Muriatic acid is an industrial-strength variation of hydrochloric acid and is considered one of the most dangerous chemicals you can legally purchase for home use. Muriatic acid is commonly used to clean masonry; it is highly toxic and will kill weeds and plants, destroying the major roots. You should use muriatic acid only in well-ventilated areas and wear protective clothing when you do. Muriatic acid is typically used as a herbicide of last resort, since it can cause severe burns if it makes contact with your skin.
Put on your protective clothing and fill your bucket with enough water to give you a 80-percent-water to 20-percent-acid mixture. According to the U.S. Department of Agriculture's Agricultural Research Service the maximum percentage of acid to water should be no more than 20 per cent.
Add the muriatic acid to the water. The mixture should always be acid added to water and never water added to acid. Adding water to the acid can cause a violent reaction and actually propel the acid out of the bucket.
Pour the mixture into a plastic spray bottle and seal the top. Spray the mixture directly onto the weeds you wish to kill. If there are surrounding plants, take care not to spray them. Due to toxicity of the acid, it is best to spray weeds that are separated from plants that you do not wish to harm. Place the remaining mixture in a plastic container.
Have baking soda and water source, such as a hose, nearby when using muriatic acid. Muriatic acid is highly corrosive can cause serious burns; if you get splashed by the acid, immediately flush the exposed skin with water and seek medical attention (depending on the severity of the burn). A mixture of baking soda and water will neutralise the acid.