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How to Build a Ceiling Dome |
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Applying the Plaster Now that the base was complete it was time to start layering the plaster on. First problem was what type of plaster to use. While drywall paste is cheap and plentiful at Home Depot, it takes a long time to dry and it shrinks as it dries which would results in lots of cracks. I planned to put on a quarter inch of plaster over the foam (by adjusting the shaper up and inward) so I wanted something a bit easier to work with. I ended up using plaster of paris. This is also available at Home Depot, but not quite as readily as drywall paste. My Home Depot only had a two bags so I bought them both. I've never worked with plaster of paris before so I was careful to follow the instructions. I started with a few small batches just to try things out. This went pretty well except that small batches didn't cover very much area. To speed things up I tried to mix up half a bag in one go only to have the whole thing solidify before I could finish mixing it. After that I stayed with small batches. In the image below you can see the first coat of plaster has been applied by hand and it looks terrible: 
I figured I was past the point of no return so I kept mixing and applying layers until I figured I had a reasonably think layer over the entire dome. As you can see in the image below this is a far cry from the perfect finish I was envisioning: 
At this point all my hopes were pinned on the sanding process. I figured if I could sand the ridges down like I did with the foam then there was no reason why the results couldn't be as good. Knowing that the short strips of sandpaper left rings in the foam, I was careful to using long strips of sandpaper glued directly onto the shaper: 
After carefully applying the sandpaper, I tried a quick pass at sanding the plaster. This didn't work at all. The little bit of sandpaper on the edge of the shaper clogged up almost instantly. Given how much material I needed to remove this wasn't going to work. I happened to have a few pieces of copper lying around so I cut a blade out of copper and screwed it to the shaper. This worked much better as I could now shave the inside of the dome rather than sand it: 
Given how well this worked, I added another blade to the other side of the tool to help shape the rim of the dome. 
By shaving down the high spots and building up the low spots I was able to get a very uniform shape: 
The big problem I ran into was that the plaster of paris cured so fast that I couldn't get a good finish coat. While the scraper resulted in a very uniform shape, the finish was far from perfect as it left 'chatter' marks. To solve this I did a final coat using drywall paste. Since this dries slowly I was able to use the shaper to spread a very thin and very smooth coat over the entire surface: 
This left a few rough spots where the shaper stopped but I sanded these down and filled them manually after everything was dry: 
Another quick sand and the dome was complete: 
Next step was to remove the drywall form to yield the finished dome: 
Now that the dome was complete and my wife was finally starting to believe that this project might actually work, it was time to install it. NEXT > | ||||
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