Finding a Better Plaster for Model Building

[@brunswicklord6365]

I was a Dental Technician for over 42 years and mixed dental plasters every working day. Firstly plaster of Paris is a complete waste of time. In the laboratory it was used 50/50 with a harder dental stone to produce cheaper preliminary models. For hard working models 100% dental stone was always used. The hardest stones were the Die Stones used in crown and bridge work. Have a look online in a dental laboratory catalogue for a dental laboratory spatula. Forget the silly little sticks to mix the plaster. A rubber bowl to mix the plaster is essential, see the lab catalogue! Now a couple of tips. Use the correct plaster / water ratio. In the lab we initially mixed in a rubber bowl, then the mix was transfered to a vacuum mixer and whilst the mix in the machine automatically stirred, air was drawn out of the mix producing an incredibly strong stone but you will not have a vacuum mixing machine. And sometimes our machine broke down and we did have a solution. Get an air tight container something the size of a large coffee jar. We used platic containers that had had 1 kg of powder in them. Mix in a rubber bowl and transfer the mix to the container and shake vigorously. Then pour slowly back into a clean bowl. You will now have a close approximation of a vacuum mixed solution. You poured the solution into the mould and had to thin the mix to fill the mould. As an apprentice dental tech, one of the first tasks was to learn how to cast a thick mix into a rubber mould. Then you would learn to cast into dental impressions producing models of teeth and it was critical not to have air bubbles in the teeth. It can be done. But not by pouring. Take some of the plaster from the bowl with the spatula and drop a small amount into a corner of your silicon mould ( you were correct in reducing the surface tension of the mould with your spray) Agitate the mould by holding the mould and knocking it on the table as you drop in more solution from the spatula. It takes some practise but you can get a bubble free model made with the correct powder water ratio.

[@Spark_Chaser]

Master Mold video, please. A thought on scratches to the plaster: is it possible to ad diluted paint or ink to the plaster, or concrete pigments? Adding them to the mix will give you a base color, but it will also make scratches less noticeable.

[@Bluecho4]

^This

[@Electro_Dust_Bunny]

wow two videos in a week cool, so I found that mixing in modpodge helps gave the plaster more strength and when it is dry I gave it a coat of modpodge helps a lot too, and I would love to see a video of how you made it 😁👍

[@E1drad_]

What great timing ... I was just about to head out to the store to get some plaster for making concrete rubble, which means I'll be deliberately breaking the final product, so it's great to see the different types of plaster and how they break. Medium strength looks like it would work well for what I need - stronger than normal stuff, but still breakable.

[@sirkenneth18]

Thanks for doing this science for us all and making such a nice video. Ive been testing plaster too but so far resin seems the trick ror light and strong. Just even more money and scare chemicals

[@michaelmanning5379]

I have some second-hand Linka moulds and a set of moulds supposed to build "The Grand Cathedral" which I expect will be great for skirmish gaming with Robin Hood or the Three Musketeers. I have been hesitant to get started as the instructions for both were lost and I've never mixed plaster for moulding before. It looks like a trip to Michaels or De Serres is in order to find the high-strength plaster!

[@JaxiPaxified]

How about adding fibers to the mix? Very enjoyable video, happy to see Danish products, it's so frustrating to see US products with no Danish alternative 😅

[@thecultofcrafting]

Yeah, that'd probably help. :-)

[@kaneblaireau4864]

Maybe dental plaster with pva? Or Mod Podge?

[@nonamo5700]

Have you heard of glass fiber reinforced concrete? Basic idea is the fibers help hold the cement together and strengthen it. Glass fiber might be over kill for plaster, perhaps some other fiber could work. Maybe take scissors to a length of twine and mix that in? edit: apparently fiber reinforced plaster is a thing, sold as stucco

[@Bluecho4]

I think burlap mesh might be good, for thicker casts. It won't stop it from breaking, but it will keep the structure together so it doesn't fall apart.

[@nonamo5700]

@@Bluecho4 might be possible to make a stuff by running said burlap through a food processor or the light - just to get small fibers that mix into the plaster. The idea with the small fibers is they keep neighboring plaster bits together. I'm wondering if the fibers mixed in could help keep the plaster from scratching away so easily (with the paint on it) I don't have any molds or the like for plaster terrain or I'd try this myself, but the idea has my interest; maybe this could be what gets me to try it

[@Bluecho4]

@@nonamo5700 Trent from Miscast demonstrated in a video that textured food packaging can be used as free plaster molds for terrain. It's from him I learned you can use burlap mesh to potentially strengthen the cast.

[@nonamo5700]

​@@Bluecho4 Might try that then As for the burlap and fiber; I'm thinking more loose fibers, unwoven like in a stucco rather than burlap which acts like rebar in cement. It'd be mixed throughout the plaster as a component; and I see no reason why you couldn't use both fiber and burlap for (possible) scratch and break resistance. To bring it back to my analogy to cement; this'd then be like glass fiber reinforced cement with rebar for it's structure. Also as an aside, glass fiber is probably overkill for plaster. As I understand it, glass fiber is used in cement because it doesn't interfere with the chemical process that occurs when portland cement is curing/drying. Burlap and twine fiber is likely fine for plaster

[@erniea3501]

Great video! Thanks for sharing! Master Mold video, please.

[@meinemeinungzuxy]

Very good and helpful video 👍

[@warthog45]

Durham's water putty is pretty good, made for plumbers

[@Spoonergasm]

I honestly really love watching experiments for stuff like this. Would be a lot of fun to try even more zany experiments to find a strong but cheap plaster option- Would a more durable wood glue work better than PVA? Does sinking in paper clips or toothpicks work as a sort of rebar? Can plaster and a small amount of resin mix together? Would CA glue be able to be mixed in before the moisture cures it, and would that even help??? Love the video!

