The two most common problem areas modelers have with resin kits are gluing and painting. The most important part of assembling any resin kit is to Read the instructions!
There is a definite difference between styrene ("plastic") kits and polyurethane resin kits. While both materials are technically a form of plastic, they are chemically different. Assembling resin kits requires different glues and techniques than used when working with styrene kits.
Most manufacturers or resin kits use a mould release
agent to allow the resin castings to release better from the rubber mould.
This decreases breakage of parts, and greatly increases the number of parts that may be
made from a mould. Both of these factors help to keep costs significantly lower.
Mould release does, however, prevent paint from adhering well to the parts. For this reason, castings must be cleaned to remove the mould release agent. Soap and water alone will not remove most release agents.
The best product to remove our release agent is our own ResinPrep, available only through our dealers. Floquil's Diosol will also remove our mould release agent, but please be sure to read the safety precautions and warnings on the label.
Both of these products should be successful in removing other manufacturer's mould release agents from their kit parts, but please check with the manufacturer.
Pour a small amount of ResinPrep in a glass or non-styrene container, and then carefully and gently scrub all castings. A soft toothbrush works well for cleaning larger parts. Tiny parts may be allowed to soak in the cleaner for a brief time.
Do not clean any styrene parts that may be included with the kit, such as strip styrene, Tichy steps, ladders, and other Tichy or Grandt Line parts. ResinPrep or DioSol will dissolve styrene.
Using a container in which to clean the kit parts reduces the amount of cleaner required, as well as lessening the chances of losing a part down the drain.
After all parts have been cleaned with the ResinPrep, carefully rinse the parts with lukewarm (not hot) water. A sieve is great to hold tiny parts so they are not rinsed away. The ResinPrep will turn a milky colour when it comes in contact with water. Ensure all parts are well rinsed, and allow to air dry.
kits may contain parts that have warped.
These may be straightened with the use of gentle heat; cover the part with boiling water for a few seconds. Remove carefully so as not to burn your fingers, and reshape the part until the warp is gone. To flatten a straight casting, lay it on a flat surface, and hold flat. For curved pieces, hold in correct shape. Allow to cool in position. Once cool, it will keep the new shape. If the part will not straighten, contact the manufacturer.
Resin kits must be
assembled using Super Glues (ACC) such as Zap-a-Gap, H&D's Own, Super-Jet,
Pacer's Hot Stuff, etc., or 5 Minute Epoxy. Solvent glues that are for
bonding styrene (Testor's Liquid Cement, Tenax, Plastruct, etc.) will not
bond resin parts together.
The most common mistake many modelers make with super glues is using too much glue. Less is best!
Do not apply glue to kit pieces directly from the bottle; instead, pour out a tiny "puddle" f glue on a scarp piece of styrene and use an applicator (toothpick, dental tool ,wire) to pick up a drop of glue from the puddle, and apply to the kit piece.
Use one tiny drop about every half inch to an inch along a long joint (such as a structure's wall, or car frame to body). Once this has set you may reinforce this joint with additional glue along the inside of the joint.
There are different thickness' of super glues, the most commonly used are the thinnest (fastest setting), and the medium (a littler slower setting). There are also thick glue for filling larger areas.
The thin is excellent to use on a good fitting joint. Hold the two pieces to be glued in position, and place a drop of thin super glue on the inside of the joint. Capillary action will draw the glue along the joint.
The medium glue is good for the joints that may not fit as well. This type of glue is often referred to as "gap filling". Place required drops along the joint edge of only one of the two pieces to be joined. Do not put glue on both pieces. Place the two pieces together, and hold for a few seconds. The joint may then be reinforced on the inside if necessary.
If you are unsatisfied with the resulting glue joint, it may be easily broken by using a debonding agent. These are available at hobby shops in the same department the glues are sold in.
We have also found that Testor's Liquid styrene cement is an excellent debonder; it will not affect the resin pieces, and effectively softens the glue. The joint may then be separated by carefully using a single edge razor blade, or exacto blade as necessary.
After you have separated the two parts, you will need to sand or scrape all traces of the first application of glue from the parts. Super glue does not adhere to itself, and if you do not remove the glue, the new joint will be weak or not set at all.
Super glues also have a short shelf life; if glue is not bonding well, it is time to discard it and buy a new bottle.
Resin kits may
occasionally have small air bubbles in the parts. If these are on the back of the
part and will not show on the finished model, there is no need to worry
Air bubble holes that will show may be filled with a medium super glue (gap filling) and the patch sanded or filed smooth. A good filler for larger holes or gaps is a mixture of gap filling (medium) super glue and either talc or corn starch. File or sand the patch as soon as it is hard to the touch; as the mixture will become harder than the surrounding resin.
If the bubble is in an area that is not easily repaired, contact the kit manufacturer for a replacement.
Painting resin kits
requires different preparation and techniques than styrene kits.
As stated previously, all parts must have the mould release removed with ResinPrep or DioSol prior to painting. Cleaning the parts before assembly ensures you will not accidentally get the cleaner on any styrene parts (steps, etc.).
If removing the mould release agent step is omitted , the paint will not adhere properly to the kit.
Do not assume that a soap and water wash is good enough--it isn't! Be sure to use one of the recommended mould release agents, unless the manufacturer's instructions indicate soap and water is sufficient to remove their mould release. Soap and water will not remove the mould release agent on our Sylvan Scale Models' kits.
The completed kit may be carefully washed with lukewarm water and mild soap to remove oils and dirt from handling during construction. Allow to air dry.
Lacquer based paints provide the best adhesion to resin, however water based acrylic paints will also give excellent results with careful preparation.
When painting a multiple colour paint scheme where masking is required, be sure to "desticky" the masking tape before using it, and carefully and gently remove the masking tape as soon as possible.
If you have difficulties with a particular brand of paint, contact the manufacturer of the paint for their suggestions on how to best use their product on resin.
If you are unsatisfied
with your paint job on a resin kit, do not use the "traditional" methods of
removing the paint. Brake fluid, acetone, and other strong solvents
will ruin resin castings.
Our ResinPrep will remove most acrylic and solvent paints from resin kits, but care must be taken not to get any on the kit's styrene parts, or they will become distorted.
Floquil's DioSol will remove Floquil and other solvent based paints, but again take great care not to get it on styrene parts.
Resin casting has proven
itself to be ideal for low volume prototype kits. Most of the kits offered in resin
would never be offered in injected molded styrene plastic, as the set up costs would be
prohibitive for such a small market.
With careful assembly and painting, a resin kit can rival its counterpart in styrene or even brass.