General materials questions - long and messy post

[Geuse]

Ok, so I've just been thinking about different types of materials and techniques lately and basically just wanted to discuss some ideas.

Basically I want to do 2 things.

1. Build a larger sculpt out of PU foam
and
2. Make a helmet.

I've watched some videos, but I have some questions regarding materials.

For number 1. I've recently been drawn to sculpting in large foam blocks, but before I get started I have some questions. After getting my initial shape I clearly need to seal it and coat it to make it smooth and durable. What are the types of materials you'd recommend? I've tried a polyester putty from Sweden which you mix with a hardener, but I wasn't impressed. It was very hard to sand and the surface was very plastic like obviously so the dust was extremely fine, ugh. I thought to try to put some paper mache on top instead and continue sanding that, but the heat from the glue ended up cracking the polyester putty so I had to throw it all out. Now obviously I might have had the wrong kind of putty, but I thought it was similar to bondo.
Now I would like something along these lines:
https://youtu.be/XeeSsmsm9h0?t=525
Something easyily sandable. So could you effectively use hobby putty for this to get the shape perfect? The strength would be added on a finishing coating like in the previous video.

Moving on to number 2.
I've been messing around in 3D and will go the pepakura route for some helmets. I have been thinking about using cardstock and hardening it on the ouside with epoxamite(brushable resin), then actually casting plaster or shooting expanding foam inside so when I cut off the pepakura form I'll have a crude cast of the helmet I can continue working on. Either cast it in plaster which is easily sandable to a smooth finish and/or easy to carve if you don't let it dry fully or sculpt on top of it with clay or hobby putty? Would that adhere to the surface? To me it just seems easier to sand down to a round finish than to add bondo and sand it and repeat forever as you would traditionally with pepakura.
The expanding foam idea, do you have any comments on that? Cause that would be even easier to sand down than plaster and then I could go about it as in number 1.

Thanks for reading.
Best Regards/ Dag

 

[yaris]

There's a huge difference between 'making one helmet and making a mold to cast from that one helmet'

It sounds like you want to make a mold to make many helmets??......youtube it, there are some awesome build videos, I find videos better than 30 pages of instructions

As for a one of helmet, I've built a few pep helmets and there's no need to internally fill the helmet and I'd stay clear of plaster for anything.

200gsm card stock, fiberglass resin the outside until it's very firm, you can fiberglass the inside or rondo it, then bondo the outside and spend the next 8 years sanding it to shape. there's usually A LOT of sanding involved, but it's all part of the journey.

There's no cheat in Pep work, many folks think it makes the prop building easier, but I reckon it simply makes it more accessible.

Good luck

 

[Geuse]

200gsm card stock, fiberglass resin the outside until it's very firm, you can fiberglass the inside or rondo it, then bondo the outside and spend the next 8 years sanding it to shape. there's usually A LOT of sanding involved, but it's all part of the journey.

There's no cheat in Pep work, many folks think it makes the prop building easier, but I reckon it simply makes it more accessible.

Good luck

Exactly. I just want to skip the part about sanding bondo. I'd rather sand something a lot softer and then hardening it at the end. So preferably skip bondo. To me, making a cast of the helmet in the end wouldn't involve much extra time. time spent bondo would be a lot more, no?

Thanks!

 

[Blaxmyth]

There's no cheat in Pep work, many folks think it makes the prop building easier, but I reckon it simply makes it more accessible.

Well said. :thumbsup

 

[yaris]

Exactly. I just want to skip the part about sanding bondo. I'd rather sand something a lot softer and then hardening it at the end. So preferably skip bondo. To me, making a cast of the helmet in the end wouldn't involve much extra time. time spent bondo would be a lot more, no?

Thanks!

if you're talking about using plaster instead of bondo, I wouldn't recommend it. Sounds like you want to make a nice accurate helmet and then cast it?? That's something I don't do, so I'm sure someone will jump and advise....all I know is that plaster is brittle and I've never had any luck using it compared to bondo, rondo and fglass.

Good luck though

 

[NextGenMaker]

Body filler, like Bondo, should be pretty easy to sand, that is what it is designed to do. Are you starting with a coarse grit and working your way down? What particular body filler are you using? I haven't dived too deep into the foam + bondo combo and the biggest problem I've had when I did was adhesion.

