# Casting bridge piers



## virgal (Sep 25, 2009)

I am building some bridge piers for project I am working on. I am finishing up the master and next week I will be creating a silicone rubber mold of it. 
 I am looking to cast these piers in a light weight material that would be easily transportable with a somewhat tough exterior (chip resistant). I have some ideas but am not sold on them.
Does anyone have experience using aerosol foam insulation as a casting material?
Alan  www.thegalline.com


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## Burl (Jan 2, 2008)

I considered expanding foam resin for some past projects, but abandoned the idea and went with rotational casting instead. 

One problem I ran into was that foam by itself makes a textured surface when it expands against the face of the mold. I was told the way some casters got around this was to make a thin pour with regular resin to make a skin on the mold, then follow with foam. 

Another problem was that it was hard to control when it started to expand. My mold design was such that it was a mostly enclosed cavity, with a small pour hole. If your mold had one large face open, I don’t think it would be so hard to control. 

Foam does tend to shrink some too after it has solidified. I found that I had to let it sit overnight before I trimmed it. If I cut it too soon, trying to get a flat face, the next day it would be concave.

Foam is a neat material, but like anything else, I think you have to learn to work around it’s limitations.


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## virgal (Sep 25, 2009)

Thanks Burl.I was thinking about a resin “skin” and then foam: A lot more work and cost.
Here is the pier design. It is a combination of weathered concrete and ruff cut stone. I am planning on standing it upright in the mold box when I pour the silicone so the bottom would be open. This way I can keep it a simple one piece mold.The master was created from floral foam blocks smoothed to a degree with spackle.I am looking for some texture.
What type of texture does the foam create on the mold surface? Would the texture complement or detract from the look I am trying to achieve. 
Also should I try to contain the foam when filling the mold?

Alan


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## Burl (Jan 2, 2008)

The texture looks rough. For a stone pattern, it might be ok. If the bottom of the pier is the top of the mold, I think it would work. I would build a mother mold around the whole thing though. Foam can exert a lot of pressure.


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## virgal (Sep 25, 2009)

Thanks again Burl. I did design a strong mold box that I am having cut out of styrene. A lot of long tabs and slots to hold it together.
I talked with a specialist at DAP about their aerosol foam and he did agree about surface texture in a mold. I have some very pure silicone oil that I will coat the mold surface with. It may help the foam flow and smooth out better.
Alan 
www.thegalline.com


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## d_sinsley (Mar 29, 2011)

I am going to chime in even though I really have no idea if what I am going to suggest would work. I know you want to keep this a single part mold but I may have an idea. Model car guys will make shells for their cars that are thin and very light weight. Given that these will have a flat featureless bottom why not cast them as a shell. you make your blank with the desired outside and then hollow out the center to your desired thickness. You make a one piece positive mold of the outside and then make a one piece negative mold of the inside which is really a plug. then when you cast the thing you pour resin into the positive mold and press the negative plug into it forcing the air and access resin out. When cured you pull out the plug and then pull out the shell. Now you have pier that is light weight and open. Fill it with expansion foam let set and cut flush. Here is the tutorial to explain what I am talking about. basically you would make a shell like this then fill the void with foam.


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## d_sinsley (Mar 29, 2011)

Another thing with foam is there are different degrees of expansion and weather resistance. They make a black pond foam which doesn't expand as much as others and is made for continual submersion.


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## virgal (Sep 25, 2009)

Thanks D.  I guess I should explain some more of what my goal is.
I only need 4 light weight piers for myself to move around at will for display purposes. The rest of the piers I will be making from that mold will be cast out of either Plaster of Paris or a light weight concrete and will be solid. 
The method in the video, will work, but is over kill for my purposes.
Again thanks for the input.
Alan


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## Totalwrecker (Feb 26, 2009)

Indoors or out?
John


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## virgal (Sep 25, 2009)

John, yes.
The foam 4 will be for indoor display. Concrete outdoor. Plaster indoor or out.

Alan  www.thegalline.com


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## virgal (Sep 25, 2009)

Here are 5 plaster piers. They have been drying out for the last week and a half. I have not experimented with the foam yet.

Alan www.thegalline.com


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## Totalwrecker (Feb 26, 2009)

Those look good, if they break or start to crumble, a better plaster is Hydrocal. It was touted for the hard shell technique of scenery making. 
I used to drive from Laguna Beach to the City of Industry in LA to buy 90lb bags from US Gypsum. Great for details.
John


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## Gary Armitstead (Jan 2, 2008)

Totalwrecker said:


> Those look good, if they break or start to crumble, a better plaster is Hydrocal. It was touted for the hard shell technique of scenery making.
> I used to drive from Laguna Beach to the City of Industry in LA to buy 90lb bags from US Gypsum. Great for details.
> John


John,

Better yet is Ultracal........the green stuff. Twice as strong as Hydrocal. We used it in our trade to pour tracing models to use in Cincinnati hydrotels (before CNC).


