Step 1
Buy your mortar bag from a hardware store. It looks like a plastic cake icing bag (or pastry bag). A mortar bag is also a pretty inexpensive tool to have.
Step 2
Mix the mortar. To get the mortar to come out of the bag properly you need to have a good mixture--not too thick and not too runny. If it is too thick, you will have problems getting it to come out.
Step 3
Lay out your drop cloth. You may want to do this before you mix your mortar so you will always have protection from spills underneath.
Step 4
Fill your mortar bag. The bag will have a small end and a large end. Fill the bag at the large end. You may want to have someone hold the bag while you pour in the mortar.
Step 5
Use the mortar bag. Once the mortar is in, twist the end and squeeze (don't squeeze until you are ready for the mortar). Once you squeeze, the mortar will begin to come out the small end of the bag through the tip.
Step 6
Guide the bag as you squeeze. This makes it easier for you to place the mortar in cracks and small areas. You will also likely need your pointy trowel to help you work the mortar in the right areas and get rid of any excess.