Stone that can be found on homes and buildings in this area include limestone, sandstone, marble and granite. There are different physical characteristics of stone.
Sedimentary - Includes limestone, sandstone, soapstone, fossil stone and travertine. These types of stone come from glaciers, rivers, wind, ocean and plants.
Metamorphic - Includes marble, slate and serpentine. This stone originates from a natural change from one type of stone to another. Example when limestone is crystalized its turns to marble.
Igneous - Granite which is formed thru volcanic material such a magma.
Before preparing an estimate we first analyze and determin the type of stone to be repaired. Sandstone and limestone are very similar in appearance.
We determine if there is water infiltration by inspecting cracked mortar joints, missing mortar joints or mortar joints that are too hard for the surrounding masonry. Hard mortar can spall and delaminate the face of the stone and will allow water to penetrate behind the stone. Other causes for stone spalling include expansion and contraction of the stone due to temperature changes, lack of control joints and flashings. Stone can be repaired but if the damage is too extensive it will have to be replaced. Many stone restoration projects it will be a combination of repair and replacement.
Our company repairs limestone, sandstone, granite and marble. Our product of choice for our repairs is Cathedral Stone Products Jahn M-70 Patching Mortar. We are a certified installer for their repair mortars. We send samples of the stone to be repaired to their laboratory where they analyze the stone for the type of stone and for a color match.
In return, they send us a sample mortar that we then install into the stone to be repaired and allow the patch to cure. Once we find a repair mortar that matches the stone to be repaired the patching material is then delivered to us in 5 gallon pails. The stone repairs are breathable and don’t shrink. Please visit our Mortar page for more info on Jahn M-70
Many stone quarries still exist throughout the region that have provided stone to this area for decades. For small stone repairs we look at salvage yards first and then we do online searches. Cast stone can replace limestone as a cost saving option if it is not of historical consequence.
Our stone repairs always include mortars to match the existing as close as possible in color and content. It can not be overstated the importance of using a softer mortar than the surrounding masonry.
Mortar is the material used for bedding, jointing and rendering brickwork and stonework. Mortar consists of lime, cement and sand.
Prior to the advent of portland cement in the United States in the latter part of the 19th century all of the masonry mortar was a straight lime-sand mix that possessed very low compressive strength. The low compressive strength of this softer mortar allowed for movement, contraction and expansion of the masonry and aided in controlling cracking or delaminating of the masonry. Lime slowly gain strength overtime in the masonry wall, absorbing CO2 from the air and converting itself back to limestone. As the lime absorbs CO2 from the air, the masonry wall gains an extra benefit. If a hairline crack develops between the brick and mortar joint, the lime acts as a "self healer" and sealing the cracks in a process identified as autogenous healing.
Ottobein 3.5 Natural Hydraulic Lime is our choice of lime for our historical projects. NHL Lime has a minimum compressive strength of 508 psi in 28 days. In 1818 while building the Erie Canal a limestone deposit contaminated with clay was discovered. When this impure stone was ground into powder form it gave birth to the term "natural" cement as it was naturally occurring obtained directly from the earth.
Analyzing or testing a mortar for the correct compressive strength is so critical to a successful restoration project. Consider the following differences in compressive strength of portland cement and also of the most common mortars used today.
When trying to match a portland cement mortar between 1871 and 1920 into today's times there are compressive strength issues to be considered. Today's portland is burned at a much higher temperatures than portland from 1871. In 1871 portland cement tested in the 1800 psi range and today's portland cement can be in the 8000 psi range. Indeed the portland cement of 1871 bears more relation to a modern higher strength hydraulic lime mortar than it does to modern portland cement.
Modern mortars follow ASTM (American Society Testing Materials) guidelines for minimum required compressive strength for the various mortar types. To meet this requirement the mix has to just be at or above the minimum psi but can be considerably higher.
ASTM Minimums for Compressive Strength
Type M 2500 psi
Type S 1800 psi
Type N 750 psi
Type O 350 psi
Type K 75 psi
Type K is mentioned but it is a historical restoration mortar.
But be careful these mortar mixes can have much higher PSI's as noted below
Type M can have a 28 day strength 3000 to 3800 psi
Type S 2300 to 3000 psi
Type N 1500 to 2400 psi
Type O 750 to 1200 psi
So as we decide on a design for a mortar mix we must be concerned not with a mortars minimum strengths as much as with its maximum strength.
Jahn Restoration Mortars let water salts migrate to the surface for atmospheric release. Other patching mortars use polymer "bonding agents " which trap water and salt behind the repair. Over time winter freezing, summer heat and salt crystallization build pressure which leads to spalling and other failures.
The tenacious chemical adhesion and natural breathability of Jahn Restoration Mortars
assure repairs that last. In addition the color and physical characteristics can be matched to almost any masonry stone brick concrete precast concrete or terra-cotta. Jahn Restoration Mortars don't shrink during curing.
Masonry Construction Inc. has been a licensed Jahn installer since 2005. We have successfully installed their products on brick, limestone, and sandstone restoration projects with great success. We would greatly appreciate the opportunity to bid on your masonry restoration project.