When restoring historic Masonry Contractor Nashville it is important to identify the composition of the original mortar used in the construction of the masonry structure. While this may sound like a suggestion and an attempt to sell you on an idea, there are many reasons why you need to analyze the mortar and determine the composition of the original mortar used.

Older or historic Nashville TN Masonry Contractor units were hand made and tend to be softer or more brittle than the hard fired clay bricks used in construction today, and stone will have different variant factors. Depending of the type of stone, it will have different crushing pressures, and will require a mortar that is softer than the rock. This is true of the hand made bricks also. Mortar must be softer than the masonry unit being used to prevent damage to the bricks or stones. This part carries over into mortars today, but is often overlooked by the builders of today.

Each mortar type is based on a variant range of composition or compressive strength. An example of this is type n masonry cement ( which is most often used today) has a compressive strength of 750 psi and is generally made using one part Portland cement mixed with one to one and one quarter parts lime and about two and a quarter to three parts sand by volume., and a lime mortar has a compressive strength of about 75 psi.

The various types of mortar are lime mortar, historic lime mortar (which contains historic lime), type k mortar, type o mortar, type n mortar, type s mortar, and type m mortar. And the crushing pressure of these types of mortar are 75 psi for lime mortars, 150 psi for type k, 350 psi for type o, 750 psi for type n, 1800 psi for type s, and 2800 psi for type m mortar.

As you can see, there is a huge difference between each mortar type and will certainly effect the results of any masonry repair.

Historic mortars tend to range from lime mortar up to type o mortar in part due to the cost of Portland cement, but also to protect the masonry units. The lime used was often slacked on location and tended to have large pieces. This is known as historic lime. These large pieces are the difference between historic lime and the type S/SA lime used today which are screened to ensure smaller particles. The only real effect these pieces have in the mortar is visibility. They change the appearance of the mortar color and texture.

As there was often a need to add strength to the mortar, but not exceed the compressive strength of the masonry units, fibers were often mixed into the mortar. The most common fiber used was horse hair. Horse hair and different grasses were also used to make the bricks and hold them together.

In order to preserve historic masonry, a great deal of attention must be paid to the details. To do this, you must first collect the details available about the mortar and the masonry units. This requires testing of the hardened mortar and/or the bricks or stones.

Through mortar analysis, you identify the mortar composition, compressive strength of mortar, the type of lime used, if fibers were used, and the type, color, and graded size particles of the sand used in the old mortar.

These are the required details to make a matching mortar for repointing.

Now there are some fancy and often expensive testing methods used in analyzing mortar samples that just aren't very reliable. Some of these tests take pretty pictures of the mortar sample that identify different elements of the mortar by color. This picture is then looked at visually and a best guess of the proportions are determined. This method has many limitations, and the worst is the understanding, experience, and knowledge of the technician testing the samples of mortar. If they don't understand masonry, how it is used, and how it is built, they cannot interpret the data accurately.