Using a Grout Bag: When to Bag Grout and How to Fill, Strike and Clean Up

A grout bag (also called a mortar or pointing bag) squeezes grout straight into the joint instead of spreading it over the tile face. Use one for wide joints, rough or porous tile, brick-look and saltillo installs. Mix sanded grout stiffer than for floating, fill each joint slightly proud, let it firm up, then strike it with a jointer and brush off the crumbs.

When a grout bag is the right tool

For most tile with joints of 1/16 to 3/8 inch, a rubber float is faster and packs grout well. A grout bag earns its place when floating would smear grout into a surface that cannot be cleaned, or when joints are so wide and deep that a float scoops them out.

For grout selection on these materials, see grout for saltillo and terracotta, grout for natural stone and wide grout joints, which covers maximum widths for sanded grouts.

The bag and the tools

• Grout bag: a heavy canvas, coated fabric or reinforced plastic cone, usually holding several pounds of grout, with a metal or plastic tip. Disposable heavy plastic bags work for small jobs. Choose a tip opening slightly narrower than the joint, often 1/4 to 3/8 inch.
• Jointer (striking iron): a masonry tool with a rounded, flat, or V profile, sized to the joint width. A concave jointer is the default for brick-look work. A length of smooth dowel or a rounded spoon handle works on small jobs.
• Margin trowel: to load the bag and dress joints.
• Stiff and soft brushes: a stiff-bristle brush to sweep off crumbs and a soft brush for the final dusting.
• Grout sponge and buckets: for limited damp cleanup only. See grout tools for options.

Mix consistency for bagging

The mix is the make-or-break variable. Too wet and it slumps out of the tip, runs over the tile edges and shrinks as it dries. Too stiff and you cannot push it through the bag, and it will not bond to the joint walls.

The target is a stiff paste that holds its shape on the margin trowel, will just drip slowly when the trowel is turned on edge, and squeezes through the tip in a continuous rope under firm two-hand pressure. Mix toward the lower end of the water range on the bag, never beyond it, and slake as the TDS directs. The fundamentals of ratios and slaking are in how to mix grout.

Prepare the joints and tile

Joints should be clean and open to at least two-thirds of the tile depth, with no thinset ridges. Vacuum out dust. On very porous terracotta and some stone, the tile manufacturer may call for a pre-seal or grout release on the face before grouting. Keep it out of the joints, where it would stop the grout bonding. In hot, dry rooms, lightly dampening the joint edges with a barely damp sponge can prevent the clay or stone from pulling water out of the grout too fast; leave no standing water.

Leave perimeter and change-of-plane joints open for sealant per TCNA EJ171, as explained in caulk vs grout movement joints.

How to use a grout bag, step by step

1. Mix a small batch. Mix only as much grout as you can bag and tool within the working time, often a quarter to half a bag of powder for a first run. Mix stiff, slake, and remix briefly.
2. Load the bag. Fold the top of the bag down like a cuff, hold it open in one hand and fill it about two-thirds full with a margin trowel. Unfold the cuff, twist the top closed and push the grout down toward the tip to remove air.
3. Fill the joints. Hold the tip in the joint, close to the bottom, and squeeze steadily with the top hand while guiding with the lower hand. Move along the joint at a pace that leaves it slightly overfilled. Fill horizontal or long joints first, then cross joints, so intersections are fully packed.
4. Pack and consolidate. Press the grout into the joint with the jointer or margin trowel tip to push out air, especially at intersections and deep spots. Top up any low areas with the bag.
5. Wait for thumbprint firmness. Let the grout stiffen until a light finger press leaves a faint impression without sticking. This is often 15 to 45 minutes depending on the grout, the tile and the room. Tooling too early smears; too late leaves a rough, torn surface.
6. Strike the joints with a jointer. Run the jointer along each joint with steady, even pressure to compact and shape it. Do long runs first, then intersections. A concave profile sheds water and looks like traditional masonry; a flush or recessed profile changes the look, as described in anatomy of a grout joint.
7. Brush off the excess. Once the crumbs are dry enough not to smear, sweep them away with a stiff brush working diagonally across the joints, then a soft brush. Return to any joints with gaps and touch up with the bag.
8. Clean the face lightly. Wipe residue from smooth tile faces with a well-wrung sponge, touching the joints as little as possible. On terracotta and rough stone, let residue dry and remove it with a dry brush or pad rather than water.

Cleanup and curing

The point of bagging is to keep the tile face clean, so cleanup is mostly dry. Any grout smeared onto porous clay or stone should be removed before it sets, but with as little water as possible. Rinse the bag and tip immediately after use; dried grout ruins canvas bags. Discard disposable bags rather than washing them.

Protect bagged joints as you would any cement grout. Wide joints contain more water and grout per foot, so they are more prone to rapid drying in hot rooms and to shrinkage if mixed wet. Keep drafts and direct sun off the area during the first days, and follow the curing schedule in grout cure time. Sealing schedules for bagged grout are the same as for floated grout once cured.