The capping stones are not nec to add to the mold itself. The mold can be made easier and those caps can be installed using styrene or stips of Hydrocal (cast a panel and rip to width required- bandsaw is excellent for this) I perfer working w/ Hydrocal for castings, just like the properties of the material. As for cut stone over flat concrete, I was quite lucky to have a real expert, Jeff Adam of Motrak models in the club during all this casting work. he would carve a master to fab a mold in RTV. I ended up w/ dozens of castings of cut stone to match the WS portrals/ retaining walls. I believe Jeff (Motrak) offers these cut stone, rubble and block cast panels. Other simpler castings I will fabricate by building the appropriate mold. Various textured sheet material can be laid in the bottom to simulate differing textures to the finish of the casting. One in particular that works well is that sheet "crinkled" foam packaging.
This arched bridge was done w/ the cut stone panels glued to 1/4" ply substrate. The arc was cut into the ply and the panels cut larger allowing for the arch/ keystones space to be glued. the capping stones are ripps of hydrocal placed to match the WS portals and retaining walls.
The long retaining wall is modified production molds. Height, panel width and caps altered on a master and new mold of RTV.
This abutment done by club member fabricating stepped mold by stacking acrylic sheets within the mold.
I would like to note: A good portion of the castings shown are basically the dried/ cured color of the "dyed" Hydrocal. I find it much easier to add powdered masonry dyes to the dry hydrocal and adjust that dried color before mixing. If you add dyes to wet plaster they are far too dark to guess the dries/ cured result. (think of tile grout- how it returns to it's origional color once dried)
Once castings of structure or rock is placed final coloring, staining and weathering can be done.
You can see some of the scoring, cobbling, chipping. I find that hydrocal works best for doing this. Carving is done mostly w/ #11 blade and chisel. To aid in heavy carving simply wet the casting and it will carve quite easily. Cobbling, chipping is better done totally dry.
