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Dispelling Modeling Myths


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#41 mr68gts

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Posted 11 May 2013 - 06:53 PM

I have a model that is over 18 years old now and I used single part putty with ZERO shrinkage and nothing showing. Don't remember the putty, may have been squadron's putty. Might be the 8 coats of paint and the 15 coats of clear? LOL. (all coats were sanded inbetween.)

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DSC_0379.jpg

Most times I use either Squadron or Evercoat glazing 2 part polyester putty.

Still do the tried and true method of the ol exacto reverse scribing to open up panels. Generally cut my own tape but may have to try that stuff Tonio has. I use alot of Alclad and have had some teething problems but at the same time use it pretty reigiously now.

case in point......

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DSC_0391.jpg



#42 plowboy

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Posted 12 May 2013 - 06:49 AM

How old is this build?

IMO while one part putty can be sanded smooth and then painted over before it gets a chance to shrink it will shrink given enough time. I;ve got builds in my cabinet that were filled and sanded smooth 5 or 6 years ago but which now exhibit sinking along all the filled seams.

Now I used automotive cellulose knifing putty not something intended for model use but I maintain that a one part putty which dries by evaporation will reduce in volume as the solvent evaporates.

If all the evaporation has occurred before sanding and painting then I can see how no more shrinking would take place but is that going to happen without a long drying time or thin coats?

I don't know.

Good luck with your builds as they age and if you are happy with what you are using then by all means stick to it (after all there is no wrong or right way to do stuff in our hobby - despite what certain posters on this forum I could name think) but I learnt from experience that I prefer a 2 part filler as the 1 part one I was using shrank.

 

That build is only a few months old. But, I have a few builds that are at least fourteen years old that look the same as the day I finished building them. If nothing has happened by now, it's not going to. I built a Revell '69 Nova X years ago (whenever it first came out) that I ground off the incorrect fender arches and made them entirely from putty. If there was a time that putty would have failed, it would have failed on that build. I also have a resin '61 Falcon that was built a year or longer before it. It had what had to be a thousand pinholes and three through holes (one a 1/4", two 1/8") and I filled them all with Squadron's white putty. Still looks the same. I guess it was a good thing that I hadn't heard the myth about not using putty on resin.  ;) 



#43 Harry P.

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Posted 12 May 2013 - 07:56 AM

In regards to one-part vs. two-part putty... here are the facts.

 

Fact: One part putties harden, or "dry," the same way that paint does: the liquid part (the solvent) evaporates away, leaving behind the hardened solid part. Since all one-part putties harden this way (via evaporation of the solvent, leaving behing the "putty" part), they by definition shrink as they dry– because they lose a part of their volume (the solvent) as they dry. This is an irrefutable fact.

 

Fact: Two-part putties (the kind where you have to mix the resin and the hardener) don't dry via evaporation. In fact, they don't "dry" at all... they set via a chemical reaction between the resin and hardener, the same way epoxy sets. Once this reaction has finished, the putty is as hard as it'll ever get, and it won't shrink two months down the road. There is no loss of volume because the putty has hardened via chemical reaction, not evaporation.

 

However... that's not to say you can't get perfect results using one-part putty. You can, if the putty has completely dried before you prime and paint. If you laid it on thick, after a while it may seem dry, and even sand well, but deeper down the solvents have not all evaporated away, and in a case like this you will see evidence of shrinkage marring your finished model down the road.

 

That's the pitfall of one-part putties. They do shrink (and crack if applied too thick). If you know what you're doing and have had experience using one-part putties, and you know enough to let the putty dry completely before finishing, yes, you can get good results. Many modelers, especially beginners, don't know that, and they're the ones most likely to have the problem of visible shrinking down the line, after the model is finished. And of course, there's nothing you can do to fix it at that point.

 

Since two-part putties don't have this problem to deal with, IMO they're the better choice. A two-part putty, if mixed in the correct ratio (approx, 10 parts putty to 1 part hardener) will not shrink or crack, ever.



#44 mr68gts

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Posted 12 May 2013 - 09:17 AM

Harry, and thats where the vega fc probably hasnt cracked or shrank as I put the filler on in thin coats. Unfortunately for me there is NO place to get 2 part with driving 4 + hours. (Hell I have to drive 1 to get to a hobby shop that I have more of than they do!!!!)



#45 Ace-Garageguy

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Posted 12 May 2013 - 09:21 AM

 Unfortunately for me there is NO place to get 2 part with driving 4 + hours.

 

You can buy it online, and this is not the cheapest.   http://www.shop3m.co...CFdCZ4Aodj3QAVQ



#46 Harry P.

