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Other Stuff => Workbench => Topic started by: aircav on October 31, 2009, 03:09:38 PM

Title: Gap filling technique
Post by: aircav on October 31, 2009, 03:09:38 PM

I have been lent some Osprey modling books & they have a great tip for gap filling.

First fill the gap with super glue then sprinkle on baking powder then cover with super gue again ann it goes hard sop that it can be sanded.

I have just tried this & it works a treat  :D


Keith  :?

Title: Re: Gap filling technique
Post by: Hauptgefreiter on October 31, 2009, 03:19:57 PM

Thanks for this information, Keith.
I know about a substance specially created for such a task. The 30g bottle costs 2.79 EUR. Your solution sounds as effective but cheaper  :)

Title: Re: Gap filling technique
Post by: Dewbakuk on October 31, 2009, 03:35:07 PM

I'll give that a try, cheers. How big a gap can it cover? Do you need thick super glue?

Title: Re: Gap filling technique
Post by: andekmcc on October 31, 2009, 07:14:11 PM

thanks for the tip I might have to give this one a go  ;)

Title: Re: Gap filling technique
Post by: aircav on October 31, 2009, 07:17:26 PM

I just tried it on about .5mm gap and it worked ok with a really cheap superglue. :)

Title: Re: Gap filling technique
Post by: archangel1 on October 31, 2009, 07:24:56 PM

The technique works best with the thinner glues but be warned.  When it's set, it's HARD! It can even be harder than the original material you're filling so don't mound it up and expect to sand it down easily.

You should also be warned that, as it flashes off, it's a very hot reaction.  It may give off a puff of smoke.  No sniffing! It's got cyanide in it!

Title: Re: Gap filling technique
Post by: Wirelizard on October 31, 2009, 10:23:39 PM

I use this technique regularly; as a method of mounting figures to bases it's hard to beat.

Given a large enough pile of baking soda and enough superglue, it's a fairly exothermic reaction, though. I singed a fingertip through a metal base a few years back (not a real burn, more a "Damn that was warm!" moment) and the little puff of vapour/smoke - well, remember than with standard CYA superglue, the "CYA" part is Cyanoacrylate - so as archangel1 says, yes, there's cyanide-related chemicals in our favourite glue. Isn't modern chemistry wonderful?

Title: Re: Gap filling technique
Post by: Mr. Peabody on November 01, 2009, 01:45:41 AM

As long as you get to sanding the newly filled gap promptly you will have no problems smoothing down the material. You have about a 15 to 30 minute window of easy-peasy filing/sanding time and working within that window the job is a breeze.

I've used the baking-soda (not powder!) and CA glue method for all kinds of jobs and it is really the bomb. You can (and I have; to good effect) mix talc 50/50 with the bicarbonate to get a cooler reaction and slightly longer working time since the talc works as an inert filler.

for fine gaps, you can push the powder into the gap, smooth it all off and run in a dab of the super-liquid CA glue. That works a treat as well! But as with any technique, practice makes perfect.

All of this saves hours over other gap-filling methods that require time to cure and use solvents in their composition.

Title: Re: Gap filling technique
Post by: Dewbakuk on November 01, 2009, 03:49:03 PM

So is it baking powder or bicarb soda? They're very different things...

Title: Re: Gap filling technique
Post by: Mr. Peabody on November 01, 2009, 05:08:09 PM

Household quality Bicarbonate of soda is the stuff you want. Results with this technique are not guaranteed with double acting baking-powder or any product intended for pancakes.

Lets compare terms:
Baking-Soda = bicarbonate of soda, sodium bicarbonate. A white crystalline compound, NaHCO3, with a slightly alkaline taste, used in making effervescent salts and beverages, artificial mineral water, pharmaceuticals, baking powders and fire extinguishers. Now with a bonus hobby application!

Baking Powder = Commercial product consisting of three ingredients: an alkali, often baking soda; an acid, such as cream of tartar, calcium acid phosphate, or sodium aluminium sulphate; and a starch such as cornstarch (cornflour), to prevent the powder from absorbing moisture before the intended use.

Bicarbonate of Soda carries lots of water molecules apparently... I know nothing of chemistry, but I read this is what sets the CA glue off so effectively. Someone feel free to jump in here and clear this up if I'm off-base.

Title: Re: Gap filling technique (Danger ??)
Post by: Major Weenie on November 08, 2009, 08:09:28 PM

Samurai Bob used to use this back in the 1980's
I think it was baking soda & super glue (cynoacrilate).  Anyway, it was something & superglue which made a rock hard, gap filling, solid plug that he began to use quite a lot.
He joked about how it used to generate white smoke.
Then a gamer/chemist at the local hobby store pointed out that this was cyanide gas, and maybe he might want to give the technique a miss in the future.
Don't know if the chemist was joking, but I've always steered away from it.
I'd be interested if someone with a more complete technical background could answer the question for me.