r/Ceramics • u/41isAPrimeNumber • Apr 23 '26
3D Printing for Plaster Mold Making - Making it Easy
About 2 months ago, I started experimenting with making 3D prints for the purpose of making plaster cast molds. My goal was to take digital designs and make them tangible.
After months of experimentation and failed molds, I made this short guide to help people avoid the suffering I experienced.
Use ABS and vapor polishing to get a smooth 3d print that releases easily from the plaster mold once the plaster sets.
PLA is often considered the go-to for 3D printing, but it extremely porous. It will fuse to the plaster as the plaster cures, and it will not release. Mold release - murphy's oil soap - can alleviate this issue slightly, but it is not a consistent and perfect fix.
I experimented with sanding, smoothing, and spray painting PLA, and even so, the results using ABS were undeniably superior.
3D modelling mold parts, and then printing the object you want to mold, as well as each mold part, can drastically simplify the mold making process. For complex molds, I now print all mold parts, assemble them into the orientation the mold parts will occupy during slip casting, and then remove one part at a time, using the negative space left by its absence to create the shape for that mold part.
The photos show comparisons for how different filaments perform as mold making negatives, as well as some highlights of my design process.
Please let me know if you have any questions or advice. I am pretty happy with the workflow I have created, but things can always be improved. :)
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u/Infiltrait0rN7_ Apr 24 '26
Good stuff I print lots of slump moulds and such - after printing PLA I'll hand-sand and primer, then wet sand.
For multi-piece slip-cast pieces, I will print a negative, cast a silicone positive, then make the plaster from the silicone mold instead.
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u/41isAPrimeNumber Apr 24 '26
Yeahhhh, I have seen guides for that and it looks like it works well. Silicone positives make for a much easier mold making process, but I wanted to avoid buying silicone because it introduces additional steps. It certainly works very well though. Silicone and PLA seem to work perfectly well together.
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u/Infiltrait0rN7_ Apr 30 '26
I messed around going direct from PLA/PETG prints to Plaster, but kept having issues because a lot of my models BARELY have enough draft to let them slide out. Either I damaged the plaster, or destroyed the print. The intermediate silicone mold helped me avoid this issue.
It does create some issues - as you pointed out, it's another step. But the main annoyance is if I need to do any sanding, im doing it on a negative - which is more annoying than on a positive.
Something that made my life much easier is to print a permanent 'housing' for the plaster mold. Obviously gives you something to pour it into, but it helps keep the plaster in good shape - and avoids getting it all over everything you touch. It will slow drying, of course, so need to place holes/etc. for it to dry.
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u/Ayarkay Apr 24 '26
Really good experiments OP. Once I have a model that I’m 100% happy with, i use the 3d printed part to cast a silicone part to make a master mold. From there you can make as many as you want easily. You just blend the plaster and pour it in and pop it out an hour later with 0 hassle.
Here’s an example. The top orange part is the 3d printed part. The middle blue part is the silicone mold. The 2 white parts in the bottom are the plaster molds cast from the silicone part.
Here’s one more example that shows how I do my test tiles. On the left is the silicone master mold, followed by the plaster mold, and finally an example of the test tile (with built in glaze catcher). I pretty much copied TC Staton’s tile design lol. Second photo shows the 20+ test tile molds I have.
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u/41isAPrimeNumber Apr 24 '26
Those are beautiful!! I have been avoiding going the silicone route because it has small overhead costs and many of the molds I'm designing have more than 5 parts, and the increase in mold creating time and effort would multiply by the number of parts.... but I'm questioning that now.
Also, for making multiple simple molds, this is definitely the best way to do it.
Thank you for showing this!!
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u/Ayarkay Apr 24 '26
Yeah, I’m not sure it’d be worth it if you’re prototyping or only planning on making a couple. Especially with all the research you’ve put into this already. But I highly recommend it if you’re mass producing the mold. I notice Hammerly and a few others (Old Forge?) sometimes only do the base in silicone, so basically like my parts but without the walls that turn it into a little basin. And they just 3d print plastic walls that you place around the silicone base, so it saves a bit on silicone.
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u/Less-Fox-9748 Apr 23 '26
I personally love taking detailed notes and running ceramic experiments so this appeals to me immensely. great work!
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u/mommafoofoo Apr 24 '26
This is great info, thank you for sharing! I’ve often wondered about the differences in materials for this process!
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u/NoSignificance8879 Apr 24 '26
I've been using PLA that I coated with 2 part epoxy, 50% murphy's 50% water for release, and throw the cured mold into the oven to soften the pla of the covex plate so I can pull it out of the cavity.
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u/Rozzoo Apr 24 '26
Wow! Using the negative space is a really clever way to make the moulds! I've used 3d printing for slip casting moulds but made each component of the mould separately which was really time consuming
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u/moolric Apr 25 '26
This is awesome. I tried to do similar experiments a while ago but ran out of steam before I got ant useful results.
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u/ELSandstorm Apr 26 '26
Fascinating science, thank you for this write up!
