Thank you all for your knowledge on this. I plan on doing more concrete "wood", so which is better, change the mix I use when I aam doing wood projects like this or just do what you guys sudgested above?
Sorry Dion that you have come across this dreaded issue. The previous feedback is correct. Thin applications in any mix can be an issue at times. In those cases the scratch coat needs to be pretty wet, or as suggested, you can use a primer, though make sure the primer is not fully cured before application of the carving mix. If the primer is cured, you have basically succeeded in "sealing" your scratchcoat providing you with the more frustrating - perpetual delamination syndrome. Just check with the information about your primer to verify the cure times. Also, the scratchcoat itself can make a big difference. A very porous, super rough coat will really wick the moisture from your carvable faster than a bit smoother, less profiled coat. Keep in mind if you are going thin on top you will not need to be so aggressive with the scratchcoat. Lastly, one can also fortify the scratchcoat mix which will not only increase the integrity of the surface but will reduce the absorption rate of the moisture from the carving mix once applied. Or sometimes, no matter what, it just happens....
Sorry to be long winded.
The answer could be both. You may find that by tweaking your process a bit, the mix will be fine. If not, then I would suggest changing over to a "non" vertical mix if you keep it at about 5/8 or so. Working time will be cut down a bit but the woodgraining process can be fairly quick anyway so time should not be an issue. Stay in touch.
Dion Battles said:Thank you all for your knowledge on this. I plan on doing more concrete "wood", so which is better, change the mix I use when I aam doing wood projects like this or just do what you guys sudgested above?
The tweaking refers to making sure the scatchcoat is proper for what you are doing, in this case the wood graining.in order to prevent as a rapid a dryout as you have had. A light prime will help with the moisture retention. Masonry cement as an overlayment will not be so good. It may end up like a dry river bed when you are through. Really, the best choice if you are purely graining would be to use an standard overlayment mix and Nate had mentioned. It is made for thin applications, many are designed to take texture, will actually offer a finer finish and structurally will offer more integrity. Jody may be able to chime in on this as well.
Concrete Coatings Inc makes a stampable overlay in both white and gray mixes (http://concretecoatingsinc.com/stamp_tek_stampable_overlay.html). It has fiber in the mix and feels kind of granular, but it holds texture well and works pretty well in shower applications. We made a great barn-wood sample for our last home show display with it. (You have to use a VAE primer or it'll delaminate -- http://concretecoatingsinc.com/duraset-vae.html )
All the other showers I do, have either used their G-100 grout & modifier or Tru-Pak.