Working with resin 101

[Aaronw]

Because of the greater variety of subjects available, many people will eventually end up buying some resin parts or kits. Resin is a bit of a mystery for some, but luckily it really isn't all that different from working with styrene.

Resin is a plastic like substance, and well cast resin parts may be hard to tell apart from plastic. Resin starts out as two different chemicals, and when combined they solidfy. It is very similar to a two part epoxy which you may have used (JB Weld, 5 minute epoxy etc). When in the liquid state resin can be poured into a silicone mold to form a part. Resin is used by aftermarket suppliers because it is relatively cheap to work with compared to styrene plastic which requires very expensive machines (hundreds of dollars vs millions of dollars to get started).

There are a couple of different ways you can buy finished resin.

Parts - resin may be used to make custom parts like wheels, motors, a modified hood etc. This is the easiest and least expensive way to see what resin is all about, because you are just adding something or swapping the resin parts for kit parts.

Body - This will require a plastic model to finish, often a very specific kit. This is usually done to provide a slightly differant body style from that offered in a kit, like going from a hardtop to a convertable, or from a stock body to a custom body. This could also be considered as the simplest form of a transkit.

Transkit - This is a more than a body shell, and generally involves a more complex modification. It also requires a plastic kit to finish, but usually will include far more than just a body. A new interior tub, seats and other parts are usually included. When you are done you will probably have a lot of the plastic parts left over (great way to start a parts box if you don't already have one).

Common transkits are changing from a 2 door body style to a 4 door, or station wagon, also a different year or make of vehicle (Chevrolet to Pontiac for example). As the plastic kit frequently is just used for the Chassis and running gear there will often be much more flexibility in the selection of a kit used to complete a transkit.

Full kit - This is a complete kit, it includes everything you need to build it, just like a plastic kit (although decals may still be needed). Full kits may not technically be complete, as some resin casters will sell wheels or other parts seperately allowing the customer to do a little personalization of the kit without adding redundant parts.

OK, on to techniques for working with resin. I put together a little walk through of how I build a resin kit, there are many options, this is just how I do it. Plastic and resin share most techniques, but there are a few differences.

#1 is glue, you will need to use a CA glue (super glue) or an epoxy. Regular plastic model glue will not have any effect on resin and can not be used to attach resin parts, luckily CA glue and most epoxies do work on plastic.

#2 is paint, resin often has an oily mold release left over from the casting process. Even if the resin caster does not use a mold release, unprepared resin will frequently repel paint, so resin needs some additional preparation be fore it is ready for paint. On the plus side "hot" automotive paints that can damage plastic will not usually hurt resin.

#3 resin is much more brittle than plastic. You can often trim plastic very closely with a sharp knife. When working with resin it is better to use a razor saw for removing large bits and a sanding stick for the final shaping. Cutting resin with a knife or sprue cutters may cause resin to shatter. When you are sanding a part check your progress frequenly, it is very easy to sand right into the part.

#4 resin dust is not toxic but it is an irritant, so it is best to do major sanding outside and a dust mask is recommended. If you can't sand outside, sanding over a box will at least make it easier to catch the dust for later disposal.

Other than these issues, there is not much difference between working with resin and plastic.

Recommended tools and materials

A plastic container large enough to hold your resin parts and enough liquid to submerge them.

Westley's Blech Wite, this is a tire cleaner you can find at most auto parts stores. This is my choice for prepping resin parts, but there are others.

TSP, and rubbing alchohol are other popular cleaning solutions.

Sanding sticks, sand paper, razor saw, epoxy and / or CA glue, model putty, paint.

I'll be going though step by step with a 1950 Jeep pickup from RMR.

Step 1

Seperate the parts, clean up flash. Thin flash may be trimmed away with a sharp knife, thicker flash should be sanded.

Step 2

Place parts into cleaning solution. Most of these solutions are very harsh on bare skin, so gloves are highly recommended. I prefer a container with a liquid proof lid to help avoid spills. Times very, I usually leave the parts overnight but if I am in a hurry a couple hours usually seems to be long enough.

