I used thin plaster followed by thick plaster. After drying i pour in acetone to dissolve the foam. I have no problems with turbulence from melting foam.

This was a good attempt. One thing to note for the future is all lost type castings are in a negative cavity created by what is lost- in this case the foam is lost, not the plaster. There is no need to smooth the outside of the plaster. The internal negative void of the plaster is what is most important. You can try adding multiple layers of plaster to increase the supporting structure the molten aluminum will fill into. It may also be beneficial to burnout or chemically washout the foam, before the pour. It is likely the off gassing from the foam as it melted entrained gas inside the casting. It is also beneficial to have a hot mold to pour into, in order to extend the time the material remains liquid. The sand and plaster you poured into likely acted as a heat sink to suck the energy out of the metal and sped up the hardening time.

The term "Thin Plaster" implies less than filling the entire mold with plaster. Removing the extra plaster is not needed as the only thing needed was a solid surface to prevent the metal from mixing with and sticking to the dry sand that is not going to be holding it's shape. Also there is no way for the gases to escape so removing/melting away as much of the foam with acetone before burying it is best, so a thicker plaster shell would hold up much better.

3:15 You could use a vibrating body massager to liquefy the sand while setting your mold. Also, I'm not familiar with this technique but it seems that you could create a thicker plaster coating and then pre-vaporize the foam to create a cleaner form.

I liked the feeling of drama he gave to the process haha

I agree with you that the green sand keeps the pattern from moving so much. I have had lots of blowouts when I try to do a lost foam casting using loose sand only. I do you like using a plaster coat and then green sand

For a first attempt that was pretty good. Next attempt use plaster cornice adhesive, not just plaster, highly heat resistant, where basic plaster is crap with heat, and do a double layer. It will work a treat.

Back when you were still doing lost foam casting. Look how far you've come, with you making some excellent investment castings.

Useful and interesting

In conclusion, always worth trying something new. And thanks to your efforts I can make a decision weather or not to try these ways myself (very limited playtime).

this is great info! I bought some styro pumpkins from the dollar store, they are hollow (about 3/8 thick styro walls and 7.5 inches tall. my earlier experiments with these was the sand would start caving on the inside and I would loose my $4 investment. I plan on coating the inside only with plaster then fill with sand. once I clean the 40 pounds of brass I accidently spilled in my foundry I will have a go at this and tell you the results

Jeff, your videos are awesome! well done mate!

Nice work, Sir. Ignore the negative comments. Doing something is more important than "paralysis by analysis" or never doing it because you are waiting to do it "perfectly". Thank you for your kind help and enterprise.

hi, you can 3d print or cnc a mold (or both), then fill it with wax, then you cover the mold with thin layers of plaster-sand-dry, plaster-sand-dry during few days, then you heat that mold and recover the wax, then you use a two half green sand mold with well and venting orifices and done. you end using only the thin layer of plaster, the rest can be reused (included the printing filament with a filament extruder)

Great video. I too have learned that lost foam + thin plaster + sand is for people who like to have a lot of extra work after casting. Greensand forever! (Even if it's d.i.y. greensand.)

The lost foam method that introduced me to lost foam used drywall compound, a quickset hotmud(5 min), but it was used so that the caster didn't have to use green sand, but could instead just use ordinary play sand. It's a way to produce blocky low detail parts with a minimum of fuss and very little technique. It's really a technique for people that want a quick part and have to cast it because for whatever reason they can't machine it.

Sweet!

Very good....How about not using any plaster at all....will you get similar results? ...Thanks

I have been experimenting with the foam/plaster method and have had results similar to yours. I have done some research and my next plan is to coat a foam mold with thick plaster formed with several vents, then once dry pour in Xylene (or tolulene) to completely dissolve the foam before casting. I have tried Acetone and while it does dissolve the foam it doesn't do so completely. Xylene seems to do the trick. I have also learned that plaster must dry for longer than you think... At least a week in warm dry conditions. It holds on to a lot of water.

I think you should use vacume to help escape gases produced by lost foam + vacume will help improve sharp details of casting 😊

In green sand, the vaporised foam can vent through the sand, but plaster would only vent were you make vents. The foam turning to vapor would be many times the volume of the foam and that vapor caused a volcano and could have been a emergeny room deal! In investment casting, the wet clay (in this case wet plaster) would be showered with sand, clay-sand-clay-sand, six-eight times, then the wax (lost wax) melted out, then burned out, then pre heated for the metal pour. More vents may work, but I think with "not lost foam", green sand may the better way. Even in green sand, the sand can be packed to tight and also have no were for the vapors to go and all the hot metal exit with explosive force out were it entered or through the sand onto anything around and the more foam/metal, the more likely. Be safe.