I would be worried that common hardware store plaster will be too delicate to survive the shop, especially if you are making a helmet-sized piece in it. Obviously the serious stuff, like HydroCal and UltraCal, will survive better, but there are lighter alternatives for something this big.

 

[Rogviler]

Wait, isn't "Bondo" what people call body filler? It's obnoxious on those car shows because I KNOW nobody's actually putting that pink crap on their high-end hot rod, but I get that it's sort of like saying "Kleenex" to mean tissue... But if it all means different things to different people then that's even more obnoxious.

Bondo (the pink stuff) is actually more difficult to sand compared to others, although it's nice that it's cheap. The best sanding stuff that's not too expensive is Evercoat Rage Ultra, and 3M Platinum Plus is about the same, so whichever you can find.

But, there's a good thread out there where the guy makes a Fallout helmet master using acrylic gel medium and gauze for non-toxic purposes. He makes a mold off of that quite successfully. I know I'd be skipping the toxic fillers and sanding dust if I didn't have to use it.

-Rog

 

[rbeach84]

Seems like making a master from clay then taking a mold cast off of it is the way to go... might require an extra iteration of master work using a fiberglass cast to get the proper detailing, etc. but not knowing what specific subject you're going for makes further comment just guessing...

RE: expanding foam, it is tricky to control and depending on the formulation you're using, can continue to cure for quite a while... best for interior reinforcement that will never be seen again, IMO.

R/ Robert

 

[Geuse]

All right Guys, thanks for the great input. Hm, maybe I actually got a whole different kind of filler then =/ Not exacly sure what to look for here in Sweden.
I've been thinking about the stuff people use to build their RC airplanes, but it may be too brittle. Still it's only for smoothing the surface.

Then I saw this video where he's using polyester filler and by the looks of it it's extremely easy to sand. After the sanding he coats it with a pattern coat primer for finishing touches.
https://youtu.be/XeeSsmsm9h0?t=526

The products I can get nearby are the following. Wich one would you think is the one I shoul get?

Epoxy putty - http://www.biltema.se/sv/Bat/Kemikalier/Polyester-och-Epoxi/Epoxispackel-2000032989/

Polyester - http://www.biltema.se/sv/Bat/Kemikalier/Polyester-och-Epoxi/Polyester-2000017196/
Which by the looks of it seems to only be a resin for fiberglass so no putty.

Plastic spackle - http://images.biltema.com/PAXToImageService.svc/article/xlarge/36057
This is what I thought was equivalent to bondo, but obviously not what I'm looking for either.

Then I just found this brand that I should be able to get here i Sweden, do you think any of their products would work?
http://www.onefill.se/our-offer/

Thanks guys!

 

[basementdweller]

Hej Dag

Thought I'd chip in with what I am familiar with. I'm in Sweden btw, so I thought that might help Firstly though I am not sure I understand if you want to make a helmet that's supposed to be a prop or if you want to make a mold/pattern for a helmet or an actual protective helmet that will help keep your brain in your head. If it's the last case you should skip my post entirely.

It's been a while since I worked with PU-foam as the stuff is quite expensive for hobby projects. You might consider switching to insulation foam - specifically extruded polystyrene instead. Can be cut with a bread knife and you can basically glue it with PVA even if gorilla glue is better. Downside is a rougher surface. You can get pretty far with it though and it's very quick to sand.

Either way - You need a filler that doesn't shrink too much and has some working time. Personally I do smaller scale stuff, but used to do product models in PU foam. I use milliput (standard), a two part epoxy that you knead together and can even turn it into a paste with water, for gap filling and sculpting. It's inexpensive for small scale stuff, but if you need to cover larger scale stuff I'd say "Plast spackel" from Biltema should do the job. If you don't need to cover any gaps, but simply want to even out a surface and close up all the pores you can not go wrong with spray filler. Actually you need spray filler either way. Jula has it under the corny name sprejspackel. I haven't tried hagmans before, but it should do. Two layers with sanding was a minimum for any PU-models we did. Basically it's surface filling primer. Since both PU and XPS are relatively soft you should go with very fine grit wet sanding paper from the getgo when you have applied the spray filler. You can get a very fine surface that way - it's all down to your sanding/spray filling patience.

When I make models in XPS foam I just use a couple of coats of watered down PVA. It makes a hard shell and protects the foam so I can spray paint it without it dissolving. That might work for you as well depending on what the model is intended for. Also, don't forget Future floor polish It's sold as Pledge golv polish/vax here. A couple of coats of that also gives it a bit of a harder protective surface. And it's cheap. This would definitely work as master to make molds on.

