Conservation MethodologyReinforcement
The routine use of pins has been the traditional way of reinforcing broken stones. This method is in debate and controversial. The use of pins should be avoided except in some very extreme situations where it is unavoidable. Generally, the use of pins is to provide extra support to keep two pieces together. If the stone begins to lean and the adhesion joint fails between the stones, then the pins are carrying the full weight of the stone. The pin extends the moment arm which can cause a large blow out on the face of the stone next to the pin. If pins are required then stainless steel threaded rods ranging from 3/8”-3/4” diameter should be used and should never exceed 1/3 of the thickness of the stone. Stones should be drilled using a wet coring drill and at a slow speed. Pins are then secured using an epoxy structural adhesive. Repair mortars/ crack fillers Areas of missing stone can be filled using commercially available restoration mortars (Jahn Restoration Mortars, Cathedral Stone) tinted to match the stone. Tinting can be accomplished in the same way as described above in bonding mortars. Large cracks can also be filled using the same mortars. Mortar repairs should not be performed if there is a risk of freezing temperatures within two weeks after performing work. |
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