Spray-on Roof?

Hi, when following this it reminds me at the swiss architect peter Vetsch.
Take a look at his work and the ways to get it done using spray concrete.

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I think it can be done, have seen it for builing domes…
Look on youtube for shotcrete dome.

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Look at Paolo Soleri, his dome house and maybe Arcosanti.

Edit: or Dante Bini (company?) who did this house.

Did Peter Vetsch use a steel frame & shotcrete to build his houses? What about insulation? Does the grass roof insulate it? His house designs are amazing!
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@RTCool I’ve been to Arcosanti before. There are lots of domes there. The architecture is amazing!


they use a more concave shape, gravity based (but then upside down)

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I was just thinking of how Gaudi used cloth and looked at it upside down for Sagrada Familia in Barcelona to get the arches, and wondered about doing it in SU with Clothworks and then turning it upside down.


Yes, that is the method. You do not need that much rebar this way, and be using the ‘gravital intelligence’ of the concrete.
A building is not that static as one would wished it would be.

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I guess you can’t really eliminate rebar entirely because of wind load and seismic loads etc. which complicate matters.

I think they used glassfiber for this project
It is not likely to rust😃


Good point. A concrete subcontractor just told me a few weeks ago he never uses steel mesh in slabs anymore, just fiberglass. I said it’s OK with me.

What rendering program are you using here?

Twilight Render V2 (Hobby Version)

It’s really easy to use.

I concur with @simoncbevans , Sika has a fabulous set of products for roof conditions. In the US here is a link:

Good luck.


I had stuff like this applied to a metal building a number of years ago. Don’t remember the brand name but it was fantastic. Spray on - white- and stopped all the leaks and deterioration. We covered over 11,000 sq ft on just one building. Then did another 20,000. IMPORTANT NOTE - the guys installing it wore DARK sun glasses. You’ll go snow blind looking at the white surface in the sun all day. Happened to the owner on his first job. Couldn’t see for three days. Have fun!!

Fibreglass reinforcement for concrete. Is that a thing now? I must be behind the curve as all the structural engineers I know reach for steel in their sleep. You’re right that steel can rust. In theory, an adequate concrete cover will protect it because cement has inherently waterproofing qualities (hence my comment about being able to build a waterproof structure just using concrete alone). Of course, some wag will point out how often concrete spalls off as a result of rusting rebars requiring expensive repair. What is more amazing is just how often it doesn’t, suggesting that good design and implementation may be a large part of the issue.

In my part of the world, it is not uncommon to build basements out of waterproof concrete (I have done it myself) without any form of tanking. Tanking is notoriously subject to workmanship defects and if you have any water pressure (as you could underground), it will find the weakest link as sure as eggs is eggs. 'Course, the waterproof concrete also needs care in workmanship.

Concrete cracks as it cures. If it has been carefully specified and installed, those cracks will be hairline at most and evenly distributed. Providing they are no more than that, the concrete is self-healing. A bigger problem above ground is movement induced cracking, either due to wind or other loads, or ground settlement. Imagine the forces a bridge must be subject to. In those cases, cracks tend to be much larger and enough to allow water in.

The spray on concrete is interesting but has a basic problem. Good quality concrete can only be achieved by minimising bubbles of air trapped in the mix. Traditionally, that is done with a poker vibrator. You can only use one if the concrete is contained within some kind of retaining structure. If you tried it with spray-applied concrete walls you wouldn’t have concrete walls so much as a concrete floor.

Here endeth the latest lesson.


This “problem” isn’t a problem because : “Shotcrete is placed and compacted at the same time, due to the force with the nozzle.” according to Wikipedia!


Well, there you go, problem solved. Providing compacting means de-aeration… Makes you wonder why people go to all the trouble of building formers. They must be crackers.

If I had to build it, and I could get away without steel reinforcement, I would be much happier with a rigid formwork that I could loosen and form in sections.

Maybe it would look like this:

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For me, the name is hilarious (“Sika” means “Pig” in Finnish). Their products have been in our markets for at least 100 years.

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As far as i know it means the same, if you take the air out of the concrete it becomes more compact.