Fixing stal: N(B)CA Cave Conservation Handbook contains quite a lot of useful tips on this topic but here's some from my own experience.
If the stal is a clean break (i.e. simple "snapped" stalactite, for example) and is clean and dry then superglue works perfectly, giving an almost invisible repair; superglue also works on damp calcite and is really the easiest option for lightweight items - it usually fixes quickly so if a piece of stal needs to be held in situ while the glue sets this is easily done with a steady hand.
For larger pieces of stal (i.e. curtain sections) which are heavy, superglue can be put to one side in favour of araldite. There are quite a few problems with araldite, however, the chief ones being:
* It's messy to mix together
* It requires a methodical approach since the mixing board needs to be packed away and it's important not to spread the sticky glue around over yourself, overalls, gloves etc..
* It takes a long time to set and this requires holding the stal in place - fine for stalagmites but not for stalactites. To use araldite with stalactites/curtains can require the creation of a "holding" frame - usually a box containing sand/gravel and a collection of sponge blocks to support the speleothem while the araldite goes hard; obviously it's important to get the angle right otherwise the resulting fix can leave the formation being off-line!
* Araldite is good for broken stal where small bits are missing since the glue can be mixed in with sand/fine grit (strangely enough crushed volcanic pyroclastic/pumice is best since it is ultra-fine and also makes the araldite set much faster - I have a supply of VP from Mt. St. Helens in my cupboard and use this from time to time). Using this araldite "cement" means that formations can often be given a cosmetic touch up too but use should be very sparing.
* Complex fixes can involve creating wire loops to suspend the formation while the glue sets - this was pioneered (IIRC) by Dr. Stanton and he drilled pilot holes into stalactites and set in small wire loops which then hooked over reciprocating eyes set into the cave ceiling; the two are connected so the stal hangs by wire; the gaps are then filled in with "cement"/araldite/filler (or whatever you're using).
It is quite common (sadly, too common by far!) for broken stal to get broken again and again - usually because it happens to be in a vulnerable location in the first place so once it's fixed, it still gets broken off again...
Firstly it is A VERY GOOD IDEA to mark the area and possibly delineate a path to ensure that repeat incidents do not occur and then it is also worthwhile using superglue instead of other methods since when superglued formations get broken over and over again there is very little accumulation of epoxy resin which makes secondary and tertiary fixes more troublesome.
If anyone has other views or ideas on good methods for stal fixing I'd be interested to hear about them.
