Casting papier-mache as speaker enclosures

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I see the problem being with having a smooth finish on the outside and consistent wall thickness

If the mold in on the outside then the outside will be as smooth as the mold - just like fiberglass. Because the binder is a glue getting it to not stick to the mold will be an issue. It wouldn't stick to the silicone mold material that I use, but that stuff is outrageously expensive and making an enclosure mold out of it would be very expensive. Just remember things like draft and for an enclosure a two part mold would probably be required. There are lots of videos on how to make molds for architectural pieces and those techniques would work. I don't see why wall thikcness needs to be consistant. It's an interesting idea if its cheap enough - recycled paper wouldn't be expensive, plaster is and so is PVA glue, so those would have to be minimized. Pound for pound its hard to beat MDF - I mean thats what you are making right?
 
Paper mache uses water mixed with flour as a glue, that's cheap. When I use a mold I cover the mold with glad wrap. It is cheap and it either peels off or can easily be sanded off. Old 1970s plastic light shades, the big garish plastic half domes would make good molds. big stainless steel bowls are also good. Look in the kitchen cupboards, has to be something in there. Kiss the wife on the way out.

Terry
 
I just grabbed some 24" inflatable beach balls on e-pay to use as speaker forms. I intend to soak strips of paper in diluted PVA glue (I already have a gallon of the stuff), and lay it up. A good idea would be to also include some anti-mildew compound in the glue mix.Anyway, it's something to do with all the old bills and junk mail and old catalogs, etc. A couple of Mouser/Digi-Key catalogs would have more than enough mass for a dandy speaker cabinet.
 
My children do a lot of papier mache modelling. They started with scrap newspaper, but nowadays they use kitchen paper towels. They conform to curves better. The result is thicker and "deader" than newsprint papier mache. Use the cheapest paper towels you can find, the expensive ones are often heavily embossed to improve their water absorption but this makes the surface too rough.

You could experiment with varying density for damping - heavily embossed paper towels to provide a thick, light core, then plain towels over that, finally heavy paper for the outer layers.

They use standard woodworking PVA glue thinned 50% with water. I like the portland cement idea, I'll try it.
 
Hi There: About 25 years ago I cast a BLH over a form made of corragated cardboard and used dry cleaner plastic bags as a form release. The casting materal was saw chips from cutting-up some 2x4's (not really dust, like cutting mdf makes). The glue was Elmers yellow wood workers type, with some water added to make the mix workable. I frammed the bottom in timber and used plywood for the driver board. The short horn shape transisioned from round at the 15-inch driver to rectangular to fit a corner location. Still works, shakes the panel walls in basement rec room. ...regards, Michael
 
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