Step 3

Rinse parts with warm water. I like to use a clean container filled with warm water to rinse the smaller parts as it makes losing parts down the drain less likely. A soft stiff brush like a toothbrush also helps clean the surface. I give the parts a final wash in warm soapy water, then rinse and let the parts dry. You can check the surface with masking tape, if tape sticks paint should as well, if the tape won't stick to an area you might want to go back and clean it some more.

Step 4

Hunt down and fill any bubbles or other imperfections. When I can I prefer to open bubbles from the inside and fill them with putty. This usually leaves the surface clean and unblemished which means less work for me.

Step 5

Do any additional sanding or filling. I find emery boards work well on resin.

Step 6

Based on your preferences, you may choose to do some assembly before painting. With this particular kit, I chose to prime before doing any assembly.

Prime your parts, any primer should work, but I personally have found Krylon and Plasticote seem to work better on resin than other brands I've tried. All resin is not the same though so a primer that works well with one brand may not work as well on another. I start with a light mist coat, then add another coat every 5 to 10 minutes until I have a solid coat of primer. Once the parts have been primed, there is little difference between working with plastic and resin except for the glue you are. Just like when working with plastic if you have painted the parts prior to assembly you should scrape the paint away from areas you will be gluing together.

From this point on there is little difference from building a plastic kit, so I don't have any more to say. Now go find an interesting piece of resin to work with and good luck.

Edited April 19, 2010 by Aaronw

[caine440]

Good stuff.

I have found resin parts and bodies have added a lot of options I never had back when I was younger.

A very good guide for the first time user.

Thanks!

[lanesteele240]

thanks. i have always been a scared of resin kits. now i might try one. well after i am done with the other kits stacked up in my work room.

[Abell82]

Umm...resin dust is VERY toxic, too my knowledge.

[Aaronw]

Umm...resin dust is VERY toxic, too my knowledge.

Not from anything I could find, it isn't good to breathe the stuff (as with most dusts), but it isn't particularly bad for you. There are a lot of unfounded rumors out there about resin though, so I'm not surprised by your comment.

This is a safety policy from from MIT's Plasma Science and Fusion Center, it was the first document addressing the issue that came up in a search and MIT is probably a more relaiable source than Wikipedia.

"Dust released from the sanding and machining of completely cured epoxy products is generally considered to be a nuisance dust."

If you want to read it for yourself it is at the bottom of the hazard assessment section.

http://psfcwww2.psfc.mit.edu/esh/epoxy.html

From a Wikipedia article on polyurethane (the resin used in casting is polyurethane resin).

Fully reacted polyurethane polymer, CAS # 9009-54-5 (CAS registry number), is chemically inert.[22] Foams In the United States, no exposure limits have been established by OSHA (Occupational Safety and Health Administration) or ACGIH (American Conference of Governmental Industrial Hygienists). It is not regulated by OSHA for carcinogenicity. Polyurethane polymer is a combustible solid and will ignite if exposed to an open flame for a sufficient period of time. It begins breakdown at approximately 240 °C (464 °F), a temperature which can be reached if the material is cut with a power saw rather than a shearing-type tool.[23] Decomposition product can include isocyanates, carbon monoxide, oxides of nitrogen, and hydrogen cyanide. Firefighters should wear self-contained breathing apparatus in enclosed areas. Polyurethane polymer dust can cause irritation to the eyes and lungs. Proper hygiene controls and personal protective equipment (PPE), such as gloves, dust masks, respirators, mechanical ventilation, and protective clothing and eye wear should be used.

http://en.wikipedia.org/wiki/Polyurethane

Edited April 20, 2010 by Aaronw

[Harry P.]

Aaron, nice job! That took a lot of work, but that kind of work and dedication and effort is what makes this place so great!

[sweptline64]

thank you for your article i've always been afraid to do resin cause i thought it would be to hard but now i'm going to be doing it. because i've looked at resin suppliers before and seen things i really liked but was too afraid but now that's changed. thank you keep up the good work.

[camaroman]

Thanks Aaron!

