Adding Lime to Concrete

A small group of limestone.
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  • Beginner
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Lime is an excellent addition to your concrete mix, but you must use the right amount for your application. Too much could mean you have to make a new batch of concrete mix, but not enough defeats the purpose of adding it all together. Take a look at what purpose lime serves as part of a concrete mix and learn how best to mix it before considering its use in your next project.

What Is Lime?

Lime is one of the oldest materials used by humans, and it is derived from burnt limestone. It has been used for millennia in combination with concrete and mortar mixes for denser building materials. It fell out of favor in the 19th century as using cement became a more standard building practice, but there are still many benefits to using it.

Why Mix Lime with Concrete?

Lime concrete, produced by this mix, makes a good base for load-bearing walls, columns, or laying under floors because it has a degree of flexibility that regular concrete does not. It also has a certain waterproof property to it that prevents subsoil dampness in floors and walls. Additionally, lime concrete can be made easily and cheaply while still providing a durable material that resists weathering and normal wear and tear.

The ratio of Lime Concrete

Lime, sand, and cement mix must be combined in the proper amounts to get a good lime concrete solution. Three generally mixtures exist to make this material, but two have been discontinued as they had been found lacking in long term integrity. The only viable option is a mixture that calls for a 1:1:6 ratio—one part cement, one part lime, and six parts sand. This ratio is widely used for modern building purposes and will provide an excellent base, especially when working with materials like natural stone. Some experienced builders, however, will use a 1:1:4 ratio instead—one part lime, one part cement, and four parts sand.

Lime can also be used simply as an additive in other concrete mixes, as well as cement mortars. For mortars, this process can take time, as quicklime has to be mixed with water to create a putty which will then have to mature, so other mortar plasticizers will often be used instead to achieve the same effect.

Always take special care working with lime if you’re mixing your own concrete by wearing proper safety equipment. Lime is dangerous when it comes in contact with human skin, causing irritation and burns.