Rick you can sand the edge smooth as well.
Less toxic.:)

Rick,
I recall this discussion previously and am asking the same question. Are you creating a mold with the styro form, or are you covering it with some sort of mix?
If covering it, is there a reason that you want the form precise and smooth, as any additions will distort and add to the form.
Just a little more information to try and picture this, or better yet provide a picture.
Dena

Morning,Dena
I'm doing outdoor mirror frames,with leaves mounted on the frame.Similar to those exhibited by you know who.I'm looking at clean surfaces where the styro touches.
BUT...I'm not happy with the result.I'll probably go to a plywood mold instead.Styro breaks when removing it;I don't want to contribute this kind of junk to the landfill.
the styro was intended for the middle of the mirror,to create the opening for the mirror.It works but not to my ethical satisfaction.Good idea,good execution,just not what I want to achieve.
Cheers from here

Is this blue styrofoam Rick?
I use it by the ton and never have a problem with it breaking. the white stuff however is useless.
Try a release film of mineral oil. the styrofoam will just silde off.

I'm not sure I picture what you are trying to do but....... Have you tried hardibacker board? Comes in 3 by 5 ft sheets for 9 $ here. I am experimenting with the quarter inch thick size. This is a concrete impregnated board that is used under tile -. It is light weight and cuts "easily" with the score and break method. If you need a hole for that mirror it is going to take a saw. This is what I am trying to do mirrors with. Haven't had time to try much yet. This stuff is used for shower wall tile installation but it is not recomended for exterior application. I still think with an extra coat of cement on the back and edges it will do fine for exterior art work. I have had one piece outside for a couple of months through many rains and it is unchanged....

I am using this for the back of the art piece.... applying the concrete leaves to the hardibacker surface and either leaving a hole and mounting the mirror from the back or putting a mirror down and adding leaves around it..
So far I can't find my saw and I don't have any mirror. Maybe that is why my progress is so slow.

Laura

Here is the panel I tried on hardibacker board - I mean to try one with a mirror set onto the front of a board and then surrounded with leaves and concrete. This didn't thrill me (ugly prints of long skinny leaves) so it has been sitting outside in the rain for a couple of months. No changes even though I did not coat the back of the hardibacker with extra cement. The backerboard seems like an ideal surface for this kind of project.
Laura

Here is a link that might be useful: try here

Our house is sided with Hardieplank,so we know the stuff.
I've never been a fan of styro,because its simply too brittle.Good for those of you who use it a lot.I prefer plastic,because of the flexibility,or steel because of its ability to take abuse.I require the best possible as we sell our pieces and want to be able to replicate over and over again.
Our mirror frames are 34 inches by 22 inches,with a mirror of 18 by 24 inches.The excess space is used to display leaves.The frames are reinforced with the steel corner bead used for drywalling and are about 2 inches in thickness.The weight comes in at about 30 lbs.Or so,not having weighed it yet!But,the first couple are quite rigid and there's no tourque at all.These are made for outdoor displays,like that company we CANNOT mention.So far so good.BTW,I use a wooden frame to outline the mirror,and just pop the screws out when done.I'll probably do the same with the mirror area as well.Still experimenting on what is best for me!!
Chhers from here

Not trying to be dense here but.... When you say you know about Hardieplank and then say you aren't a fan of styrofoam, It makes me think you think hardibacker board is made from styrofoam. Any chance hardiplank is a different product?? Hardibackerboard sure doesn't look or feel like it has any styrofoam in it. When I cut it there is a good view of what is inside and my impression is there isn't anything inside. It looks like a sheet of quarter inch concrete. I know it must have something more than that but I don't see how it could be styrofoam..

Since you are building a mold in which to form the mirrors' frames, the hardibacker board wouldn't help. I was thinking you could use it as a backing for your 34 by 22 inch frame and thereby not have to pour such a thick (2 inches - 30 pound) frame. Another quarter inch of concrete on top of the backerboard would give a very rigid frame I think. Heck, maybe this conversation will make me go try it myself.
Laura

No,Laura.As I said,I know that the Hardie plank is in fact over 90% concrete,with some organics as well.Love to try it like you suggested.And,it just so happens that our contractor has to fix a spot and will most likely use Hardie board!
And,what about using Quickwall in some fashion for a mirror project?Thinking out loud here...

I just went outside and cut a piece of hardibacker about 24 by 27. I drilled 2 holes and ran a double strand of galvanized wire through washers across front and thru holes about 13 inches apart and out the back - trying to think ahead for once and have something to hang it by when it is done. I took mesh and put it across the wire and washers (strip about 20 by 8 ). I coated the front about 1/16 of an inch thick.... going a little thicker over the mesh so it cements in the wire hanger. In the morning I will think what to do next!

I couldn't think how to cut out a hole for the mirror (no saw) so I plan to lay a mirror down on the front and decorate around it. Hopefully I can think of some wonderfully simple way to be able to replace the mirror if it ever breaks. All I can think of now is to let my leaves make a "pocket" for the mirror and not decorate the top so I could slide it out if it ever broke. Other ideas would be welcome!

Laura

Rick,
Back to your styro thing, how about a closed cell or a piece of foam like you use for a yoga or camping mat. It could be cut to any shape you want to create the void for the mirror.
Laura,
Great use of the leaves and I can see very clearly putting a mirror down then laying your leaves on top, and around.
Dena