To make mustard plaster for a cold or chest congestion, mix one part dry mustard with eight to 10 parts flour, explains the Wellspring School. Add warm water to the mixture until it forms a paste with approximately the same consistency as pancake batter.
Once the paste is complete, spread it across three pieces of fleece or cheesecloth that are approximately 12 inches wide and contain enough length to wrap around your chest and back, instructs the Wellspring School. Wrap the cloth diagonally across the chest, starting at the top of one shoulder, then wrap it around the back and diagonally across the chest in the opposite direction. For example, if starting at the top right shoulder, wrap the cloth across the chest to the lower left ribs, then around your back to the lower right ribs and across the chest to the top left shoulder. Bandages placed over the nipples prevent irritation caused by the paste.
After applying the wrap, dress in an old T-shirt and wait approximately 20 minutes before removing, informs the Wellspring School. Remove after 10 minutes if applying the paste to a child. Red skin under the wraps and excessive coughing is normal after application. Mustard plasters help remove phlegm from the lungs and prevent infection by stimulating circulation of the blood in the chest and inducing coughing.