I have used molds I bought but they are only 12" and 10" round. Some have used rubber balls.
Paws

I'm using a large rodent exercise ball.
Worked very well the one time I've used it.
I'm trying to find a Pilates ball around 18 inches but so far 22 inches is the smallest I can find.

MAE060669,

I can't claim succuss yet but I'll tell you how I am planning to make a reusable spherical mold of about 16".

I have a 16" dia ball from WalMart, cheap, $2.50. I have purchased two fiberglass kits from the auto parts store. I plan to fiberglass the outside of the ball with two layers of fiberglass (about 3/8" thick).

Next, I plan to build two boxes from 3/4" plywood each one being 18" square and 9" deep (1" larger than a hemisphere at each axis.) The boxes will be constructed such that they can be bolted together making a cube. Drill a couple of holes in the bottom of one box (which will become the top of the cube). These holes should be about 1" dia..

I will then place the ball in the box with no holes and pour POP around it, weighting it down sufficiently to keep it from floating out of the POP but still allowing 1" of POP underneath. Then I will bolt the other box in place over the ball and pour POP through the holes to totally encapsulate the sphere.

After the POP sets up, the tricky part, I will take a fine hacksaw blade and saw through the POP and ball to separate the hemispheres thereby making a spherical mold that can be reused many times if it is cared for properly. Oh yeah, I will drill a hole in the center top of the box right through the ball. This hole must be large enough to work my hypertufa in the mold, maybe 4" dia.

Am I overzealous in this? Do any of you guys see why this would not work?

You must realize that the volume of a sphere this size is in excess of 9 gallons. A solid concrete sphere of this size may weigh nearly 100 lbs! It will be a task to handle this or else you use some packing peanuts in the center to lighten it up... alot!!!

I make spheres by using glass globe ceiling light covers. Not reusable, but they make a perfectly smooth round sphere. When done, I put them in a plastic bag, and hit them gently with a hammer. I have 5 of different sizes curing right now. One is quite large!

Jean

Jazzbone - Your idea of making a 2-part mold will work - I've done something very similar - but instead of using a hacksaw to saw through the POP, you might try painting the the part of first half of the POP mold that will be in contact with the new pouring of POP liberally with soap lather. Soap lather's quite good at preventing new POP bonding to the POP that's already set.

On the other hand you'll only get a useable mold if the joint between the upper & lower halves of the mold exactly follows the equator....but the same's true of the cut you'd have to make with the hacksaw.

Another detail - it's not easy to separate either half of your new mold from the master sphere. You'll need something to act as a dividing/parting jacket - and the same when you cast your sphere in your new mold. I've used paintable latex rubber for this - but when the layers of latex have dried you have to be sure to sprinkle both sides of it with Baby powder, otherwise, when folded, it bonds to itself.

Alternatively, you can make a sphere if you only have one hemispherical mold. You'll still need be sure that the mold stops at the 'equator' & you'll still need to use a 'parting' jacket, but you just make two castings from it & cement these together.

All that said, I think casting a sphere inside a disposable mold (whether a glass globe as Jean has done, or a or a rubber ball as the others mention) must make the best spheres because it doesn't leave a line at the 'equator'.

I just made one from a very big rubber ball I got at walmart. I made a round hole in damp sand, put the split ball in and filled it. The rubber was a bit stretchy, so it came out abit strange. Looks like an alien egg.
Jo

Jo try covering the ball with a thick coat of paper mache first. You won't need the sand.:)

I made a sphere with one of the big balls from W-Mart, I put a slurry on the ball and then started adding layers with some mesh like stuff that is used in a stucco process, took several days to finish, when it was dry, I popped the ball and painted.
I tried filling the ball first time and it colapsed, ended up as a smiley face!
Dena has a nice bunch of pics in her album on the exspheriment she did, you might want to check it out.
If you look under tufa sphere in my album, you can see how the ball turned out.
bonnie

Here is a link that might be useful: sphere

I have an order for 3 different size geodes, so papier mache or covering the ball in tufa will do me no good. The smaller ones come out fine, but the 20"er is like....interesting in a creepy sort of way.

Here is a link that might be useful: the aliens have landed...and layed an egg!

I am happy to share what I figured out.
Dena

Here is a link that might be useful: x sphere i ment behind the fence

Herb, thanks for the pointers. I can see how it would be difficult to remove the casting from the mold when there is no way for air to get between the parts. Would petroleum jelly or oil work as well for releasing the casting as the latex liner?

I was going to use one of these cheap balls from WM and make an inside casting while supporting it with a bed of sand. When I cut into the ball it collapsed like a popped balloon. I should write this in the "Things not to do" thread.

Jo, I have experienced cold joints as I see in your alien sphere. Are there any tips for avoiding this? Was my mix to dry?

