Help with Resin Kits - specifically N Gauge Road Apple Car Kits

[Bart1701]

After many years, I am finally getting around to working on a bunch of N Gauge Road Apple Automobile resin kits that I have. Many of the bodies have very small holes in the surface. I am guessing these were probably caused by air bubbles or something else when the resin casting was made.

What is the best way to fill these holes in these tiny little vehicles?

I'd appreciate any ideas or suggestions anyone may have to offer.

Thanks,
Bart

[wazzou]

Bondo.  No really, Bondo, a tube of one part body filler, available @Walmart or most auto parts stores.
Just squeeze a little out on a plastic bottle cap or paper plate and apply with a toothpick, let dry and sand, repeat.

[Philip H]

Squadron White putty also works pretty well if you already have some.  Otherwise I second the Bondo prescription.  And don't forget to post pictures when you are done.

[pnolan48]

I use bondo. But I've also used plain old joint compound with great results. It's much easier to sand than bondo, and mud cheap. It is water based, so it must be covered by a hard durable finish.

I'm not sure all the tiny holes are caused by air bubbles entrapped in the resin. I suspect many are caused  by "irregular" molecular interactions during the polymerization process. Endothermic reactions can't be uniform. I base this on my observation that many of the holes are actually wormholes that extend into the casting for many times their diameter. If an air bubble is .001" in diameter at the surface, it should be sanded out by .002" of surface removal. This, in my experience, is rarely the case.

I also suspect that cleaning the parts with strong solvents such as acetone or 91% isopropyl alcohol eats into a glossy surface to expose the wormholes, and perhaps to travel along imperfect polymer paths to make the holes deeper and wider. When I started using liquid soap rather than isopropyl alcohol to clean newly cast parts, the pinholes were reduced by 90%. Isopropyl alcohol is the solvent for many resins--thank God for it if you've ever made a mixing mistake and are trying to salvage a master!

[peteski]

Ah, the Road Apples fine resin miniatures!  The quality of those castings is about the same as their namesake: a steaming pile of hose poop!! 

I have about a dozen (or more) of these little gems I have not yet tackled any of them, mainly for the reason you mentioned: zillions of pinholes. Yes, those are air bubbles. Somehow they weren't able to get rid of them. Don't know why as most other resin casters don't have such a severe problem with their castings.  Heck, even I am able to pour almost pinhole-free models!    The other thing that bothers me is the quality of the master patterns. If the spend just a little more time massaging the master pattern, those would be excellent.  But as-is, they are barely acceptable.  Why then I own a dozen of those models? Because they are unique vehicles, not offered by any other company.  Time and time again, I picked one up at the train store, looked at it, shook my head and put it back on the shelf but then as I was just about to leave the store, I would end up grabbing another Road Apple!  "I can tackle this thing" I would think.   When Lineside Models bought out the line I was hoping that the casting quality would improve - but no so. 

OK, sorry for the huge rant - I just needed to get it off my chest.  I feel better now.

I'm not sure about Bondo. To me it seems too thick to fill all those microscopic pinholes. Also, it will be very difficult not to obfuscate whatever detail is on those models.  What I thought of trying is one of Gunze Sangyo "Mr. Surfacer" products.  I would try the "1000".  I'm pretty sure that it will not attack the resin used by ROad Apples.



You can get Mr. Surfacer at most hobby shops that cater to model car, airplane or armor modelers.
For an excellent tutorial, see http://www.swannysmodels.com/Surfacer.html

If you decide to to this. let us know how it works out. If it works for you, I might finally tackle my "Horse Poops"!

[Chris333]

You don't want Bondo body filler. You want Bondo spot putty.

[Bart1701]

Great ideas everyone - thanks!

The "Mr. Surfacer" that was mentioned is very intriguing. If I can find some at one of the local Hobby shops or online, I think that is something I will try. The Squadron White Putty method was tried last night, but it wasn't that easy to get it into the teeny-tiny microscopic holes; the quick drying nature of Squadron putty was fighting against me! I am assuming that the Bondo Spot Putty would work about the same - so, I don't think that is something I'll try.

On one of the bodies, I did use Squadron putty to fill a couple of really big holes, but did nothing on the smaller holes. I brush painted some shade of Testor's light gray paint on the body as a primer - a fairly thick but smooth coat of paint. I hoped that the paint might settle in the holes and help to seal them. Paint is still drying at the moment, but it looks promising.

As Peteski stated, these are not the most detailed kits - but they are kits that no one else makes and they do have cars from the 80s-90s for mode modern layouts. Once completed, if they look OK but not great, they will certainly work on roads and parking lots that are a little further back on the layout where you can't get close enough to inspect them!.

I'll post some photos of my work as soon as I finish some of these cars.

Bart

[wazzou]

I've found the Squadron Putty is like Playdoh in consistency.  The Bondo Putty is much thinner and therefore the workability is better.   IMO

[DKS]

FWIW, I just use paint. There are some varieties of Floquil branded as "filler" and I imagine they're thicker than normal. I just apply a couple of coats, sand down, apply more as needed, etc. Much easier to control and less likely to gunk up the valuable details (such as they are) than using any sort of putty-like fillers.

[pnolan48]

Peteski,

I agree that I can usually cast some very large parts with very few pinholes, without vacuum or pressure. I guess I don't understand the problem with small parts such as Road Apples--small for me at least. Could it be possible that poor quality castings are caused by too much release agent in making the mold? I once had the strongest hands in the neighborhood, but arthritis has led me to use more release agent in making the molds. I just can't release the molds like I used to, leading to more release agent, leading to poorer quality molds. Leading to grungy parts that I have to spend a lot of time cleaning up. I can't sell the parts as separate items because they are too grungy. I know that poor quality molds have little to do with zillions of pinholes (and I sometimes wonder why folks bother with poor quality castings with zillions of pinholes.)

[DKS]

I started out using release agents because everyone said to use them. Then I stopped, for whatever reason (laziness? forgetfulness? who knows), and found that I never needed them in the first place. Since then, I've seen the quality of the castings improve. And I have arthritis in my hands, too, yet I haven't found any of the castings difficult to demold, either. It's a real puzzle.

[peteski]

From my experience, if you use urethane resin and your mold is silicone rubber, there is no need for release agent. But if you use urethane resin and your mold is urethane rubber, mold release agent will prolong the life of that mold. In general, release agent seems to prolong mold's life.

[pnolan48]

I am using urethane rubber for now. I did use silicon for a 173' subchaser mold, and it was much easier to demold. I've had no problem demolding smaller parts with either urethane or siliicon. But demolding the bigger hulls--about 14 oz. of materials--has been difficult. I say arthritis rather than explain that I torn two tendons (middle and ring) on each hand fixing a granite tile countertop. Hands make lousy clamps.

[daniel_leavitt2000]

I have many Lineside/Road Apple vehicles, and there are a lot of issues with most of them. The Mack DM800 cleans up nice though: