Grout bags let you fill mortar joints individually, and with much more control over work that is usually associated with mortar.
1 Place newspaper or drop cloths along the floor if the installation is upright or against a wall.
2 Mix the appropriate dry mortar and water ratio in a bucket and let it slake, or rest, following the mortar manufacturer’s directions. Only mix as much mortar as you can use within the set-up time listed on the bag. Mix small batches with a paint stir stick, and use a paint mixing paddle fastened to a power drill to mix large batches. A paint mixing paddle mixes mortar in much the same way that a kitchen hand mixer blends food.
3 Scoop up wet mortar on the edge of a trowel, in a utility scoop or disposable cup and pour the mortar into a grout bag until it is filled halfway. Grout bags are similar in appearance and function to a cake decorating bag.
4 Cut off the tip of the grout bag with scissors or utility shears. The location of the cut determines the amount of mortar that can pass through the tip. Cut the tip close to the end of the bag for narrow grout joints, or make the cut further up the bag for wider mortar joints. If the bag has measurement markings, cut the bag at the mark that matches the width of the mortar joint.
5 Twist the top of the bag to close it loosely.
6 Squeeze the bag until mortar flows down to the tip.
7 Dampen the mortar joints with water from a spray bottle. Dampening the joints helps prevent them from pulling water from the wet mortar.
8 Position yourself at the top of one vertical mortar joint. It is best to install mortar in vertical joints top to bottom, then side to side in horizontal joints. Working bottom to top can cause the mortar at the bottom to sag and bulge out of the joint. In irregular layouts, work from top to bottom and then side to side to the extent possible.
9 Place the tip of the mortar bag into a mortar joint and squeeze the bag. Draw the bag along the joint as you squeeze, filling the joint with mortar. If you are filling mortar joints in a rough or unsealed brick installation, do not overfill the joints. Mortar is very difficult to remove from rough or unsealed brick. If the installation is smooth stone or sealed brick, overfilled joints can be cleaned up more easily.
10 Stop filling joints periodically to neaten the mortar with a tuck-point trowel. A tuck-point trowel is a long, narrow, metal blade tool. Drag the tip of the trowel across the mortar joints, evening out the mortar and making it more uniform in appearance.
11 Brush off excess mortar on the bricks or stones with a dry, stiff-bristle brush.
12 Continue filling the joints with mortar and neatening them with a tuck-point trowel until the installation is complete.