How-to: Grouting
Grouting is the process of filling the joints on a patio, pathway, wall or other continuous surface. Heard more often in reference to tile work, grouting can also be used to finish stone paving. A well grouted patio lasts longer and looks better.
Patios and walkways can be built with mortar or using dry stones bedded in sand. Mortared paving should be built on a continuous substrate, generally a concrete slab. Only grout mortared paving. Grout in the joints of dry stone patios cracks and pops out as the stones start to move, which they inevitably will.
Bed the patio stones in mortar as you build, but do not fill the joints. Ideally the recessed joint will be almost as deep as the stones used in the patio.
There are two commonly used techniques for grouting. One way is to use a tuck pointer trowel to push mortar into the joints. This is advised for vertical surfaces, small areas or when working alone. The second technique, grout bags, is detailed below. Grout bags are much more effective for covering a large area and when there’s someone to help. Used properly, grout bags are very clean, minimizing the need to touch up the patio after you’ve grouted.
Clean the area well before beginning to grout. Pressure wash or hose the patio down to remove any grit, dead leaves and other junk from of the joints. This improves adhesion and reduces the risk of the grout cracking as it cures. A powerful pressure washer can take the paint off a house; watch out for vulnerable surfaces as you clean the area.
Grout with the joints damp, but without any standing water. Wash the patio the day before grouting.
Grout on cool, dry days. Don’t grout if there’s any risk of rain.
Make the grout using the your usual mortar recipe but mix it really, really wet. Dry mortar won’t flow out of the bags and will make the project take forever. It’s really hard on your wrists too.
Use very clean sand and make sure your mortar is well-mixed. Congealed portland cement, little bits of gravel or dry chunks of sand will clog the bags and slowly drive you crazy.
Grout bags are just like monster frosting bags. Cut an opening at the tip that allows the grout to flow out smoothly and fill the joint with a single pass. Hold the bag closed with your right hand and twist with the left, forcing the grout out.
Wear gloves. A day of grouting can scrub the skin right off your fingertips. I’m not wearing gloves in the picture and my hands were a red, raw mess by lunch-time. Heavy-duty dishwashing gloves work really well and come in a variety of stylish colors.
Push the tip into the joint and squeeze out enough grout so that it completely fills the joint from the bottom up. Mound it up over the top of the joint, about a half an inch. It will settle as it cures and you’d rather not have to add any later.
Keep the outside of the bag as clean as possible. This will prevent you from dripping grout water onto your paving. Attention to detail here will save you several hours of tedious scrubbing and acid-washing later.
Let the grout dry until you can push your thumb into it and the impression stays but no sand sticks to your skin. When it reaches this state, you can work it without smearing or staining your rocks. Push it into the joints with a margin trowel. Don’t finesse it, just push it down and fill the joints. Add extra if needed.
The biggest thing to watch out for is that once the grout starts setting, it goes fast. Pay attention to areas in direct sunlight. If you get there late you’ll wear yourself out trying to force cured grout into the joint. If you get there too early you’ll smear grout everywhere.
Give it more time to set and then scrape the joints with the edge of a margin trowel to get up all the residue and reveal the edge of your stones. Sweep way all the extra grout. If your stones are rounded, just work the edges until they look right. You can brush the joints or whack them with a broom to get various textures and looks.
Cover the grouted patio if there’s any risk of rain before it’s completely cured.