I’ve never done molds before (except WS rocks with their molds) but I want to try to make some bridge abutments that look like concrete. I read a suggestion here to use legos to build the mold, which I think I can do easily from my son’s (now in college) legos. I want to use the lego mold several times to make several abutments. What do I use for mold release to allow reuse? What material would be best for the casting? Some people use actual cement, some seem to use hydrocal and some use some type of resin. What’s most appropriate for me to buy and try with the legos as a mold?
I prefer plaster of paris for my abutments, pillars, etc. In your case since you are experimenting plaster of paris is cheap and you can get a lot of casting experience with your lego molds without much expense. Since Legos are a hard plastic you can probably get by with just “wet water” as a mold release. You could also try a kitchen oil spray such as Pam. I’ve never used Legos as molds so I’ll be interested to see how your work comes out. Keep us informed.
Joe
Thanks, I’ll put plaster of paris on the list of materials to experiment with and I’ll try the wet water and PAM to see if there is any difference.
Do you want the casting to look like the Lego wall, or do you want it to be the “negative” of the wall? If you build a mold with Legos and then pour in Hydrocal, you will end up with a negative casting.
I’ve made a number of casting molds with Woodland Scenics latex rubber. First, I find the item I want to cast. Then I apply several layers of latex to the original. After I’ve made the mold, I remove the original and then do castings with Hydrocal. (Making the mold isn’t quite as easy as “paint it on and use it,” but it’s not rocket science by any means.)
A latex mold can be peeled off the casting. A solid mold is likely to be more difficult to release. I’ve used all my home-made molds over and over, with no problems.
This is from a latex mold I made. The original was a section of plastic artificial honeycomb, used by beekeepers. Here are the castings, first as they came out, and second after cutting and painting, and installing on the layout.:
I was thinking I would use the legos for their smooth surfaces, not the round parts used as joiners. This seems to work in my imagination but I have to get home to see if I can really make that work - tied down to work for another couple of hours.
You will get a smooth surface with the grid pattern of the blocks. You will see the individual blocks in the casting. I made tunnel portals using plastic sheet and wood with the base being a chunk of plywood and the sides pieces of 1x2 screwed to the plywood base. I unscrewed the sides after the casting dried. I used auto paste wax on the mold as a release and plaster of paris for the castings.
I probably will get the block lines as you say. But can I do a bit of light sanding to get rid of them? Those block lines should be protruding just a bit - right? All surfaces should be flat with no curves. My problem with wanting to mold in the past is that you seem to have to have a good version of what you want to mold first. Then you make copies of it. I don’t like any of the commercial abutments because they’re sized wrong for bridges with shoes, or my own handiwork using wood blocks and styrene. So I thought if I cast one square using the legos with something like hydrocal or plaster, I could put sandpaper to it to rough it, change it to fit, etc.
Called my son at college to ask if I could use a handful of his lego blocks (from a bin holding, conservatively, several thousand) for this experiment since he had previously said no to a similar request and he said ok, if I cleaned them and returned them when I was done. Told me I could not CA them together or use any lego guys!
One of the clubs that puts on shows around here uses extruded foam for abutments and bridge piers. They have scribed theirs to look like rock, but they could also be make to look like concrete. Took my camera to the fall show so I could post some pictures (when I figure out how), but they didn’t have that layout there. This fall they had the layout, I forgot the camera. They do look very good and can be made any size needed, just carve away. Carving with a hot knife and spraying with textured paint should work fine. Scribe some fine form lines if needed.
Good luck,
Molding and casting is usually reserved for when you need multiple copies of the same exact item.
It may be easier for you to use wood blocks and cover them with styrene sheet material with a block or brick pattern. That is what I do on occasion.
If you want to duplicate a poured concrete abutment in a form, you can build up a mold using bass wood or balsa wood. Then the plaster would show the wood impressions.
However, if you did use the Legos for the form or mold, once you smoothed off the ridges, you could scribe in the wood seams and grain that a wood form would take on, or brick or block.
I also think that Pam may introduce oil onto the plaster surface which may not allow an even color to be obtained when painting them.
I’m a little worried about PAM too. What I’ll try this weekend is some hydrocal in a lego mold to see what comes out. It may not work for this purpose but could be useful for something else. Wood block with styrene is also a good solution. I’m not feeling too crazy about using foam only because I’m worried its not tough enough to tolerate too much abuse. These abutments are going on a club layout which periodically visited by the public. Even our adolescent members seem compelled to look with their fingers. Thanks to everyone for all your suggestions and help.