I have had success using Hydrocal to cast bridge abutments and piers. However, I'm willing to try Anchor Cement as shown by Lance Mundheim.
But if I make a master bridge pier mold for the longest pier length and have to cut the casting down for shorter piers, I'm worried. Cutting the cement without investing in some extra equipment (at least a masonry saw blade) doesn't sound cost effectice in comparison to Hydrocal. With the Hydrocal, I can just use a saw.
Has anyone cut a casting made from the Anchor Cement?
Victor A. Baird
www.erstwhilepublications.com
I was just thinking, duh, I can just make a mold for the longest pier, pour to the shorter height necessary from the bottom and use shims in the riverbed for any adjustments.
Yeah, if your mould is made so that it's upside down when being filled, you can make it the height of the tallest one required, then make all subsequent ones to whatever height is necessary to cross an area of varying terrain simply by pouring only to the height desired. You could also make the top (bottom of the mould) interchangeable, so that it could support bridge spans of varying types - say a truss span and a deck girder, where the deck girder would require a step-down in the pier in order for the track from it to line up with that on the truss span. This allows the tapered sides of the piers to remain in alignment when viewed from the ends of the bridge, regardless of their individual heights.
I cast mine with Durabond patching plaster - in most cases, it can be filed or sanded to the proper height, but a saw is useful, too, when I misjudge the height to which the plaster is poured.
Wayne
Those are some great molds and modeling Wayne. Thanks for sharing. And I see you set them up so you can pop them open with grooved siding inside! I did the same utilizing wood molds built painstakingly with individual planks glued together to simulate the wood forms for a bridge abutment. When the mold was all put together it had the shape of a piano! (I also used track nails to hold the form together and the rubbery kind of window caulking to make sure it was sealed.)
Incidentally, I use a thin mix of soy sauce from a packet from the local Chinese restaurant. It gives the Hydrocal “concrete” a realistic tint. I also finish off with thinned India ink for tone and rust colored chalk for rust drippings.
My next molds will be plastic like yours so I won’t have to use a mold release. (I used a thin layer of pam cooking oil from a spray can for a mold release with my wood molds, but blotted it, especially in the corners to make sure it didn’t build up too thick.)
Thanks for your kind words, Victor.
I simulated the form-board impressions by scribing the styrene, then selectively scraping individual boards to give a slightly irregular surface. The effect is more visible in the photo showing the open mould, and, in person, when the pier has been weathered - they're not weathered in those photos.
Before assembling the moulds, I used a paper towel to wipe a light film of vegetable oil onto the interior surfaces, as I was unsure how easily they would release. Once opened, there appeared to be no trace of oil left on either the moulds nor the castings, and it caused no difficulties when I coloured the plaster using a wash of water-based PollyScale. The cooking spray is, I think, the same stuff, and probably easier to use.
Dr. WAYNE,
Would you be so kind as to give us the dimensions of your abutment molds. they look great.
Thanks in advance,
Johnboy out................................
from Saskatchewan, in the Great White North..
We have met the enemy, and he is us............ (Pogo)
Wayne:
I'm not sure, but if you did scrape and scribe the inside of your plastic molds, you might indeed have to use the vegtable oil.
Now, if the interior of your styrene molds were shiny and smooth, you wouldn't have to use mold release.
When I use styrene, I am going to glue the appropriate siding inside and then sand it to simulate wood grain. In the early days, it's my understanding, wood forms were built with planking, but later wood forms including sheets of plywood.
Thanks for your kind words, Johnboy.
That particular bridge needed only one mould for the four piers - I simply poured each to a little more than the required height, then trimmed the bottoms to fit.
For making the moulds, I use .060" sheet styrene, and assemble the various components using lacquer thinner as a solvent-type cement. If you're going to be making a number of moulds or if you do a fair amount of scratchbuilding, it's much cheaper to buy the plastic in 4'x8' sheets. I've gone through several, as it's useful for making roofs, foundations and unseen back walls when you re-arrange a kit to use all of its walls on the visible side of the building. Look for "Plastic Suppliers" in the Yellow Pages or on-line.
While the tallest pier is only 32', the mould is about 40' (HO) in overall height, with the inside dimensions at the base of the pier, which is the open top of the mould, 9'6"x17'. The top of the pier (upon which the mould sits when you're filling it) is 5'6"x13'6".Those dimensions aren't based on any particular prototype, but simply on proportions which I thought looked reasonable.
If you use any of the Durabond patching plasters (various setting times) for casting the piers, remove them from the mould as soon as they've set, but before they're fully hardened - if they need to be trimmed to the proper height, it's much easier before they've fully-cured.
The abutments for that bridge, as for many bridges, were built to suit the terrain, and are often more complicated than the piers. The abutment on the left was poured partially in a mould, with the wing walls poured on-site:
If your bridge is one of multiple but dissimilar spans, the tops of the abutments may need to be customised for each. This may require a separate mould for each, but in some cases you can use one mould with various tops to give the step-downs required. Here's one which starts at the east abutmentment with a deck girder (modified from an Atlas through girder) and meets a Central Valley truss at the first pier:
...that meets with another Atlas deck girder, which in-turn connects to a Micro engineering 50' deck girder:
...and that to an even shallower M.E. 30' deck girder, mostly hidden in the undergrowth:
Again, that's great modeling. I'd share some of my photos, but I still haven't figured out how to get them to post here with Photo Bucket though I can post links.