[NHCOLL-L:2284] Re: Appropriate Crack filler

[Paul Callomon]

Hi Bob,

Something else you might consider is Cement Fondue. This is a powder that you mix with regular polyester resin (Fiberglass resin) to make a goop of whatever consistency you desire, from runny to a stiff paste. It sticks to most things, penetrates quite well (especially when thinned with Toluene) and hardens into a concrete-like substance that can be machined and polished. CF comes in many different shades, and looks exactly like rock when sanded and buffed. Worth a try, maybe.

Regards,

PC. 

Paul Callomon
Collections Manager
Malacology, Invertebrate Paleontology and General Invertebrates
Department of Malacology
Academy of Natural Sciences
1900 Parkway, Philadelphia PA 19103-1195, USA
Tel 215-405-5096
Fax 215-299-1170
Secretary, American Malacological Society
On the web at http://erato.acnatsci.org/ams/


>>> "Bob Glotzhober" <bglotzhober at OHIOHISTORY.ORG> 05/11/04 02:48PM >>>
We have a very large (3-4 feet diameter) fossil stump from Lepidodendron/Stigmaria that needs some conservation work.  It is quite old, and without tearing apart the cabinet that contains it, I would guess that the bottom of the stump was either concave, or at least had huge hollow areas (rot during life?).  When it was originally mounted this space (which is not visible from above) was filled with a fine, white sand.  The entire fossil and its case into which it is embedded is at least 1000 if not 2000 pounds. Part of the weight is the fossil, part is the wood case, and part is plaster that was poured around the fossil to make it conform to a rectangular case bottom.  The bottom of the case is made up of thick oak boards, each about 6-8 inches wide.  Unfortunately, over the years, some of the filling sand seeped out of the cracks between the oak boards, creating a hollow that eventually caved in.  Apparently years ago some of the cracks between pieces were caulked -- which !
 we will remove.

The plan is to fill as much of the void as possible with a dense ethafoam (to avoid the weight and other problems of both the sand and the plaster which surrounded the specimen.  At the moment we do not plan to fill whatever small voids exist between various blocks of ethafoam and the fossil that we may end up, but to try and cut and fit the foam as much as possible to support the pieces above.  Then we will piece back together the cracked pieces of the surface of the fossil to form the top of the stump.

This will undoubtedly leave some fairly large cracks -- some 1/4 to 1/2 inch wide we suspect.  We really don't want the white ethafoam below to show and have debated methods to cover or fill the cracks.  I believe I mentioned above that someone years ago used a caulk here, painted black to match the fossil.  I am wondering what various members of the list-server would recommend here.  Two ideas we have had were to use a 100% silicone caulk -- already colored black.  Another idea was to use an acrylic modeling paste, painted black after it is dry.  What are the advantages or disadvantages of the above -- and what alternatives might be suggested?



Bob Glotzhober
Curator, Natural History
Ohio Historical Society		bglotzhober at ohiohistory.org 
1982 Velma Avenue		614/297-2633
Columbus  Ohio  43211-2497	fax 614/ 2972233