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Posted 12 May 2013 - 09:34 AM

Harry, and thats where the vega fc probably hasnt cracked or shrank as I put the filler on in thin coats. Unfortunately for me there is NO place to get 2 part with driving 4 + hours. (Hell I have to drive 1 to get to a hobby shop that I have more of than they do!!!!)

 

Most auto parts stores sell it. And like Bill said, it's available from tons of places online.

 

http://www.google.co...iw=1267&bih=723



#47 Hollywood Jim

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Posted 12 May 2013 - 10:11 AM

Here is what I use.  Bondo.  A two part putty made for car body repair.  It now comes in these tubes that are very handy for model car building.  Available at most auto parts stores.  The only problem is, if you mix in too much hardener (stuff on the right) it will set up in about 3 minutes.

 

 

Img_3657-vi.jpg

 

 

The stuff is easy to sand and works great !

 

z3-vi.jpg

 

 

IMG_3407-vi.jpg

 

 

 

.



#48 Ace-Garageguy

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Posted 12 May 2013 - 10:34 AM

Cool salt-flats Merc !!!

 

And if you don't get ENOUGH catalyst in it, it won't stick OR harden.



#49 Hollywood Jim

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Posted 12 May 2013 - 10:53 AM

Cool salt-flats Merc !!!

 

And if you don't get ENOUGH catalyst in it, it won't stick OR harden.

 

Thanks !

 

You are Correct !!

 

The reason I mentioned using only a tiny bit of hardener is that for modeling purposes, I usually only mix up a tiny amount of this stuff and it is easy to use too much hardener.

 

IMG_3417-vi.jpg

 

 

.



#50 Harry P.

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Posted 12 May 2013 - 11:08 AM

Jim, that's the stuff! Can't beat it.

 

It' a 10 to 1 ratio–10 parts putty to 1 part catalyst (hardener). Obviously there's no easy way to actually measure, so you eyeball it. The ratio isn't super-critical. I go by color... after it's mixed it should be a light pink. Too white and you don't have enough catalyst, too red and you have too much catalyst mixed in and it'll set up on you really fast. As long as the mix is pink, you're ok. A tad too little catalyst, there's no real harm done... it'll just take a few minutes longer to set up.

 

And oh yeah... Jim, that model is super-cool!



#51 plowboy

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Posted 13 May 2013 - 07:44 AM

Fact: Squadron White Putty does not shrink or crack. Here's a photo of a hood I just primered. The tear drop scoop is made entirely from Squadron White Putty. This was started last night around 8:30 and primered just a few minutes ago. Myth busted!

 

017-7_zps6fe97b58.jpg

 

 

019-5_zpsecf8dbb6.jpg

 

 



#52 Longbox55

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Posted 13 May 2013 - 07:58 AM

So, what you're saying is that Squadron White putty can defy the laws of physics?



#53 Harry P.

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Posted 13 May 2013 - 08:30 AM

So, what you're saying is that Squadron White putty can defy the laws of physics?

 

Apparently so. Must be magic.



#54 Danno

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Posted 13 May 2013 - 08:49 AM

at

Fact: Squadron White Putty does not shrink or crack. Here's a photo of a hood I just primered. The tear drop scoop is made entirely from Squadron White Putty. This was started last night around 8:30 and primered just a few minutes ago. Myth busted!

 

017-7_zps6fe97b58.jpg

 

 

019-5_zpsecf8dbb6.jpg

 

 

 

 

1.  Do you have precision micrometer measurements of several key dimensions upon completion of application, and correspnding measurements upon "drying" so that a meaningful conclusion might be reached as to how much shrinkage did or did not occur? 

 

Perhaps Squadron White shrinks less than other formulations, or perhaps it shrinks so uniformly and so little that it is not detectable/noticeable by its true believers, but it has to shrink . . . it has no option.  Squadron has no exemption from physics or chemistry. 

 

 

2.  Check back with us later . . . weeks,  months, or years . . . we'll wait patiently.



#55 Art Anderson

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Posted 13 May 2013 - 09:36 AM

There's a few myths, or maybe "Half-truths" floating around on the forum about how people go about certain meathods or achieve certain results. Some of these may have some folks confused, or even scared to try a new technique. There are a few "myths" that I would like your help to get straightened out, and if you guys can think of more, please post them!

 

#1- Alclad, I've read on several instances where Alclad was hard to work with because of it being so delicate, but I've also read where it's just as tough as kit chrome... so which is it?

 

#2- Scribing open panels, BMF makes a tool just for this, yet guys insist on claiming to use the back-side of a #11 blade (which I can never get to follow the groove). How many of you actually use an Exacto blade to open panels?

 

#3- Fine line masking, again something that can be purchased, but when people ask the painter how they get such fine lines masked, they always come back with the old "stacking of the blades" response...

