Concrete to use for small picture frames

[jarboejoe]

I am interested in a way to use concrete to make small picture frames, maybe a 1/4 of an inch thick.

My background is mechanical engineering so i understand a little about the strength of concrete and its limitations. I know that it is not useful in tension and just picking up a concrete frame would probably subject it to tensile forces.

However i was thinking about using a fiberglass or plastic mesh to reinforce it or maybe just those plastic fibers you can buy.

What i don't have any idea about is the chemistry of concrete. So my question is how would you make a strong thin concrete that will not shrink or crack?

Also, what about the use of smaller fibers like cellulose to reinforce the concrete matrix?

 

[MikeHalloran]

I'd be inclined to try epoxy, filled with short glass fibers and sand.



Mike Halloran
Pembroke Pines, FL, USA

 

[jarboejoe]

Epoxy, glass fibers, sand and cement? or with no cement. I want it to look and feel like bare concrete

 

[AELLC]

You might try plaster over mesh fabric as in casts for broken bones, because any concrete 1/4" isn't going to cure properly or develop any tensile strength, fiber or not.

 

[MikeHalloran]

In that case, I'd fill the mold with mortar, rock it sufficiently to coat all the exposed surfaces, then pour out most of the mortar and let it dry a few days, then fill the resulting shell (still in the mold) with epoxy/sand/fiber, let that cure, and then demold it.

OR,
Cast the object in epoxy/sand/fiber, demold it while the epoxy is still tacky,
(that step may not be as easy as it may sound)
and submerge the demolded object in dry mortar mix until the epoxy cures.

OR,
Cast the object in epoxy/sand/fiber, let it cure, demold it,
spray it with varnish,
dip it in dry mortar mix, and let the varnish dry.

OR,
Cast the object in any of a number of proprietary reinforced grout mixes sold for bedding large machinery.



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

ISTR applying some 'heat transfer compound' many years ago, between a pump housing and a heat trace tube. It came out of the can as a coarse paste, could be troweled on easily, stuck to everything, retained its shape,and hardened to look like a greenish-brown weathered concrete. It smelled vile until it had cured. I forget the name, but it was clearly some kind of resin, filled with coarse sand.


I should also mention that you might try to get access to a 3D printer. If you run them fast, you get a rough surface. Not so much like concrete, but maybe sufficiently 'arty' for your purposes.



Mike Halloran
Pembroke Pines, FL, USA

 

[jarboejoe]

Those are some good ideas, i guess i got some experimenting to do.

The idea you had of making the mortar shell and then filling that in with the epoxy, you dont think the mortar would crack?

 

[MikeHalloran]

I think the epoxy would bond to the mortar during its exotherm, then cool, shrink and leave the mortar in compression, and somewhat resistant to cracking.
... but that's really just a guess.



Mike Halloran
Pembroke Pines, FL, USA

 

[hokie66]

1/4" thick concrete? I'll nominate this for worst idea of the week.

 

[jarboejoe]

like how do you think they make this stuff

http://www.culinariumkitchenware.com/

 

[jarboejoe]

and i have seen impregnated concrete cloth that is super thin and hardens without concrete

http://www.concretecanvas.com/

 

[MikeHalloran]

The promo does not say the concrete cloth is super thin.
There are structural reasons why it should not be thin.

I suspect the kitchenware may be made of concrete dust and polyester resin, just as 'marble' countertops are made of stone dust/chips and polyester or similar. If there's no plastic in it, it has to be very fragile.

( Concrete or mortar would make a good coaster because of its porosity. We use a lot of terra cotta coasters here in SoFla in the summer. First drop on a terrazzo floor breaks it, so we really use a _lot_ of them. )

Back to concrete picture frames: Concrete includes aggregate of varying sizes, from sand to pebbles. If you really want actual concrete, the cross section of the molded article should probably measure 3/4", maybe a bit more, in its smallest major dimension, else you get a weak area around every pebble.

Concrete mix is pretty cheap at the building supply stores. Buy a bag and see what's in it.
Also buy a bag of mortar mix. You'll see the difference right away.



Mike Halloran
Pembroke Pines, FL, USA

 

[jarboejoe]

Actually just found some concrete picture frames

http://concretepicture.wordpress.com/picture-frames/4x6-picture-frames/

 

[ornerynorsk]

There are faux stone casting materials available. Variety of colors and finishes.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Ron]

Use glass fiber in the mix, fine sand and a high cement content. Use tile grout mix for the liquid instead of water. Create a small wire frame (about the gauge of a clothes hanger for instance) for internal reinforcement.

You can buy pre-mixed repair mortars that are similar...add glass or plastic fibers. Another source is fiber enhanced stucco mix. Get this pre-mixed dry material and add the tile grout liquid and ....voila.....polymer modified mortar. Use the wire frame in all.

 

[TXStructural]

Try Buddy Rhodes countertop concrete mix. (

http://www.buddyrhodes.com/)

Use glass fiber instead of discrete reinforcement (because any crack is too much). Cure it sufficiently, and avoid using any more water than absolutely necessary in the mix, since shrinkage will cause cracking as it tries to shrink around the form with a hole in the middle (the form will restrain the shrinking concrete).