This is how we (the wife and I) created a cement cigar ashtray. We learned a few things along the way that we would definitely do differently, which I will note along the way.
Step 1: Materials and Tools
Plastic butter knife, toothpicks, florist foam, paint brushes, sealer/glue, plaster of paris, cement, water, buckets, foil and a shoe box.
Step 2: Creating the Model
I carved a prototype or model of my ashtray from florist foam using a butter knife. Florist foam is very soft and super easy to carve. I used my fingers to smooth the transitions and round corners. While carving, this stuff makes an incredible mess; be sure to lay down paper in your work area. This is the creative step and is the most fun. I had a few cigars out to test the size of the bowl and rests. This was by far the most fun step of the process.
Step 3: Attaching the Parts
A single piece of foam was not large enough for what I wanted to create, so I used two blocks of foam. Once I was done carving both pieces, I joined them together using toothpicks... this idea was Ong's. I imagine that you could join multiple parts with just about any method.
Step 4: Sealing the Model
Since I was using two separate pieces, it was important to seal them together. This was to prevent the plaster from running into the joints. We also thought that the plaster might seep into the pores on the foam; turns out that this was not the case. The pores on the florist foam is too fine. For my next ashtray, I will not be using sealer; it ended up being a pain at almost every step.
Step 5: Creating the Mold
Once the sealer was dry, it was time to create the plaster mold. We used a shoe box lined with foil; plaster is very wet and would have killed the cardboard. We could have used plastic wrap, but the foil is easier to work with. For this step, we needed A LOT MORE plaster than we thought; take note and make too much. We attempted to glue the foam to the bottom of the shoe box with rubber cement, which turned out to be a complete failure. When pouring the plaster in, the foam decided to float. We freaked out... but while freaking out I was holding the model down with my (gloved) hand. Upon letting go, the plaster had set enough to hold the foam down. This worked out very well.
Step 6: Removing the Model
We had hoped the foam would be easy to remove; we were wrong. Once the plaster had dries, we had to carve the foam out of the plaster... all while being very careful not to crack the mold. The plastic is much stronger than we thought it would be... so be careful, but not not like handling eggs careful. This step took a lot longer than estimated; this was mostly due to the sealer. The sealer bonded with the plaster more than the foam, so it was like gluing our model to the plaster. Not fun.
Step 7: Pouring the Cement
With a clean and dry mold, we made our cement. As to not repeat an earlier mistake, we made entirely too much cement. Cement sets crazy fast, so too much is a good thing. Pouring the cement was fast and easy. Since our foam floated while making the mold, our mold was not quite level. We had to level the cement by placing a paint brush under one side of the mold.
Step 8: Removing the Mold
After letting the cement dry for 48 hours, we broke away the plaster. All was going well until we got to the bowl. The plaster had been re-wet by the cement and had turned into clay. I suspect that letting it dry for another day would have made life easier, but I was in a hurry to use my ashtray. We chiseled, scraped and dug to remove as much plaster as possible. Here again, the sealer was an issue... it bonded with the cement over the plaster and was not part of the ashtray.
Step 9: Clean-up
There was still patches of plaster and sealer all over, so we washed it with hot water and soap. Turns out that the glue came off easier with dry rubbing. After a whole lot of scrubbing and rubbing, it was ready for use.
Step 10: Enjoy
Light up a cigar and start smoking!
In the end the project was fun, but ended up being a lot more work than planned. By skipping the sealer, we could have saved a lot of trouble. Any plaster that seeped through the cracks was easily removed in Step 5. The other thing that I would have done differently is to use concrete instead of cement; I have no idea what the difference is, but concrete is way cheaper and would have done the same thing.
I will be doing this again... in fact, I already have my second prototype