Hydrocal Hardshell - How Thick?

[jimsrpo]

Thickness would depend on how close it is to the front of the layout.  If it might be leaned on by visitors, then go thicker.  Why take a chance?!  Where it will never be touched, thin is OK.

Actually I prefer a brand of dark base coat plaster called Structolite, found at Home Depot for about $10 for a 50 lb bag.  It has close to the strength of Hydrocal, but sets very slowly (overnight) so a big batch can be mixed at once.  It takes a couple of days to reach full strength.

It also has a granular nature that makes for interesting rockwork.

Jim

[jktrains]

On thickness, generally a 1/4" to 3/8" if nothing is going to be pushing against it.

For straight hydrocal, as used in traditional hardshell scenery, a 1/4"+ in thickness to overkill and far too much.  For the substructure of carboard webbing you've described two layeers of dipped paper towels will be more than sufficient.  Because of its density Hydrocal is very strong.  And, because of its density it does not take water based stains, dyes etc. well at all.  Plus, it is very gray and change to color of the stain or dye you use.

[jeffrey-wimberly]

On thickness, generally a 1/4" to 3/8" if nothing is going to be pushing against it.

[HarryHotspur]

Latex works fine on hydrocal.

[CTValleyRR]

The Woodland Scenics stuff is a special blend of plaster, softer and more porous than run-of-the-mill hydrocal.  It takes paint very well.

I've never had a problem painting regular hydrocal with latex paint, so long as it's clean and dry.  It doesn't take water colors (like the Woodland Scenics colors) very well.

[DeadheadGreg]

So you can't even paint hydrocal with latex paint?  I remember using the stuff because it comes with the Mountain Valley scenery kit from Woodland Scenics, and my dad and I used that when I was a kid to make tunnels, and I remember using regular paint on it, and it painted.  I don't remember how good it was, but I remember that we got it painted.  We used crappy, non-earth-toned paint but it still painted. 

Has anyone here ever made a liftout section out of hardshell?  I've been thinking of building up the cardboard webbing on the layout, and then removing it and covering it with plaster somewhere else, so that it doesn't drip all over the layout and just to minimize layout cleanup in general.  Then, once it hardens, just move it back to the layout. 

[bogp40]

I will apply a veneering plaster (Unical, Diamond etc) for the final coat of hardshell. These plasters have a much longer working time as compared to Hydrocal. I will vary the thickness. Usually up to 1/8" is more than thick enough, but in any spots for tree planting or areas at the layout edge that may receive some handling or abuse, the plaster should be thicker.

[selector]

A few things:

Hydrocal is very hard and dense, as pointed out already.  So, it can be kept thin, say between 3/32" and 1/8".  It can get expensive unless you find a bulk supply, such as at builders stores.

It doesn't paint well at all.  If you have places where plaster and hydrocal share space, and then overpaint and pour ground foam, save yourself the trouble and just use glue and cover the hydrocal completely...it can be that bad.  Alternatively, use masonary dyes (powder form) or use small quantities of acrylic paints as dyes in the mix so that later all you have to do is overspray with a glue or matte medium and then use ground foam.

Supporting trees "stuck" into hydrocal will not be easy.  It is for this reason that most of use eventually use foam, if only where we intend to plant a lot of trees.  Otherwise, a composite goop with vermiculite, plaster of paris/patching plaster, and Portland Cement works well for this.  Must be dyed as well if you want good results.

No matter what product you use, work fairly quickly, and then rinse it all scrupulously clean, vessel and utensils, outdoors....never down any drains.

[CascadeBob]

The last time I used Hydrocal in hardshell scenery, which was a number of years ago, I dipped strips of industrial weight paper towels in a soupy mixture of Hydrocal and placed it over crumpled newspaper as support.  I used two layers of these paper towel strips to get the final thickness.  The two layer were applied at the same time.  After the Hydrocal set, the resulting structure was very strong.  Be aware that Hydrocal sets very quickly so don't mix too large batches.  Using it can be very messey, so take precautions to protect the floor, your shoes, etc.  I've never tried to paint or stain Hydrocal, but I've heard that it does not take paint or washes of color very well.  I used a mixture of molding plaster over the Hydrocal hardshell to facilitate the application of colors.

You might want to look at the following website to get additional info. on hardshell scenery and various plasters that can be used: www.girr.org/girr/tips/tips4/hardshell_tips.html

Hope this helps,

Bob

[jktrains]

It can be rather thin because ofthe strength of hydrocal.  Hydrocal is much denser than plaster and therefore the hardshell layer can be thinner.  Another thing to remember about hydrocal is that it does not take dyes and stain well because of its density.  Most people apply a thin layer of plaster overtop of it to take stains,etc.

[Johnnny_reb]

How thick should hydrocal hardshell be if using cardboard strips and cheesecloth as struture under the hydrocal? I've seen pictures that show it to be very thin, (like heavy paper) but I wonder if it would be very strong if this thin.

It should be thick enough to support but not so thick that the layout cannot be moved. Now with that said, if your not walking on it or expecting it to hold up your weight, all it has to do is hold up what is sitting on it. So thickness is normally kept to a minimum.

[mechengr]

How thick should hydrocal hardshell be if using cardboard strips and cheesecloth as struture under the hydrocal? I've seen pictures that show it to be very thin, (like heavy paper) but I wonder if it would be very strong if this thin.