lost foam finishes
- I just added an album to the photo section called UKJohn,
I have put a photo of one casting made using lost foam technique to show the surface finishe I get myself. The papers the casting is resting on are A4 sized sheets to give some indication of the size and finish obtained.I do not coat the pattern with any sort of mud, plaste, tape, wax or anything else. I use a high density insulation foam(extruded polystyrene foam) which has very small cell structure and what is called here in UK Silver Sand purchased from a garden centre and sieved through an anti-spatter mesh used over a fry pan.
The surface finish is determined by both sand grit size and foam cell size and from my experience over the past 10 years or so coating a packaging foam with anything that does not burn out will only reproduce the foam structure, if the coating does burn out then surface finish will be determined by the sand grain size. Of course EPS foam is none too simple to fill with a sealer that will burn out easily. I myself have not tried a wax and then smoothed the surface but have heard of some having had a degree of success with that method. I prefer to use the foam with the compressed structure created by the extrusion process and a fine sand. Perhaps this year I may try using a dry cement powder but due to the density I will certainly need to add some drinking straws in order to vent the gasses created when the foam burns away.