Dena, darlin', you've done it again. I get into your webshots and scroll and scroll and scroll... great stuff! And your yard is beautiful.

jb - I doubt petroleum jelly or oil would work as well as a latex jacket that has been sprinkled on both sides with Baby Powder. Think of suction disks that you can apply to a smooth wall & that stay in position: they sometimes give a better grip if they're moistened - I think it helps keep the air out. I suspect that oil and petroleum jelly would have a similar effect - and tend to hold the casting in the mold. Herb

gottatufa I used a papermache covered basketball to make 3 balls and it's still in perfect shape to make more.
Covering a twenty inch ball should be easy, just need more newspaper.:)

Oops, I think you misunderstood me.
I cover the ball, let it dry then cut it in half. The papermache is a shell on the outside that prevents the ball deforming when you fill it with tufa and styrofoam chunks.
I have no problem with suction because I drill several small holes thru the ball mold.
Using the exhaust from my vacuum cleaner I press the hose against these holes. It forces air inbetween the tufa and the mold releasing it. Works to release most 'stuck' molds.:)

Tufaenough, that sounds like a good idea but more labor intensive. Guess it's worth it for the finishing product. It has got to be less messy!

Jazzbone, what's with that cold joint. It looks like I did this with 2 different mixes at 2 different times? It's really got me baffled cause I have never seen this weird thing happen before.
Jo

Papermache keeps the ball round and the mold can be used quickly.
When I find the right sized ball, 16-18 inches I may papermache it using Titebond III water proof glue in the paper.
I will keep the two halfs of the cast separate so I can remove the ball without damage.

A papermache mold made with a waterproof glue might be usable as a cast by itself.
Dry packing the inside of both halves with a layer of super light tufa than cementing the halves together later might make some light weight large balls
Eventually I will get around to testing this.

Jo, I cast some half spheres in a wet sand bed once and got nearly the same effect as your alien egg. I was doing two casts at once using the same wheelbarrow full of tufa mix. I think I may have let one set while I filled the other and then I went back and added to the first. Even 3-4 minutes between layers made a cold joint (I call it that, its where the obvious addition of more mix doesn't meld with the rest and a line or layer appears.) It may have been a combination of working directly in sand such that it wicks water out of the mix and using a slightly dry mix.

David

How about using water putty instead of glue to make a paper or even fabric (or gauze) mache mold? Water putty is waterproof when it cures, so would produce a durable mold. Durham is the only brand I am familiar with. It is easy to work with and sets up quickly and is relatively inexpensive.
A couple of years ago, I found plastic bowls that are a perfect half-spheres with about 12" diameter. They were at one of those clearance type places (Ollie's). They came with clamp-on covers with handles apparently are meant for picnic ware but made wonderful 'tufa molds. I molded the two halves and let them set up then "glued" the halves together a couple of days later and filled the seam and spread a very thin layer over the entire sphere and you cannot tell that they were molded separately.

spiderwoman

Spiderwoman I have never heard of water putty before.
I'll look into that.

As for bowls that are perfect half spheres, I've been keeping an eye out for months with no luck.:(

It reminds me of wood filler but since it comes in powder form, you can make it as thin or thick as you desire. You can also slow the curing time by adding an acid like vinegar or milk. It is actually an old product and intended as a repair medium. It should be found at either Lowe's or Home Depot. I live in a very small old (colonial age) town and find it at my local hardware store in 4# canister for about $6. I imagine it is a bit less at the bigger stores. I think model railroaders use it a lot as a "building" material. You should be able to find lots of information by putting the term into any search engine.
Now that I've suggested using it in this way, I think I will try it myself. Tomorrow perhaps.
spiderwoman

As I mentioned in another thread about clay projects being adaptable as forms or ideas for concrete, paper maiche' opens a whole other world for the work. A sphere could be made out of papermaiche, much like the pinata is made,cut it in half if you like or leave it whole, but cover it over all with shellac it hardens it water proofs it etc....and can be used as a form to cast in, on or make a mold from using silicone, or latex or well you all get the general idea.

As Herb said, latex molds do need to be dusted with powder or cornstarch, as latex does not really adhere to much except itself..................
Happy experimenting,
Dena

Have any of you guys used the paper mache' (sp?) molds for large spheres, i.e., greater than 14"? It seems to me that if one casts a solid sphere that weighs 60-100 lbs that the mold would be too fragile to handle while de-molding the casting.

David

David it depends on the glue and you can reenforce.
A strong collar would be required.
A glue like Titebond turns the paper into one very tuff material.:)

I bought an old globe at the thrift store so I could take it apart and use it as a mold. My concern is that I want to be able to reuse it...after all, I paid $7 for the darned thing. (USSR? What's the USSR? ;-) )

Deb

I bought a globe light cover from HD that was made of plastic. I cut it in half with a hot knife. I used it once already and it came off fairly easy. It's about 12" around
{{gwi:69560}}

Remember the Matt's Beer Balls? Do they still make those? If so, it would be a great excuse to have a party!
Jo

OK here is the supreme beginner's question. With the glass globes are you putting the tufa on the outside and then letting the glass once broken rattle around inside or are you filling the glass globe w. tufa for a solid ball???

Is there some posting or site where I should be looking for this kind of info???

thanks

Deborah

I am making balls from a basket ball I cut in half. I set it in a basket to keep it's round shape. I glued one up with portland cement but would like to know if a pre mixed thin set would work outside.It would be quicker than mixing
cement.