Good work.I would try a coat of plaster,then whilst wet cover with a layer of dry sand then more wet plaster,sand again.Very important to dry very well.Airing cupboard for a week ,top shelve were the wife can see,works for me.I do prefer green sand method, but your way could be an easy way for certain jobs.Thanks.

An excellent attempt. Perhaps some further investigation into what constitutes ‘thin’ plaster. It may need to be several millimetres thicker. Also, after the first coat or two of plaster, it may be necessary to add something to help hold it together better. Definitely worth a revisit...

Love your videos. I need your help ! I am trying to do lost shell PLA casting. Which we all know sucks because PLA does no burn out clean and the mold keeps breaking because PLA expands and all that fun stuff. In order to do this right I would have to use wax or wax like materials from a 3D printer I know this. And also some proper investment plaster. My problem is the plaster needs a hight temp oven to burn out right and is also expensive. So I want to do zinc casts for cheap but with undercuts from 3D printed masters. Anyhow here are my ideas and you tell me what you think Master caster =) 1. Using fire proof spray paint (800°C fireproof) and spray painting coats of the paint and mixing with sand (kind of like suspenda slurry). Then burning out the PLA in a household oven (that´s all I have, my method is supposed to be cheap and easy doable at home with little tools, material I want to use is zinc so I can melt that on a camping stove. 2. Using high temp sealant (from the caulc postol) hold up to 1300°C --> again building up coats burning out the part and casting. 3. Using castable refractory / zirconium refractory / puty repair compounds (don´t know which ones yet) and then again coating the part, burn out the plastic, casting. 4. Air drying clay ---> burn out --> cast (proper clay would need again too hight temps) So basically I try to find a mold material comparable to investment plaster but with less heat needed etc.

I like you videos and thought I would pass along some of my experiments. I have used water thinned drywall spackling compound with very good success very similar to what you did. I have heard plaster actually has some plastic in it and will out gas and cause problems. I coated the hot wire cut foam pattern a few times by dunking it in then thinned Spackle and let it dry a few days between coats. I did not do any sanding and just placed it in the play sand and added a can as a feeder. The results actually showed the hot wire cut ripples in the pattern. Much better than any attempt with green sand! I am trying to make some aluminum gears with the method now.

Very interesting! Your channel is awesome. Could you make a video explaining the how to of the technique of many thin plasters layers that are spread with "some unknown" powder when wet in order to obtain a hard but thin hollow mold?

Very interesting, I know when hot metal hits the foam it's vaporized but what does the metal do to the plaster, forms inside or out side of the cast , if out side what about spraying thin dry coats till it's covered with out dripshnbnm

I think there could be difficulty with foam that lost wax does not have; the gases escaping create turbulence and eddies within the flowing metal. maybe more vents could help but compared to wax it can be done cheaper and quicker but needs certain considerations. def the volcano out of the vent is worrisome haha

Maybe you could try adding fine sand to the plaster and applying it with a paintbush .Also poking holes with the needle as it drys might be solution to venting problems.Maybe using a cement( mix it with some fine sand ???) instead of plaster would be better idea.It would take less time to dry-especialy if made into a thin layer.I dont like plaster for casting i tried it with fishing weights several times and result was volotile even after several days of curing the plaster-that thing just keeps too much water in it. Just couple thoughts.

I just found your channel a few days ago (approx 4-6-2019) and have enjoyed your content, and learned a few things as well, of the 4 to 5 videos I have watched so far, plus, my lady enjoys hearing your Aussie accent, (reminds her of ClickSpring, Lol) but anyway... I was wondering, if doing this (thin wall plaster method) while in loose sand, just like in this video, if making an "L-shaped" runner vent or filling vent out of more plaster........ But, filling/pouring and venting the cavity from the side of the parts cavity, or maybe even doing a "J-shaped" runner/filling and vent gate, so the molten material flows in from the bottom, if that would prevent the splits areas in the finished part? Or am I making things more complicated then they need to be. I time to time, get these splits in my parts, and I don't understand why, and these splits are always at the bottom of the part, and my tiny mind, would like to think that that if the splits happened on top of the part, as if there wasn't enough molten material in the cavity to fill it up , but nope, these splits, when they happen, are always on the bottom corners/edges of my parts, if they were on top, as if it was a partial fill and gravity, they would make sense to me, but on the bottom, lol... I seen another channel about 6 to 8 months ago, talking about side filling and or bottom filling, as stated above process... I have not tried it yet, just wondering if you know why these small hair line splits happen on the bottom, and they never happen in the same location for the same part either? is the aluminum is being cooled to quickly as it has to flow around the multi faceted cavity? Meaning, I need to bring the temp up an additional 50°F to 100°F before pouring? Maybe placing something under the cast box on the vent side, so the cavity is no longer level and the vent side is higher? Maybe pouring the molten aluminum very rapidly into the cavity, and not worry about sand being knocked into the cavity? Anybody can answer this issue for me, and there is no hurry, as my next project is about a month away

Makercise has had good results with this technique check his gingery shaper build out.

