Sphere attempt

mariana2007(6a ON Canada)July 13, 2009

After reading lots of old posts here, I made a few hypertufa pots, and a few concrete leaf castings. They are OK, and curing right now.

Yesterday I started my two spheres using a recipe someone posted here somewhere.

The recipe: 4 parts Portland cement, 1 part sand, 1 part admix, and 1 part interior latex paint. The recipe called for 1/4 fibers, but I couldn't find any, so my intention was to use the fiberglass mat after the first layer. I understood a sphere will be completed in 3 layers. The mix was nice to work with it, I guess the paint made it smooth.

I'm not sure what was the problem, but in the morning one of my two spheres was full with cracks. I started misting them, and the one with cracks just started to fall apart. The other one seems to be free of cracks.

My questions are: What should I do now with the one that has no cracks? First, how long should I wait to get dry/cure before I'll put the next layer? Use the same recipe for the next 2 layers with admix paintbrush first, and using the fiberglass mat, or using something else? I'm afraid to even touch it.

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Mike Larkin

Cracks are possibly from allowing the mixture to dry. In additon maybe too thin or no reinforcement. (I use mesh drywall tape for the reinforcement)
Also - Is it possible that you tried to cover too much of the ball on the first round of application. I usually cover about 1/3, then late the next day when the mix is firm I turn slightly and cover some more. It takes several days to cover the entire ball but this method has worked great.

I use the admix - Bonding agent - in my mix in the place of some of the water. I guess that is what the paint may be for in you formula- I do not use the paint. When I apply layers I use mesh drywall tape, It is tough and you must cut it with sissors. I cover most of the ball with the tape firdt. The I apply the mix, For the other coats I first wet the cement then I apply some more of the bonding agent on the damp cement mix.
I cover the ball with plastic and spay to keep it wet.
When I get a chance I will post pictures.


    Bookmark   July 14, 2009 at 10:10PM
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mariana2007(6a ON Canada)

Thanks Mike!

Yes, I didn't have reinforcement and plus I covered 3/4 with the first layer. I didn't know how much to cover, so I went with the mix as much as I could.
Today I started all over again. First I covered the ball with lots of adhesive drywall mesh, and applied the first layer. I used admix with the water. I put some more mesh and I put another layer. I covered again 3/4 of the ball. I know, I shouldn't have rushed before I got an answer here.....Well, I hope it's going to be OK this time, with so much reinforcement.

The other ball made 2 days ago was still strong with no cracks, so I decided to go ahead with the second layer. I didn't turn it over to cover the entire ball. I put another layer on top of the existing one, after I brushed it with admix and covered with fiber glass mat strips. This time I used for both balls 1 part Portland cement, 1 part sand, 1 part peat, 1 part perlite and admix.

That mix with paint was so easy to work with, didn't harden it while working, no need to rush, soft and smooth. Now, that you told me that the paint is in place of bonding agent, and my failure was not because of the mix, I will try it again. Thanks again!


    Bookmark   July 14, 2009 at 11:32PM
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