This is one of those questions we get reasonably often here at Bridge Street Stone, especially from our customers who are brand-new homeowners. We stock both calibrated and uncalibrated Indian sandstone amongst our range, and while picking between them often comes down to a matter of personal preference, it helps to make absolutely sure you know the key differences first!
What is calibrated Indian sandstone?
Calibrated Indian sandstones are those which have gone through a machining process to ensure that they have a fairly regular and even depth. This makes them quicker and easier for professional installers to lay.
Now, this all comes down to the fact that Indian sandstone is an entirely natural material. Understandably, very few natural materials stick to a neatly uniform build and structure, and in the case of Indian sandstone this means that significant variations can occur from one stone to the next.
This isn’t a problem as such; all it means is that these variations need to be accounted for when laying them, in order to successfully achieve a level surface. Indian stone requires a full bed of mortar in order to be properly installed, and uncalibrated paving requires the installer to correctly judge the bed depth for each individual stone, to ensure that the entire surface ends up level.
For experienced installers, this often just amounts to a quick check of the thickness of each paving flag before laying the mortar, which results in nothing more than a slight inconvenience at best. However, DIY installers with less experience obviously have to take extra care during these checks.
Calibrating the stone keeps the thickness variations to a minimum, which allows for an entire ‘screeded’ (or uniform) bed to be laid underneath the entire patio area to support all stones. This saves the installer the time required to check each individual flag, which makes things simpler and easier not just for professionals, but especially for DIY installers. Here at Bridge Street Stone, this is a large part of the reason why we would always recommend calibrated flags for any DIY installation.
How are paving stones calibrated?
The calibration process is sometimes known as strip milling, and essentially it involves the flagstones being run through a series of closely-spaced saw blades, which are diamond-edged to give them the necessary strength to cut through the stone. As you can imagine, that makes the process very dusty and very noisy, requiring the specialists on hand to wear extensive protective gear to prevent any damage to their ears, throat or lungs.
The blades cut grooves or channels into the underside, leaving a series of ridges running up the length of each slab to give it a ‘toothed’ appearance. These teeth are then ‘nobbled off’ - basically, chiselled off to leave a calibrated flag with what’s now a consistently even thickness.
If you’re planning on laying your stones yourself, we’ve got a laying patterns guide right here on our site that you may find useful. And of course, we’ve got a huge range of natural Indian paving slabs for you to choose from for your own patio or garden. Some of our most popular types of calibrated sandstone include Kandla Grey, which is great for achieving that understated, contemporary look for your outdoor space, and Golden Leaf, which create a warm and inviting atmosphere that’s perfect for helping you and your family or guests to relax.
And of course, if you’ve got any questions or you need any advice, don’t hesitate to get in touch with us. You can email us on firstname.lastname@example.org, or give us a call on 01282 860 571, and one of our friendly members of staff will be only too happy to help!