunately the use of thinner paving slabs creates problems further down the line, both for the contractor laying the slabs and the end user, normally the homeowner.
What are the benefits of buying a thicker paving slab?
Thicker paving slabs, although more costly initially, will give better value over the longer period.
To explain why this is so we need to look at the best practice for laying a sandstone patio:
The Ideal Method for Laying a Natural Stone Patio
It is always advisable to lay natural stone slabs on a full bed of mortar made from a Mixed Sand and cement mix (ratio 5:1). The reason we advise the use of Mixed Sand is as follows:
If the mix is made from 100% sharp sand, too much air is incorporated in the mortar mix which prevents good adhesion to the underside of the slab during placement.
If the mix is made using 100% building sand, the resultant mortar will be too “fatty” (squidgy) and will have no strength to support the weight of the stone slab during the setting process.
A moist mortar made of 50% sharp sand and 50% building sand, known as Mixed Sand, is ideal: just enough moisture, air and strength to create the ideal conditions to manoeuvre the slabs into position and set.
The method used to lay a natural stone paving slab is to lay it on a full bed of mortar, adjusting it manually til it aligns correctly with its neighbour. It is then necessary to beat the surface of the slab with a rubber mallet to attain the correct level. At the same time this beating process is necessary to loosen air bubbles in the mortar mix, which on releasing, will create a vacuum, which in turn creates the required suction between the mortar and the underside of the slab, for a permanent fix.
The use of thinner slabs prevents the use of this method, because as you have probably already realised, thinner slabs are weaker and, as they are more prone to breakage, it is not advisable to lay them using this method.
Therefore thinner calibrated slabs are usually laid using a slightly different method:
The cause and effect of using thinner sandstone paving slabs
To avoid breakage contractors will generally lay thinner slabs directly onto the mortar bed without beating them into place, and therefore without creating the required suction for a permanent fix.
Initially all will be good and no difference in the finished patio will be discernable against one made using thicker slabs. However, after a single hard winter the effect of this laying method will be noticeable. After the freeze/thaw of winter weather conditions the mortar mix will separate from the slabs above. In itself this is not a disaster, as the thinner slabs will still be laying on a solid base, but over time, the constant movement of the slabs on the base will cause cracking and breakage, which will require maintenance and replacement.
Laying a patio using thicker paving slabs will cost more, but as they were able to be laid using the correct method, they will last a lot longer, and it is therefore a serious consideration to mull on before deciding which natural stone retailer to go to for this important purchase.
Stoneworld have a wide selection of natural sandstone and limestone paving slabs. Our range is 25-35mm thick as standard. For exceptional quality and strength we also have a range of paving that is available at 50mm thickness.
We also sell Mixed Sand as recommended above, which can be added to your order when purchasing paving. Buy Mixed Sand here>>