Came out pretty darn good consisering that dirty trick the mold played on you! Next time you try the dry sand method, try skipping both the coating and the vent. When you're bare-doggin' it like that, the foam can vent into the dry unbonded sand just fine. If your sand is fine enough and you were conscientious with your vibrating, the finish may be acceptable. Effective vibration is especially if there important where there are undercuts (also true when using the plaster).

The first time I did lost foam I was surprised at the height of the flames and stopped pouring for a moment. I ended up with lines similar to the tears he mentions. 8:40

Hey thanks for the info were could I buy this etruded foam?

With lost wax casting, the wax is melted out before the metal is poured. If the plaster shell were thick enough to hold up that might be an option with foam.

the sodium silicate method I like best with the foam it needs gas ports so you don't get the bubbling out like you did and you lose some heat in the exchange proses and if you use a very fine sand you can get a very good finishes as well the best is the lost wax . and I know how to make sodium silicate if need to know how ask me :)

Back in the day if I tried something and it didn't work out, the words "well that was a waste of time" would be heard. Usually shouted and with a few added expletives! In later life I have learned that it's never a waste of time buddy, I have just found another way that doesn't work is all, a step closer to getting where I need to get. Seems a long winded process fella with less than perfect results, I def think the green sand gets my vote.

Have you tried sheetrock mud instead of plaster? I've been using very thin mud (about like latex paint consistency) painted on just thick enough to add a little color. It dries overnight or less and disintegrates during pouring but it makes the surface finish exactly like the foam was, hold the loose sand back. With only the sprue (no vent), a lot of the gas from the foam goes into the sand and i get clean castings. Recently did a burner body and it hydrotested with no seeps.

@0:57 VegOilGuy; is it your wife doing the video graphics overlays? :D

"Lost" casting process I have seen used wax, then a refractory mixture of plaster mixed with fine clay, silica flour, zircon dust etc. Was sprayed on with fines, then with larger refractory ballast, ie 3-4mm size pieces. All air dried, then warmed, then when ALL moisture slowly cooked out, was placed in oven to bake in the setting components, ie clay, and probably water glass, and this of course removed "lost" the wax model(s). As these were commercial castings these were ganged together in trees etc. Results always spectacular, no gassing etc because nothing was there to burn, that is the entire concept of 'lost' process. The model needs to be 'lost' before pouring in molten metal. And this plaster process is very dangerous, as there is still water present in plaster unless it is cooked out slowly, if the thickness is sufficient, it will explode due to the steam etc, been there, done that, molten brass is no fun when flying around.

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What would happen if you used a thicker plaster coating?

What type of foam are you using there???

Make the plaster thicker and let sit for 2 days Bake it for 45 min at 600c and pour

What is this used for?

that was moister making the metal pop like that from plaster lol!

you need to plaster dip and then slowly spin out of the dip also it my help your surface finish to use a denser foam also turbulence is generated from the burning chemicals that the foam consists of, It defeats the method of foam casting but if you were to burn out the foam first, that would help turbulence

Why does the plaster have to be thin? I am not following. It seems to be that all you have to do is have the part coated. The sand holds the plaster in place while the metal is poured in. It seems to me that the thickness of the plaster is irrelevant other than being thick enough to coat the part. What am I missing?

I think your plaster is too thin.. and perhaps you should have done this with the cast object oriented vertically to reduce trapped gasses...

No casting should froth and bubble and spit AT ALL when poured. Anything that does this much is going to be a casting woefully full of gas and oxide film inclusions to the point of complete unreliability. I would expect this casting to show much porosity and may flaws when machined and to break in service unless extremely lightly loaded. Your green sand is a much better technique as plaster is NOT porous and apart from its own water content it will NOT let out the gases that come from the decomposing foam. The commercial coats used for this process are porous (they are also very thin at around 0.2 mm) and I do not believe that they contain any plaster. An interesting experiment though, but with predictable results... Martin

I think the plaster inhibited the escape of gases.

either of those could be machined, plenty good enough.

i don't think this is how it's supposed to be done. you should use multiple layers of plaster and sand on the mold.

It seems to me sanding off the plaster did nothing but cause issues.. why sand it off? the thickness of the plaster should not even matter..it's going to burn off just the foam and hold its shape better inside a thicker casing of plaster. thinning it out only lets the loose sand give way and intrude into molten aluminum.. ok I have never tried it this way but it just seems logical...

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