 

I don't want to start any arguements amongst the members, just would like to bring the truth about some things to light is all! ^_^ 

#1  I have known of Alclad for years now, never tried the stuff.  

 

#2  I have, and have used, the BMF scribing tool, still the best on the market.  However, I still use a modified razor saw blade whenever I need to scribe a long, straight door or other panel line.

 

#2, Fine (or narrow) masking tape:  I've made my own for decades--a piece of thick tempered plate glass, a metal straightedge, and a #11 Xacto (no "E" in that name BTW), to cut my own fineline masking tape.  It's worked for me through 40-some years of making multi-color paint jobs, starting with 20 years (1954-85) building models of Indianapolis cars--why should I change?

 

Really, I don't know of any "modeling myths", just that I along with countless other model car builders have techniques, materials, and tools that we've used for years that have served us pretty well, so why change (unless something we see as better comes along, or some "old friend" material or tool suddenly becomes unavailable.  In other words, if it works, if it's still available, why change?

 

Art



#56 Art Anderson

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Posted 13 May 2013 - 09:43 AM

 

Apparently so. Must be magic.

All solvent-based paints and putties do shrink--they simply have to as the solvents evaporate (dry).  Some shrink more than others of course.  Even catalyzed putty will shrink ever so slightly as it "kicks" from soft to hard--that is a given there, as any polyester resin engineer will tell you.  However, catalyzed putty shrinks by less than one-tenth of one percent, or 1/1000, and once cured (which happens in a small fraction of the time that it takes any solvent-based putty to dry completely) it doesn't shrink any more, nor does it crack when doing so.

 

With solvent-based putties (any and all of them) the shrinkage is related to the material thickness--the thicker the layer of raw putty laid down, the more (visibly) it will shrink.  For that reason, I used very little of the stuff--in fact, most minor bodywork I do gets done with gap-filling CA glue, which once kicked with an accelerator, becomes hard, and doesn't shrink at all, along with filing and sanding to perfect feather-edging, and, in my experience, never shows through even a hot lacquer paint job.

 

Art



#57 Dr. Cranky

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Posted 16 May 2013 - 02:43 AM

I use a #11 blade to open panels.  The trick is to go very very slowly at first and use a very light touch (light pressure on the blade).  After a while you can press harder.

 

When masking, hit it with a little bit of clear first.  That way the color coat will not bleed through.  Any bleed through, under the tape, will be clear.

 

Another myth:  You can paint and build a model car from sealed box to finished car in 24 hours.  I am about to check out this myth.  I'm signed up for my model club's 24 hour build fest.

 

 

.

LOL,  you have to say abracadabra five times over the kit wearing foofy slippers in your pajamas while you open the kit in front of your neighbor's door.



#58 Draggon

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Posted 16 May 2013 - 04:43 AM

And as for the myth that Testor's Contour Putty shrinks forever, this chop was done around 1984. Very thin coats have minimal shrinkage, if any. I still use it today to fine-tune areas where primer alone isn't enough.

 

photo-vi.jpg



#59 Harry P.

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Posted 16 May 2013 - 04:56 AM

And as for the myth that Testor's Contour Putty shrinks forever...

 

 

Nobody ever said that one part putties shrink "forever."

 

They shrink until all of the solvent has evaporated. Once all the solvent is gone, they don't shrink any more. But the time it takes for all of the solvent to fully evaporate, and the shrinking to stop, varies greatly, depending on the brand of putty, the air temperature, how thick it was applied, the humidity in the air, etc.

 

That's where many people get into trouble... they think the putty has fully dried, and they go on and finish the model... only to see very visible signs of shrinking marring their paint job weeks or months later, especially along seam lines or joints or panel lines that were covered with the putty. Of course, by that point it's too late to fix the problem.



#60 Scale-Master

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Posted 16 May 2013 - 05:38 AM

4. Paint won't stick to polished plastic.

 

 

I figured that more people would comment on this one. To me, the conventional wisdom is that you need some "tooth" on the surface to be painted -- such as scuffing with 400 grit wet-or-dry for a coat of flat primer. On my next model, I'm going to try the polished plastic method and spray on many light coats of diluted gloss paint, skipping the primer.

 

How about posting some more myths?

It depends on the paint too.  Mechanical vs. chemical bond.  Mechanical bond paints need a texture or "tooth" to bite onto.  Chemical bond paints "melt" or meld into the surface.

It also makes a difference if you are going to mask.  For example, I have had great results with Tamiya TS paints on raw shiny (Tamiya) plastic, but they don't adhere well enough to mask without the tape pulling the paint off. 

 

 

What about the myth of red and yellow plastic bleeding through paints...?