Why You MUST Slurry Indian Sandstone?

When laying paving one of the many pieces of advice that you might hear of is slurrying or priming the backs of the slabs.

This is a big question because a lot of people do prime the slabs saying that it’s a must and a lot not saying that I’m laying sandstone for more than 20 years now and never ever primed Indian sandstone and never came across loose slabs.

However, to let you know, priming the backs of the slabs now has become a standard practice for the fail-proof bonding between the slabs and mortar. So, should you be priming the slabs too for your next project?

The short answer is you must slurry or prime Indian sandstone or any other paving as not only it almost guarantees the bond of slabs to the mortar bed but acts as a kind of barrier in between, reducing the absorption of moisture and salts by the slabs from the mortar bed underneath.

There was no need back in the days when the sandstone was at its finest quality. However, now it has become a good practice and can be said as a standard to prime not only sandstone but also other paving slabs while laying them which is mentioned in our DIY Start to Finish Guide here.

Sandstone paving these days is very thin (20mm) compared to what it used to be several years ago (30-50mm) which means there’s just not enough weight to it to hold itself down in the place which affects bonding.

DIYer? Definitely do not avoid it!

You may hear many people saying there’s no need to use a primer if you get the mortar mix right but what if you’re a DIYer first time laying paving.

It’s kind of hard to guarantee that the mix you create will hold the slabs in place. That’s why the priming slurry comes into play.

It ultimately means that you can be a little bit lazier with mortar mix and still no need to worry whether the slabs will stick to the bed. So, even if you’re not lifelong experienced in mixing mortars like most of our readers who are DIYers, it’s actually giving a chance for the slabs you lay to no matter how is your mix.

There are very simple mistakes to make as a first-timer just to realise the job needs to be redone from starting because of some small things that you lack to know before the job, and it’s not your fault, it is just because you don’t have prior experience in laying the slabs.

This is why we put together this DIY Start to Finish Patio Cheat Sheet to bring to your attention how DIYers can approach the job a little differently so that you can give yourself the best chance of success even without any experience.

And, even if you have some prior experience in paving or you think you could manage to get the mix right, the extra adhesion won’t hurt and you are only going to benefit from it.

Even some professionals who have been in the trade for years, now also have adopted this practice.

We’ve been laying sandstone for 30 years and never used it in the early days but now the thickness of the slabs is down to 18-20mm I would strongly recommend you prime the backs of slabs.

Which is the best primer to use for Indian sandstone?

There are several great manufactured and ready-to-use primers available on the market today for this purpose.

There is nothing wrong with mixing your own slurry made with SBR and cement but again it’s the same, the mix needs to be correct for the best adhesion, so ready-to-use primers are the best, easy and quick.

For the sake of some extra money, getting doing the priming is definitely worth it instead of mixing on your own. Go with mixing it yourself if you’re on a really tight budget

Pro-prime which is around £25 per bag (25 kg) covers almost around 30m2, so it’s hardly any expensive for the security that it gives you.

If you have relatively a smaller job to do, you can also try this primer here from Azpects on Amazon. It’s a little bit expensive and covers around 20m2 per tub but it doesn’t affect that much if you require only a couple of tubs for the entire job.

also read: Why 6:1 is the best mortar mix for laying sandstone paving?

How to slurry Indian Sandstone

There are already dozens of tutorial videos available on Youtube on how to mix the slurry yourself or even if you get a ready-mix product, there are instructions mentioned on it on how to mix and use it.

A few important points to remember here are, prime the entire area without leaving any clear bits visible on the back of the slabs.

After you’ve entirely covered the back of the slab don’t wait too long to keep the slab without laying. As soon as you prime the slab, let it go down there in its place, otherwise, it can cause bonding issues if it’s gone off.

That’s why ready-mixed slurries are the best for DIYers because you’re always going to mess up with the things and will not be the quickest to lay the slabs.

Also, keep a bucket of clean water and a sponge to clean off the slurry or primer going on the sides and the face of the slabs before it dries out.

It doesn’t matter which priming slurry you’re going to use, but it’s better to have some kind of bond bridge than nothing at all. Watch the video below to see a little demo.