I’m about to take on a kit with a resin hull. The hull castig has lots of little pits in it. I need advice from somebody with more resin kit experience about the best way to get rid of them. Green putty? Bondo? Milliput? CA adhesive? Is there a consensus? Thanks in advance.
I’ve done a few solid resin subs, depending on the size of the pits green putty or auto bondo will work. Sanding CA is a pain compared to filler, but it will work, but it’s not needed.
Ditto on the Bondo or green putty. Just be sure to have plenty of ventilation and a good mask when you sand.
Jim [cptn]
I generally will drill out the pin hole so it’s more hole than bubble. Then, I fill it with baking soda, scrape the excess off or tamp it down, and put in a drop of thin CA. It dries almost instantly and sands well. Doesn’t shrink, and is a lot better than just plain CA, even the thick stuff. Model Horse people have been using the combo for years to fix broken ears. You can also use it from the back by putting some tape down on the outside of the opening, filling as before, and then dropping in the CA. Sometimes you don’t need anything more than a drop of paint then sanded down to complete the fix.
Only downside is that it’s still harder than the plastic, so rescribing things like planks may be “interesting” when you transition materials.
I’ve never heard of this technique using baking soada. What is the purpose of doing it this way and not just filling it with CA? Does the thin CA get pulled into the baking soda? Is this what makes it easier to sand?
I second (third?) the bondo. For smaller pits I just use auto body glazing putty (same as green putty but red).
The baking soda helps give the CA glue some body. I don’t know about you, but I’ve never been able to get plain CA glue to perfectly conform to my desires; it either hardens with a depression in the center, or you have to use thick CA glue and sand a large mound down. With the baking soda and thin CA, you can fill it, then scrape off the excess, so that when you hit it with the thin CA, it’s already pretty much level. Plus, like I said, it kicks it hard, so that it dries almost instantly (puts out some heat too, so I wouldn’t advise trying to do really big fills all at once).
I prefer it over putties in that when you have pin holes, you tend to have a lot of them. This allows me to pretty much get them all in one sitting as opposed to putty - wait - sand - inspect - refill areas that shrunk, etc.
Makes sense, kinda like adding sand to cement. Cement on it’s own is horrible to work with.
Another autobody filler fan for resin here:
From days of old, baking soda acts as a CA accelerator.
As a guess, the baking soda is probably a lot softer than the ‘pure’ CA can be. Which ought to make for better sanding.
Here’s the thing. Those bubbles are not a surface defect. They are a result of the caster introducing gas, usually air, into the mix.
If you sand the raw resin one pit becomes ten.
I just put on enough paint to solve it, with an airbrush.
Once you’ve seen a few bubbles you can recognize even some of the sub-surface ones. That’s one reason why I drill them out so that they’re pits/holes more than bubbles - I’m trying to get them all at once. Some casters are better than others with or without a pressure pot and there will be relatively few bubbles. Others… well I’ve seen a froth in resin that would just make you shake your head and pack it away for a while.
CapnMan - yes, it is a bit softer, and it doesn’t harden up the same way pure CA glue does. It doesn’t feather out quite as nice, but I don’t usually use it in applications where it needs to, or if I do, I coat it with something like Mr. Surfacer and expect that to feather.
There is a gel form of CA widely available. I generally use it more than the regular (thin) stuff. I use it primarily because it sets slower and gives me more time to position, and it does not require as good of a fit. But it also holds its shape and is often used for small filling of pits or seams of die cast styrene assemblies. I use the Locktite brand of gel.
Yup, I’ve used that and like I said, I always have a mound or depression with it.
And I want to hammer this point again because I feel like people are missing it… it dries nearly instantly. Meaning that within ten seconds of dropping the CA on it, I have a sanding stick out and am taking down the little bit of excess. I find that a lot easier and more pleasurable than laying something down that I have to wait hours or a day to then finalize.*
More power to you if thick CA and auto putty makes you happy, I’m just saying that thin CA and baking soda is a good tool to have in your “war chest” of techniques.
- I also use two-part epoxy putties specifically for their long work time and workability though, so it’s not all about speed to me.
Many thanks to everybody for the suggestions. I think Bondo or green putty will probably work for the hull I’m working on; the indentations aren’t very deep.
That method of “fusing” baking soda with CA used to be fairly widely discussed in magazines. It certainly does work - but sanding it smooth is a bit of a challenge. Even within seconds of application it’s hard as a rock - and considerably harder than the surrounding styrene or resin.
I’ll summarize.,Resin is not like root beer, it’s like Swiss cheese.?the comparison is apt - if there are bubbles on the surface they exist throughout the piece because there was no atmospheric pressure in the resin mold that overcame the gravity influence on the casing medium.
What kit?
Treat it like bad wood. Can’t excise the pulp, just need to deal it.
Any fill operation involving CA is a loser unless you have a bunch of experience. Tracy does I don’t so I prefer Tamiya putty.
It’s the same technique as using “micro balloons” with fiberglass…