Female Mold for Carbon Fiber Motorcycle Bodywork

I've taken up teaching myself how to build my own carbon-fiber/kevlar composite motorcycle fairings using some old fairings as my template. Originally I was just going to use the old fairings as my mold and layup directly on them but changed my mind and decided to do it right.. So I started building female molds out of plaster. I tried making a small mold out of fiber glass but after researching further decided to give the plaster a shot and it came out surprisingly well I think. The surface is not totally smooth but I was planning for that and will smooth it out with sandpaper and glaze. I'm just glad I separated the part without cracking the mold and the impression successfully got all of the edges.

Step 1: Pour the Plaster

I laid the plaster (100% plaster of paris - 1 large box from Home Depot) last night at about 6:30 finishing up at close to 8. I used cheese cloth soaked in plaster directly against the part and after fully covering it with cheesecloth, I mixed up the last bit of plaster (about half a bucket) and poured that over the top just to build up a base for the skin I'd layed down.

The next day I started around 3:30pm (having let it sit outside all night and all day up until then). In the middle of summer Los Angeles weather I was satisfied it was dry.

This is how it looked after wiggling it loose a little bit.

Step 2: Flip and Trim

First thing to do is flip it over. You'll see I let the plaster wrap around the edges and covered the backside with papertape..

Flipping it over and removed the paper tape I had used to seal it off as you can see.. I had draped some of the plaster and cheesecloth up and around the part to ensure I got the edges.

Step 3: Strengthen Your Mold

I read somewhere that mixing wood glue or coating the plaster in wood glue would strengthen the plaster, so I flipped it over, coated it with wood glue and used a heat gun on it for about 10 minutes to cook in the glue and to comfort my nerves that the plaster was totally dry.

Step 4:

After that using a combination of scissors and a cordless Dremel I carefully trimmed away the excess plaster so I'd be able to lift out the part.

Step 5: Prepare the Removal of Your Part

And positioned some scrap wood around the part to prevent sensitive edges from crumbling due to their own weight once the part was freed. I also positioned an assortment of clips, screwdrivers, a bondo squeegee and a plaster piece of junk I found in my tool bag around the part to act as my wedges.

I was concerned it might not come loose because I really didn't use much release prior to pouring the plaster and definitely didn't give it much time to dry but I was able to separate the part VERY easily in about 5-10 minutes being probably more careful than I needed to be.

Step 6: Strengthen Your Mold AGAIN

After I got the part free, I did the same thing to the inside that I'd done to the outside.. Wood glue and heat gun for about 10 minutes.

Step 7: Pretty Much Done

Here you can see the comparison between the part and the mold. I think I will come back with a marker to draw out the edges just so it's totally clear since there are some cut away areas.

Step 8: CLEAN UP

And last but not least.. the longest part of the process. I cleaned up and organized my work area because I'm OCD like that.
You see I used a pallet on top of a trash can as my work table and built a wooden bed lined with trash bag plaster to hold my work.. With a cardboard top and some string for peace of mind.

My buckets for mixing plaster. Off to the far right I have some more part in a large Rubbermaid container waiting to have plaster poured over them.

I just wrapped up and am going to take a break a bit longer and probably come back and work on smoothing it out so I can start the resin infusion / carbonfiber build up tomorrow