A technician who uses a non-Epoxy.com product to repair tombstones wrote me recently looking for help with problems that he was having. He goes on to say that the epoxy that he uses never fails, but rather the stone fails. When a secondary break occurs, the stone always re-breaks about 2 mm (about ¾ inch) above or below the epoxy joint. The epoxy attached to about 2 mm of the stone and holds well.
He asked me if the epoxy shrinks so much that it will ‘ pull away ‘ from the stone it’s attached to, and in his case, it pulls about 2mm of stone with it.
No I doubt it is epoxy shrinkage causing the problem. High quality epoxy has little or no shrinkage. It would have to be a very poor quality epoxy to be shrinking enough to do that.
The reason his epoxy is not working is that it is too rigid. His existing rigid material has a “high modulus of elasticity”. A material with “high modulus of elasticity” is a material that is stiff and/or rigid. A “low modulus of elasticity” material is semi-flexible, and is not rigid or brittle.
Smaller pieces of the stone structure (in this case a tombstone) and pieces not in touch with the ground tend to get hotter and cooler faster than the larger pieces and pieces with ground contact. This is called “differential timing of the event”. For example the top of a tombstone can be heated and cooled on 5 sides, the top and the 4 sides. The base of the tombstone which is buried in the ground has earth or stone on all of its surfaces. This earth and stone tends to keep the temperature of the base more stable by insulating it and slowing the change in temperature. This works much like the insulation in your house slows temperature changes inside your house.
When an object like a piece of stone is heated it expands (gets bigger). When an object cools it contracts (gets smaller). For example 100 feet of concrete will be 1 inch longer once it is heated 100 degrees F. That is why expansion joints are cut into concrete.
In the case of tombstones all the pieces of the same type of stone have very similar if not identical “coefficient of expansion”. Since the pieces are positioned with potentially different timing of heating and cooling there is a “differential timing of the event” (see above). The result is stress areas you are seeing in the closest weakened plane in the stone near the bond line.
Product #2005 was specifically designed for tombstone (monuments) and/or stone bonding, or repair. Epoxy.com Product #2005 is very strong yet it is has a “low modulus of elasticity” (semi-flexible). The low-modulus of elasticity helps to absorb differential movement (two sections of stone heating and cooling at different times), making it much less likely to cause a stress area in adjacent weakened planes.
Camouflage the bond line rubbing stone dust(ground off the original stone or a similar colored stone) into any exposed epoxy material while the epoxy is still “wet”. That way the dust will stick in the wet epoxy making the epoxy difficult to impossible to see.
Please send your additional question and blog ideas to norm@epoxy.com
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Posted by Norm Lambert 
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