To use a mustard poultice to treat chest congestion, mix mustard powder and flour with warm water to form a thick paste. Wrap the paste in a piece of fabric and apply it to the chest area for about 20 minutes, says the Wellspring School.
There is insufficient evidence that mustard poultices work, according to WebMD, and they may cause burns to the skin. They also should not be used by pregnant women, as mustard may begin labor, or breastfeeding mothers.
The main component of a mustard plaster or poultice is wheat flour. Herb Wisdom recommends using 4 tablespoons of flour to 2 tablespoons of mustard, while The Wellspring School suggests using up to 10 parts flour to 1 part dry mustard. The paste that is formed should be easy to spread but not thin enough to drip.
The mustard paste should not come into contact with the patient's skin, as it may cause burns or blisters, notes Herb Wisdom. Spread the paste on half of a large piece of flannel, and then fold the materials over to create an enclosed package around the paste. Apply the flannel pack to the patient's, chest and cover with a heavy blanket to encourage sweating.