broke mold

[borderbasser]

I made a 2 cavity, 2 piece mold of a 10in worm last night out of Wel-Cote water putty (no durhams in my area). I mixed it pretty thick like cake batter and both halves about 3/4in thick. The mold turned out great, but one problem....the top half broke prying it apart. Prior to prying it apart, I let the mold set until you could hardly dent it with your fingernail. I even brushed the bottom half with vaseline before pouring the top half. Anybody have any tips for me that might aleviate this problem in the furture. Also it was a pretty clean break and I was wondering if anyone knew of an epoxy I could use to repair the mold. I tried searching this topic, but no luck. Thanks.

[woodsac]

Another member recently said that he coats his plaster type molds with WD40 Just a light spray and he's never had a problem with them sticking.

For repair, I would try some devcon 2 ton epoxy.

[jm]

Hi,

I'm new, too, but I know a little about "plaster"

These "hard" plasters are really a mixture of plaster of Paris and Portland cement. Usually they are 20 - 40 percent Portland.

Portland cement cures by reacting with the water and forming a solid. There are actually several stages to this cure.

Set 1 you can take the forms off, minutes to hours

Set 2 appears hard and can be dry 8 to 24 hours

Set 3 Nearly full strength, a few days to a week.

(You'll notice that after they pour a section of road, they keep it covered for up to a week. That is to hold the moisture in. Concrete doesn't cure by drying, but by taking up the water into the rock. Also, though the road looks ready, it can't yet take a full load.)

Set 4 Watertight, usually about 6 months. At this time the lime in the cement has taken up all of the water it can and achieved maximum strength and integrity.

The first 3, and maybe all four can be accelerated by using a catalyst, and they are helped by heat and humidity. Concrete block manufacturers usually cure the new blocks for about a day in a steam room. Then they are well into set 3 and can be handled normally. They finish curing in the wall. I increase the strength of my molds by wetting them several times in a couple of days. (Actually I fuss on them with a little fine sandpaper, and then wash them off and leave them wet.) Then if I'm in a hurry, I'll "bake" them at 200 degrees just long enough so that they will take the water based acrylic coating I put on. I've only had one crack, and it was so tight I broke the master worm pulling it out.

You probably tried to separate your forms when it was just into set 2. waiting a day would make a lot of difference.

Thickness helps in big forms. the forces you can create on a piece of plaster a foot long and 3/4 in thick can easily exceed the strength of the rock, which ain't much to start with.

A lighter release agent, like worm oil, might help by lessening the forces described in the last paragraph.

I bet a gel type super glue would stick it back together. I would wait at least 3 days for it to dry out, though. Maybe someone else knows of a better glue for rocks.

[borderbasser]

Thanks for the help. I got anxious and already put it back together with devcon..seems to work out allright. I just poured my first worm with it but I can't get it to flow up into the tip of the tail. Finally, I poured the tail first, and then put the mold together and poured the rest of the bait, but it didn't fuse 100%, almost though.

[Mattlures]

You can also reinforce you molds by pushing dowels or other things down into your plaster while it is still wet.