Making Fake Rocks Using Fiberglass

by M. R. Daniels

Original Note to rec.ponds

Questions Sent to M. R. Daniels

Comments by David Modine

Comments by Vern

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Original Note to rec.ponds

From: "M.R. Daniels" mrdan@epix.net

Subject: Making fake rocks, Epcot style

I see a lot of posts about fake rocks, so maybe this is one contribution I can make here. (I sure can't make many others!) Having owned a scene shop in Philadelphia for 20 years that built scenery for theater, opera, TV, theme parks, etc, and being the head designer for Phila. Flower Show exhibits, I've made a few fake rocks in my day. This is the way the pros do it:

It's really pretty easy. Get some chunks of styrofoam....trash pick them or look in the dumpsters behind places that sell electronic equipment, or on the loading dock of hospitals (they get drugs packed in styrofoam coolers) or as a last resort, buy a sheet of blue insulation board and break it into chunks, tape them together in sizes you want. These will be the forms. You can also use crumpled cardboard boxes, bales of hay, milk crates, just about anything that will support the fiberglas fabric until it dries and has a shape you like, but the styrofoam can be left in place as extra support, and even carved into and patched for alterations.

Go to an auto supply shop. Buy fiberglas (don't get the kit; it's cheaper by the yard. In fact, some fabric stores sell it as drapery material) and a gallon of resin with whatever catalyst they use with the brand they carry. You can also use burlap, even cotton, but fiberglas will last longer and is easier to work with.

Arrange the forms however you want them. Cut the fiberglas into 4" squares. Mix a small amount of resin (wear gloves, and a mask if you are not in the outdoors) and dip the cloth square into it and slap it on the form. Apply the squares, altering the angle and overlapping as much as possible. Smooth down edges. By using small squares, you will be able to stretch the fabric to fit into crevices and over curves. Fiberglas is nasty stuff---be sure to work outdoors or in a well ventilated area and wear a mask if you are sensitive to stuff like that. Our shop used an outdoor area with fans blowing the fumes away from the workers.

Allow it to dry overnight. The next day, paint another coat of resin over everything, allowing it to really flood on. Allow to dry overnight again. Sand down any rough edges. Paint with latex paint. The easiest way to get a natural look is to scumble three or four colors all over in blotches---gray, brown, gray-brown, light gray brown, etc---let it dry. Then dip a wide brush into each color and shake it on the rocks with a hard downward motion to finely spatter the color. Do that with each color, so all the colors mingle and give a slightly granite look. If desired, you can mix your darkest color very thin and shadow the crevices with it. Oh and the paint spatters better if you thin it a bit first.

We have used this technique for waterfalls, beaches, islands, etc. If the fiberglas resin is applied heavily it is totally waterproof. Flower show exhibits have used the rocks year after year after year and they hold up well. We have made rocks that were walked on by a cast of 40 and they never showed wear. There are other materials on the market (Celastic comes to mind) made for this purpose but the cost is enormous compared to what this will cost you. MR

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Questions Sent to M. R. Daniels

• Question to M. R. Daniels
  > I would like to build the cement type of large rock but even with my experience
  > as a model maker, you would have to work fast before the cement set up and it
  > probably wouldn't look right with a first time attempt of sculpturing cement
  > to look like rock.

• Answer from M. R. Daniels
  Correct. Also, "Carving" cement really isn't feasible... you can sort of model it like frosting on a cake, but you can't get hard edges and chiseled looking anything. It's even a bit of an art in fiberglas, but at least the technique makes it easier to handle, and if you play around with forms and draping methods you will get pretty natural looking shapes. (This is why they hire scenic artists at $60 an hour to make those things!)

• Question for M. R. Daniels
  > At least with foam, you have time to cut, carve and play around with it. If you
  > could buy rock faced molds, they would probably be too expensive for a one time
  > use. You could make your own molds but here in Indiana we don't have the larger
  > cliff like rock that I would want.

• Answer from M. R. Daniels
  To use molds with foam, you would need the spray on foam which is a whole other ball game. Just get a pile of scrap anything---crumpled cardboard boxes, chicken wire, styrofoam, whatever, and experiment by wetting a piece of fabric---say, cheesecloth, and plopping it over the junk. Tuck it here and there, let it tent over some areas and fit closely in others. You will be amazed at how "natural" it looks. Different fabrics will have slightly different looks.

• Additional comments by M. R. Daniels
  Someone just emailed me about making pavers, I assume for edging a pond, and I thought of another scenic technique, this one for "stone" surfaces such as platforms, steps, etc. We would get a bucket of water-based ceramic tile adhesive and trowel it on. That's it. The edge of the trowel could make chisel marks, swirl it for more natural looks, just like icing on a cake. It takes a day or two to dry thoroughly (esp. if it is built up more than 1/4") but we used it for areas where a chorus of opera singers tramped across it every night for six weeks and it held up fine. It takes paint well, and well gee it's made for showers and tubs. I guess for pavers you could trowel it over slabs of something---cinder block pavers, would make them look more like stone. I wouldn't use styrofoam for edging because it has no weight to it, and if it were to be used underwater I think I would worry about being sure there was no way the water could get in or under the adhesive or it might lift off. Maybe coat it with....fiberglas?

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Comments by David Modine

• From: David Modine modine@erols.com

• If anyone plans on using polyester resin & fiberglass to create their own rocks or whatever, I would like to make a couple recommendations.
  • First apply some sort of thick lotion on your hands & forarms. Vasoline, Corn Huskers, or silimar lotion.

  • Wear some rubber or latex gloves that come up above your wrists.

  • Get a good quality dual cartridge respirater. Get the element type "GMA", or "Organic Vapor" for your respirater.

  • Be sure to have a can of acetone on hand before you start. Acetone is the only good solvent for removing polyester resins from wherever you may spill or splatter some.

  • Work outside, or in a well ventilated area.

  • Work when temp's are 70 degrees & humidity is low. Cool temp's & humidity dramatically slow down the curing time of resins.

  • Do NOT use more hardener than is recommended. Less is always better than more. If you use too much hardener, the cured product will be more liable to crack when cured.

• I have never made "fake rocks" myself with resin & fiberglass, My experience with resins comes from long experience in Marble fabrication, including a specialization in repair & restoration.

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Comments by Vern

From: Vern vrolson@micron.net

Mr. Daniels, I am sure it was an oversight, but I don't think you mentioned that
regular styrofam and regular fiberglass resin are not compatible. The resin will
melt the foam. You have to use urethane foam with the common fiberglass resin
or use epoxy resin with regular foam. Other wise you end up with a sticky mess.

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