If you want to try out XPS foam Byggmax has that stuff in single sheets and it's light green/cyan in colour.

Hope this helps.

PS. I haven't tried hagmans on XPS, try it on a small piece first in case the solvent eats the foam - then you need to go the pva route (first at least).

 

[Geuse]

Hej Dag
"LONG POST"

Hej!
Thanks for the post!
Yes, my goal wasn't exactly clear. Basically I just want to find a method for creating sculptures using peakura as a base. The sculptures are then to be molded and at last casts can be made. I'm going to use this for both helmets and other props such as a set of hulk fists I'm going to cast in soft foam for my nephew so it won't hurt as much as it does now when he hits me.

I actually tried plastspackel, but wasn't impressed at all. It's not supposed to be sanded? It leaves an insanely fine powder that's hell to clean up. Also it crumbled apart when under heat. Don't want to risk that when making a mold of it, in case I'd use some material that transmits heat when hardening.
Never heard of sprayspackel. seems great. Gotta get me some of those =)

I have aquired two blocks of a nice densed blue foam. Not sure if it is XPS or PU though. I was planning on picking up some insulation foam at one of the hardware stores here, but first I need to build a hot wire cutter But sculpting in foam is very interesting.

I also have some foam glue already, guess it's PVA then. But don't I need to spray on a protective coat or something before adding the spackel and sanding in order to cover the pores and protect it? Or could I just go ahead spraying the spackel on top of my sculptured PU block. Sprayspackel seems ingenious, so I don't really "need" body filler then?
I have apoxie sculpt which I assume is comparable to milliput?

When sanding foam with wet sanding paper, I shouldn't have it wet?

Thanks a ton

 

[basementdweller]

Sorry for the insanely long posts

Spoiler

a set of hulk fists I'm going to cast in soft foam for my nephew so it won't hurt as much as it does now when he hits me.

Had to lol.

I actually tried plastspackel, but wasn't impressed at all. It's not supposed to be sanded? It leaves an insanely fine powder that's hell to clean up.

I don't know if you mean it leaves a powdery surface or you geta large amount of dust when you are done. If it's the latter - it's doing what it should You can't get a fine surface without a lot of dust/powder after sanding - that's why you should wetsand (with wet sandpaper) and use a dustmask always when sanding.

I have aquired two blocks of a nice densed blue foam. Not sure if it is XPS or PU though. I was planning on picking up some insulation foam at one of the hardware stores here, but first I need to build a hot wire cutter

You don't need a hotwire cutter to do stuff in XPS foam. Cut it with a knife, start with a rough sandpaper and finish with a fine. You will make a mess with a lot of static tiny pieces, but that's just part of the process Here is an example of bridge made in XPS. You can see the raw material on the ends. Cut with a knife, glued with PVA, textured with a pen and coated with watered down PVA. It was an experiment to see just how well defined you could make XPS alone.

PU-foam (at least the kind related to this instance) is hard and rigid and is short for polyurethane foam. It's commonly used for mockup models in industrial design and comes in blocks. If this is what you are using You need powertools to do any sculpting in it - a lathe, dremel etc. You can also buy it in liquid form and cast it to make lightweight solid objects. It expands 3-4 times depending on the exact specifications of what you buy (density). a trick is to slush a normal resin to coat the inside of the mold and then fill up the bulk with PU-foam so you get a fine detailed surface with a solid rigid foam body. Here is a video example of the process:

I also have some foam glue already, guess it's PVA then. But don't I need to spray on a protective coat or something before adding the spackel and sanding in order to cover the pores and protect it? Or could I just go ahead spraying the spackel on top of my sculptured PU block. Sprayspackel seems ingenious, so I don't really "need" body filler then?
I have apoxie sculpt which I assume is comparable to milliput?

XPS is probably what you have. Most solvents will eat it so try to test spray on a small piece to see what happens. Like I said - a good trick is to cover it with watered down PVA glue (TRÄLIM). Paint it on with a brush or put it in one of those flower spray bottles and spray it on. Gorilla glue can be bought in Sweden as well - funnily enough gorilla glue is basically expanding PU foam (And only used in this instance to sandwich large surfaces together). Spray spackel is like I said - a primer with filling properties. What it means is you get your surface as close to what you need before you apply it. Then you use sprayspackel to close up all the pores and even out the roughness. So it's for smoothing a surface. You still need a type of filler to even out gaps or sculpt any fine details. Apoxie should do fine If you check on biltemas different spackel you will see that there is one that is heat resistent otherwise.

