Has anyone had experience using light weight joint compound or some other drywall product instead of Hydrocal and/or Plaster of Paris for their layout? If so what was and is the verdict?
I’ve tried the pre-mixed compound on a test module and it wasn’t bad. It was cleaner than Hydrocal or PoP in terms of installation but it does work differently. I’ve heard if you apply it too thickly, it will crack but I kept it to an 1/8th or 1/4 of an inch when I used it. I had almost no cracking and it dried completely in about 48 hours. I’d use it again when I run out of PoP and plaster. I’d suggest you try it out on as a test with a small bucket to see if you’re happy with the results.
I use joint compound all the time, but I don’t use it as a substitute for hydrocal. Hydrocal cures to a rigid shell when used as it normally is in model railroad scenery, whereas joint compound will remain “soft”, so to speak. Get it wet again and you can work it again.
The way I use it, instead, is as part of a plaster mixture that I apply as a top finishing layer over carved foam. The foam gives it the support it needs. I blend joint compound with a papier-mache product called Cell-U-Clay, in roughly equal proportions, although you can vary the amount of joint compound to produce different textural qualities (more joint compound = smoother). To the base of Cell-U-Clay plus Joint Compound, I add various color and texture agents, including real sand/dirt, brown and black tempera paints, and even scoopable kitty litter - the kitty litter imparts a limestone color and rough texture, which is how I create exposed rock surfaces.
Basically, the Cell-U-Clay is a binder, the joint compound is a bulk filler, and then all the rest is for color and texture. You have to go really dark with the color, because it will dry a lot lighter, much as real soil looks darker when wet. But the benefit of this system is that you can re-wet it and work it again later, if needed; if you do develop a large crack (and thick application will indeed crack), you can wet that area and either add more material to patch it, or else just push the wet plaster around to fill in the crack.
The other benefit of this system is the primary reason why I first adopted it - the “soft” plaster has some ability to flex in it, it’s not as brittle as hydrocal. My layouts have always been built with an eye towards portability, and as much as my N-Trak module and other sections have moved around, I don’t develop chips in my scenery (and even if I did, all I have to do is rewet and rework). The Cell-U-Clay is much lighter than hydrocal, but as you add joint compound the weight savin
I use joint compound all the time. I buy the premixed type in tubs, not the powder. I use plaster of paris only for rock moulds. I’ve never used hydrocal so I can’t comment on it. I like the joint compound because I can just scoop it up, slap it on and work it like cake icing. Yes, it will crack if it’s too thick. I try to keep it to 1/8" or so. It can take a long time to set, depending on the humidity and thickness, maybe as long as a couple of days. When it’s set, it’s rock hard (I don’t find it “soft” at all) and it can be re-worked by wetting it. That’s an advantage if you’re making something like a road that you want perfectly smooth. Just rub it with a wet sponge–no sanding. An offset spatula, like they use for spreading cake icing, is a great tool to use. You can find them in any kitchen gadget store or in the kitchen tools section of your grocery store. You need to keep the container air tight or the compound will start to harden. The container I’ve got now seems to be air tight. i’ve had it over a year and the contents are still soft. One trick I was told for long term storage is to pour a layer of water on top of the compound and pour it off when you go to use it again. A sheet of plastic food wrap on the surface of the compound should work too.
I have use all three you mentioned for me POP no good, joint compound works well but is no substitute for Hydrocal. I use Hydrocal light for all my rock castings and have no complaints. It is a little pricey but I bought 10 boxes of it form a LHS that was no longer carrying model railroad stuff for less then $4.00/box so I can’t complain.
Joint compound tends to shrink a little when drying. Do not use it thick or it will take days to dry. I use it mainly to patch some damaged parts of my modules.
Pete
Hydrocal can be purchased at a much more reasonable price if you buy a large bag from a contractor supply outlet that deals with Gypsum products.
Plaster of Paris is ok but pricey.
Joint compound has it’s uses in thin coats. It smooths well with a sponge as was mentioned. Don’t try using it for casting, IMO.
Or use “structolite”. Lighter than plaster, long working time, just as hard, nice texture, brown not white.
In my experience doing rockwork on my garage (“California Basement”) layout, I’ve found out that Hydrocal is impossible–sets up WAY too quick, no matter how you work it–Plaster is really too heavy, Joint Compound is okay if you just need to do a thin layer, but what really works for me is Sculptamold. Lighter than Plaster, just a little heavier than Hydrocal, sets up slowly enough to work and carve, and has a nice ‘grainy’ texture that actually looks like rock.
If mixed per the instructions, you get a mixture somewhat like Quaker Oats that goes on nice and thick and remains pliable for carving for several hours, and dries as hard as Hydrocal (and takes stains better). If mixed for rock castings (50–50 Sculptamold and water), just pour it in the casting, let it set for about 20 minutes–to get the plaster part of it to seep into the casting–slap it on where you want, let it set for about 15 more minutes, peel off the casting, and you’ve got yourself a really terrific rock-face that you can also detail for the next several hours as you want.
I like the stuff. Lighter than plaster, a little heavier than Hydrocal, gives you good setting time to work with, and takes stains extremely well. And when dry, it’s rock-solid. I mean, ROCK!
Tom [:)]
…still have Lynn Westcott’s two original Model Railroaders for March 1965 MR and April 1965 MR unveiling the new Hardshell (Zip-Texturing) hydrocal scenery technique - check out the Model Railroader covers.
Thanks to all who responded with the great information in response to my question.
Bob
Many times I have used drywall compound powder and made a mix from that . Most of the scenery forms I make are made of drywall compound and paper towels . It worked great . I also use light weight spakling to fill in any voids . Its always worked well for me . If it didnt , I wouldnt have used it as much . Try this also . If you have any styrofoam laying around , find an old kitchen blender or food chopper and grind it down so you can add this to your mix . It adds texture to the scenery base and it adds a softer look , plus gives the mix more volume to work with . Not a bad idea in recycling some of that old foam .