Why is My Lime Mortar Turning White? (How to Fix it)


Have you ever noticed your lime mortar turning white after application? This common phenomenon can cause quite a bit of concern for property owners and builders alike. The primary reason lime mortar turns white is when it dries too quickly, interfering with the important curing process. In this article, we’ll delve into the causes of this issue and offer some practical solutions to prevent it from happening.

When working with lime mortar, ensuring the right curing conditions is crucial to achieving the desired strength and durability. Optimum curing conditions for limes fall within a temperature range of 15-20°C and a relative humidity (RH) of 55-85%. If these conditions are not met, the mortar can dry out too quickly, developing white patches.

Understanding the factors influencing the curing process is essential in preventing the undesired whiteness of your lime mortar. By keeping a close eye on temperature and humidity levels, as well as protecting your mortar from exposure to the elements, you can avoid the issue of mortar turning white and ensure a strong, long-lasting result for your project.

Understanding Lime Mortar

Lime mortar is a widely used building material composed of lime, sand, and water. It is known for its breathability and flexibility, making it suitable for use in older buildings with solid walls. One of the properties of lime mortar is that it gains strength through a process called carbonation, which allows the mortar to set and harden over time.

However, you might encounter issues with your lime mortar turning white. The primary reason for this is that the lime mortar is drying out too quickly. It is essential to provide the right conditions for curing to ensure the optimum performance of your lime mortar. Optimal curing conditions for limes are usually a temperature of 15-20°C and a relative humidity of 55-85%. When these conditions are met, your mortar should be fully cured within 90 days.

It should be noted that the temperature has a massive impact on curing time. An ambient temperature of 10°C will increase the overall curing time by a whopping 50%!

When it comes to materials, it is crucial to use the correct type of lime for your mortar, as using the wrong type may lead to an unsatisfactory outcome. Two main types of lime are used in mortars: hydraulic limes and non-hydraulic limes. Hydraulic limes gain strength more rapidly than non-hydraulic limes, making them appropriate for use in damp environments. On the other hand, non-hydraulic limes take longer to set and require exposure to the air for proper carbonation to occur.

Another factor that may contribute to the whiteness of your lime mortar is the surface texture. A lighter or whiter finish may appear on a closed surface, whereas the true colour of the mortar will be revealed when the surface is cut back and becomes more open.

In conclusion, when working with lime mortar, it is important to consider the materials you are using and ensure that the mortar dries slowly to avoid turning white. Pay attention to the curing conditions and be patient, as the curing process takes time. By taking these factors into account, you can ensure a successful application of lime mortar in your building project.

Related article: The Difference Between Hydraulic and Non-Hydraulic Lime Explained


Causes of Whitening in Lime Mortar

The primary reason for lime mortar turning white is when it dries too quickly. This can be due to several factors, such as exposure to harsh wind, sun, and fluctuating weather conditions. Protecting your lime mortar from direct rainfall, frost, and rapid drying effects of sun and wind is important to prevent whitening.

It’s recommended that lime products be kept damp for a minimum of 10 days after application and much longer if possible. This can be achieved by lightly mist-spraying the surface whenever it appears to be drying. When mist-spraying fresh lime mortar, plaster or limewash, you should only dampen the surface. You should never apply so much water that it begins to run down the surface.

In warm conditions above 20°C, fresh lime work will require more protection from rapid drying to avoid it turning white. This is best achieved by hanging hessian sheeting in front of the lime to shade it and protect it from harsh drying winds. If you still find the lime is drying very quickly, you can dampen down the hessian sheeting as well. This should help to slow the drying process dramatically.

Failure to adequately protect fresh lime work from drying too quickly will always lead to some level of whitening. Additionally, the mortar, plaster or limewash may lose its strength. In mortar and plaster, this will lead to cracking and crumbling. When limewashing, it will cause the limewash to rub off due to poor adherence easily.

Related article: Why is My Limewash Rubbing Off? Causes and Solutions

Impact of Whitening on Mortar and Masonry

When your lime mortar turns white, the primary reason is often that it dries too quickly. This rapid drying affects both the appearance and the integrity of the mortar and masonry.

The fast drying prevents the proper formation of calcium carbonate within the mortar – a crucial component responsible for mortar strength. An insufficient amount of calcium carbonate results in a weaker mortar and, in turn, affects the overall strength of your brick or stone construction. Moreover, the white appearance indicates that some of the calcium hydroxide has not transformed into calcium carbonate. This calcium hydroxide reacts with the atmosphere to form a powdery white substance on the surface of the mortar.

This whitening also impacts the colour and appearance of the lime mortar. The colour of lime mortar varies depending on the aggregates used in its composition. The whitening effect, however, masks these colours, leading to a bland white appearance. This can cause concerns if the mortar is used in visible or aesthetic areas in a building, such as rendered walls or decorative brickwork.

To minimise the impact of whitening on your lime mortar and masonry, it is crucial to control the moisture content of the mortar during the curing process. This may involve protecting the mortar from harsh weather elements like rain, wind, and direct sunlight. Additionally, you should regularly dampen the surface for at least the first 10 days after application.

By keeping these factors in mind, you can ensure that your lime mortar and masonry maintain their intended strength and appearance through the construction process and throughout the ageing of the material.

Properly restored lime mortar.

Importance of Quality Materials in Lime Building

When working with lime mortar in your masonry projects, using high-quality materials and maintaining good on-site supervision is essential. The primary reason for lime mortar turning white is when it dries too quickly. To prevent this issue and ensure the durability of your construction, follow the advice below.

Firstly, select the right aggregate and sand mixture for your lime mortar. The colour and texture of sand have a significant impact on the mortar’s appearance, while the aggregate particles provide its colouring. Ensure you use suitable, consistent sand to maintain the colour consistency of the mortar.

When it comes to lime itself, opt for high-quality lime products. The best quality limes can be found at specialist lime builders merchants like Limebase. Avoid using standard builders merchants for purchasing lime as they often don’t have the deep knowledge specialist lime suppliers can help you with.

During the application process, take care to follow the correct procedures for mixing and applying the lime mortar. The optimum curing conditions for hydraulic limes are 15-20°C and relative humidity (RH) of 55-85%; ensure you do your best to provide these conditions to achieve the best results.

Bear in mind that proper protection is crucial, particularly during the initial stages of the curing process. Protect the freshly-applied mortar from direct sunlight, rain, and extreme temperatures that can cause uneven drying. Adequate protection with hessian sheeting will minimise the likelihood of your mortar turning white due to rapid drying.

In conclusion, using quality materials and maintaining good on-site supervision will help ensure your lime mortar maintains its desired appearance and durability. Remember, a successful project relies on practising proper techniques and following specialist advice throughout the process.

Related article: What Type of Lime is Best to Use for Brickwork?


You may have noticed your lime mortar turning white, and the primary reason for this is it drying too quickly after application. Lime mortars gain strength through carbonation, which can only occur if the mortar remains damp and is allowed to cure slowly over 2-4 weeks for proper carbonation to occur.

To ensure your lime mortar achieves the necessary strength and doesn’t turn white, there are a few important steps you can take. First, always work in temperatures between 5°C and 30°C, as these are ideal conditions for lime mortars. Secondly, protect your lime work from direct rainfall, frost and strong winds. Moreover, avoid letting the mortar dry out too quickly by maintaining an appropriate level of moisture control, which helps achieve good carbonation.

Following these recommendations, you can prevent your lime mortar from turning white and ensure it gains the strength and durability necessary for your construction project. To achieve the best results, it is crucial to be mindful of the environmental conditions and moisture during the application and curing process.