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I used some milliput a couple days ago and its still fairly soft. Is there a way to harden it?

Assuming you mixed the two parts together roughly 50/50, it should be pretty hard by this point.

I just tried some of the stuff myself. Not unsurprisingly it seems to dry faster when it's thinner or has more surface area. I had some big globs that I made into slab shields for my old ogryns, took them almost a full week to harden. I kept having to pull them up from the plate to keep them from sticking.

I'm a bit confused by this, in my experience standard milliput becomes unworkable after maybe an hour or two, and is rock hard within 6-12 hours.

Greenstuff takes a bit longer to harden up, and remains somewhat flexible when cured. Unlike milliput which is rock hard and brittle.

A mix of the two is a good happy medium to be honest.

...under what conditions have you got it not setting? you did mix both parts in a 50-50 ratio? what is the temperature like?
Does any one know what might slow down the chemical reaction that is the hardening?

I think there are different kinds of milliput, which might account for the differences.

Also how old is the box?

Box is brand new. It's "superfine white" Milliput, and I did a 50/50 ratio, or as close as I could. Standard room temperature, a little dry. I've considered taking a hair dryer to it to see if that helps it harden up

If it's not mixed properly you can tell as parts of it will be harder than other parts.

The reaction is quite temperature dependant. I've had some in a room at about 20degC take overnight to cure (at 25degC it's taken 2 hours to be mostly solid), but I've not had to wait longer than that.

Putting it somewhere warmer will speed up the reaction. The warmer it is, the faster it'll cure.

 Dr H wrote:
If it's not mixed properly you can tell as parts of it will be harder than other parts.

The reaction is quite temperature dependant. I've had some in a room at about 20degC take overnight to cure (at 25degC it's taken 2 hours to be mostly solid), but I've not had to wait longer than that.

Putting it somewhere warmer will speed up the reaction. The warmer it is, the faster it'll cure.

That makes sense, my roommates keep the place frigid.

 TheSilo wrote:
I just tried some of the stuff myself. Not unsurprisingly it seems to dry faster when it's thinner or has more surface area.

Actually that doesn't make sense to me at all, isn't milliput an epoxy putty? Every epoxy putty or gel I've used cures as fast or faster when you have a large bulk of it (potentially faster if the reaction is exothermic enough to raise the temperature of the bulk). Are you mixing a bunch of water in to it as well?

I've used water on my tools and hands when working it. Would that keep it from curing?

HairySticks wrote:I'm a bit confused by this, in my experience standard milliput becomes unworkable after maybe an hour or two, and is rock hard within 6-12 hours.

Yeah, that.

jreilly89 wrote:Box is brand new. It's "superfine white" Milliput

I think that throws a little light on the situation. As both parts are white, you don't have the convenience of, say, the blue + yellow = green of green stuff to let you know the putty is fully mixed. (IIRC that's why green stuff is blue and yellow) You need to really mix it for a good long while to make sure the resin and hardener are properly... mixed. Heck, people had a similar insufficient mixing problem with procreate, even though there's a greater difference in colour between it's white and dark grey parts.

If you do that and there's still a problem, well, square one.

jreilly89 wrote:I've used water on my tools and hands when working it. Would that keep it from curing?

Nope. It's very slightly water-soluble, which helps with smoothing and feathering (even creating a slurry for painting over and filling pitted surfaces), but Milliput 'sets underwater'. As Allseeingskink hinted, the curing process is a chemical reaction between the resin and hardener - little to do with water. So saying that epoxy putty 'dries' is good-'nuff shorthand, but inaccurate and in cases like this, somewhat confusing.

heat will speed it up. So a cold room will slow the reaction.

but I have no idea why after so long its still soft, that doesn't sound right at all. You said you mixed it, there is nothing else to it. It reacts and hardens.

Even with a large blob you shouldn't be looking at the 'days' timescale.

Always a chance that there's something wrong with the product. If not, then my guess would be that it wasn't mixed well enough. You could always roll a fresh ball, give it a good few minute mixing, and see if it cures faster.

I agree that thicker resin sections usually cure faster due to exothermic reaction - if you can actually feel them warming up. Depends on the resin, though. I did a wedge-shaped cast with PU resin, thickest end being around 3", and it reached maybe 50-60'C when curing. Funny enough, the 1" thin end of the wedge stayed soft (= didn't warm much over room temp) where the 3" end heated up and solidified quickly - apparently (PU) resin doesn't transfer heat very well.

Well, I took your guys' advice. The dryer didn't seem to have much effect other than heating up the model, so I pulled off all the old putty, remixed some new putty as close to 50% as I could, mixed the hell out of it. I then reapplied it and smoothed it out to my liking. I will check it later today and hopefully it will have begun to set up.

 jreilly89 wrote:
Well, I took your guys' advice. The dryer didn't seem to have much effect other than heating up the model, so I pulled off all the old putty, remixed some new putty as close to 50% as I could, mixed the hell out of it. I then reapplied it and smoothed it out to my liking. I will check it later today and hopefully it will have begun to set up.

If thats still no joy I'd really consider that the product is faulty in some way ; Ive never had super fine milli... both parts white? Could be as simple as a packing error and you got two part a's. How could they tell if they did?

HairySticks wrote:

If thats still no joy I'd really consider that the product is faulty in some way ; Ive never had super fine milli... both parts white? Could be as simple as a packing error and you got two part a's. How could they tell if they did?

One part is noticeably more 'crumbly' or 'powdery' than the other, and they're each wrapped in different-coloured bags (clear and blue). I assume the bars are extruded and wrapped before getting anywhere near each other, but, that is just an assumption.

