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    Thread: Smoothing out faux boulder

    1. #1
      Subersibo is offline Senior Member
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      Smoothing out faux boulder

      Iíve been experimenting with using a resin boulder as a mold to make some more faux boulders to put around the pond. I used some concrete mix for the first one . I also did one using hypertufa (portlnd cement, peat moss, and perlite). That one broke in some places when I took it out if the mold. Perhaps it needed more time to harden.
      What is a good way to smooth these boulders out as they donít look too nice? Will a thin layer of hypertufa fill out those visible holes?

      Pic 1 just the concrete one
      Pic 2 made from hypertufa
      Pic 3 resin boulder and concrete side by side
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      Last edited by Subersibo; 02-26-2019 at 09:05 PM.

    2. #2
      Grumpy's Avatar
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      I use a bagged sand mix with modifications to build and finish fake rocks. I use the same mix to cover concrete blocks as well as steel mesh armatures, and it works best as long as each layer it isn't over 2" thick.

      20lbs of Sand Topping Mix (Sakrete works best for me, it seems to have finer sand at my location)
      6 lbs of Portland Cement
      0.11 lbs of Xypex 1000NF
      small handful of fibers (fiberglass, or similar)

      mix the dry ingredients with drill and paddle

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      Using a mixture of 1 part Acrylic (used for ceramic tile mortar) and 1 part water I work up about a 10 lbs batch. Let it sit for about 5 minutes to achieve a slight "false set", than stir with your margin trowel and apply to the surface. If you get the mix at a consistency of soft clay you will soon be able to have it stick on vertical walls. For my work it takes at least a couple of coats usually to get the shape and texture I am happy with. In your case with the mould you can get by with just a texture coat over the concrete shape. I would gently wet the concrete shape and wait until it is just slightly damp to the touch before coating it with this mix. There is definitely a learning curve, but you will get the hang of it fast.

      For texture tools I use almost anything I have: paint brush, toilet brush, clay shaping tools, large spoon & fork, .... Again, you will need to practice and try to get the finish and texture you desire. Lots of youtube videos to guide you.

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