Because the mortar between this stone is missing, it provides a direct avenue for water and its damaging effects.
This repointing job was done with excessively hard mortar, and is unattractive.
This repointing mortar was not professionally matched, and therefore caused the brick to fail.
Another example of inappropriate and unattractive repointing mortar.
More inappropriate and unattractive repointing mortar.
Correctly preparing the mortar joint for the new repointing mortar is critical.
Frequently Asked Questions
about Repointing (Mortar Repair):
Question: How do I know if my masonry needs to be repointed?
Answer: Your masonry requires repointing if:
The mortar is cracking, missing, or deteriorating. If left in this condition, it provides a direct avenue through which water can penetrate the masonry wall. The water is then subject to the expansive forces of freeze-thaw cycles, and over time deteriorates the masonry units. The water can also contribute to the crystallization of soluble salts. This is known as efflorescence, or if the salts crystallize under the outer surface of the masonry, sub-efflorescence or crypto-florescence. These also cause the masonry to rapidly deteriorate.
It has been inappropriately repointed in the past. Perhaps the mortar in the area previously repointed does not match. (See Mortar Analysis & Matching for more information.) Maybe the previous repointing mortar is excessively hard or water vapor impermeable and is causing the masonry units it surrounds to deteriorate. In either case, it is wise to consider repointing.
Question: How do I know what mortar recipe to use?
Answer: It is very important that the new repointing mortar be formulated and applied so that it will give way before the masonry units it surrounds do. In other words, historic mortar should be sacrificial. The reason for this is that repairing failed mortar is easier and less costly than repairing the original brick or stone. Often, the original brick or stone is no longer available to use as replacement units.
In order to craft a repointing mortar mix that meets the above criteria, a sound understanding of the environment the masonry will be exposed to, as well as the physical characteristics of the host masonry units, is essential. A relatively small amount of money invested in a mortar analysis and/or a professional mortar match at the beginning of your project will save a lot of money over the life of the wall. Contact us for assistance.
Question: What must I do to be assured that my repointing job will both look good and last a long time?
Answer: These are the 10 primary elements of a successfully executed repointing project:
Thoroughly evaluate the physical and performance characteristcs of both the original mortar and the masonry units it surrounds.
Determine which mortar joints get repointed and which ones don't.
The mortar joint must be properly prepared to accept the new repointing mortar. This step is more involved than most people think and therefore is often overlooked.
Accurately determine the most appropriate mortar recipe for your situation. (See Mortar Analysis & Matching)
Follow correct mortar mixing procedures. This can vary substantially depending on the mortar recipe used.
Control suction (the rapid transfer of water from the wet mortar into the masonry) as you insert the new repointing mortar into the joints.
Use the correct tools and procedures to ensure the mortar is firmly compacted into the mortar joints.
Carefully control the curing conditions (temperature, humidity, wind, and direct sunlight) of the mortar after it has been inserted into the wall. This step is very important and often overlooked.
Make sure you have thorough, expertly written specifications for the contractor which clearly outline the procedures to be followed, what is expected, and what is not acceptable. Make the specifications part of your contract with the contractor. These specifications are best prepared by an historic masonry expert who has had substantial hands-on experience repointing historic masonry buildings. Abstract Masonry Restoration has extensive experience developing custom specifications for historic masonry restoration.
Select a trained and experienced craftsperson who has respect for your historic masonry fabric to perform the repointing work. Most masons are very good and experienced at performing new masonry construction, but few are adequately trained to work with historic masonry materials.
At Abstract Masonry Restoration, we are genuine experts at repointing historic masonry. Contact us for assistance with any repointing needs you may have.