![]() ![]() The hydrated lime I’m talking about here is the dry hydrated lime powder commonly found in builders’ merchants. They will usually have matured for at least a month. It’s important to note that proper fat limes are wet and look like very thick cream. ![]() Fat lime (lime putty) is technically (and confusingly) a type of hydrated lime. They are confused with hydraulic limes because of the similar name. Hydrated lime can often get confused with hydraulic lime and fat limes. Hydrated Lime (also known as builders lime) If you aren’t sure what strength of hydraulic lime to use, speak to your local lime supplier or expert. ![]() Generally speaking, you want to use the weakest possible lime for historic renovations this will give the masonry the most protection. They are also used in areas more exposed to the weather and elements. Hydraulic limes are best used in situations where putty-based limes cannot set (constantly wet areas). The number represents the approximate compressive strength of the mortars and plasters made with the lime. There are three strengths of hydraulic lime. This is the same way cement sets and produces a harder and faster set. Unlike lime putty mixes, hydraulic limes cure via a reaction with water called hydrolysis. They are mixed with various sands and aggregate to make mortar, plaster and render. Hydraulic limes are sold as a dry powder like cement. This can be a very slow process, and the long set times are the main drawback to using fat lime mortar, plaster and render. They undergo a carbonation reaction in which they absorb carbon dioxide (CO2) from the air. Putty or fat lime-based mortars cure by a different process than other mortars like cement. This makes putty-based materials the first choice for restoration projects on historical buildings. The mortar, plaster and render made from lime putties are the most breathable, flexible and softest. Quicklime is slaked with water to produce lime putty, also known as fat lime. Each type of lime has its specific use and strength characteristics. Quicklime ( lime putty or fat lime), hydraulic lime and hydrated lime (not to be confused with hydraulic lime). There are three main types of lime used in the construction industry. Related article: What Happens If Mortar Is Too Strong? The Strengths of the Different Types of Lime It’s far easier to repoint a wall than to rebuild it with fresh masonry because the wrong mortars have been used and caused damage to the masonry of the building. The soft mortar protects the masonry, unlike when cement is used. Lime mortar, plaster and render are softer, breathable and flexible, which makes them perfectly suited to restoration projects. This is where lime building materials come in. However, a cement mortar used on an older building with soft masonry can lead to severe damage. In modern buildings, masonry such as bricks and concrete blocks are engineered to be stronger than the portland cement mortars they are built with, so there are no issues. Over time, the masonry will deteriorate and will need to be replaced. Usually, the masonry will crack and can pit and blow out. If a very high-strength mortar is used with soft masonry, the masonry can be severely damaged over time. When building, the masonry must be stronger than the mortars used. They have a compressive strength of 0.5-5.0 N/mm2, compared to cement which can have more than 50N/mm2 of compressive strength, making them much stronger. Lime mortars are usually weaker than cement mortars. The Difference in Strength Between Cement and Lime This makes them a great choice for eco-buildings and historic restoration. However, weaker lime mortars are both more breathable and flexible. This makes cement perfect for high-rise projects where compressive strength is very important. Cement can be over ten times as strong as lime. Generally, cement has a far higher compressive strength when compared to even the strongest limes. However, there are many benefits to a weaker mortar. However, lime is often overlooked as a weak and expensive building material. Lime and cement both have their place in construction. ![]()
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