Do I need to use a primer before paving?
Frequently asked questions about priming paving slabs

Our experts answer frequently asked question about the benefits of using a primer before paving and how to apply this strong adhesive. Find out our recommended priming products and how to apply them to secure paving slabs in place and to prevent grouting cracks and efflorescence.

Do I need to use a primer before paving?

Yes, you should use a primer before paving as it will prevent grout from cracking or breaking.

The main reason why paving grout cracks and breaks is because of the paving mortar and not the grout itself. The paving ‘debonds’ from the bedding mortar below it. When the paving slabs or stones move, the mortar can crack or break altogether. 

As a bonding agent, a primer helps to prevent the paving debonding from the bedding mortar. A good primer has another big benefit too: by using a primer water is less likely to soak underneath the paving slabs, which will reduce the risk of efflorescence stains.

We recommend using Pro-Prime slurry primer for your paving project as it offers an exceptional bond between slabs and the bedding mortar layer. Pro-Prime is available in 20kg bags. Discounts are available for bulk orders.

Why should I use a paving primer?

Paving primer creates an exceptional bond between the bedding mortar and paving slabs. A good quality primer can substantially extend the life and quality of your patio. 

Although paving primers are recommended for all types of paving slabs and blocks, always apply a primer before laying non-porous stones such as porcelain, slate and granite. Without a primer, these non-porous stones will not bond to the bedding mortar.

What is a paving primer used for?

A paving primer will help to:

  • Ensure an exceptional bond between the paving slabs and bedding mortar
  • Create a powerful barrier for the pavers against moisture and salts
  • Reduce the risk of efflorescence (reflective staining)

What are the benefits of using a paving primer?

A paving primer provides an extra-strong adhesive bond between paving slabs and the bedding mortar below. The main benefits of using a paving primer are to: 

  • Reduce the risk of pavers moving, especially with increased foot and vehicle traffic
  • Protect paving slabs from efflorescence or reflective stains
  • Secure non-porous pavers in place, e.g. slate, granite and porcelain

What are the different types of paving primer?

There are two types of paving primers: 

  • Slurry primers
  • SBR primers

A slurry primer provides a strong, adhesive bond between paving slabs and bedding mortar and helps to protect against efflorescence. Slurry primers such as Pro-Prime are practically impermeable. They provide good, solid adhesion for non-porous paving stones made from slate, granite and porcelain. Equally important for porous paving stones, such as sandstone and limestone, a good slurry primer will form an impermeable barrier to prevent minerals and salts being drawn up through the stones as moisture evaporates as part of the drying process. 

An SBR primer – which stands for styrene butadiene rubber – offers increased durability making it ideal for paving areas subject to heavy traffic. SBR primers are recommended for protecting against efflorescence on light coloured paving slabs.

How does a slurry primer prevent efflorescence?

A slurry primer provides solid adhesion between a paving slab and the bedding layer it is laid upon. Primers are practically impermeable – in other words, a primer does not allow water to pass through its protective barrier. Without this primer, a porous paving slab, such as sandstone or limestone, would draw up minerals and salts as moisture evaporates while the stone dries. It is this drying process that creates efflorescence or reflective staining.  

A slurry primer provides a protective barrier to prevent efflorescence. As a strong adhesive, a primer also offers an exceptional bond to secure a slab in place on the bedding layer. 

Primers, such as Pro-Prime, are highly recommended and widely used for all types of paving slabs and stones in professional paving projects. 

Do porous paving slabs need a primer?

All paving slabs, stones and cobbles will benefit from a good quality primer. Porous paving slabs, such as sandstone and limestone, are particularly at risk of developing efflorescence. A good primer, such as Pro-Prime, will add an impermeable barrier to the bottom of the slabs to prevent minerals and salts being drawn up through the stones while they are drying. This drying process is the cause of these common reflective stains.

What types of paving slabs should a primer be used for?

All types of paving slabs will benefit from a primer. Always use a paving primer before laying non-porous pavers such as porcelain, granite and slate as they will not bond to the bedding mortar without it. Porous stones, such as limestone and sandstone, will also benefit from a primer as it will prevent reflective stains from developing on the slabs. 

These days, more people are aware of the benefits of using a paving primer. As such, primers are commonly used to secure in place all types of paving slabs and natural patio stones, and to prevent efflorescence.

How do you prime a paving slab?