Any size inflatable ball, Make sure the ball is fully inflated so there is no give
Flower Pot big enough that when you set the ball in it that only about a quarter of the ball sets in the flower pot. You want to be able to set the ball in the pot and the ball does not fall out of the pot. This is important and so very helpful when working with a large ball
You will need the following
Couple of large Trash Bags
Concrete Bonding agent.......Lowes, HD next to concrete dyes looks like Elmers glue. Bonding agent helps new mixture to stick to dried project. Use half water half bonding agent when you need extra hard hold or for really large projects
Fiberglass drywall tape you can get this at lowes, home depo one roll last forever
1 sturdy plastic Flower Pot Do Not use Terra Cotta pot.

I use a light mix works well
1 Part Portland Not concrete mix that you buy this has to be PORTLAND CEMENT
1 part peat moss
1 parts perlite
1 Part water
This makes a lightweight but very strong project
Vaseline
Caution Do use gloves, Do use a mask when mixing as the dust is very fine and will get in your nose and mouth, use goggle over glasses trust me the dust will scratch your glasses
1 Make your hypertufa mix well and let it set
2 Place one opened trash bag in the flower pot so that the bottom of the bag is inside the pot let the rest fold over the sides. You will use the part of the bag that is hanging over to cover your Speer once done.
3 . Totally cover your ball with Vaseline be generous. Then rub what is on your hands into your hands really well. Your hands will thank you later
4 Locate the Air Valve on your ball, Place your ball in the flowerpot making sure that the air valve is at the bottom when ball is setting in the flower pot
Getting started is the hardest part many people find it helpful to take a hand full of mixture and rub it all over the ball its helps the rest stick better
Start applying your tuff to your ball. There are many different ways to start everyone has their own style.
I usually start at the bottom and go all the way around the ball turning the flowerpot as needed and working my way up the ball.
Trying covering your ball in equal amounts all the way around. The ball can get very heavy and will flip on you really quickly.. The bigger the ball the easier it will flip on you

******** It can be hard to get started DonÂt Give up
Once your ball is totally covered and your feel itÂs held well then takes the part of the trash bag that is hanging over and brings it up over the project and cover.
I then take the second trash bag open and cover the entire project again. Place in a safe place and let it set
Now try really hard not to open the bags and look at your project for a week. Amount of time depends on weather
After a week I then open the ball and depending on the size of my ball or what effects I want I will apply a second coat of mixture in a different color
This is also where you pick up the project out of the flower pot and if the opening is larger then you want then you use the mixture with the bonding agent to fill in as much of this area as you want. Remember you will have to leave a large enough opening to deflate the ball and pull it out or not some people just cover the opening and leave the ball in. I always deflate the ball and pull it out.
If you do not want an opening at this point you deflate the ball and pull out, take some very thin chicken wire and the tape, cover the opening and apply mixture on top and blend in with rest of hypertufa and you will have a hollow Speer.
Depending on the size of your project closing the opening up you may want to take a two step approach. Patch in as much as possible leaving just enough room to deflate ball and pull it out let project dry for a couple of days in same fashion as above then deflate ball pull out then use chicken wire and tape cover remaining hole which should be no more then 3-4 inches across and cover with hypertufa
Applying mixture really thick is not necessary I have many Speers that are no more then 1/2 in thick and they are very strong
*******This part is important on the second coat or for closing openings instead of water in your mixture use half water and half concrete bonding agent. If project is really large also apply some of the fiberglass drywall tape to the Speer several strips from top of Speer to the bottom helps.. Do not apply a heavy second coat and DO NOT PRESS IT HARD OR YOU WILL CRACK FIRST COAT. The second coat is really just for special effects or to cover small areas you didnÂt apply enough of first time and is not necessary for Soccer ball, BB ball sized projects.
. **** Remember the inside of your project will be very smooth you can always cut this Speer in half and use itÂs for future mold by simply lining it with a plastic bag.
Once project has cured 2-3 weeks in a safe spot I then just unwrap them set them in the garden for several weeks and let nature take care of things 2 or 3 good rain storms and you can plant in them . If project is more than 1 inch thick some drill holes in the bottom will be needed for drainage

If your mixture is to dry add a little bit of water and mix well continue to do this until you can squeeze a little water out of a handful
If your mixture is to wet try laying your mixture on some newspaper for a few min and newspaper will absorb excess water or add more ingredites just remember to add equal parts of each .
If your mixture continues to slide off your ball then it has to much water
Happy Tuffing Ladies itÂs like being a little kid again and getting to play in the mud as long as you want.
WARNING Tuffing is fun and will draw neighborhood kids by the dozen, so work in a secure place or be willing to answer lots of questions.
This whole process is very confusing to children they just canÂt understand an adult playing in the mud like that and having a good time.

I've discovered that I can do without the hassle of papier mache to strengthen a ball! I just buy a box of plaster casting material and cover the ball with it!

It's basically cheesecloth that has been impregnated with plaster and dried into flat sheets - you just dip it in warm water and apply it like you would papier mache! You can buy it online or at any craft supply store.

My next experiment is to actually use the plaster as my base for the sphere, with a layer of plastic drywall mesh and then a thin layer of concrete mix on top to finish.