Week 8 of 12Module 5: Conservation Interventions and Treatments; Criteria for Selection and Implementation
The Study Tour: Collecchio, Parma
We were back at Stefano Volta's Workshop all day today for more hands-on trials. Today we looked at methods of grouting, pining and cleaning stone.
The dry results of the pointing Jiyoung and I carried out yesterday.
Grouting. Stefano explained the need to a grout to be hydraulic (either naturally or by adding a pozzolan) to allow the mortar to carbonate within the stone where air cannot reach. He mixed up two grouts, one with 1 part lime putty to 1 part pozzolana and one with 1 part NHL 5 to 1 part cocio pesto (brick dust). The cocio pesto is added mostly as a filler to the NHL 5 but it will also provide an additional set. Water and alcohol was added to the mortars to make them more fluid. We were shown, and tested for ourselves, the technique of using a syringe to add a grout into a crack working from the base upwards and closing up any outlets with sculptors clay to hold the grout in the stone. The clay can be removed and brushed off once the grout has dried although a different technique may be needed on more porous stones where the clay may go inside the pores.
Pining. We were shown the wide variety of pins available including stainless steel, fibre glass, ceramic and wood by Gionata Rizzi and Stefano.
Pinning two parts of a column together. We were shown the technique for reattaching two pieces of stone together with a simple break by pinning. Stefana showed us a good technique to ensure that you correctly position the pin so that it creates a good fit; 1. place a spot of paint on one of the broken edges where you want the pin to be located. 2. Put the second piece into position on the first piece and then remove, the paint spot should be transferred onto this piece so now you have the position of both drill holes. 3. Mark two lines down the side of the object perpendicular to each other (in the case of the column around 90o apart around the column drum) and perpendicular to the direction that the drill bit will move. 4. Reposition the second piece and continue these lines across onto its surface then remove. 5. Drill the holes into both pieces aligning the drill bit with the lines drawn (it is best to do this with other people watching the alignment). NOTE: you should only ever use a rotational drill on stone- a hammer drill will produce micro-cracking. 6. Place epoxy resin into the hole and push pin with an angular end into the hole, place epoxy resin into the other hole and place onto the pin attaching the two pieces together. If required mortar can be placed between the two pieces before piecing together.
Pinning two parts of a column together.
Gionata Rizzi showing us a historic pining system. Molten lead was poured into a hole around an iron bar in one stone to attach one side of the 'bar' and allowed to cool. Lead was then poured into the other hole and the first piece was inverted and the other end of the iron bar was inserted into the molten lead.
The historic method for clamping two pieces of stone together. Stefano demonstrated the technique of melting lead and using it for fixing a clamp in place.
Close up view of a steel clamp fixed with molten lead. A small scratch-sketch can be seen to the right of the clamp where David Odgers (who is with us on the tour Tuesday-Saturday) demonstrated the 'butterfly' system often used in the UK where notches were cut out of each piece of stone and then molten lead poured in the space creating a tie.
Some of the shelters created by Stefano in collaboration with Gionata Rizzi.
Dry air abrasive cleaning system.
Nebulised water sprays which act like an even rain falling on the stone and may produce a washing effect but also aid the use of brushing the stone.
Atomised water sprays- a recent improvement to the nebulised water sprays which produce a 'cloud' like emission of water which allow it to penetrate further into the stone but uses far less water than the nebulised water system.
JOS- wet pressurised abrasive cleaning system using CaCO3 (Carrara white marble dust) as the abrasive.
Micro-abrasive cleaning techniques (like a dentistry tool) can be used for fine details and in combination with other techniques which can remove the majority of the undesirable layer.
DOFF- super-heated steam cleaning system. This acts in a similar way to the atomised water but because it has heat as an addition this can aid certain forms of cleaning.