When sanding foam with wet sanding paper, I shouldn't have it wet?

When sanding raw XPS - in short - no. When sanding on top of sprayspackel or spackel yes. Primary reason is to minimse the fine powder getting airborne. It also doubles as a way of making the sprayspackel into a watery paste that helps fill in pores. You don't sand until it's dried though or you will just undo your work.

 

[cavx]

If I may share.

One of my favorite (because I am getting positive results) materials to coat things with right now is epoxy (AKA Liquid Glass). This is a 2 part resin that is intended for casting, but seems to work really well as brush on coat and sealer as well. You may have seen some of the guys using this for their 3D printed parts when they want to smooth the surface without having to sand. I generally cast in this stuff, but found it is awesome way to seal the end grain of MDF and it will seal paper.

When I do use it it seal, I use a small brush and wash the brush out later in acetone so I can re-use it. When coating, only mix really small amounts. The product I have is mixed at 100:50, so I will mix 10g to 5g to make just enough to coat a part and not have wastage. It has a very long pot life (over 30 minutes) but the stuff takes about 3 hours to cure (temp pending) and when applied with a brush, may take up to 12 hours to cure because the layer is so thin. Note that once it kicks, it will get hot, like 110 degrees C hot.

If you are going to use this stuff for paper (and it does work to make the paper into a plastic) like a PEP, you need to go lightly and repeat. The only issue is that sometimes you do get drips that form on the ends. These can be sanded off, but it would be nice if you had the glass smooth finish all over.

 

[Geuse]

a set of hulk fists I'm going to cast in soft foam for my nephew so it won't hurt as much as it does now when he hits me.

Had to lol.

To his defense, he has a mild autism and/or aspberger so he's a bit different, but he loves to play and be hulk or ben10 and as any good uncle would I'm doing my part =)

Sorry for the insanely long posts.

Not at all. Great! but quoting your whole post just seemed so excessive =)

I don't know if you mean it leaves a powdery surface or you geta large amount of dust when you are done. If it's the latter - it's doing what it should You can't get a fine surface without a lot of dust/powder after sanding - that's why you should wetsand (with wet sandpaper) and use a dustmask always when sanding.

Yes, but I just thought it was too fine and hard to sand. Body filler doesn't seem to have the same characteristics, or does it?

You don't need a hotwire cutter to do stuff in XPS foam. Cut it with a knife, start with a rough sandpaper and finish with a fine. You will make a mess with a lot of static tiny pieces, but that's just part of the process Here is an example of bridge made in XPS. You can see the raw material on the ends. Cut with a knife, glued with PVA, textured with a pen and coated with watered down PVA. It was an experiment to see just how well defined you could make XPS alone.
View attachment 623482

Looks great. Did you glue several blocks together to form a bend and then carved it smooth? Much like you would a wooden arc.

PU-foam (at least the kind related to this instance) is hard and rigid and is short for polyurethane foam. It's commonly used for mockup models in industrial design and comes in blocks. If this is what you are using You need powertools to do any sculpting in it - a lathe, dremel etc. You can also buy it in liquid form and cast it to make lightweight solid objects. It expands 3-4 times depending on the exact specifications of what you buy (density). a trick is to slush a normal resin to coat the inside of the mold and then fill up the bulk with PU-foam so you get a fine detailed surface with a solid rigid foam body. Here is a video example of the process:
https://www.youtube.com/watch?v=t9_CuA63zK4

Ok, hm...
Most videos I've seen of people carving in foam, they usually use a hot wire cutter to start with, but for PU-foam, you really need this?:
So then what's the benefit of using XPS versus PU?

XPS is probably what you have. Most solvents will eat it so try to test spray on a small piece to see what happens. Like I said - a good trick is to cover it with watered down PVA glue (TRÄLIM). Paint it on with a brush or put it in one of those flower spray bottles and spray it on.

Yes, I think so too. But I actually tried to blend in water with wood glue before. Maybe I didn't stir long enough as it never blended as desired. Could be old glue as well =/, but it is actually supposed to be very fluid?

