AMR Labs
817-366-8376
MortarLab@gmail.com 

 

Historic Mortar Testing & Matching Services

We offer many types of mortar testing.

You can send samples of hardened mortar for testing to us at the following address.

AMR Labs
1525 Corona Dr.
Granbury, TX 76048

We are making brick mortar cracks disappear. - AMR

 

AMR Labs is dedicated to matching historical mortars.
This is why we offer various forms of matching mortar including historic mortar analysis, mortar testing, sand analysis, historic mortar composition testing, and lime mortar analysis.

 

Click here to order/get prices and procedure for historic mortar testing.

 

Historic Mortar

Historic Mortar Matching Services
Historic masonry structures were built a little different than today's standards and require mortar matching services to match historic mortars before attempting to restore or repair the damaged mortar. Many of these historic buildings are built with hand made and sun dried bricks that are much softer and break or crumble easier. These softer bricks require a softer mortar to prevent damage. The mortar of a structure serves two purposes in masonry. It is the binder that holds the brick together, and is designed to protect those bricks. Because the bricks or stones were difficult to replace, the mortar was designed to be the sacrificial lamb as it could be replaced easily.
The historic mortars were made softer than the bricks or stones. This was done with historic lime based mortars which contained little or no Portland cement. Portland cement helps the lime mortar to cure or setup as in its chemical reaction, Portland releases CO2 and lime mortar requires CO2 to cure and generally absorbs it from the air. Adding Portland to the mix speeds the setting/curing process, but it also increases the crushing pressure. Therefore, with these antique brick, only small amounts of Portland could be used.
Additionally, Portland cement had to be hauled in from other areas and made it very costly, but the lime was generally available much closer if not on location already. In historic masonry, the lime was generally slacked onsite and didn't use the fine screens if any that are used in producing lime today. This resulted in larger lime particles. These larger lime particles are visible in the mortar and are what is known as historic lime.
Since Portland cost more and increased the crushing pressure too high for these soft bricks, hair and grass were often added to the historic mortar to help strengthen the mortar and hold it together, and calcium was added to increase the chemical reaction (generally when temperatures were low).
Understanding how these mortars were made and used is vital to historic mortar matching services because these historic/antique bricks cannot be replaced easily if at all.

Matching Historic Mortar

Mortar Matching
Matching mortar is a much more detailed process than matching mortar color or compressive strength. In fact, with historic mortar, the mortar color and texture are often matched by matching the crushing pressure, mortar composition, and sand in proper ratios. There were generally little or no pigments added and the color results from sand and contaminates of soil in the sand. In some cases, the dust from local coal mines stain the local mortars and are easily matched by adding a little coal to the mix (not iron oxide pigments). If you are concerned about matching the mortar color, we offer color matching services that can be added to the analysis of historic mortar composition.

Historic Mortar Analysis Testing

Historic Mortar Analysis
Analysis of historic mortar samples provides a complete mortar composition formula and ratio for matching historic mortar through a series of testing methods that identify the performance of the mortar sample and the ratio of mortar composition. Through the analysis of mortar samples, we examine the composition and identify if the mortar sample contains historic lime in the mortar, how much if any Portland was used, and the ratio of the formula for different sand gradations and binder proportions. In historic mortar analysis, we watch for and identify if horse hair or grass fibers were added to the mix and in what proportions.
When analyzing historic mortar, it may be necessary to test the compressive strength of the masonry units. This crushing analysis test can be added to your historic mortar analysis for more information about how your mortar needs to perform.

Historic Mortar Testing

During analysis, mortar samples are tested for their compressive strength, visual analysis under magnification, acid digestion, weight loss, and a visual or sieve analysis of the sand gradation and particles. This is all part of the mortar composition testing.
AMR Labs is an independent mortar testing lab and provides a proprietary mortar testing method that includes several astm testing methods including C-109 crushing analysis, acid digestion, and E-11 sand sieve analysis. However, in our proprietary mortar testing method, we collect additional data that is generally over looked in these tests and combine these results with some scientific mortar testing methods to provide better results than other testing methods can provide. The standard composition analysis provides general details about the sand used and a package of the original sand is returned to you with your mortar testing report. For a more detailed analysis of the sand using sieves and E-11 testing method, you can add the sieve analysis of the sand to your historic mortar testing.

Composition of Historic Mortar

Historic Mortar Composition Testing/Analysis
Testing historic mortar mix composition starts with a visual analysis of the mortar sample to identify hairs, fibers, larger aggregates, unmixed binders, and historic lime particles. This portion is repeated in other portions of our mortar testing method.
Then the mortar sample goes through a crushing analysis to test the compressive strength of the mortar sample. Once the mortar sample is crumbled, it is re-examined visually and weighed before acid digestion testing.
During the acid digestion test, we identify certain chemical reactions and binder material proportions and pigments, dirt, and stains. Mortar samples are then dried and weighed, and their weight loss during testing is determined and used to confirm ratios of binders and sand using the weights of the known binders in the mortar.
The sand is then separated into three grades (or sieve tested if sand sieve analysis is added to the historic mortar testing) and analyzed. To get more detail about the sand if needed, we recommend a sieve analysis.
After all data is collected about the mortar sample, calculations and interpretations are made from the testing data and the formula and ratio of the mortar composition are provided along with a cleaned sand sample, and other recommendations or notes about the historic mortar composition analysis or matching.

Sand Sieve Analysis
The sand analysis provides detailed information about the original sand used. This includes a gradation analysis of the sand particle sizes, color description of particles, and identifies the shapes of sand particles used. Through this analysis, we are able to provide recommendations of quarried sand or river sand particle distributions.
Add this test to the composition analysis testing to get a more detailed composition formula with more information about the original sand used in the mortar mix and the ratios of graded particle sizes.

Matching Historic Mortar Composition Formula

Historic Mortar Testing and Matching
Through testing historic mortar samples and matching the existing mortar composition, you are able to match the original mortar for repairing or preserving the masonry and its historic values.
In many historic mortars, there are stains used but not often are they iron oxide pigments, and you will want to be careful not to use pigments that don't meet the historic guidelines and the original mortar composition.
The iron oxide dyes do not fade the same as more traditional methods of staining mortar. This can result in making the repair stand out where repointing and mortar replacement was performed. This is why we provide notes and recommendations of pigments and mortar color matching tips as needed with every testing report even if the option for color matching is not selected.

Historic Lime Mortar

Historical Brick Mortar
AMR Labs can produce bags of custom brick repair mortar using the formula provided by the mortar testing report and color matching. However, as we do not have access to historic lime, we use type S/SA lime and are unable to produce the historic lime mortars containing historic lime.
If you need historic lime, we recommend Virginia Lime Works, US Heritage Group, or Limeworks.us for ordering historical lime and mortar mix containing historic lime mix.
If your mortar uses Type S/SA lime, AMR Labs can produce custom mortar mix or brick repair mortar mix.