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## virgal (Sep 25, 2009)

John and Gary

Great suggestions. I went with plaster of Paris because I could not find Hydrocal locally. (I paid about $10.50 for a 25lb bag.) I used the better part of a 25lb. bag for the 5 piers. Mail ordering Hydrocal was more then the budget allowed. At about $11.00 a half gallon it would have been pricy. 


I checked out Ultracal on line, none of the online retailers posted any prices. Also, it seems a bit toxic according to their data sheets. I did find it on Ebay. About $55.00 for a 30lb bag delivered.


The piers that I cast will be used for indoor display. Once painted and sealed I think they should hold up fine if they are not handled a lot.


FYI it took 6 pours per pier. The center of each pier has a large block of floral foam in it to help keep down the weight. Each pier weighted in at about 77 oz. when pulled from the mold. After about 2 weeks they have lost about 10 oz. to evaporation. 


Alan www.thegalline.com


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## virgal (Sep 25, 2009)

*Scherzer single track rolling lift bridge*

The piers have dried out enough to start painting. Gave them a basic cement colored wash. Will continue to add washes until they look well weathered.

The Scherzer single track rolling lift bridge is 1/29th scale and about 8 ft long. 

Alan www.thegalline.com


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## Dick Friedman (Aug 19, 2008)

If they are not too large, you might try 3D casting them. I've done some small arches, ands they look pretty good to me. Once you've made one, you can stretch it tall or wide or deep as you need it.


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## virgal (Sep 25, 2009)

Dick
Thank you for your comment. Please explain what you mean in regard to 3D casting and stretching it once it is cast. I do not follow. 

Thanks Alan www.thegalline.com

Here are a couple of more pictures of the bridge.


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## jokensa (Dec 4, 2014)

looks great!


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## Dick Friedman (Aug 19, 2008)

*3D alternative*

When you design an item (or find it on Thingiverse, Shapeways, Tinkered or the like, you create a file of the design. Let's say you make a cube that is 2 inches or 50 millimeters on a side. Should you want a column, you just stretch the vertical dimension. To make a slab, you could increase or decrease all three dimensions to give you a new item, etc.

Some programs have a steeper learning curve than others, but for me, Tinkered.com offered an easy way to design simple items.

If I could figure out how to add photos here, I'd show you some windows and an arch I've made.


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## virgal (Sep 25, 2009)

Ok Dick I know what you mean now. All of my design work is done in cad including the piers. I could convert them into solid models with the program that I use. 


Thanks for the suggestion.

Alan www.thegalline.com


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## East Broad Top (Dec 29, 2007)

Plaster will not hold up outdoors long term, or even short term if you live in a moist environment. (Hydracal and Ultracal included.) For casting outdoors, we've had very good luck with using vinyl patching cement. (Quickrete makes the stuff we use.) It's not quite as "fine" as plaster, but it's still pretty smooth. There are other similar cement-based products that you can use (Hot Wire Foam Factory offers one) which have very smooth finishes as well. 

Later,

K


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## Totalwrecker (Feb 26, 2009)

For outdoor castings I use Cement-All with the additive that reduces water used but makes flow better. It is low-shrinkage and easy to work. I mix with a 'mud' mixer borrowed from the sheet rock stuff. A long rod with 2 mixing discs, chucked into my 1/2" drill.
As this thread was about indoors, we made appropriate suggestions...
Happy Rails
John


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## virgal (Sep 25, 2009)

When I poured the plaster of Paris I had to do it in multiple pours based on recommendations from a technician from DAP. 

My question to Kevin and John is, can the products you recommend be poured solid in one pour? How long to de-mold? Based on the size and shape, would it need rebar or some sort of re-enforcement added?

John is the additive you mentioned in the mix or bought separate? 


Thanks Alan www.thegalline.com


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## Totalwrecker (Feb 26, 2009)

Hi Alan,
The specs say up to 4" thick and the additive is separate and a couple of bucks I think. A small flat plastic bag about 4" sq.
CementAll by RapidSet. 

OK I went out and got a bag, it's called:
Flow Control; 
Increase compressive strength and Increase Fluidity.
Does that while reducing the amount of water used. From their Concrete Pharmacy, mix into water and then mix into powder/cement.
John
PS; Sets in 15 minutes, how complicated the mold? How fragile the detail. I usually wait until I feel the heat and start with the easy break aways first. That is the trial and learning part.
JC


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