Dwp

[softworm]

Well I've misplaced ( lost ) my notes on making molds from DWP, and its been a few years since I've made one. The only thing I'm not 100% sure of is the temp and time to cure the mold. I'm thinking its around 200 degs. for 1 hour. I'm I close on this?? Thanks for the help.

Softworm

[Piscivorous Pike]

Well I've misplaced ( lost ) my notes on making molds from DWP, and its been a few years since I've made one. The only thing I'm not 100% sure of is the temp and time to cure the mold. I'm thinking its around 200 degs. for 1 hour. I'm I close on this?? Thanks for the help.

Softworm

Most of my molds are DWP. I make it up like runny pancake batter. Some times for strength inlieu of water I use 50% elmers white or elmers wood glue solutions or imbed hardware cloth screen in the base. To make the glue solution that into an ice solution I make it stronger 60/40 or 30/70 and add the appropriate ice water to bring it into ratio. I delay set up time by adding vinegar (say so on the can!) and use ice water. I bump the mold as it first sets with a vibrator and shake the bubbles of and out, touching them when they surface with a torch flame, lighter flame, even a hair dryer will pop them out. After it set up enough to take out I do and trim the edges and if a single piece mold I may trim the top opening but do not remove the critter, too soft because of the vinegar. If makeing a two piece mold this is a good time to engrave vent slots and channels. Often I cut sprue holes by hand twisting a drill and again this is a good time for that.

To set it up consider this. The plaster that makes POP and DWP degenerates back to powder at temperatures starting at 150 degrees C and above. The dryer it gets the hotter it gets. If you bake pop or dwp to long at a high temp it will get weak and crumbly. I avoid weekening the mold by baking at lowest temperature on my oven 170 degrees, two hour set at first, then check it for dampness and set again. Size of mold determines the run time. Once dry enough to take a sealer I seal with elemers yellow wood glue 50/50, recently switched from white there is a good thread about this. After the first coat of the yellow sealer I make it stonger, thicker, not enough to fill detail but thicker. Fill the mold and then shake it out, I save the excess.

Obviously, the 150 C is 302 F so 300 is your ceiling but time v. temperature can get the same results. Another consideration is heat above 212 will boil water and any voids or porous nature, even microscopic,will be affected by steam pressure if you go too high to fast. I would not go above 200 myself.

What happens when you heat gypsum, short version, you can Google this for more answeres:

http://www.instructables.com/community/Reusing-Plaster-of-Paris/

Reusing Plaster of Paris?

...or simply plaster, is a type of building material based on calcium sulfate hemihydrate... It is created by heating gypsum to about 150°C.

...When the dry plaster powder is mixed with water, it re-forms into gypsum ...

So...if I heated the gypsum to +302F (150C), it would turn back into plaster of paris, to be reused agian? Of course you would need to powder the used plaster (gypsum), but would it work?

[Piscivorous Pike]

Well I've misplaced ( lost ) my notes on making molds from DWP, and its been a few years since I've made one. The only thing I'm not 100% sure of is the temp and time to cure the mold. I'm thinking its around 200 degs. for 1 hour. I'm I close on this?? Thanks for the help.

Softworm

Most of my molds are DWP. I make it up like runny pancake batter. Some times for strength in lieu of water I use 50% elmer's white or elmer's wood glue solutions or imbed hardware cloth screen in the base. To make the glue solution into an ice solution I make it stronger 60/40 or 30/70 and add the appropriate ice water to bring it into ratio. I delay set up time by adding vinegar (says so on the can!) and use ice water. I bump the mold as it first sets with a vibrator and shake the bubbles off and out, touching them when they surface with a torch flame, lighter flame, even a hair dryer will pop them out. After it sets up enough to take out I do and trim the edges and if it is a single piece mold I may trim the top opening around the critter but do not remove the critter, the DWP is too soft because of the vinegar as this point. If making a two piece mold this is a good time to engrave vent slots and channels. Often I cut sprue holes by hand twisting a drill and again this is a good time for that.

To dry and set the DWP consider this. The gypsum plaster that makes POP and DWP degenerates back to powder at temperatures starting at 150 degrees C and above. The dryer it gets the hotter it gets when baking it. If you bake POP or DWP too long at a high temp it will get weak and crumbly. I avoid weakening the mold by baking at the lowest temperature on my oven, 170 degrees, two hour run at first, then check it for dampness and run again. Size of mold determines the run time. Once dry enough to take a sealer I seal with elemer's yellow wood glue 50/50, recently I switched from white, there is a recent good thread about this. After the first coat of the yellow sealer I make it up again a little stonger, thicker, not enough to fill details but thicker. I fill the mold and then pour off the solution and shake it out, I save the excess a bake one more time to dry the final seal coat.

