Preparing plastic models for painting.

It is always a good idea to wash plastic with soap and water. Dish washing liquid is usually a good idea because it makes water weter and allows the removal not only of the geasy stuff that comes with the molding process but also the stuff your hands leave on the surfaces. It would be a good idea to use rubber gloves when handling the plastic aftre washing as well as there willl be little of the natural oils yor skin leaves on the dried parts that way.

As for painting, I would suggets you paint before you put the parts together as you may not be able to reach all of the spots once the kits are put together. You can then use either a hand brush or an air brush. If yu want an even color, you'll usually need to use and air brush. However, if you intend to weather the kit, you can got resuts with a standard paint brush.

Irv

I was always....

I was always taught to put the model together and paint it last then decal and weather. Then again I guess it depends on if your spraying or brushing. If your brushing the technique may be different.

Mike Martin

PollyScale Plastic Prep

Plastic Prep does a good job of lifting oils and mold release off of plastics and is reusable; you can run it through a coffee filter to keep it fairly clean.  A good 10-20 minute soak followed by a warm water rinse is usually enough.

If you use dishwashing liquid buy the cheapest stuff -- some brands have lanolin and other additives that will do your paint job no good at all.

91% alcohol also works but you need to rinse it quickly before it evaporates and leaves all the gunk back on the surface. It also gets a bit heady in a closed room.

Dawn dish soap is the best as

Dawn dish soap is the best as it removes almost all oil and grease.

You should soak the pre-assembled plastic Model parts in the Dish soap 4-8 drops in a1/2 gallon of warm water for 10-12 minutes and then rinse in clean warm water and allow to air dry. Then depending on the type paint your using you may want to use "Barrier" if your using oil base enamel.

Polly "S" makes a product called plastic prep #546007 it's a pre-painting cleaning agent for plastic surfaces you use it after the soap and water wash to remove any remaining mold release,Silicone or grease & oils still in crevices and again allow to air dry before painting.

Dan

Thanks to all

Thank you, all of you, for the great tips.  Just the information I was looking for.

How do you prepare the plastic model for painting

I've read to use liquid laundry detergent. No lanolin and will clean the oils and release agents from the plastic as well as the dishwashing liquid.

Thoughts on vinegar

What is everyone's thought on using white (distilled) vinegar. I first came across this building an older roundhouse steam engine. The instructions said to clear the parts in white vinegar. It seamed to do a good job, but nothing special.

Etching the Metal

I believe folks use vinegar on metal models because it's thought that it acts as a mild etchant to the metal, giving it a bit of tooth.  The paint should adhere better to the model.

-Jack

Effect on decals?

If the model already has decals applied, would washing it in Dawn soap and warm water have any ill effects? Vinegar? Isopropyl alcohol?

Yes, maybe, no

Assuming that you have properly set the decals with setting solution, I think that a very gentle washing would be safe.  I cannot imagine why you would want to use vinegar, but I would not recommend it unless you're tried it on a sacrificial model and found it safe.  I would definitely not use alcohol.  Just this morning, I began stripping a previously painted model in alcohol.  Since there was no clear coat, the decals came off easily after soaking in the alcohol bath.

Two thoughts.  First, I would always suggest leaving the decals off until you can complete the paint process and will not need to handle the model.  Second, if that is not possible, or after the decals have been applied, I always suggest a clear coat of some sort to seal and protect them.

Preparing Plastic Models for Paint

I usually will wipe down a plastic model with isopropyl alcohol; it will flash off very quickly and leaves a nice clean surface for paint; on something that is "more truss than solid surface" you might spray the alcohol on the structure and give it some time to flash off.

I also used isopropyl alcohol to thin the acrylic paint, when necessary.

Jim Brewer

Dish Detergent

I typically wash all the parts of the model with dish detergent before gluing together.  After putting the model together, I wet sand and then wash everything again.  I use an old tooth brush to get into all the "nooks and grannies".  Depending on the model, I may pre-paint parts before gluing together.  I ALWAYS prime plastic parts using inexpensive primer from a spray can before applying acrylic craft paints (they don't adhere as well to shiny plastic).  I switched to acrylic craft paints years ago because they're cheaper than enamels and easier to clean up. This station model was painted this way, using washes and dry brushing to weather it and a misting of Testor's dull coat to seal everything. 

I see this topic began in

I see this topic began in 2009!  Just now being refreshed?

For an informative discussion of prep for painting, take a look at a previous post - http://model-railroad-hobbyist.com/node/3557. Specifically the post by LKandO,  Sat, 2010-10-30 22:58.  It is comprehensive, and was endorsed later by another chem expert.

For convenience, a copy of the comments follows:

Plastics and Paint, A Love Hate Relationship

Sat, 2010-10-30 22:58 — LKandO

...when it comes to paint and surfaces to be painted well I know a pinch more about that!

There is an important distinction between detergents (earlier mentioned dish soap) and solvents (your alcohol). Detergents emulsify contaminants while solvents dissolve contaminants. Emulsifying is a relatively slow process hence the reason your wife lets dishes soak before washing them. Solvents on the other hand work relatively quickly depending upon their solvency strength relative to the containment. Therefore, soaking is not as advantageous for solvents.

To muddy up the picture further, solvents are picky about what they will dissolve. Generally they are most effective at removing organics - petrochemical products. An example would be how well lacquer thinner cleans off grease and oil but is almost useless at removing soap scum. This finickiness of solvents makes it challenging to say what solvent will dissolve what containment without testing. And we have no way of knowing what mold release was used in the manufacture of the trucks. Could be wax, could be an oil, could be a silicone. Who knows. One thing is for sure - your plastic trucks are organic (began life as oil) so many solvents will dissolve them as well as the contaminants. Don't soak plastic in any solvent.

Detergents don't dissolve things, they lubricate the mating surfaces of the containment and the object causing virtually any containment to "lose its grip" and float away in the water. Ever notice how slippery detergents are? That is what makes them work. Because detergents lubricate uniformly they are far less picky about what they will remove hence their widespread use as universal cleaners. Only highly hydrophobic contaminants are resistant to detergents (hydrophobic and hydrophillic are another discussion later )

One of the most universal of all solvents is n-Butyl Acetate (commonly used in paint reducers). It is available at Home Depot and Lowes in their paint department. With it you can dissolve many, many organic contaminants. Alcohols are some of the most finicky of solvents. They clean some things nicely and others not at all. Rubbing alcohol should be avoided at all costs since it contains an oil.

I would suggest the dish soap soak and wash (hot hot water is best), rinsed very well, dried completely, followed by a wet wipe of n-Butyl Acetate just prior to paint as a very effective mold release cleaning process. Another option, and also a very good universal cleaner, is aerosol foaming window cleaner with amonia. These products are both a detergent and a solvent in the same can. Great universal cleaners.

Alan

All the details: http://www.LKOrailroad.com  

Good luck to all.

Bob Kingsnorth