I’ve got what I consider a slightly strange question for you tonight: Can Hydrocal be thinned down enough and the curing be extended enough for it to be piped into an area. (Think like decorating a cake with icing or mortaring stone on a decorative brick or stone fireplace.) I have a few holes where I put my Woodland Scenics retaining walls together and would like to fill the areas to make the holes look better and to get them to take the tint the same as the rest of the walls. If this isn’t possible, if anyone has any other ideas, feel free to expound on them. Thank you for all your assistance.
Plaster can refuse to set properly if thinned too much with water, but I’ve successfully moved small amounts of it (mixed normally) around using the tip of a skewer or toothpick, and you can also try an eyedropper. Plaster that’s mixed too thin also tends to take paint or stain very differently from areas mixed at more normal ratios, something else to consider depending on how you plan to apply color.
You would be much better satisfied if you did like covering the intersection of two drywall sheets. Use plaster cloth or drywall tape to cover the hole. It can, then, expand and contract without cracking,(as plaster will do}. Hydrocal plaster is excellent to making river and lake bottoms water proof, roadways, or for casting rock outcrops, but is expensive and requires a paint primer. Bob Hahn
Get some Durabond patching plaster from any building supply or one of the big box home improvement stores. It comes in several different setting times, indicated by a number following the name: I like Durabond 90 for scenery, as it has a working time of approximately 90 minutes. You can mix it to varying consistencies and it will begin to set in about 90 minutes. I’ve applied it up to 2" thick with no cracking, and it can also be used as a skim coat. Once set, it’s extremely hard, although there’s a window between the beginning of set-up and actual curing where some carving is possible.
Applied over aluminum screen, it makes decent landforms:
…along with bridge piers and abutments:
…and water:
Wayne
To clarify, the gaps are 1/16" to 1/8" wide and the thickness of the casting deep so the tape idea wouldn’t work. I hadn’t thought of the Durabond idea. I have heard of that in construction (drywall), but I hadn’t thought of it for scenery. Given that it has the extended work time, in theory, it could be piped for my small cracks. Am I correct that you should be able to carve it with a hobby knife while it’s wet?
As for the coating, I use a certain acyclic paint that a lot of the people seem not to like. However it is the color that meets the proper rock color for my area.
If you wish to inject it into the cracks, I’d suggest covering the face of the opening with masking tape first. After the filler is in place and starts to heat-up (a sign that it’s beginning to set), remove the tape and carve as necessary.
You could also use a putty knife to force the plaster into the gaps (pre-wet the area first for a better bond) then smooth with the knife and carve as it begins to set.
Wayne
I don’t think it should be all that difficult. I’d use a plastic pipette, but cut the tip off to make the opening wider. Experiment with small batches. Have a big container of water ready to rinse the pipette out after each injection, or you’ll go through a lot of pipettes.
I think you’re right to use Hydrocal to get the same surface for painting, by the way. Using any other material will make it more difficult to get an exact match and hide the gap. Where I have gaps in walls, I often end up with a drainage pipe or a tree in front of it to make the gap less obvious.
Wayne, you – or perhaps it was someone else – has brought up this use of Durobond technique for patching scenery before – at least I have it tacked away in the back of my mind somewhere. Thank you, sir, for the refreshment of my memory.
I don’t know about Durabond patching plaster, but I just checked the “ingredients” of DAP patching plaster and it contains vinyl acetate, which is basically a plastic filler. I’ve noticed that when I used it to blend rock molds made from plaster or hydrocal, that it doesn’t take stains as well, leaving white areas. To patch holes or blend in rocks that I’ve made with molds, I mix up a paste using plaster of Paris, with vinegar added to extend the working time. Since, it’s made from the same material as the rocks and surrounding plastered area, it stains exactly the same.