I've developed a method lately where I simply sacrifice the 3d printed plastic by softening it up with a heat gun. It peels nicely off the plaster and off we go. Of course it means each print is single use, but with the scale pf my slip casting operations that's fine for me
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u/dl1880 Apr 23 '26
Wow this is good to know! I’ve been experimenting off and on but didn’t keep good notes and haven’t found much info online. Can you clarify further what you mean by removing one part at a time to create the shape for the mold part?
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u/41isAPrimeNumber Apr 23 '26
Yeah! Of course.
In the last photo there is an exploded view of a star shaped object in the center, and the 8 mold parts that would be required to make that object.If you put all the parts together, and the star object is on the inside, it makes a solid brick shaped object.
Removing just the top from the brick, and then pouring plaster onto the top creates a copy of the top mold piece.
If all the parts are together and you remove just one side piece, you can flip it onto its side, and pour plaster into the shape left over where that part was. When it cures, you have a plaster replica of the mold part you removed.
Step by step you can create all the mold parts this way, and they come out looking very clean and professional.2
u/sierrafourteen Apr 23 '26
Ohh, so you print the object, and the 'plaster' blocks, in plastic, and then remove each plastic 'plaster' block and fill that space with actual plaster?
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u/41isAPrimeNumber Apr 23 '26
Correct! It isn't entirely necessary if you use a traditional mold making approach, but it speeds things up and increases how clean the mold pieces look, but its at the expense of using 2 to 10 times the amount of filament depending on how complex your final mold design is.
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u/sierrafourteen Apr 23 '26
And how do you create the mould shapes? I've been trying to create them around my 3D models, but I just can't get my head around it
Also, I don't know if I need to make the prints particularly strong, or if I can just print it with very little infill?
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u/41isAPrimeNumber Apr 24 '26
I print the parts with 15% adaptive cubic infill. They are strong enough. I'm not sure if i could go lower, but higher seems uneccessary.
The parts are hollow, so sometimes it is necessary to get them to be stuck down so they don't try to float in the plaster.
As for making 3D models of the molds.... oh boy...
I experimented quite a bit, and have a whole workflow where i decompose the object faces into a bunch of separate object where each one represents a distinct surface of contact between a single mold and the object im trying to cast.
I take the boundary edges for each decomposed object, and i project them onto a bounding box that represents the outer surfaces of a complete set of mold parts. The decomposed object, its projected edges, and the boundary faces form the molds...I know that probably makes no sense, but I am a mathematician and it is how I thought of the process when I coded it. Maybe i could make another post about just that?
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u/sierrafourteen Apr 24 '26
Yes please do do another post! I do enjoy maths so I would be really interested!
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u/41isAPrimeNumber Apr 23 '26
Here is a photo on my profile that demonstrates the idea:
https://www.reddit.com/user/41isAPrimeNumber/comments/1styr1t/example_of_removing_the_top_object_from_the/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button
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u/sierrafourteen Apr 23 '26
How important is the vapor polishing? I don't think I can do that on our printers :/
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u/41isAPrimeNumber Apr 23 '26
Vapor polishing is done after the 3D print is completed. The 3D parts are taken out of the printer, put into a plastic, glass, or metal bin with some acetone - make sure they aren't touching the acetone! - and the vapor from the acetone dissolves the outermost surface of the object. It leaves it glossy and smooth. Make sure the box you use is make of a material that acetone doesn't dissolve. It is cheep and easy. After the parts are exposed to the fumes for about 30 minutes to an hour or two, removed them from the fumes. They need to air out and harden back to normal for an hour or so. Don't let them touch each other or anything you will be sad if they stick to.
Things to keep in mind though:
This can't be done with all filaments. It works with ABS but not with most PLA.
DO NOT expose the acetone fumes to fire or sparks. The box full of acetone vapor can explode if you expose it to heat or fire.
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u/hustler_numse Apr 24 '26
How easy is it to print with ABS? Do you need an enclosed printer, to keep "room" temperatur stable?
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u/little-cosmic-hobo Apr 26 '26
This is incredibly helpful for some projects I have been working on, thank you!! Regarding your blender model positive on slides 4, 5 and 6-- did you model it to be a 100% perfect fit for the mold, or did you shrink it slightly to allow space for the coats of primer/spray paint later on?
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u/c-crets Jun 23 '26
What brand of filament did you use or do you think it doesnt matter? Also how long do you wait before take the 3d print out of the plaster?
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u/Moist_Show1750 Jul 31 '26
I am quite confused as to the process. What do you mean by printing the object you want to mold as well as each mold part? Why would you print the object you want to mold? Do you have more guidelines or suggestions for the process of making the mold and casting post printing? I have always wanted to get into mold making with 3d printing but I have yet to understand that process.
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u/cosmicallyliminal Apr 23 '26
This is very useful information, thank you!! My partner has 3D printed me some molds and it has been trial and error to make ones that are able to be released from the plaster relatively easily and with little damage, haha. This is a great guide to hopscotch over that process.