Why NOT to use Building Sand for laying Paving Slabs?

There are many simple doubts that DIYers have throughout the job when they lay paving slabs. One of them is what type of sand is best to lay them on. Is it sharp sand or building sand or both?

It’s really overwhelming in this trade like landscaping is all opinions. If you ask 5 different people even a simple question like what mortar mix to use, you’ll have 5 different answers.

We already have a separate page on what ratio of sand and cement to use for the mortar mix. That page will help you make a decision on what ratio to use for the mix if you’re currently nowhere near deciding on one.

It is not advised to lay any paving just on building sand alone but if you have some spare, you could use it in a certain portion like 5 (sharp), 1 (building), and 1 (cement), and by certain, it means very little, like the majority of the mix should consist of only and only sharp sand.

Some people use building sand in the mix because it increases the workability of the mix, and that’s true because building sand is soft and round, when added into the mix, it makes the overall mix creamier and playful hence some people find it easier to work with.

On the other hand, sharp sand being coarse (sharp, of course), it takes slightly more effort if you were to use just sharp sand but there’s a reason why sharp sand is used to lay slabs. That’s what will create the best bed for “load bearing” because of the interlocking capability of the sharp sand.

Now, if someone is doing it by adding building sand to their mix, it doesn’t mean they’re wrong. It’s not like you should not use building sand, it’s about not using ONLY building sand for the mix. It’s not the end of the world if you add a little bit of building sand in the mix. It’s what works for them.

If laying paving slabs is not your day job and if you absolutely don’t have any idea how workable is the mix without building sand, and how workable it gets with building sand or past experience with the products to use. This is the reason why we created DIYer’s Start to Finish Patio Cheat Sheet which gives no-brainer answer for DIYer’s making your job less confusing and more confident (for that click here).

Some people prefer plasticiser in the mix which increases the workability of mortar without having to use too much water.

Sands and their characteristics vary around the country, and for this reason, British Standards states sharp sand which is a universally understood material. In some places, ‘builders’ sand is pretty much gritty enough to use in place of sharp sand, however, it is safest to stay with the term sharp sand.

Some people says when used building sand along with sharp, the mix is more sticky and that’s just their personal findings and may or may not be true.

If this is the thing for which you intend to use building sand then there is absolutely no need of it if you’re using a “proper” primer on the back of your slabs, not sbr or cement slurry. You can benefit a lot more by using a primer than if you were to use building sand in your mix.

Read more: Advice on priming porcelain paving
Why you must prime Indian sandstone paving?

Mortar mix using only Building Sand (No Sharp sand)

It could be very bad idea to lay paving slabs on something that’s not as great as something that’s easily available in terms of “load bearing” as well as “drainage”.

Building sand is 0-2mm in particle size and is very fine. As the particles are round, when building sand alone is used to make the mortar, it will try to escape from the bottom of the slabs.

Also, being round, it’s not as free draining as sharp sand and will eventually hold water which can cause issues further down the road.

This doesn’t mean that you should never use building sand in your mix. It’s fine to use it to some extent like already said, majority of the mix should be your sharp sand and then it could be some building sand, and of course, cement accordingly.

Sharp Sand on the other hand, is 0-4mm in particle size and coarse (angular) sand which makes it free-draining and will not escape as building sand because of the interlocking capability.

While knowing all these things, using building sand alone to make the mortar mix does not make sense as better than sharp sand.