AMR Labs
817-366-8376
MortarLab@gmail.com
Lime Mortar
Over the years, thousands of articles have been written about repointing mortar joints with lime mortar that express various benefits of repointing cracked mortar joints using lime mortar mix. The biggest reasons for pointing with lime mortar are: pliability and softer mortars. Since lime mortar is slightly more flexible and considerably softer mortar, it is quite useful in repointing mortar cracks in walls that tend to have subtle flexing or older softer bricks. Lime mortars help protect these older hard to find bricks from damage that is often caused using newer harder Portland based mortar. Which raises the question, What is lime mortar?
What is lime mortar?
Lime mortar is a much softer mortar type having a crushing pressure of about 75psi which makes it ideal for repointing soft bricks. Lime based mortars primarily consist of lime and sand, but may have a variety of other ingredients added such a hairs, fibers, or grass as well as different grades and shapes of sand to increase or reduce compressive strength. Often, the mortar color of lime mortars comes from the sand, but on occasion, pigments are used to add color.
Since lime mortar has been around from the origins of masonry, and Portland based mortars are newer to the industry, most of the older historic mortars are lime mortar. After the discovery of natural cement and Portland, many historic mortars started using these to increase strength. This produced mortar types K and O which are stronger but still much softer than current mortars.
Lime mortar, type K, and type O mortar are traditionally what you find in historic mortars, and for repointing them, it is important to identify which mortar type was used. This is because harder mortars don't bond well to softer mortars, and softer mortars may not meet the requirements of the design to carry the weight load on the mortar.
Testing and Matching Lime Based Mortar
The only way to know the composition and mortar type of old mortars is to have them tested and matched. The process of identifying composition and mortar type is called mortar composition analysis. Through testing samples of the mortar, you get a mortar formula for matching old lime based mortar. By matching your mortar type and materials used, your mortar color and texture will match the existing mortar better, and your repointing mortar will bond better allowing masonry repairs to last longer and without damaging the bricks. While lime mortar is great for repointing mortar cracks, it is not always the best choice. You should match the existing mortar for repointing.
Buying Lime Mortar And Lime Based Mortar
After testing and matching your existing mortar, and determining it is lime mortar or lime based mortar like type K or type O mortar, you will have a mortar formula for manufacturing your exact mortar match. With this formula, we can produce custom bags of lime mortar mix for pointing, or you can take the formula to another manufacturer or get the materials and mix the mortar following the recipe. Click here to buy lime mortar.
You can send samples of hardened mortar for testing to us at the following address.
AMR Labs
1525 Corona Dr.
Granbury, TX 76048
Click here to order/get prices and procedure for mortar testing/matching.
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