Lessons Learned Using Plaster of Paris Molds

[Patrick]

I left the mold dry for 24 hours and poured some lead into the mold tonight.


As soon as the lead hit the mold it began to "spatter" indicating that the mold still had moisture in it. The remaining moisture in the mold heated up and expanded when it met contact with the lead. This expansion resulted in several cracks in the mold. If the mold was completely dry I still don't know if it would be useable for a second pour.


The mold was also pretty thin at the bottom. This lack of thickness resulted in the lead breaking through slightly.


I could salvage the piece of lead that was molded, but will likely make two new molds and let them dry for at least 24 hours (or a week if possible). I am under a time crunch to get this done and test the fish this weekend, so anything will do right now. I've only got 5 weekends of the boating season before I have to pull the boat out (due to normal expected October snow).


It was not worth posting a photo of it. But if any wants to see one, send me an e-mail and I'll forward you the end result of the lead and trashed mold.


Remember ... thicker mold is better and llet it dry for as long as possible.


Patrick

[Jan]

Re: Lessons Learned Using Plaster of Paris Molds

Patrick,


Perhaps the best think is to bake the mold before you pour lead.


Any normal oven should work.


Do not know what microwave would do..


Heating will get moisture out fast.


Also a preheated mold will not crack that quickly when you pour lead.


I hope it works, as I was planning to use the same principle to pour more complex forms than I can do with sand.


Regards, jan.

[Patrick]

Re: Lessons Learned Using Plaster of Paris Molds

Jan,


I made another mold and made this one thicker on the bottom. I would say that the mold was about an inch thick on all sides.


I left this one dry for the same amount of time ... 24 hours. I then placed it in the oven for 2 hours at 175 degrees.


The mold was still hot when I poured the hot lead, but this time the mold did not crack or break through the bottom.


I had a little too much lead in the mold and did not want to spend time cutting it to size so I cut a chunk off and placed the lead back in the iron pan and melted it again. This time I lowered the temerature and slowly pored the lead into the oven. This was a nice pour with no splattering and resulted in very little cutting of the lead.


I should note that I did not warm the mold before pouring in the lead on the second pour because of the lead residue form the prior pour. Keep in mind that the plaster of paris mold was warmed in my kitchen oven.


On the second pour the mold did have one crack in the side.


Lessons learned ... make a thick mold on all sides, warm the mold prior to pouring for a couple of hours at 175 degrees, pour the lead slowly just after it is at it's melting stage.


I hope this helps a little.


Patrick