Making your own molds for casting

[Trucklover]

Josh, I made my moulds from .060" sheet styrene - look in the Yellow Pages for a plastics supplier, as it's much cheaper buying it in 4'x8' sheets than as small sheets from the hobby shop.

This is somthing i always forget about when i buy sheet styrene lol. Thanks!! This will save alot of money buying in a 4x8 sheet lol

For casting, I used a product from Canada Gypsum called Durabond. U.S. Gypsum has the same stuff, under the same name, too. The name is followed by a number, which represents the setting time, in minutes. I used Durabond 90, the same stuff that I used for my landforms and rivers on the layout. It sets in approximately 90 minutes, at which time you can remove the mould. When fully cured, it is extremely hard and durable. Various setting times are available, as quick as 20 minutes, and it can be had, I think, in 2 and 5 lb. boxes, or in 33 lb. bags - the bigger the quantity, the lower the cost per pound. It will set no matter to what consistency it is mixed, although very thin mixtures don't seem to be quite as strong. When fully hardened (it depends on the thickness), it is difficult to file or sand, although, when first removed from the mould it can be carved or scribed to represent cut stone. It takes water-based stains reasonably well, although it's best to use a fairly wide brush to apply it, in order to avoid blotchiness - use a thin mixture and make several applications, as required.

I know exactly what you are talking about When i worked at Lowes, we had this stuff down the DryWall aisle and it was next to the Mud. I used to hate stocking the pallets of this stuff, because we had to get 3 pallets in an 96" beam opening in the racking which is almost impossible because each pallet seemed like it was 3' wide but really only 2' something (they were odd sized small pallets and always stacked horribly which also did not help when stocking the pallets and shoving them into place), and almost everytime, no matter who put the pallets in there with the forklift, bags would tear and it would just absolutely make a terrible mess all over the aisle that would take about an hour to clean up LOL. I think we discontinued and stop stocking the 5 and 90 minute, but i know for sure we had the 20 and 45, the 45 should be fine for me

I used vegetable oil, applied with a paper towel, as a mould release, although my moulds were very simple shapes - it didn't seem to affect the plaster's ability to take a stain.
To make the bridge spans modular may be as simple as casting a "key" (a simple protrusion) extending across one end, with a corresponding keyway (depression) in the opposite end. Since some modellers may wish to shorten their spans (a mitre saw - hand-powered or hacksaw should work) I'd leave placement of the piers up to the individual. You could build the abutments with a "seat" to accept the end of the spans, though, which would both support the bridge and prevent it from moving sideways.
To join the spans to the piers and abutments, white glue or yellow carpenters' glue should work well - I used yellow glue to glue the footings to both the Durabond scenery and the plywood riverbeds.

Thanks for the tips, this is what i was thinking for the bridge spans, something like you mentioned. I was thinking that i would leave it up to the modeler to cut off the key whole or connecting piece on each span if it was not needed....

Having the bridge spans sitting in the bridge abutments is a great idea, and i will definitely have to do that, it will also make it look alot more realistic

And i agree with you, the placement of the piers would be up to the modeler and his/her scene. I really wanna come up with at least a few different style of bridge piers, i think more choices will be the best, since there are such a variety of them i see just around here in Cali on the highways