Pavid Pawley asked: > >Object - a vertial south sundial of 1700, in a sandstone type of material. >It is 24 inches square. with carved numerials and hour lines. > >Went tapped, an area about 12 inches diameter sounds hollow where a thin >surface area is detached from the backing of the 1.5 inch thich dial. > >Does anyone know how to secure this loose area to the sound stonework >behind ?. > >I quesstimate this loose area is about one eighth of an inch thick. > >Perhaps maybe drilling a tiny hole, and injecting some bonding agent. > >It is planned to do this work next year in warm weather. > There is a bonding agent called 'Gorilla Glue' which foams and expands in a joint space which *might* be the answer but I've no direct experience in such a situation. Alternatively the silicone sealant/adhesive available in in DIY 'gun' tubes adheres very tenaciously to stone, has excellent gap filling properties, and, as it remains resilient, absorbs differential expansion due to surface heating by the sun. The gun/nozzle would be ideal for injecting.
But BEWARE! you may be creating a sort of crude 'hydraulic press' by injecting into the exfoliation space which might well force the existing gap further apart or cause it to burst altogether. Some sort of mechanical restraint may be needed. - e.g. an offcut piece of thick 'kitchen worktop' chipboard clamped in front. Also you may have to drill two holes, the second one to let the air escape. This would also confirm when the space is full if the inlet hole is near the bottom of the cavity and the outlet is higher. Blowing air through the cavity beforehand should dry out any moisture. Good luck! Tony Moss -