Obviously, the 150 C is 302 F so 300 is your ceiling temerature but time v. temperature can get the same results refering to degeneration. Another consideration is heat above 212 will boil water and any voids even the porous nature, although microscopic,will be affected by steam pressure if you go too high in temperature too fast. I would not go above 200 myself for about an hour.

Hey, that is exactly what you said!

What happens when you heat gypsum, short version here, you can Google this for more answers:

http://www.instructa...aster-of-Paris/

Reusing Plaster of Paris?

...or simply plaster, is a type of building material based on calcium sulfate hemihydrate... It is created by heating gypsum to about 150°C.

...When the dry plaster powder is mixed with water, it re-forms into gypsum ...

So...if I heated the gypsum to +302F (150C), it would turn back into plaster of paris, to be reused agian? Of course you would need to powder the used plaster (gypsum), but would it work?

[Piscivorous Pike]

Most of my molds are DWP. I make it up like runny pancake batter. Some times for strength inlieu of water I use 50% elmers white or elmers wood glue solutions or imbed hardware cloth screen in the base. To make the glue solution that into an ice solution I make it stronger 60/40 or 30/70 and add the appropriate ice water to bring it into ratio. I delay set up time by adding vinegar (say so on the can!) and use ice water. I bump the mold as it first sets with a vibrator and shake the bubbles of and out, touching them when they surface with a torch flame, lighter flame, even a hair dryer will pop them out. After it set up enough to take out I do and trim the edges and if a single piece mold I may trim the top opening but do not remove the critter, too soft because of the vinegar. If makeing a two piece mold this is a good time to engrave vent slots and channels. Often I cut sprue holes by hand twisting a drill and again this is a good time for that.

To set it up consider this. The plaster that makes POP and DWP degenerates back to powder at temperatures starting at 150 degrees C and above. The dryer it gets the hotter it gets. If you bake pop or dwp to long at a high temp it will get weak and crumbly. I avoid weekening the mold by baking at lowest temperature on my oven 170 degrees, two hour set at first, then check it for dampness and set again. Size of mold determines the run time. Once dry enough to take a sealer I seal with elemers yellow wood glue 50/50, recently switched from white there is a good thread about this. After the first coat of the yellow sealer I make it stonger, thicker, not enough to fill detail but thicker. Fill the mold and then shake it out, I save the excess.

Obviously, the 150 C is 302 F so 300 is your ceiling but time v. temperature can get the same results. Another consideration is heat above 212 will boil water and any voids or porous nature, even microscopic,will be affected by steam pressure if you go too high to fast. I would not go above 200 myself.

What happens when you heat gypsum, short version, you can Google this for more answeres:

http://www.instructa...aster-of-Paris/

Reusing Plaster of Paris?

...or simply plaster, is a type of building material based on calcium sulfate hemihydrate... It is created by heating gypsum to about 150°C.

...When the dry plaster powder is mixed with water, it re-forms into gypsum ...

So...if I heated the gypsum to +302F (150C), it would turn back into plaster of paris, to be reused agian? Of course you would need to powder the used plaster (gypsum), but would it work?

[gone2long]

HaHa Pike I think he gets it Sorry had too its winter!

[Piscivorous Pike]

HaHa Pike I think he gets it Sorry had too its winter!

I had to quit while ahead! I emailed the BOSS, dont know what happened hit edit got a copy, hit delete and got a second copy. I now am looking to see if I could apply that technology to my bank balance...

[softworm]

thanks Piscivorous Pike. I baked mine at 170

[bluegrasslover]

I bump the mold as it first sets with a vibrator and shake the bubbles of and out, touching them when they surface with a torch flame, lighter flame, even a hair dryer will pop them out.

Damn I love this site! I never thought about using a torch flame to get those bubbles that just will not pop! Definitely adding this to my arsenal.

Thanks Pike!

Greg

[Piscivorous Pike]

Damn I love this site! I never thought about using a torch flame to get those bubbles that just will not pop! Definitely adding this to my arsenal.

Thanks Pike!

Greg

You are welcome, but like you say, I love this site, I got it from someone else on TU! Just passing it along is all. Also works on bubble when casting plastic into POP, DWP molds.

Edited February 8, 2010 by Piscivorous Pike