Large Scale Central

What material to use?

Modeling
#1

I’m almost ready to start work on a new building, similar to my abandoned stone cabin. I plan to use the same technique – creating a foamcore form to cast the walls. When I did the abandoned cabin, I used rectangular blocks of styrofoam to make the openings for doors and windows in the cast walls. The openings were not very precise, but since that was supposed to be a crude, older structure, it was acceptable.

This time I want the openings to be much more accurate. I want the sides to be parallel and perfectly level, and sized correctly to fit the door and window castings.

But I’m stumped as to what kind of material to use as “blocks” in the form. It needs to be at least 1/2" thick, but no more than 3/4" thick. It needs to be able to cut cleanly, hold its shape, and yet must be either flexible or fragile enough to allow me to get it out of the cast wall without damaging the wall.

A large part of the problem is that I have no decent tools. I can think of lots of materials that could be cut to shape with a bandsaw or tablesaw, but I need something that can be cut with an x-acto knife.

Any suggestions?

#2

Pink or blue foam insulation board fits the bill. More dense than styrofoam. You can find it in 3/4" thickness. Cuts nicely with a sharp utility knife and a straight edge. Glues well with hot glue.

-Brian

#3

In prototype building we used wood forms that we’d oil down with 50-50 fuel oil and drain oil to allow for spray application and easy release. Maybe a solid wood block, oiled, will simply slide out after your “mortar” sets.

A simple four sided frame that can be knocked down rather than a solid block may be better.

#4

I used the dense foam, like Brian suggested, but mine was pink. :wink:

You could also make forms out of styrene on edge, and glue it to the base with rubber cement. These wouldn’t be solid “forms” - they’d just provide the outline, but that’s all you’d need.

#5

Around here, those pink and blue foam sheets are on par with leprechauns and unicorns. I’ve never found any place yet that sells them.

#6

Well, you’re going to be a problem child aren’t you Ray? :wink:
How about building up layers of corrugated cardboard and sealing off the edges with painter’s tape?

How large are the pieces you need? Maybe I could send you a box of it.

-Brian

#7

So go with styrene. Easily and accurately cut.

#8

OK Ray…
If you show me a picture of a real prototype deck “truss” bridge with a concrete surface … I will guide you on how to aquire 1/2" thick by 11.75" width PVC fascia board in 12’ lengths .
The stuff is the cats ass and i have thought about structures with it but right now I’m using it for my infastructure.
Fair enough?
:wink:

#9

OK David R,

On that PVC-Board, who makes it, where do you get it? Is it textured at all?

#10

David, ummm, no pictures???

#11

What I’m really looking for is something in a thick, flexible sheet, like rubber or foam. Being able to just cut blocks out to size, and glue them into the form, would save a lot of time – and if they could be salvaged for reuse, that would be an added bonus.

I considered pouring some silicone rubber mold compound into a pan, to the desired thickness, but that would be too expensive.

Today I bought one of those foam rubber “beer can insulators” and cut it open. It cuts ok but won’t lay flat. It might work, but only if I could get it in sheets, and the pink or blue foam would probably hold its shape better. So I guess I need to find someone locally who can tell me where to get that foam without having to order it by the truckload.

And yeah, I’m putting a lot of work into something that’s supposed to help me avoid a lot of work. :slight_smile: But I hate repetitive tasks, and I think this idea will be worth it in the long run.

#12

What about Perfic Panels? - http://www.appliedimaginationinc.com/precision_products/perfic_panels.html
I know Bruce has used these before maybe he can chime in on their usefulness.

-Brian

#13

Yep, they’d work. But I think Ray wants a solid piece for some reason. If you were to use the Perfic Panels then you’d have to use them on edge, like a wall. They’d be accurate, but would have to be assembled. Just like styrene. :wink:

#14

Yes, solid blocks would save me the trouble of assembling individual window openings.

Luckily I found a place online that cuts and sells various foam sheets for model airplanes, and they have the pink foam. They can even cut it to the desired thickness for me. So I’ll try that.

#15

No criticism intended , but can someone enlighten me as to what the problem is ? I must have misunderstood something , but honestly cannot see a problem with making shuttering to pour concrete in .
What have I missed ?

Mike M

#16
Andy Clarke said:
David, ummm, no pictures????
Andy....should have bought that mig my new one works great???:lol: Hans....it is textured on one side but the rest is top secret until I'm finished unless Bruce remembers what it is as I did tell him about it briefly...Do you have any pictures of a concrete decked truss bridge?....saw lots of neat Canadian ones but none show the surface. I have see it done on plate girders but not deck girders. Guess I'm just wondering if it's allowed? Now I'm gonna stop jacking Rays thread as were not to 3 pages yet...sorry Ray;)
#17

David, thread hijacking is required, here. Or, at least it used to be…

#18

Yes I know but I was under the impression it must go to at least 3 pages first!!
:lol:

#19

Mike, what I’m trying to do is find a quick and easy way to “block” the window and door openings, without having to build up individual forms for each opening. This should be quite easy, except that I’m limited to using only material which can be cut cleanly with x-acto knife. “Pink foam” would be perfect and is what most people use, however it’s not sold in my part of the country.

The reason I’m trying to avoid building up individual forms for each opening is (1) it’s difficult to make built-up forms that are perfectly square and true; and (2) it’s very time consuming and annoyingly repetitive.

I’m hoping to perfect and simplify a construction technique not only for my own use but also so I can write up an article and it could be used by others.

#20

Something like this, I suspect?

(http://www.jbrr.com/assets/images/stonemill04.JPG)