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Can you grout in hot weather?

Wondering whether you can grout in hot weather and the maximum temperatures when using mortars, grouts and concrete for outdoor projects? Read our guide to working with these paving materials during warm and sunny conditions including seven essential tips for grouting on hot days.

Can you grout in hot weather?
Can you grout in hot weather? Find out in our guide

Here at The Paving Experts we want to ensure you are armed with all the important information and support for your paving projects. 

Whether you’re a professional landscaper or completing a paving job at home, these hints and tips will ensure you get the most out of our popular grouts and mortars, whatever the weather. 

General advice on warm weather grouting

The first thing to note is that our materials can generally be used in all weathers.

Products from each of the quality brands we stock, including UltraScape, Ultracrete, Fuga-Pave, Larsen, Nexus and EasyJoint, are all formulated and manufactured to perform in most weather conditions.

However, during warmer temperatures – of 20°C and rising – you need to take a little extra care while mixing, applying and cleaning up. This is due to product performance tests generally being carried out around the 20 degree mark. 

Hotter than normal temperatures can accelerate the setting and drying process, so it’s important to be aware at these times.

Read on to find out our warm weather tips.

What about other weather conditions?

During colder weather, the chilly temps can certainly slow down the curing process. Find out more in our article on cold weather grouting.  

It’s also important to take care in the rain. A little rain won’t hurt, but a lot can add additional water into the mix and risk failure of the materials. Over time, it can even cause efflorescence. 

See our specific advice for using Flowpoint in the rain

What is the maximum temperature for grouting?

Now that we’ve cleared a few all-weather grouting tips, let’s go back to the question at hand on using grouts and mortars during hot weather. 

Grouts, mortars and concrete can be used in warmer weather. 

But, as a word of caution, we advise not using most grouts and mortars if the temperature is set to be over 30°C. This is particularly the case for cementitious slurry paving grouts.  

As the heat of the day accelerates the curing process, fast-setting slurry paving grouts in particular may set almost instantly. 

At temperatures of 20°C, fast-setting paving grouts such as Flowpoint slurry grout and Larsen FJM, should set at their optimum time of 30 minutes. 

When temperatures exceed 20°C, Flowpoint can take as little as 15 minutes to cure. 

But if the temperature reaches over 25°C, these grouts are likely to flash dry. This could potentially cause the paving mortar to set on the surface of your slabs if they are not kept damp.

Guide to Flowpoint during warm weather

Mark Talbot, an expert paver with 30 years’ experience in the trade, is a big fan of Flowpoint slurry grout. He offers some tips on using Flowpoint during warmer weather. 

“Flowpoint can cure within as little as 15 minutes at temperatures above 20°C,” explains Mark. “So I only ever grout small areas at a time during warmer weather. And I never apply Flowpoint if the temperature is above 30°C.”

When a warm day is forecast, Mark strongly advises moving grouting jobs to earlier in the day when the weather is cooler. 

Mark adds, “Although it’s not essential, we always have a pressure washer rigged-up on standby in case the grout turns too fast.

“Especially in hot conditions, you may need to remove the excess slurry grout more quickly.”

Larsen FJM grout mortar in hot temps

Another popular slurry grout you may be wondering whether you can use during hot weather is Larsen FJM, which is a Flowable Jointing Mortar from Larsen’s Streetscape range. 

Similar to UltraScape’s Flowpoint, you should also be wary when using Larsen FJM during the heat of the day, especially at 25°C and rising. 

Follow our seven essential warm weather tips below to get the most from your bags of Larsen FJM and other paving grouts and mortars. 

Using Fuga-Pave products during hot weather

Fuga-Pave grout is not applied as a slurry grout. As such, so you can be a slightly more relaxed about using their products during warmer weather.

Fuga-Pave Flex CH paving grout in particular can be used at temperatures from 5°C and rising, and all the way up to a staggering maximum of 35°C. Saying that, we doubt you and your team of landscapers will fancy doing the job in that kind of heat!

But these extra allowances do come with a word of warning on hot, sunny days.

Temperatures above 20°C can reduce the workability of the product. You still need to apply the grout quickly, and certainly within 60 minutes after mixing.

In warm climates (let’s face it, it sometimes starts to feel like this in the UK!), Aquacut suggests cooling the paving surfaces first and mixing the grout with cold water.

And whatever the climate, the team also recommends protecting the grout from both sunshine and direct rainfall for at least 12 hours after applying Flex CH.

Fuga-Pave grout is not a slurry grout so can be used on hotter days

7 essential tips on warm weather grouting

Whether you’re using Flowpoint, Larsen FJM or Fuga-Pave products, our experts offer these essential tips for grouting during warm weather. 

#1 Grout early morning or late afternoon

Certain products, especially slurry grouts like Flowpoint, must not be used during hot temperatures. You can get around this by grouting earlier in the morning or later in the afternoon when the temperatures are cooler. 

Read the technical datasheet for specific instructions covering the products you are using. If you need any datasheets for the products on our website, just drop us a line

#2 For slurry grouts, keep the area damp

Especially when applying slurry grouts or external paving mortars, we recommend keeping the area damp until you have finished the application. 

For products like Flowpoint, a constant very light misting with a hose is all that’s needed. 

"We always have a pressure washer rigged-up on standby in case the grout turns too fast. Especially in hot conditions, you may need to remove the excess slurry grout more quickly.”
Mark Talbot, Master Pavior & Landscaper
Mark Talbot
MPave Ltd

#3 Store materials away from direct sunlight

The temperature of cementitious powders can drastically increase in a few short hours if material is left outside in the sun. This can result in faster setting products losing significant pot life and result in being difficult to apply. 

We recommend storing your pre-bagged grouts and mortars in the shade. This will help to keep the product cooler and maintain a longer pot life. 

#4 Use cooler water when mixing

If you are using water from a mains connection, run it for a few minutes to allow colder water to flow from the taps. 

When using water from a container, keep it in the shade to keep the water cool. 

In really hot weather, putting a little ice in the water can help to extend the pot life of a product. 

#5 Be organised and prepared

Keep your eye on the weather, or be prepared to fail! 

Use MetCheck – or a similar app – to assess the forecast for the days you’ll be completing your project. Plan ahead accordingly. 

Organise your work and team to ensure you have all necessary tools and materials to hand so you minimise any down-time. 

#6 Pre-soak your substrate

For cementitious materials, a thorough pre-soak of the substrate, paving slabs or setts will help to reduce the loss of water from the mixed product. This is especially the case for really porous slabs like sandstone. 

Pre-soaking paving materials will help to increase the pot life of the applied products. 

A quick note on substrate:

While pre-soaking substrate is important, this substrate also needs to be free of standing water prior to application. Use a leaf blower to help remove any standing water from the face of riven slabs, or from between the joints. 

#7 Use a slower-speed mixer

Friction from a paddle mixer’s mixing speed can increase the heat generated in the mortar and grout powder. This can reduce its working time and curing time. 

When mixing a product during warm temperatures, we recommend using a mixer set on the slowest speed. This will help to maintain a low mix temperature and can even extend the pot life of the product.

Contact us for specific advice

We hope you found our guide to warm weather working useful and informative. 

If you have any further questions – on any specific product from our brands – and how they are affected by warmer weather, please contact us on 0330 122 1025 and we’ll be happy to advise you as best we can. 

And if you have any additional tips for using mortars and grouts during warmer temperatures, please do share them in the comments below.

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