How to model spalling concrete

[Jesse6669]

How would you model this underpass:

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I want to scratch-build to replicate the structure accurately, and was going to use styrene--but I have a feeling I won't be able to effectively capture the spalling/crumbled concrete look with styrene.  I don't really want to build up a form and pour the whole thing in plaster.  I thought about pouring hydrocal into 2cm x 2cm strips and building up from that... where I could gouge out the plaster to get the crumbled sections.

Thoughts, suggestions?

[Dave V]

Build a thinner structure from styrene and then build it up with spackle?

[peteski]

For the piers I wonder if blocks made from snapped PVC tiles would do the trick.  That technique was very successfully utilized by Ian here back when he was modeling in N scale.  That thread is somewhere in the Layout construction section of the forum.

[tom mann]

I would cast it with portland cement and then kick it around.

[Jesse6669]

Hmmmmm... a little scenic S&M you say? 

[jwb]

Balsa, distressed, and then sealed with sanding sealer.

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[ednadolski]

Anchor bolt cement, cast in stripwood forms, slightly over-watered mix and with insufficient release agent:




(Full disclosure: this pic is HO scale.)


Alternately, cast hydrocal in a wooden, styrene, or RTV mold, then chip away with a combination of x-acto blades, dental picks, and other things that you should not hold while running.



Ed

[GaryHinshaw]

That's awesome Ed.  Is the colour variation natural, or have you stained this portal?

[Scottl]

What are the typical dimensions of wood formers used to cast concrete in railroad structures?  I'm interested in trying this...

[Santa Fe Guy]

That portal does look awesome.
Rod.

[ednadolski]

Is the colour variation natural, or have you stained this portal?

That's the natural color.   It does look rather dark under room lighting.

What are the typical dimensions of wood formers used to cast concrete in railroad structures?

These are a scale 6".  I'm not sure that 'typical' applies, it really varies depending on the construction standards.


Ed

[GaryHinshaw]

That's the natural color.   It does look rather dark under room lighting.

It looks a bit dark in the photo too.  If it were about 50% lighter it would be perfect (except for the big honkin' cracks). 

[Jesse6669]

I had a bit of an 'a-ha' moment while thinking I really needed some 0.5 cm thick styrene while I have a sheet of foamcore poster board sitting by the workbench.  Problem is, the pesky paper really doesn't score well to make the horizontal joints, and just seems too smooth..  Well some hot water and peeling/rubbing took care of the paper and I was left with half-cm thick sheets of foam.  Cut, scored, painted... with a little picking/prodding with a knife and toothpick for the crumbling bits.  I'm pretty happy with the result and am going to try making the underpass with this technique.

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[chicken45]

Great techniques!

[davefoxx]

+1 on the anchor bolt cement.  I poured two bridge abutments in homemade molds out of that stuff on my layout.  Can't beat the look of using the real thing.



DFF