Wondering what jointing compound to use? We take you through the reasons to use GftK’s brush-in patio grout instead of traditional sand and cement.

Driveway of granite setts, bushes on far side, metal gate onto road, with brush-in patio grout.
Driveway using GftK vdw 850 brush-in patio grout with granite setts. Built by PDG Groundworks.

Difficulties with using sand and cement mortar

You probably don't need us to tell you that traditional sand and cement mortar needs to be applied in optimum conditions and kept dry while it cures. Even if you've got the most precise mix, any residual water between the slabs, or any poured on by the heavens, will alter the ratio of moisture to cement. This is likely to result in increased shrinkage and reduced strength.

So, on cold, damp days with the ever-present prospect of rain, you don't really have much choice but to wait for better conditions before you can get on with the job.

Person in orange day-glo trousers pouring hardener into GftK 850 jointing compound.
Adding hardener to GftK epoxy resin mortar.

Brush-in patio grout

While brush-in patio grout seems more expensive than traditional mortar, when you take into account ease and speed of application (saving you considerable time), the facts that you can apply it in almost all weathers and that you won't have to do remedial work make it suddenly look a whole lot more attractive than the alternative.

We don’t recommend anything at London Stone without trying it out ourselves and our recommendation for brush-in mortar is GftK. We’ve given it a tough work-out ourselves in comparison with the alternatives, and it’s come out exceptionally well.

Mixing hardener into brush-in patio grout with drill.
Mixing the hardener into the brush-in pointing mortar until thoroughly combined.

What is GftK jointing compound?

GftK jointing compounds are epoxy resin mortars: resin-coated sand mixed with a hardener that creates a free-flowing mortar.

Advantages of brush-in jointing

Saves time

GftK is applied as a slurry with lots of water (in fact, you really can't use too much water). In practice, this means 3-4 minutes to mix the tub to the right consistency, then 20 minutes to brush in the contents of the tub. With two to three men working, you'd finish two to three hundred square metres in a day, even in the pouring rain.

2 men brush GftK mortar into paving joints, one holding a hose.
Applying GftK joint mortar with plenty of water and a squeegee.

Saves physical effort

It's also an enormous saving on your body. We've found that, once people have used these mortars, they really don't want to use anything else. Why? Well, a huge bonus is that they can be applied standing up, with a long brush. No more time on your knees, compacting the sand and mortar.

Benefits of GftK mortar

GftK jointing compound hardens to a permeable, high-tensile mortar that prevents weeds from growing, resists the burrowing activities of ants, bees and other annoying insects, and doesn't fall prey to freeze-thaw action. It won't stain stone, so even if some is accidentally left on the surface of sensitive stones like limestone or Indian sandstone, it doesn't cause a problem.

Feet of people standing on sandstone paving, washing off mortar residue.
Rinsing off residual joint mortar with plenty of water.

Choosing between GftK 850 and 815 mortars

The vdw 815 and vdw 850 that we supply are very similar. Both are highly suitable for domestic and commercial patios and for light to medium vehicular traffic on driveways. They're abrasion-resistant, even when it comes to mechanical sweepers, and unaffected by de-icing salts. They'll also withstand high-pressure water-jetting with no problem (check out similar products and you'll often find that a power-wash requires certain precautions).

The difference between 850 and 815 is in the grading of the sand, making vdw 815 suitable for joints up to 3mm wide, and vdw 850 for larger joints (try using the 850 in 3mm joints and it just won't fit in).

Man in shorts removing residual GftK brush-in patio grout with a brush from sandstone paving.
Brushing off any final residual joint mortar.

When not to use GftK

Are there any times when we wouldn't recommend using GftK? Only when the temperature is really low, below 3ºC. This is because, if there's a chance of frost, the formation of ice crystals would interfere with the mortar's self-compacting action, weakening the structure. However, low temperatures in general are no hindrance; although it slows curing, the mortar will continue to cure when the temperature increases again above 8-10ºC.

You also need to bear in mind that you need plenty of water when using GftK. If your site doesn't have access to a hose, then you might like to look at alternative pointing materials.

Street cleaning machine blasts water onto paving jointed with GftK mortar.
Here GftK vdw 850 mortar stands up to simultaneous high-pressure water-jetting and mechanical abrasion to no ill effect.

So that, in a (rather large) nutshell, is why we recommend GftK. We've tried it ourselves and are confident you'll really like it. If you have any questions, please contact us, or take a look at the product information on our patio grout pages.

Post updated: July 2023