I bought a small tin of clear resin and some transparent blue pigment to make some lightbars for some fire & police models ive been working on, but im having some problems with it - it always dries horrible and tacky, which is no good at all.
I had a look at some sites, and found one that said to get rid of the tacky surface rub neat washing up liquid over the tacky areas then rinse with warm water - tried this and it didnt work.
Another said to rub the tacky areas down with fine wet & dry - wet sand paperthis worked, but because of the parts been quite small is fiddley and almost impossible with some parts.
Is there something im doing wwrong that is causing it to dry tacky.
Here's another possible solution. Heat the mold before pouring the resin. A professional caster told me that he did his clear casting on a hotplate. Can't remember the brand of material but he did some nice work.
Is this polyurethane resin or polyester? Different situations.
When I last had problems with polyurethane resin doing this, a few folks on this group suggested I was not premixing it enough. This turned out to be the problem.
With urethane resin, even the resin itself has a tendency to seperate when not used frequently. I found I had to shake/turn over the bottle at least six inversions before I poured the resin out (before, of course, mixing with hardener). This did the trick. Polyester resins have other gotchas.
Possible fix for the parts you've already cast: Bake them in an old toaster oven at the lowest heat setting for an hour or so, then let them cool off. That might force the resin to finish curing. (Do this in a well-ventilated room or garage, and NEVER use that oven for food again!) If the parts are still tacky, and you can be patient, just set them aside; given enough time, the resin may finish curing, but it could take many months.
Check the label. Is it a polyester resin? If so, try using more catalyst. With polyester resins, a small or shallow mold requires a lot more drops of catalyst per ounce of resin than does a large & thick mold. If you don't use enough catalyst, it doesn't get hot enough to cure properly.
Another possibility is that the mold is incompatible with the resin, and prevents it from curing. (I've seen this with polyester resins, but I don't know whether it can happen with urethane resins.) Try using a different mold compound or a different clear resin.
If you used a mold release, it may have been incompatible with the resin. Ideally, the mold compound, mold release, resin, and pigment should all be from the same manufacturer, and advertised by that manufacturer as being compatible with each other.
Finally, it's possible that the mold, mixing cup, or stir stick was contaminated with something that keeps the resin from curing properly. Make sure everything is perfectly clean & dry before you start.
Thanks for all the replies, the actual part does cure solid, its just the surface always stays tacky, i tried with one of them to heat it up with a hair dryer for quite a while, but that made no difference as it still stayed tacky on the surface. Ill try adding more catalyst when i next have a nother try at it.
The resin is polyester, the instructions say upto 4% catalyst can be added, but its quite hard working out the catalyst, since the resin is liquid and the catalyst that came with it is a paste.
I'm not 100% sure, but I think that clear polyester resin is always tacky when it cures in contact with air. Perhaps you can apply a small piece of plastic foil to the surface of the resin while it cures, or alternatively, add another mold part to make a closed mold. Good luck!
This is half-forgotten lore from my long-vanished childhood, but isn't there a waxy additive you can add which migrates to the exposed surface and seals it off, permitting the resin to cure fully?
I've experienced the same problem. IIRC the hardener actually evaporates from the resin right at the surface (on open molds), so the resin will remain tacky.
Like Rob said - try to tightly cover all exposed resin. That might help.
You might also try to carefully brush some hardener onto the tacky areas. That might "kick" the resin over.
If there was a simple answer to this, you would find more than just Meteor doing clear casting for models. Dave guards his "secret" very closely, but since we see relatively few clear parts from him, I suspect he is still swimming upstream with the process. But he is far ahead of the rest of us.
A few years ago I embarked on a rather intense search for a workable clear casting resin. I had the help of a major distributor of casting materials and after trying a dozen or so different brands the end conclusion was that none of them would make satisfactory parts.
The tackiness you have described seems to be a mark of the species. I, nor several other people whose casting expertise I respect have ever solved the problems associated with clear casting as applied to model parts.
The real mystery for me is that the same material would do different things with each pour. Once in a while it would behave and we would get good looking parts, and the next pour was back to the same mess.
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