Concrete Coating Harder Than I Thought

[nalbright]

Trying a new approach .... Steeping away from my regular assemblage. And, Never fails - read, talk to folks and then go after a big one and it bites you.

Built a great wood frame, wrapped it all in chicken wire, then a wrap of 1/4" hardware cloth .... Was about to make my concrete / mortar & thought 'I'd better do a trial' ... So I make a simple box with same process - wood, chicken wire and 1/4" hardware cloth. Found the best mix to be 1/2 sand topping mix, 1/2 mortar, water and some acrylic bonding additive ...

Covers area where the wood is a backer pretty well but where there's just chicken wire and hardware clothe it either pushes through or just falls off. Had done some studying and was sure it was going to be more like frosting a cake ... far from it. In fact, it's going to take at least one maybe two additional coats (if first coat even adheres) of my concrete mix to have a decent surface to work with. It's roughly human size piece and lots of time in the project so far. Need to see this through.

Can anyone make sense of what I've written and maybe give me a tip or two to make this a bit more feasible? Maybe Portland Cement? Fill all 'gaps' with Great Stuff so there's 'backer'? I must be doing something wrong.

Any help greatly appreciated. Thanks!

[grommet]

have only done two pieces in concrete...First, google "ferrocement" or "cimentfondu" or similar. What I ended up doing was cramming that styro (that seems to accumulate) into larger forms just so stuff wouldn't fall all the way through. I also used concrete with the tiny gravel in it for the first coat, making a stiff mixture that I applied in patties, wiggling it slightly onto the mesh to make it adhere, smoothing over the seams.I used a bonding agent between coats, using a finer mixture for later concrete. One piece has been outside for a few years now through 4 seasons and looks the same.

[raspero]

The development work in this type of construction was done in two separate, albeit related, areas: construction and boatbuilding. Developed in Italy by Pier Luigi Nervi, it was used extensively by Eero Saarinen, e.g. in his TWA terminal at JFK. (Makes me weep when I look at the inhuman monstrosities airports have become today.)



In English speaking countries the method is called "ferro-cement". I was a wooden boatbuilder, but still, I had some contact with it.

One problem I see in what you are doing is that builders in ferro-cement use multiple layers of wire mesh, whereas you seem to only have two. There is nothing to prevent your cement mix from passing on through and falling away. You are going to have to have something to push against behind your mesh. One possibility is foam. Styrofoam. Polyurethane foam. Yes I know, getting it in there, now that your form is made, would be a real problem.

Another problem may be your mix; you need a concrete mix that has body. Traditional ferro-cement is typically Portland cement and sand, mixed to a thick trowel-able consistency.

You may want to read up on it. There are books, all out of print, but available, and boatbuilders web pages as well. The method has fallen out of favor, in both boats and buildings. In buildings because of labor costs; in boats, I'm not sure; they are really good boats. One possibility: almost all ferro-cement boats were owner built, and fewer people are building anything anymore.

Richard

[mantrid]

Originally Posted by raspero

Styrofoam. Polyurethane foam. Yes I know, getting it in there, now that your form is made, would be a real problem.
Richard

Maybe that spray foam they use to fill cavities and around window frames

[grommet]

www.ferrocement.com/Page_1/english.html
lots of follow the link sculpture there.

[ironman]

Thanks for the photo of the TWA building at JFK, it's one of my favorite buildings, my friends and I used to wander all over that place when I was 12-14 and no one ever stopped us.

[The Forge]

What you need to be using is 'lath'. It is like an expanded metal, but, is made to be used as the support for stucco. In the old days, they used it under plaster when they made real plaster walls in houses. You might have heard the 'lath and plaster' . Look at www.clarkdietrich.com.

[Andrew Werby]

You can also try adding some fiber to the concrete mix. There are special polymer fibers made for concrete reinforcement, or you can just use hair swept up from a barbershop floor. A little lime in the mortar mix helps it stay on a vertical surface better.

Andrew Werby
Juxtamorph.com

[Nelson]

I do quite a bit of cement work, but would like to see a couple pics of your trial to have a better idea of your process.