Posted by Mark Darrah on November 25, 1999 at 07:00:54 in 12.75.148.5:
In Reply to: model putty? posted by RS on November 23, 1999 at 17:10:47:
RS,
I bet you'll be sorry you asked after reading this :-) I kinda went nuts.
You have a multitude of choices and it all depends on the application.
1. Squadron makes both Green and White versions of their putty. The green has been the standard for years, but many alternatives have come about in recent years.
The white is newer, but I really can't tell the difference between them except that the white is obviously easier to paint over (you should prime anyway). The green
stuff is easier to tell when it's cured, as it changes from a dark green to a light, "powdery" green. The way to use it would be to squeeze a dab on a piece of paper or
foil and then use a home made "spatula" to apply it to the model. Like PJ said, it is good practice to mask around the area before you apply it to keep it confined to a
small area. Same goes for when it's sanded. Masking the area around it keeps the sandpaper from obliterating detail that you don't want to remove.
There are a few problems with this type of putty:
* Shrinkage. This stuff will shrink while drying, forcing you to possibly apply several coats. Don't be tempted to apply a huge glob of it though. Thin coats are best.
* Rough surface. Due to the grains in the putty and air bubbles that cannot be avoided, the puttied surface can end up with a rough surface, even after sanding. Again,
thin coats help alleviate the bubble problem, but it's still hard to get a nice smooth finish and it can't be scribed easily without chipping.
* Short working time. It doesn't take long for this stuff to start to cure and start balling up as you try to apply it. Squeeze small amounts at one time. A way around
this and the roughness problem is to thin the putty with liquid cement. Just add a drop to the putty while on the foil and mix it up into a nice goo. As it cures and gets
difficult to work with, add some more cement. This may drastically lengthen the cure time and can damage the plastic if too much is applied, so go easy.
* Long cure time. Even though it starts to set up quickly, it won't become hard for several hours or even several days. Remember that the green stuff is easier see
when it's dry. Look for the powdery medium/light green color. However, I've built models where I thought the putty was cured, sanded and painted, only to find that
the seam is visible again because the putty shrank even more over a period of weeks.
2. A great alternative to Squadron and Testors putty is Acryl-Blue auto body putty by 3M. You can find it at any auto parts store that sells auto body repair supplies.
Acryl-Blue has a MUCH finer grain to it and does a decent job when it comes to feathering. There's just one problem - the cost. You'll have to buy it in a great big
tube (like 16oz), which can cost about $20. Rest assured though that you will have plenty of putty to last a lifetime! Keep the cap on it always and it'll last years.
3. Superglue (or CA glue - NOT the brand) is a great filler, but get the good stuff at a hobby shop and not the stuff from the drug store. Use the thick stuff for filling
moderate gaps or filling in sink holes in the plastic. A couple of applications may be necessary. You can buy accelerators that will harden it right away, allowing you
to get right back to work. Just be sure that you are prepared to sand it as soon as it hardens, because it will continue to harden until it's harder than the surrounding
plastic after a few days. That makes it very difficult to work with.
Use the thin type superglue to fill small imperfections on flat surfaces, very thin seams and also on inside corners that are difficult to reach with files or sandpaper. Just
put a small puddle on the foil and use a thin wire to apply it. I use a brass wire with the end slightly bent. Dip the end of the wire (or lay the bent end) in the glue and
run it along the seam or corner. It will run into the crevices by capillary action and leave very little excess to clean up.
The great thing about superglue is that it is almost indisinguishable from plastic once hard; in fact it cures to a form of acrylic.
You'll eventually have a problem with the tip clogging. When you go to buy the glue, check to see if the hobby shop sells extra tips for the bottles. Buy that kind so
you can put a new tip on it instead of throwing away a perfectly good bottle of glue that you can't get into. I usually buy the smallest size bottles anyway.
4. Milliput is a two part epoxy putty that can be sculpted just like modeling clay. It's use is rather limited though as far as filling gaps. Only the largest gaps (1/8th inch
or bigger) would benefit from Milliput, and by then you're better off using strip plastic. It's better for something like reshaping a large part, maybe like reshaping the
boss arms (why, I don't know). There are several grades available. Go with the fine or extra fine. It comes packaged in two sticks, individually wrapped. You cut
two equal sized pieces and knead them together for a few minutes until they are completely mixed. You now have a ball of putty that can be worked with for at least
an hour. You can mold it with your fingers, but some sort of spatula is better. Keep a bowl of water handy and keep your hands wet to keep it from sticking to you.
When it cures, it's rock hard and can be sanded and filed just like plastic. You could even mold your own shapes and then file a custom part. The advantage is that
there is absolutely no shrinkage, or at least very little.
This stuff dries out easily. It'll get all crusty on the outside, although you can cut off the "skin" and get to the good stuff. Keep the two sticks in SEPARATE
sealed ziplock bags to preserve them. I've heard that keeping them in the 'fridge helps, but I don't know.
Some porousness and tiny air pockets caused by the kneading process may force you to have to use superglue as an additional filler or see below.
5. One of the greatest things to come into the model industry in the last couple of years is some stuff called Mr. Surfacer by Gunze Sangyo. It is DEFINITELY worth
going out of your way to find! There are two grades, 500 and 1000. They both come as a liquid in bottles. The 500 is great for filling small gaps. Just brush it on.
When it's dry, use a cotton swab or paper towel dipped in some isopropyl alcohol and wipe across the seam. All the excess will be removed without having to sand!
You can sand though if the alcohol removes too much. The stuff feathers like a dream and can even be scribed like plastic. One example of a good use for this stuff
is filling the seam between the bilge keels and the hull. Just use the alcohol and there is no sanding needed.
The 1000 is really only good for a final primer coat before painting and should be sprayed with an airbrush. However it can be hand brushed on as a filler for very
small imperfections. If spraying, you'll need the thinner that goes with it which isn't cheap.
Cleanup's not much fun though. A can of acrylic lacquer thinner will be needed and it's smelly (dangerously so - use good ventilation).