But yeah. Hope it works for you this time, Jreilly, but if it doesn't, I agree that it's probably just one to chalk up.

 Vermis wrote:

HairySticks wrote:

If thats still no joy I'd really consider that the product is faulty in some way ; Ive never had super fine milli... both parts white? Could be as simple as a packing error and you got two part a's. How could they tell if they did?

One part is noticeably more 'crumbly' or 'powdery' than the other, and they're each wrapped in different-coloured bags (clear and blue). I assume the bars are extruded and wrapped before getting anywhere near each other, but, that is just an assumption.

But yeah. Hope it works for you this time, Jreilly, but if it doesn't, I agree that it's probably just one to chalk up.

Agreed. If it doesn't work, meh, it was only $8. I'll probably try the yellow next time just to see if it differs. And yeah, it was two seperate color bags, but almost identical bars. One did have a different texture though

 Vermis wrote:

jreilly89 wrote:I've used water on my tools and hands when working it. Would that keep it from curing?

Nope. It's very slightly water-soluble, which helps with smoothing and feathering (even creating a slurry for painting over and filling pitted surfaces), but Milliput 'sets underwater'. As Allseeingskink hinted, the curing process is a chemical reaction between the resin and hardener - little to do with water. So saying that epoxy putty 'dries' is good-'nuff shorthand, but inaccurate and in cases like this, somewhat confusing.

I mostly meant if a large amount of water was mixed in to it rather than just using wet tools. Sometimes people mix in water intentionally to soften it in to a paste for gap filling and smoothing, I imagine that could interrupt the curing process. Even plumbers epoxy which is specifically designed to cure underwater they'll usually tell you to mix it outside the water first.

Ah, it wasn't a swipe against you, Skinky. I know about the slurry/paste technique, but when I tried it myself with a small amount of yellow-grey milliput, it was fairly difficult to mash into a uniformly smooth 'mud'. The stuff tended to tear and fracture, and slide and squeeze about rather than mix evenly, thanks to the usual slip on the surface of the putty. (Almost like trying to squeeze together three or four freshly dug-out melon seeds between thumb and forefinger) I think it'd be difficult to introduce a significantly cure-altering amount of water into milliput, unintentionally, without losing control during mixing or sculpting.

But, I admit I don't know for sure. It's something I'll have to try again.

By the way, with green stuff, if you mix more yellow than the suggested ratio, it takes longer to dry. If you mix more blue, it dries quicker.

So after remixing it, its pretty hard. Its a little soft if I really squeeze it, but I think mixing the hell out of it is the trick.

 jreilly89 wrote:
So after remixing it, its pretty hard. Its a little soft if I really squeeze it, but I think mixing the hell out of it is the trick.

I keep it simple -- I simply knead it until it is only 1 color.

Talys wrote:

 jreilly89 wrote:
So after remixing it, its pretty hard. Its a little soft if I really squeeze it, but I think mixing the hell out of it is the trick.

I keep it simple -- I simply knead it until it is only 1 color.

Yeah, that don't work when they're both white

Sorry Talys.

Glad it worked out better, Jreilly. I think it should get harder - Milliput SFW is one of the most ridiculously hard things I've seen. (I found that out when I tried breaking some up for basing rubble.) If there isn't something faulty with the putty itself, a handy incandescent desklamp or toaster oven can help things along a bit.

 Vermis wrote:
Sorry Talys.

Glad it worked out better, Jreilly. I think it should get harder - Milliput SFW is one of the most ridiculously hard things I've seen. (I found that out when I tried breaking some up for basing rubble.) If there isn't something faulty with the putty itself, a handy incandescent desklamp or toaster oven can help things along a bit.

Yep, it definitely seems to be hardening up nice. I'm hoping by tomorrow it will be good to sand. I have the general shape I want, but I want to smooth out some of the roughness. Also, do you have a size you recommend for sanding, fine or coarse?

 Vermis wrote:
Ah, it wasn't a swipe against you, Skinky.

I didn't take it as a swipe, was just clarifying what I meant, which was if you'd mixed a large amount of water in to it vs just using wet tools or even curing it under water then it might have issues.

As has been sort of hinted at, with two different tangents never quite intersecting the actual issue:

Mixing.

They asked if you were sure you mixed 50/50.

And they said "It can be difficult to tell if it is 50/50 given that both parts are white."

But what wasn't said is that because it is white, you don't know if you have properly mixed it completely or not.

The last several contracts I had for work involved creating masters that were huge chunks of epoxy resin that were worked into various forms (usually classical sculptures in relief).

But I once had the same problem with the superfine Milliput, with it not hardening, and parts of it being crumbly, and other parts hard.

When we stuck the piece under a spectroscope, it turned out that the epoxy had not been properly mixed.

Generally, I spend two to three times as long mixing the superfine Milliput than I do the regular, simply to make certain it is completely mixed.

MB

BeAfraid wrote:
As has been sort of hinted at, with two different tangents never quite intersecting the actual issue:

Mixing.

They asked if you were sure you mixed 50/50.

And they said "It can be difficult to tell if it is 50/50 given that both parts are white."

But what wasn't said is that because it is white, you don't know if you have properly mixed it completely or not.

The last several contracts I had for work involved creating masters that were huge chunks of epoxy resin that were worked into various forms (usually classical sculptures in relief).

But I once had the same problem with the superfine Milliput, with it not hardening, and parts of it being crumbly, and other parts hard.

When we stuck the piece under a spectroscope, it turned out that the epoxy had not been properly mixed.

Generally, I spend two to three times as long mixing the superfine Milliput than I do the regular, simply to make certain it is completely mixed.

MB

That makes a lot of sense. Thanks for the tip!