Concrete Canvas for domes

[timbau]

Here's a poser for you guys. I've seen a couple of You Tube vids showing some domes being constructed using concrete canvas. What about using this as the out side of the dome. Then cover the inside with foam and them shotcrete just like existing method. Then maybe we wouldn't need to cover the outside of a dome with some other method.

See following for concrete canvas.
http://www.youtube.com/watch?v=LBHVKFCoYFc

Just a thought ....

[DBS]

Good thought. But expensive to do. I will do more looking into it. DBS

I can not imagine it working very well with augments, etc.

[timbau]

Good thought. But expensive to do. I will do more looking into it. DBS

I can not imagine it working very well with augments, etc.

David

Thanks for the feedback. Just wondered if this was as expensive as say trying to stucco or to use concrete? Maybe you guys could come up with something similar to cover the domes.

As usual just my 2 cents ....

[DBS]

We try to look at everything. My first look is to expensive. But we will contact the manufacturer. But I can tell you we can put monolithic stucco on pretty fast and reasonable. With no extra forming. DBS

[timbau]

David

Thanks for the heads up. I'll keep that in mind for future reference.

[BWARDEN]

DBS would know this better than I, but one of the functions of the airform is to allow you to pressurize the inside of the dome during construction. This alleviates a lot of problems with supporting the weight of the wet, curing concrete. My guess is that if you didn't have the counterforce of the air pressure, the required mechanical support to hold up the weight of the concrete might counteract any price advantage of substituting a cheaper material than the airform. The air pressure support is also, by laws of physics, uniform over the shell, as opposed to possible weak spots in mechanical supports that may result in localized sags in the shell. So, I wonder the value of using the canvas to replace the airform. But then, Mert Hull, and others have used light weight polyethylene plastic airforms with low air pressure to successfully build domes.

That said, to me, one of the largest problems with MD homes is the outer coatings. My polyurea coating has bubbles, and does not seal over some of the airform seams due to problems during spraying. The nature of the coating makes it difficult to over spray it to repair the problems. Perhaps concrete soaked canvas, laid over a finished dome, similar to putting paper mache sheets over a blown up balloon, would be a better alternative than chain shell. The canvas strips could be laid in an "artful" manner, such that the overlapping seams made some sort of pleasing pattern. MDI had done similar things with sheet metal coverings. The possible downside is that the canvas may rot over time, eliminating the concrete reinforcement of the shell. The canvas could be woven out of a synthetic material instead of cotton that may not rot. Or use a synthetic mat, similar to that used in landscaping weed suppression. Any non rotting material that could be soaked in fine sand concrete and applied to the dome. Lots of possible experiments here.

Too many possibilities, and too few homes being built to try them out.

[timbau]

DBS would know this better than I, but one of the functions of the airform is to allow you to pressurize the inside of the dome during construction. This alleviates a lot of problems with supporting the weight of the wet, curing concrete. My guess is that if you didn't have the counterforce of the air pressure, the required mechanical support to hold up the weight of the concrete might counteract any price advantage of substituting a cheaper material than the airform. The air pressure support is also, by laws of physics, uniform over the shell, as opposed to possible weak spots in mechanical supports that may result in localized sags in the shell. So, I wonder the value of using the canvas to replace the airform. But then, Mert Hull, and others have used light weight polyethylene plastic airforms with low air pressure to successfully build domes.

That said, to me, one of the largest problems with MD homes is the outer coatings. My polyurea coating has bubbles, and does not seal over some of the airform seams due to problems during spraying. The nature of the coating makes it difficult to over spray it to repair the problems. Perhaps concrete soaked canvas, laid over a finished dome, similar to putting paper mache sheets over a blown up balloon, would be a better alternative than chain shell. The canvas strips could be laid in an "artful" manner, such that the overlapping seams made some sort of pleasing pattern. MDI had done similar things with sheet metal coverings. The possible downside is that the canvas may rot over time, eliminating the concrete reinforcement of the shell. The canvas could be woven out of a synthetic material instead of cotton that may not rot. Or use a synthetic mat, similar to that used in landscaping weed suppression. Any non rotting material that could be soaked in fine sand concrete and applied to the dome. Lots of possible experiments here.

Too many possibilities, and too few homes being built to try them out.

Bob, I'm not sure the airform would rot under the concrete canvas. It doesn't seem to do that under other coverings. My worry like Dave's would be if the material was too cost prohibited. I was looking for something that might be permanent and not have the issues that the other coatings have according to some of the home owners.

Anyway, just my 2 cents .....

[BWARDEN]

Tim,

I wasn't afraid of the airform rotting, but rather the canvas that was soaked in concrete. Canvas is usually made of cotton.

I'm thinking the appropriate material soaked in concrete might be a better alternative to chain shell. There is a need for some experimentation here.

[mkrepel]

Some of the ferrocement enthusiasts have done experiments with various combinations of cementitious mixtures with different reinforcement. Some have tried a fiberglass mesh or grid with a cement/latex mixture with sand. This seems to be a very viable method for a thin shell over a frame or substrate. The latex helps to keep the cement from rotting a wood substrate. That is not an issue with MD's but I think this might be useful for the stucco coatings. A variation might also work for the air form, but I don't see how that would be more cost effective than monolithic's air forms.

As someone pointed out above, the air form system works very well and would be very hard to improve. Cotton canvas is good if used the right way, but it will begin rotting immediately if if is not allowed to dry out very soon after it gets wet. I would think that the insulation under the canvas would hold water against the canvas and it would start rotting right away. Anyone who has ever used a cotton canvas tent knows that the canvas does soak all the way through in a good heavy rain. It will direct the water down the roof and on down the walls of the tent as long as nothing touches the tent while it is raining. Once that happens, a leak starts. It may be possible to treat the canvas to keep this from happening, but I have never seen a fool proof method.

[Nick Howes]

The "concrete canvas" referred to by the OP is not cotton cloth - it's a durable synthetic fabric that is impregnated with concrete. Here's the URL for the company that makes it http://www.concretecanvas.co.uk/.

HTH, Nick

[Sammual]

This looks like it might be a fantastic airform covering.
Can it be painted?

[timbau]

This looks like it might be a fantastic airform covering.
Can it be painted?

I got the impression from the web site that it could be painted and/or sealed. Seems like a nice product. My only concern would be cost. I read were they were using it to fortify Gabions(wire baskets that are filed with stone) for the military. Also, as culverts for water drainage. So naturally I thought why not try and utilize then as a concrete coating for Domes. David said that he was checking in on applications and pricing.

Interesting