[sjordan2]

Thanks very much for a clearly described and well-illustrated tutorial. I haven't worked with resin, but I now I have important information in my reservoir. It was particularly good to see your comparisons between plastic and resin. This is the way a tutorial should be.

[Aaronw]

Your welcome, I hope it gets a few more people to try using resin parts with their kits.

Nice tutorial. very informative. Kind of thing I'd like to see more of here.

One thing though, I'd be careful using alcohol to clean resin and would never let parts soak in it. It can make resin soft and rubbery. I ruined a couple wheels doing that.

Probably a good thing to know. I use Westley's but mentioned the rubbing alcohol because I've seen it mentioned as an alternative, I haven't used it myself.

[weasel]

the only thing i've found different 'tween plastic and resin, resin is a little more brittle than plastic, cracks easy, ya just can't 'widdle' like ya can with plastic, other than that, resin acts like soft plastic, ya don't need to sand a lot or you sand away detail...

my 2pennies...

[Karmodeler2]

the only thing i've found different 'tween plastic and resin, resin is a little more brittle than plastic, cracks easy, ya just can't 'widdle' like ya can with plastic, other than that, resin acts like soft plastic, ya don't need to sand a lot or you sand away detail...

my 2pennies...

Try Task 9 from Smooth-On. It has a 7000 lb tensile strength and you can tap and die it. I can throw bodies on the floor, and they won't crack. Great stuff. I don't know why the other casters don't use it because it's the same price as the white/yellow stuff. (321)

The only draw back is it's translucent, and to see the detail, you have to put a coat of primer on it, but you were going to do that anyway before you painted it.

David

[weasel]

i'm not casting, just cuttin'!!! lol

[1930fordpickup]

This is a very good read. Well done and I like the truck also.

[Art Anderson]

That Jeep pickup is a recast of the one I did back in 1998. As for resin dust, no--it's not toxic--polyurethane resin is so stable, the scraps of the stuff I sent to the landfill over the years will be their hundreds, if not thousands of years downroad.

As for resin dust itselt--easily overcome by wet-sanding, that can get washed down the drain pretty easily.

Art

[Bartster]

I'm so glad this got brought back up. It's good to have all this information in one post. It might be good to pin this.

[Art Anderson]

The whole business about "dangers" from polyurethane resin "dust" comes from what is/was one of the biggest industrial uses of the material, that being in the low-medium-priced furniture industry.

Furniture manufacturers, when making reproductions of styles common in the 19th Century (think "American Country" oak furniture, which was highly popular particularly in the Midwest (the styles having carved "applique" decorations glued to solid (or veneered) oak bedsteads, dressers and commodes, would carve a master for a particular appliqued decoration, then make RTV molds off of those, use them for resin castings, which had to be faced off on their back sides to a flat surface for gluing to the oak background. That meant a lot of dust in the air, and for sure, that sort of dust is very irritating to breathing passages, due to its being tiny, sharp particles (incidently, the same cautionary statements appear in OSHA regulations regarding the sanding of most hardwoods as well in industrial settings!). However, fully cured, hardened urethane resin is not particularly toxic, toxic meaning poisonous--the stuff is pretty nearly inert, as it doesn't dissolve in water--and we humans are made up of primarily......water.

One other cautionary statement, which shows on any MSDS sheet for urethane resin is flammability, not only of the liquid components, but also of the mixed and cured resin itself--to test that for my own education when I was using the stuff in quantities of 10-20 gallons a week, I actually set fire to some scraps of flash and defective parts (outdoors), and yes, the cured resin is quite flammable once ignited.

However, most modelers have learned to file carefully, and wet-sand, which pretty much eliminates fine dust particles in the air, and from experience using a Dremel on resin, there is really NO dust, just a fine stream of particles that arc up into the air, fall directly to the floor.

As a former resin-caster, I find all the misinformation, and "fear-mongering" to be, at the very least, disappointing.

Art

[MikeMc]

Thanks Art for the REAL FACTS!!

yes all dust can be harmfull in your lungs....common sense....

And thanks Aaron for the great tute!

Edited March 29, 2012 by MikeMc