General Paving FAQs
Common paving questions, answered by the experts

Wondering what the difference is between a brush-in and flowable grout and which is best for your paving project? Hankering after some tips to avoid stains and how to prime your paving for the best results? Find the answers to these and other general paving frequently asked questions (FAQs), all answered by our team of experts.

Paving FAQs

Flowable grout is a cement-based slurry which is used to fill the joints in patios, terraces, paving and pavements. Applied as a wet slurry, a flowable grout can take 24–72 hours to set, although rapid-setting grouts can set within the hour and some within as little as 15 minutes. When applied correctly, weeds will find it very difficult to penetrate through the cementitious jointing compound between the pavers.

Flowpoint is a flowable grout that can last as an effective jointing compound for as long as 40 years when applied correctly. As a dry, pre-mixed product that forms a wet slurry after adding water, Flowpoint makes it easy to get the right consistency of flowable grout. Mixing only takes a few minutes.

Ideal for pointing joints in both manufactured pavers and natural stone, Flowpoint can harden within just 15 minutes at temperatures of 20oC, is ready to be cleaned after 30 minutes, can be walked on after an hour and can receive vehicle traffic after four hours. A pressure washer can be used on Flowpoint grout once fully set without risking cracks or breaks in the mortar.

A brush-in grout is permeable and made of a sand-based compound, while a flowable slurry grout is impermeable and made of a cement-based slurry. Brush-in grouts can be easier to apply when grouting small areas. Whereas a wet slurry grout is often more durable and ideal for larger projects such as commercial projects and professional domestic landscaping.

Some brush-in grouts, such as Premjoint, can last for as long as 20 years and even beyond 40 years when applied correctly. Premjoint comes in coarse or fine grain, and is available in black, natural or grey, which you may prefer for the aesthetics of your paving project. Premjoint can be used with any stone – whether manufactured or natural – and is ideal for use with premium quality natural stone including granite and porcelain.

There are some flowable slurry grouts, such as Flowpoint, that can last for as long as 40 years without the need to regrout. Flowpoint comes as a dry, premixed product that helps you to achieve the right consistency of wet slurry each time after adding the required amount of water. Rapid setting within 15 minutes at temperatures of 20oC, it can be used with all types of pavers – both manmade and those made from natural stone including granite and porcelain – and comes in natural grey and charcoal.

A permeable grout allows water to freely pass through the paving joints and drain away – but only if the bedding mortar below the pavers is also permeable. Permeable grouts are often sand-based. When used on a domestic project, a permeable grout such as Premjoint can be very handy to avoid puddling.

A non-permeable grout will not allow water to penetrate through the mortar. They are cement-based grouts and often more cost-effective than permeable grouts. Non-permeable grouts, such as Flowpoint rapid-setting grout, are much easier to apply on a larger and commercial scale.

When used on domestic paving projects, a permeable grout can be better for the environment as rainwater can easily flow into groundwater systems rather than puddling and running into drains. This is beneficial to reduce flooding and can also help in drought situations.

In commercial projects, drainage systems are often in place when a non-permeable paving grout is used.

It depends on which bedding mortar you use. Many traditional bedding mortars will take between 24 and 48 hours to properly set before laying the slabs and grouting.

Fast-setting products are now available. These rapid-setting products allow you to complete a whole paving project in just one day after applying the bedding mortar in the morning.

Eco-bed is a premixed and blended bedding mortar that is rapid setting. When applying a laying course of between 10mm and 75mm, both products take up to 12 hours (maximum) to be ready for laying slabs, but in most cases six hours.

A major benefit of choosing a premixed, blended bedding mortar is that you can predict the exact amount of time the product will take until it is ready for laying paving. When mixing and blending the raw ingredients yourself, the laying time is much more difficult to predict.

Yes. A primer is always recommended before laying paving slabs and cobbles.

The number one reason why the grout around paving slabs crack or break is because of ‘debonding’ from the bedding mortar below. A primer is a bonding agent that will stop the paving debonding. A primer also reduces the risk of efflorescence stains as water is less likely to soak under the slabs.

Pro-Prime slurry primer provides an exceptional bond between paving slabs and the bedding mortar layer on your paving project. Pro-Prime is available in 20kg bags.

The best way to avoid efflorescence on paving is to ensure the pavers are in full contact with the bedding mortar. Water can collect in gaps between the bedding mortar and slabs, allowing efflorescence to develop over time. Use a quality, high-strength primer to secure the pavers in place. 

Ultrascape are so confident their BS 7533 Mortar Paving System won’t create efflorescence, they say it can last beyond 40 years without needing to regrout. Ultrascape’s system involves using Eco-bed for the bedding mortar, Pro-Prime for the primer and Flowpoint for the wet slurry grout.

When applying wet slurry grout, avoid washing it off with excessive amounts of water as this may increase the risk of efflorescence stains. If using a hose or pressure washer, do not spray this directly into the joints – instead focus on washing the paving surfaces.

Read our article for more advice on preventing efflorescence and other stains.

A patio should have a fall of around 1 in 80 to stop pools of water forming on the surface of the paving slabs. This means slightly sloping the pavers so that for every 80cm, your patio falls by 1 cm. The fall can vary depending on the size of your patio, but 1:80 is considered to be the optimum slope level. 

A sloped patio is not essential if you are using permeable paving products including permeable bedding mortar and jointing compound. Read our permeable paving FAQs to find out more. 

Still have a question about paving?

If you still have an unanswered question that will help you make the best product choice for your paving project, see our other frequently asked questions. Otherwise, get in touch with our team on 0845 862 1099. We’re available weekdays, 8.30am to 5.30pm.