[@bradcraig6676]

Very informative!

[@PeckLoveMedia]

I wonder if using some hessian skrim would make a difference for walls like this?

[@thecultofcrafting]

I think it would. 👍

[@jamescampos8128]

The issues you were having with the PVA could probably be mitigated by adding in some isopropyl to break the surface tension of the glue in the solution, it should just evaporate out without any major impacts to the plaster curing process. Also, the reason resin is stronger than plaster is because it's a polymer rather than a grain structure like plaster. If you want to really boost the strength of your plaster you'll need to add something to replicate the polymer properties of resin such as glass fibers.

[@thecultofcrafting]

That's interesting. 👍 I don't know much about that or even what a polymer really is, come to think of it. I'll have to look into that - thanks for suggesting it. I believe plasters forms different crystalline structures depending on how the gypsum is processed. Some of it is fairly hard and there are materials with crystalline structures out there that are a lot harder. It seems that plaster has a fairly low tensile strength - I don't know if that's always the case, but it has been with the materials I've worked with. And that's of course why you're suggesting adding fibers, which will definitely help with the tensile load (in the case of polymers, I have resins that seem ductile and some brittle, so I guess polymers can be both?) It seems I made a mistake in how I showed and explained the issue in the video, because plaster snapping in half isn't really much of an problem - at least for me. Chipping is the real issue, and I don't know which types of strengths and loads that factor into that. Unless there are some very fine fibers (I believe the ones you're talking about are more than 10mm) I don't know about, I don't think it'll help with chipping, unfortunately.

[@jamescampos8128]

@@thecultofcrafting My bad, I totally missed the real issue you were trying to solve! Yeah adding fiberglass would increase the tensile strength and make it less brittle, but if you're trying to solve paint scratching you'll want to focus on a surface treatment after the plaster dries instead of additives. I think your best bet would either be to put down a couple layers of matte spray varnish after painting or to apply something like PVA glue watered down enough to absorb into the surface of the plaster before painting. The second option would probably mess with the painting technique you like since it would change how well the plaster absorbs the paint, but might solve the chipping/scraping problem better than varnish.

[@crapparc]

I would enjoy a video on making my own molds. I tried once but failed miserably, even beyond what was expected.

[@thecultofcrafting]

Ouch. What went wrong, you think?

[@crapparc]

@@thecultofcrafting If I had to hazard a guess, I measured by ratio, not by weight.

[@spaceguy-637]

cool video!

[@ShuishuoKa]

This is amazing!Stronger and better than the foam😍But how did you make the mould of the wall？😳

[@thecultofcrafting]

Thanks! :-) In essence, I made a wall out of foam by cutting thin stones and gluing them to a thin rectangle. Then made a silicone mold from the foam wall.

[@ShuishuoKa]

@thecultofcrafting Thank you bro,I get it😊

[@NotOnLand]

Plaster does _not_ work through evaporation, it's a chemical reaction like cement. Adding PVA can interfere with that reaction making it take longer.

[@thecultofcrafting]

Well, I didn't say it _works_ through evaporation. I said it _dries_ . 🙂 Water causes plaster to set through an exothermic chemical reaction, yes. That usually happens within half an hour, give or take. There is still water in the plaster, though, and the plaster dries as the water evaporates over the next week or so. Of course, depending on the type of plaster, water to plaster ratio, etc. Feel free to correct me if I am mistaken. 🙂👍

[@Griffonbait]

How about fine white grout? It may take a couple of days to dry, but better than a week.

[@thecultofcrafting]

I haven't played much with grout.I did give it a try in this case with some random grout I had lying around, but it wasn't great. Is there a big difference in hardness between types of grout?

[@kentellis5384]

I don't know if this was one of the plastic you tried but tried dental plaster

[@mikemcculloch7118]

Sink straightened out paper clips into the wet plaster and your golden... cheers.

[@Bluecho4]

Maybe some thin metal wall mesh, for repairing drywall? (Drywall tape won't stop it from cracking, but it might keep the pieces in place at least).

[@MagnusMoerkoereJohannesen]

Hvorhenne køber du den stærke(re) gips? Det er altid rart at kunne støtte de lokale hobbypushere :)

[@thecultofcrafting]

Direkte fra makemake.dk :-)

[@michaelhearn3831]

It’s not the plaster….add a small piece of cut old net curtain to strengthen it easy…🤦🏼‍♂️

[@thecultofcrafting]

That'll reinforce the structure and help prevent stuff from breaking in half, but it won't prevent chipping, which is more of an issue, but perhaps I didn't make that clear. 🙂

[@karlkarl93]

@@thecultofcrafting Would a stronger primer help with the paint chipping at all? Something that gives it a strong plastic layer on top essentially? Or perhaps smth like modpodge?

[@thecultofcrafting]

It won't hurt, but in my experience, it won't help that much. It's not so much the paint that's chipping as the plaster, which of course takes paint with it, leaving a white spot. So a different approach is to add some pigment to the mix, so the chips aren't as noticeable.

[@newtybot]

You're not north of the border...

[@thecultofcrafting]

Well, I'm north of _A_ border. :-D

[@derekburge5294]

Only half joking... Why not use actual mortar and rocks?

[@thecultofcrafting]

Speed. Some people do actually use mortar and rocks, so I might give it a go eventually. It's a bit of a long story, but initially, the idea was to have a fast way of making lots of walls for a project I was thinking of making where I make a full Mordheim board. I can mold and paint one of the sections in the video in about 10 minutes, so that's hard to beat.

[@derekburge5294]

@@thecultofcrafting Makes sense! Might want to consider adding fiber into the plaster mix then. Helps!