When sanding raw XPS - in short - no. When sanding on top of sprayspackel or spackel yes. Primary reason is to minimize the fine powder getting airborne. It also doubles as a way of making the sprayspackel into a watery paste that helps fill in pores. You don't sand until it's dried though or you will just undo your work.
[/SPOILER]

All right, great. Thanks!

 

[basementdweller]

The bridge is just 3 pieces. 2 sides for the railings and one piece for the main arch. It's just a small model. I just cut it with a knife and sanded it - that's all there is to it.

XPS - is much cheaper and way easier to work with and you can build much bigger stuff that does not weigh much. PU-blocks are much more dense and suited for milling and machining so you can get very accurate models - it's a different material for a different purpose imho. Pouring PU-foam into a mold like the video is what you do when you have a mold and want a solid lightweight finished product.

About the hot cutter... It is handy for freeform sculpting mountains or if you have a bed cutter - it's popular with RC plane builders to do wing profiles from templates. It's not needed nor very helpful in this instance I think - Be aware that the fumes from melted PS are not healthy at all. XPS is extruded polystyrene. There is EPS (I think) that is the common stuff here (Frigolit/cellplast)) which is expanded polystyrene. It's much less dense with large cells.

My suggestion to you is to go as far as you can with XPS. If it's easier to get the desired shape by gluing together several parts, do that. After that you have to experiment a bit to see what is best with a surface treatment. Your problems with plastspackel might actually be the chemicals eating away at the XPS. You will still need some sort of putty (like plastspackel or aves) to cover the surface both to even it out and in prep for the molding steps to take the heat. I don't think PVA will work as a sufficiant barrier for the molding process alone, but it will be a perfectly good barrier for solvent based stuff that go on top. I can not give you a sufficient answer for this as I have not gone further than having the "sculpt" be the end product.

As for water and PVA - Trälim sets by moisture evaporating so the water you add is only to make it easier to apply. I always do at least two layers to make sure. As an aside -

Spoiler

A long time ago I made a base before I was aware of this melting phenomenon and I got a cool effect out of it. The top layer was intact becaue it had a layer of PVA to glue the sand to it. Lucky accidents? I loved the resulting look of treeroots/branching - before it was like a big stone slab. Shhh Don't tell anyone. If you are curious about scale - it's in 28mm scale (roughly 1/55).

Cavx mentioned using epoxy, but 110 degress C is close to where PS at least gets soft, so you might get warpage if the piece is thin? I think it seems like a really good method though.

Here is an article I found on material selection by Volpin props http://www.tested.com/art/makers/453462-volpin-project-part-3-selecting-materials/
Seems to cover everything and even urethane foam.

 

[Geuse]

Ok, Thanks again.
Great and cool looking sculpture, You did the horse as well?

 

[Geuse]

The tips on foam are highly appreciated and valuable. I now have a much better understanding of the different foams, techniques and the different types of materials to use with them.
And I just had another idea on the sculpting process. This is both aimed toward pepakura and foam sculpting alike. How about using clay for sculpting and smoothing it out instead of polyester filler(polyesterspackel)?
Sure it will not be durable, but that's not my intention either. I'll coat the pepakura in epoxy resin to make it sturdy, then cover it up with soft clay and wait for it to cool down before going in and shaping it down. Then all is left is to mold it.

 

[basementdweller]

Actually clay is a great way to go if you are going to make molds. You might need to stiffen up your paper model before applying clay though? Not sure. I am using clay myself for a different kind of project where I am sculpting flat textures to make molds of. You have to make sure you use clay that is sulphur free if you are going to make the molds in silicone. Otherwise it won't cure properly. I did a bit of research and ended up buying an oil based clay that is hard when cold, but soft when heated and can even be melted and poured. It's called chavant and comes in different "hardness" grades. You can reuse it when you are done! Best price I could find here in Sweden is
http://www.kinn.com/category.html/lera-2
Another alternative would perhaps be WED clay? It's waterbased and if you keep it moist and covered up while working it will not dry and it too can be reused for some time. I have no experience with that though.

Oh the pegasus was a metal mini from Games Workshop and was painted up as a gift. I only did the base.

Looking forward to seeing your project here when you get it going.

 

[Geuse]

Thanks again.
Yes, I heard using oil based and sulphur free clay was important, but didn't know exactly why. I got myself a box of monster clay I'll be using. Been playing around with it and I can say I really like it =)

Ok cool. Great job nonetheless ;-)
Got the right Hulk fist done yesterday. Gonna do the other soon, then I'll be sure to show my progress.