[Domesteading 00265] Re: Flexible concrete

[Nolan Scheid]

Hello Bob,
I won't trim the post below because you asked some great questions that touch so much of the 
process.
We made the test shell by following Lloyd Turner's advice for a low pressure balloon form made from 
Tyvek. Now that I think about it, Lloyd had built the form for us. He has the simplest method of DIY 
formwork that I know of.
Using a low pressure form (LPF) requires progressive stiffening of the shell. Normally the lightest 
dusting of spray foam is shot then a thicker layer. This building up the strength of the LPF lets a 
person use much lighter and less expensive formwork. In our test dome, we wanted to step out a 
little farther and not use spray foam.
The idea was to use a light weight concrete mix to stiffen the balloon then add more structural 
material. This is the really interesting trick in the game. (No, I don't have all the answers yet).
We tried my mortar sprayers but they are best in the 1/4" to 1" thick spray range. What we needed 
was to gently kiss the structure with something to form it up. We ended up using the small 
peristaltic texture pump that is rented at home depot.
The first layers were more like spray painting than and stucco work. We started with a mix of cement 
and acrylic. Nest time I would add some micro fibers the mix.
Gradually we worked our way up to Richard McCabe's thin shell mix.
We kept the shell super thin so that it could be removed easily. The thickness was 1/8" to 1/4" in 
various places. At that point it was a firm shell that would have stood on its own fort a very long 
time.. The next thin coating would have made it strong enough to climb on without concern of pushing 
through the shell.

The next structure we did was at the first thin shell convention in Lorane. We used an air form from 
Mert Hull. Mert is a great guy, he was the fist Licensee of Lloyd's building method. Mert's form 
material is a cross linked plastic.It is very strong and does not stretch much. The seams of the 
gores are simply taped together for the form. Mert's material is smooth and shiny ( gets to your 
finishing question). His forms are also normally foamed for stiffening and insulation.
In Lorane, we used a mix of Foamlite styrofoam beads, acrylic, cement and fiber.
Here is the loose schedule from the convention:
http://www.itsa.info/Convention04schedule.shtml
It was a great time.
There are some 2004 pictures on the 2005 page:
http://www.itsa.info/Convention2005.shtml
You can see that we did the initial stiffening with a conventional texture sprayer. The goal was to 
learn more about stiffening the form without using spray foam.
Once you have a firm egg shell, you can move to a more structural mix. with something like the 
hopper sprayers. In addition to my sprayers, I have owned/tried 9 different pumps so far. That is a 
whole other email but I will sum it up by saying the key to pumping/spraying is selecting the proper 
scale of the equipment to match the job. That sounds simple but is critical for a smooth process.

Clean up for spraying will depend a bunch on what delivery system you are using. If you have a pump, 
you need to be constantly aware of the material setting up. The neat cement and acrylic we were 
shooting was a super hot/ fast mix. In the future, I would probably ice the mix to slow it down a 
little.
With the hopper sprayer and texture sprayer, I prefer to do a light spray of LPS 3 at the start of 
the day. This acts as a bond breaker to help with clean up.

The Acrylic helped hold the moisture in the very thin mix. Without it, the spray would have simply 
dusted off. To cure the structure, I would keep it moist. I have has good luck with soaker hoses and 
burlap.

We did not finish either of these shells. However; I have learned a few lessons here at home where 
we used vinyl air forms and shot the material from the outside. The interior was left very smooth. 
Too smooth for good adhesion. We ended up sand blasting some of the smoothest areas and trying acryl 
60 in others. Over all, I am not impressed with Acryl 60.

Cost? I'm not sure. Since these were experiments for steps in the process and not towards a finished 
structure I didn't keep close track. I do know that the PVA-ECC mix is several times more expensive 
per yard than regular concrete. The trick comes in the comparison. No rebar to purchase and install, 
and much thinner shell.

This email is getting long but the discussion of PVA-ECC is leading towards some really interesting 
developments that bring me full circle. Lloyd Turner's domes used metal fiber in the shotcrete for 
reinforcement. Lloyd and I shared a great moment where he pointed out one little arch where he added 
a couple pieces of rebar in an arch. He said he knew from the calcs that the didn't need it. He just 
slept better following his gut at that one point. Other than that he weaned himself of rebar. 
Richard Britz has done the same. Personally, I used it on the castle but learned and grew along my 
path. Next time I would look for a solution without it.

I hope this email is useful to other thin shell builders. My fingers are getting tired.
:)

Best regards,
Nolan Scheid
www.mortarsprayer.com




----- Original Message ----- 
From: <RoConroy at aol.com>
To: <domesteading at sculptors.com>
Sent: Friday, November 16, 2007 7:18 AM
Subject: [Domesteading 00264] Re: Flexible concrete


>
> In a message dated 11/15/2007 11:03:33 P.M. Central Standard Time,
> Nolan at mortarsprayer.com writes:
>
> When I  first met Richard, his personal quest was to spray 1/2" thick dome
> shells for  homes. He
> helped me spray a 1/4"-  test shell in my back yard. It was  amazing how
> strong it was.
>
>
>
> Nolan,
>     What were the cost for spraying your test  shell?  Such as cost per
> square foot. What type sprayer did you use?   What was the curing process?  How
> easy was the spraying process and the  clean up?  Were you able to spray the
> interior of the dome also?  Was  the adhesion good to spray curved ceilings?
> Bob
>
>
>
> ************************************** See what's new at http://www.aol.com
>