The common name “lime” is often used loosely to describe several distinct calcium-based products, causing confusion. Barn lime and hydrated lime are not interchangeable, despite their similar names and powdery appearance. Understanding their chemical and functional differences is necessary for safe and successful application. Using the wrong product can result in poor performance, property damage, or severe injury.
Composition and Primary Use of Barn Lime
Barn lime, often called agricultural lime or ag lime, is finely ground limestone. Its composition is predominantly calcium carbonate (\(\text{CaCO}_3\)), sometimes including magnesium carbonate (\(\text{MgCO}_3\)) in dolomitic lime. Mined and crushed into a powder, it is a relatively inert and stable substance.
Because of its low reactivity, barn lime is non-caustic and widely used in livestock areas. Its primary function is to manage moisture and improve hygiene on stall and barn floors. It absorbs excess liquid, keeping bedding dry and suppressing odors. As a soil amendment, its calcium carbonate slowly neutralizes soil acidity.
Composition and Primary Use of Hydrated Lime
Hydrated lime, or calcium hydroxide (\(\text{Ca(OH)}_2\)), is a manufactured product. It is created by heating limestone to produce quicklime (calcium oxide, \(\text{CaO}\)), then adding water in a process called slaking. This reaction results in a fine, white powder that is more reactive than barn lime.
This product is highly alkaline, typically registering a \(\text{pH}\) of around 12.4 in water. Its basic nature makes it a powerful substance used primarily in industrial and construction applications. It is a common ingredient in mortar, cement, and plaster, where it reacts with carbon dioxide to harden. In agriculture, it is used for rapid correction of acidic soils.
Critical Distinctions in Handling and Safety
The difference between the products lies in their handling requirements and safety profiles, tied directly to their chemical composition. Barn lime, a natural calcium carbonate, is generally safe for direct use around livestock and does not cause chemical burns. It is non-toxic and non-corrosive, making it a suitable material for routine barn maintenance, though inhalation of any fine powder should be avoided.
Hydrated lime, conversely, is a strong alkali that requires careful handling and Personal Protective Equipment (PPE). Direct contact with the skin, eyes, or respiratory tract can cause severe irritation and chemical burns due to its high \(\text{pH}\). The danger increases when the powder becomes wet, as the caustic properties pose a serious threat to animal tissue and human health. Inhaling the dust must be avoided by wearing a mask.
Choosing the Right Lime for the Job
Selecting the appropriate product depends on the intended application, as substitution can have poor results. Barn lime is the correct choice for animal husbandry, used for drying and deodorizing stalls, coops, and pens. It is safe to spread directly onto bedding or floors where animals will be in contact.
Hydrated lime should never be used near livestock, as its causticity can cause painful burns to hooves, skin, and eyes. Using highly alkaline hydrated lime in stalls accelerates the conversion of nitrogen in urine into ammonia gas, worsening air quality and respiratory hazards. For construction or specialized industrial processes requiring a rapid, high-\(\text{pH}\) reagent, hydrated lime is required.