How do you install calibrated sandstone paving? A guide

How do you install calibrated sandstone paving? A guide

So, you’ve chosen the shade of Indian sandstone you want for your space, purchased the slabs, and got them back home and ready to go. The main question left is: how do you install them? As you can imagine, it’s a question we field quite a lot here at Bridge Street Stone, and it’s one with a relatively long answer. So to save you some time, here’s a quick guide explaining exactly how to install your calibrated stone paving - as well as one or two things to watch out for as you do it!

Mark out your area

First things first. Before you do anything else, you’ll need to define the area that you’ve reserved for your paving slabs. Ideally it should be firm, level, and well-drained. It’s often helpful to physically mark out the area using spray paint, so you know exactly how much room you’ve got to work with.

Start digging

Once you know exactly where your paving slabs are going to go, it’s time to break out the shovel. Make sure that you dig deeply enough - the foundation mix and paving is going to take up at least 150mm, and if you’re laying your Indian paving stones directly next to the house, the final surface depth of the patio needs to be at least 150mm below the damp proof course of the property. (Otherwise you’re going to end up with moisture seeping into the building, which can be hugely expensive and a right hassle to fix.)


All told, that means you’ll probably need to dig out the area to a minimum depth of 300mm below the damp proof course, so that you can be sure you’re not going to accidentally cause yourself any problems later on down the line.

Don’t forget the fall

The fall is another really important aspect of any finished patio, and it’s something that you’re going to need to make sure you account for in the early stages. The ‘fall’ of a patio is a term that refers to what’s basically a very slight slope, designed to ensure that water doesn’t collect on the stone.

Your foundation needs to have a fall of 1 in 60, which means that there needs to be at least 1cm of fall for every 60cm of width. On a 3m wide patio for example, that works out to about 50mm of fall.

Preparing the mortar for the foundation

Now you’re ready to create the foundation itself. First, fill and compact a 50mm layer of sub-base material down into your paving area, then repeat the process so that you’ve got a sub-base with an overall depth of 100mm.

Here’s where you need to take care to ensure the area has falls that provide adequate surface water runoff. You can use string lines to measure falls on your foundations, and rake the general area to create levels. Once that’s done, you can then compact the whole area using a garden roller or tamper.

You’ll already know that Indian paving stones need to be laid on a full bed of mortar. Various different paving stone suppliers tend to recommend different proportions of ingredients to create the mortar mix, but personally here at Bridge Street Stone, we recommend blending between 4 and 6 parts sharp sand to 1 part cement.

Then, you’ll need to add some water to the mix. Make sure not to add too much, as you don’t want the entire mixture to be too wet and runny. Ideally, it should have a damp, workable consistency so that it all binds nicely together.

Laying your Indian paving slabs

For some people, this can be the most nerve-wracking part of the entire process! Before you start laying your slabs though, it’s a good idea to wash them. (You only need a sponge and clean water to do this.) Then, prime the underside of each slab with a dedicated priming product, or fine mortar slurry.

This is where we should say - make sure that you’re laying your slabs the right-side up! Contrary to what some people think, Indian paving slabs do indeed have a top and bottom side. The edges of the stone taper inwards slightly on the underside, which helps ensure that water runs off the edges.

When you finally come to laying your paving, you can use two taut string lines to guide the line and level of the paving. It’s easiest to work in a small area to begin with. Add a full mortar bed to an area, and spread it out to cover an area that’s slightly bigger than the paving slab you want to lay. It needs to be high enough so that it can squash down slightly once you tap the paving slab firmly into place - so about 30mm or 40mm in thickness should be plenty.

Right, now comes the moment of truth. Lift the paving slab and lower it into place on top of the mortar, making sure not to catch the corners. Here, you’ll need to take particular care to ensure that the underlying mortar bed supports the entire slab, so there needs to be full contact across the entire underside of the stone.

Then, bed down the slab firmly by tapping it down with a rubber mallet until you’re sure it’s at the correct depth. You can use a spirit level to ensure that it’s properly level, and that you’ve properly accounted for the fall. As soon as you’re happy, you’re ready to lay the rest of the paving. Don’t forget that each slab needs to be between 8mm to 10mm apart, so that you can properly do the jointing.


All you’ve got left to do at this stage is fill in the gaps. Here, you’ll need to use a mortar mix of between three and four parts soft building sand to one part cement. (If you’ve researched this elsewhere, you may find that different providers recommend different ratios. Don’t worry too much about whether you get it wrong - there’s a bit of leeway in it, much like how people have different opinions on the best way to bake a cake.)

Mix it gradually with a bit of water, until you reach the same smooth, damp consistency as you achieved earlier. Again, it shouldn’t be too wet or sloppy - if necessary, you can add a plasticiser to ensure that it’s easier to work with.

This sand / cement mixture is a time-honoured method of pointing, but if you’d like you can go for an easier and more modern method simply by using a product with a resin mixture, such as the Joint It paving mortar we supply here at Bridge Street Stone.

Whatever you choose, the next steps are the same. You can use a trowel or a pointing gun to compress the mortar mix into the joints between your paving slabs, and use a pointing bar to press it down or smooth it over anywhere you need to. It’s worth taking particular care not to get any mortar on the surface of the slabs themselves - Indian stone is porous, so it can easily end up permanently marking them. If you accidentally spill any, make sure to scoop it up as soon as you can!

Now, for best results, once every slab has been laid, they need to be left to set for at least 24 hours, or longer in wet weather. As soon as it’s all hardened, you only need to give it all a quick sweep, and then that’s the job done!

But don’t use the dot and dab technique!

We can’t finish a post on installing Indian sandstone without mentioning this. There are a select few installers here in the UK who still for some reason regularly use the dot and dab technique to install Indian paving stones for their clients, but experiences like this one demonstrate why that’s a very bad idea.

If you’re not familiar with the dot and dab technique, it basically involves using spots of cement to bed the stones on top of the initial layer of hardcore. The problem is, this can leave a lot of empty space between the mortar. Water can quickly start collecting in these gaps, which can end up causing a lot of problems.

For starters, as we touched on above, the porousness of Indian stone means that moisture can end up making its way up through the slabs, which can cause horrible rings to appear on the surface. What’s more, in the winter, this collected water has a tendency to freeze and expand, which can start to force your natural stone paving slabs upwards. In the best case scenario, this can really spoil the otherwise lovely visual effect, and in the worst case, if they’re pushed up far enough they could even create a tripping hazard. The proper method might take a little bit more time, but it brings lasting results!

And if you need a bit of design inspiration, you can find a few tips on laying patterns right here on our website. Plus, if you have any questions or need any advice, we’re only too happy to help at Bridge Street Stone. We’ve got a fantastic range of natural Indian sandstone paving right here on our website, in a great choice of colours ranging from stunning Golden Leaf to the sophisticated Kota Black. All are sourced directly from India, and we’re able to offer free delivery to most areas. To make an order, feel free to give us a call today on 01282 860571.