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Drying Plaster Molds

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#1 Donna Roes

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Posted 22 November 2011 - 08:25 AM

A while back someone discussed drying plaster molds on radiant heat flooring. Sounded interesting so I decided to try a heating pad I had. After three days the mold was warm but still damp. Maybe the humidity here is more than can be overcome with artificial means. The mold is back on the rack air drying. S-L-O-W-L-Y..... the old fashioned way.

#2 Denice


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Posted 22 November 2011 - 09:23 AM

Donna If I use molds they are ones that I have made and I'm usually in a hurry to get them dry. It can get very humid in Kansas so I decided to do a little research on drying plaster molds. I found an article on drying molds it listed a lot of technical jargon but it basically said you could dry a plaster mold in a oven at 180 F. with out damaging the plaster but it did say it could shorten the life depending on the type of plaster that was used. I don't tend to keep molds forever so I didn't mind the shortened life aspect. I would put them in my kitchen oven for a few hours and when they were warm turn it off and let them cool and then repeat this cycle until the molds were dry. If the humidity isn't to high just putting a fan on it can make a big difference on how fast it dries. Denice

#3 Kabe


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Posted 22 November 2011 - 11:41 PM

Hi. I use plaster molds for tile pieces. I even made a drying box with wire shelves and a fan to move air through it. BOY that sure turned into a turned into a moldy mess. so... I let mine dry at room temp and place them by a heat duct in the winter. In the summer I put them out on our trampoline that speeds up the process, but it will not help much now. Good things come to those who wait, they say and it seem that we have to work around the rhythm of what we are working with for the best results. Have fun. Ain't clay great. kabe

#4 Diana Ferreira

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Posted 26 November 2011 - 12:07 PM

I work with molds. I got some molds (had no time to cast my own, as I had to deliver 150 bowls 5 days later, and was about 60 short). Long story short, I got my molds (still wet) last Saturday from the moldmaker. I put them in my 'wind channel', which is a serious laughable thing. Just some wooden planks on the sides and top. On the floor I added some kiln furniture to lift the molds off the ground, and put my little fan heater on. I was at work the next day at about 7 am. My brand new molds were so dry, I had to spray them with a bit of water before I casted the first lot. And I casted each mold 6 times that day. I made my 60 target and some extra.

I will try my best to remember to take some pics. I know I have promised this previously too :-(

#5 ErinOConnell



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Posted 17 March 2014 - 11:03 PM

I've been working with molds non-stop for about two months now at UF. The first mold I made (about 26 lb of plaster) took about two weeks to dry and be usable. Then was taught three methods of speeding up the process. 


One is sun-drying. Obviously it's not great on a humid day, but if it's a hot, sunny day it can definitely make some progress. I recommend putting them in front of a brick wall (or some other dark surface) facing the sun because it makes for a toasty atmosphere.


The second is kiln-drying. Set the kiln to hold at around 115*F and keep the lid propped. You don't want the mold to go over 120*F or it will recalcine.


The thirds, which I have found most helpful is using a dry/hot box. The one we have is pretty shoddy at the moment because it doesn't get too warm, but the ventilation is good. That's the key to drying these things. Heat it good, but you need ventilation to carry the moister away from the plaster.


I imagine rigging some sort of fan-and-heat combo would do the trick alright as well.


**REMEMBER when fast-drying plaster molds be sure to stand them upright, so that it is standing on the smallest surface area. This allows air to get all around the mold and prevents warping.

#6 Mark C.

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Posted 17 March 2014 - 11:40 PM

When we had a slip business on the side and poured 50-80 molds a day we just put a box fan (2feet x2feet) and let it push air over them at room temp. on the draing tables.

I live is high humid place in winter and it worked fine. The average temps are in the 50-60s

No heat just air movement and lots of it. We poured a new batch of them every other day so every day we had dry ones


Mark Cortright

#7 schmism


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Posted 18 March 2014 - 12:19 PM

I cast a large piece of plaster that was later cut up and carved as an accessory to a costume.  point is after 2 days sitting out, it seemed no dryer than 8 hrs after i poured it.  (it was cool wet rainy fall days)


We have a good size dehydrator that we can set the temp on.    I put it in the dehydrator, set at like 100 deg.    10 hrs later it was perfectly dry.

#8 neilestrick


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Posted 18 March 2014 - 02:25 PM

A good drying box is a simple cardboard box with a 100 watt light bulb hanging in it to create a little warmth, with a fan blowing air through it.

Neil Estrick
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L&L Kilns Distributor
Owner, Neil Estrick Gallery, LLC

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#9 seancisse



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Posted 18 March 2014 - 04:21 PM

Newbie, I made some molds and I got the same problem.

Mine are small : 20 cm x 8 cm x 5 cm.

To dry them, I put them under my radiators and it work.

Problem with owen is that you speed the process to evaporate the water, but at the same time, you're damaging the molecular structure of the plaster.

So I'll suggest, if it's very humid, to dry them in a closed room, with temperature 20°C + air dryier.

#10 Jeff Longtin

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Posted 28 March 2014 - 07:42 AM

The literature I've read suggests that drying plaster over 150 degrees causes the plaster to decalcify. As such I dry plaster in the 120-130 degree range. (Most forced air heaters come in at this range.) Air movment is also important. Like air movement causes our skin to dry out it also causes a plaster mold to dry out, as well. 


When I'm casting lots of molds, and need them dry sooner than later, I create a box form, with metal shelves or sheets of plexi, and put a little room heater at one end. (Creating a heated tunnel, as it were.) This gives me heat and it gives me air movment. I can have molds dry, in just a day to two, this way.

#11 Hollyfaucheux



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Posted 10 December 2016 - 11:45 PM

Would not letting molds not dry completely be causes them to turn a yellowish color?

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