How To: Mix Grout
To ensure a great-looking, long-lasting tile job, get this all-important mortar blended just right.
Grout—the putty-like filler between tiles that keeps them sealed, solid, and set in place—tends to be an afterthought. But homeowners have reason to prioritize this DIY job: When this filler is not clean, smooth, and uniform, it detracts from the overall look of your finished tile project. Fortunately, the key to good grout lines is simply knowing how to mix grout correctly, so that it spreads on with ease and produces even lines between tiles for a perfect finishing touch.
Before mixing grout, you’ve got some decisions to make in the selection and prep processes.
• First, choose between sanded or un-sanded grout. If the joints between the tiles are under ⅛”-thick, un-sanded grout is will be easier to use and give better adhesion in those narrow spaces. For thicker joints of ⅛- to ½”-thick, go with sanded grout for best bonding and less shrinkage.
• Some tiling pros favor grout with a polymer additive, claiming it helps grout dry to an even harder final product and resist staining. For bathrooms, consider grout that includes a fungicide to help resist mold growth.
• A bonus tip from the pros: Avoid mixing grout with well water or hard water, minerals from which can cause efflorescence, an unattractive white residue, as moisture seeps into the grout. If you’ve got a well or hard water in your area, use distilled to mixing.
• Finally, resist the temptation to use a corded drill with a paddle attachment to mix grout. Automated mixing can introduce too many air bubbles, weakening the grout and potentially causing discoloration.
Pour about a quarter or half of the grouting powder into the bucket—you’ll want extra available in case you get the water-to-powder ratio wrong in the mixing phase. Refer to the manufacturer’s mixing directions for how much water to add, using a fraction less water than recommended; you can always add more later. Look at preparing grout as similar to making cake batter, in that recipe amounts can change depending on humidity.
Turn the bucket onto about a 45-degree angle so it’s easier to see the contents and mix thoroughly. Add water (remember, less is more—cautiously up the water content as needed) and stir with the grout-mixing knife or small trowel. Continue mixing until all the powder is blended, making sure to remove all lumps.
Check the grout’s consistency. Ideally, it should resemble creamy peanut butter—not that oily all-natural peanut butter, but the super-emulsified commercial kind a knife can stand up in. Some tiling pros describe the perfect consistency as being akin to soft bread dough, where you can grab a handful and it maintains its shape, and, if squeezed slightly, shouldn’t leak water.
If grout is too slack or liquid-y, or has a cake icing consistency, add some more powder and mix well. Left too thin, it’ll shrink too much after it’s applied and crack. Good grout will need a little elbow grease to push into the tiles.
If grout is too dry and clumpy, moisten the sponge with water and squeeze just a dribble of water into the grout mix. Do this in gradual additions until achieving the right peanut-butter texture.
Allow the grout to “slake,” the term for letting it rest for five to 10 minutes so that the chemicals can bond. During slaking, moisture fully permeates all the powder; without proper slaking, grout will be weaker and more prone to cracking and chipping. Don’t worry—and don’t add water—if the grout seems a bit thicker after a maximum of 10 minutes.
Mix your batch of grout thoroughly one more time, and get busy applying it to complete your DIY tile job.