After mixing a pre-blended primer with water, paint the slurry primer onto the underside of a paving slab using a thick brush such as a paintbrush or roller. Apply the primer at a thickness of 1–2mm. Once applied to a slab, immediately secure the slab in place on the bedding mortar. 

Before priming a paving slab, you must ensure that the slabs themselves are free from dust and any loose materials. Use a brush if needed. You may also need to presoak the paving slabs before applying the primer. 

Most slurry primers come as pre-blended mixtures. Fill a large container with the recommended amount of water, add the powdered primer and mix to form a smooth, lump-free slurry.

What primer should I use on paving?

A pre-blended slurry primer is easier to use and apply, and can offer exceptional adhesive strength. Ultrascape’s Pro-Prime is a recommended choice among landscapers and contractors, and meets the British Standards BS 7533. As a pre-blended primer, just add water to Pro-Prime and mix for 3–5 minutes before applying the adhesive slurry to the underside of paving slabs.

What is a slurry primer?

A slurry primer is an extra-strong adhesive that bonds the bedding mortar for a paved area to the paving slabs themselves. A high-quality, pre-blended slurry primer, such as Pro-Prime, provides an exceptional bond to the bedding mortar, helping to secure paving slabs in place and prevent reflective staining or efflorescence. 

A slurry primer can be useful for all types of paving slabs. It is especially important for areas subject to vehicle traffic, and for non-porous paving slabs such as granite, porcelain and slate.

What is an SBR primer?

An SBR primer is a paving primer that offers increased durability and adhesiveness. SBR stands for styrene butadiene rubber. This primer is recommended for paving areas that are subject to heavy traffic. SBR primers are also a primer of choice for lighter coloured paving slabs to protect against reflective staining or efflorescence.

What is Pro-Prime?

Pro-Prime is a pre-blended slurry primer that provides an exceptional bond between pavers and the bedding mortar and other types of paving elements. As an extra-strong adhesive, Pro-Prime is a primer of choice for contractors paving walkways, pedestrian areas and carriageways, meeting the requirements of the British Standards BS 7533. 

This popular slurry primer is quick and easy to apply and can be applied to all types of stone surfaces including natural stone, concrete flags, porcelain tiles and clay paviours. 

Pro-Prime is recommended for use with Eco-bed rapid-strength bedding mortar.

How do you mix Pro-Prime slurry primer?

Follow these steps to mix Pro-Prime: 

  1. Place 7 litres of water in a large container
  2. Slowly add a 20kg bag of Pro-Prime slurry primer
  3. Mix for 3–5 minutes, creating a smooth and lump-free slurry

Once mixed, apply Pro-prime immediately to the undersides of paving slabs and stones instantly prior laying them in place on the bedding mortar. Always pre-soak the paving slabs in clean water before application.

How much water do I need to add to Pro-Prime?

For the best results, use 7 litres of water for each 20kg bag of Pro-Prime slurry primer. Add a bag of Pro-Prime to a bucket, add the water and mix thoroughly for 3–5 minutes until smooth.

How do you apply Pro-Prime?

Follow these steps to mix and apply Pro-Prime slurry primer: 

  1. Clean and pre-soak your paving surfaces to remove any dust or loose material
  2. Add 7 litres of water to a large container
  3. Slowly add the 20kg bag of Pro-Prime
  4. Mix for 3–5 minutes until you have a smooth, lump-free slurry
  5. Either paint Pro-Prime at 1–2mm thick on the undersides of paving slabs, or dip them in the slurry mixture if they are small enough
  6. Immediately lay the pavers in place on your bedding mortar

Note: Take care not to cover yourself or other tools with Pro-Prime as it is an exceptionally strong adhesive. Use gloves, especially if you are dipping stones in the slurry mixture.  

How long do I mix Pro-Prime for?

After adding water, mix Pro-Prime slurry primer for 3–5 minutes. You want to achieve a smooth and lump-free consistency before applying Pro-Prime to the bottom of the paving slabs.

What is Pro-Prime from?

Pro-Prime slurry primer is a polymer modified cement-based material. As an exceptionally strong adhesive, Pro-Prime is a mixture of Portland cement, silica sand and a vinyl acetate copolymer. 

How many square metres does a bag of Pro-Prime cover?

A 20kg bag of Pro-Prime covers a paving area of 15 square metres after mixing with 7 litres of water.

Still have a question about priming?

If you still have an unanswered question about the ins and outs of using a primer, contact our expert team for instant advice. We’re available weekdays, 8.30am to 5.30pm, on 0845 862 1099.

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