I'm building a number of close-to-minimum diameter models. I'd like to paint the area ahead of the motor mount with some kind of fireproofing glop, to extend the lifetime of the kit.

I have some boric acid and borax. The classic formula to make fireproofing solution is a 3:7 ratio.

I'm wondering what kind of gunk would make a good "carrier." Thinned white glue? Acrylic paint?

I plan on painting it on the insides with a long brush.

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NAR #27085 - Oregon Rocketry - SAM

I would mix it with Epoxy thinned a bit with Acetone or MEK.
Whatever you do, DO NOT use Nitrate Dope as the `carrier`

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When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL, if you have to ask what is "NORMAL" , you probably aren't !
Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, CHAOS, and HAVOC !

You can use a thin coating of epoxy or white/yellow glue by itself. Either will act as an ablative whether you mix fire retardant chemicals in or not. If you have something that stays hot enough long enough to ignite the glue coating with retardant, it will also be hot enough to ignite the tube above the coating.

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I love sanding.

I'm envious of anyone who keeps one of their rockets flying long enough to worry about the inside of body tube above the motor ...

Seriously though, I have an old 3FNC that is a two D motor cluster, and the aft end of rocket is seriously corroded. Obviously the outside of the rocket can be wiped down after flight to alleviate the corrosion, but on many rockets I'll smear a thin coating of epoxy over the aft end to help stop the corrosion. It also helps make clean-ups easy since that area is smooth, and it's also moisture-proof, so any cleanup does not soak the tubes.

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Lee Reep
NAR 55948

Projects: Semroc Saturn 1B, Ken Foss Designs Mini Satellite Interceptor
In the Paint Shop: Nothing! Too cold!
Launch-Ready: Farside-X, Maxi Honest John, Super Scamp

When I was a kid (a VERY long time ago) I had a large Gilbert Chemistry set. Adding to it with Perfect chemicals and labware, I ended up with a rather impressive lab in my parent's basement. Mind you, this was back in the 60s when a Chemistry set was a REAL chemistry set.

Anyway, one of the chemicals that came with the set was Sodium Silicate, or waterglass. This stuff was incredible as a fire retardant - much better than Boric Acid. Of course, this stuff is not available any more (I could go on a serious rant about the strongest chemical in a home chemistry set today is vinegar, and you have to provide that - but I digress). I came across an article a while back that tells how to convert the pellets inside those silicone drying packs into sodium silicate. I;m pretty sure the article was on Make.com. You could always make some and paint that on the inside of your model - enough will soak into the cardboard that it should make it pretty much fireproof.

<Edit> I did a bit of searching on Google and discovered that you should be able to purchase sodium silicate at Lowes, Home Depot, Menards, or any other hardware store - it is also used to coat concrete surfaces to waterproof them. Also, I had forgotten that waterglass was traditionally used to preserve fresh eggs - you can dip a clean fresh egg in waterglass solution and it will remain edible for over a year without refrigeration!

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Greg Poehlein

Member of Launch Crue - http://launchcrue.org/

Hint #1: Do not use magician's flash paper for recovery wadding!

Hint #2: Clean your shoes after flyin' in that cow pasture - that ain't no dirt clod on the sole!

Thanks Greg!

I wonder if sodium silicate was what Estes & Centuri sold as fireproofing solution back in the day.

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NAR #27085 - Oregon Rocketry - SAM

Yes, the bottle of fireproofing solution you could buy from Centuri was in fact Sodium Silicate. I still have a bottle in my collection. Used it as a kid on my models.

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Scott D. Hansen
Ye Olde Rocket Shoppe - Your One Stop BAR Shoppe!
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WOOSH NAR Section #558

Thanks Greg.


I'll try that on my twinkie that I saved years ago and have yet to launch. (dang thing is as hard as a brick now!)

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If it flies, I can crash it!

Should be able to get it from most any good auto supply... waterglass is also used as a radiator sealant to cure a slight leak in head gaskets and such without having to disassemble and replace.

Later! OL J R

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The X-87B Cruise Basselope-- THE Ultimate Weapon in the arsenal of Homeland Security and only $52 million per round!

+1 to the comment above being able to get "water glass"/Sodium Silicate at any GOOD auto supply.
If you ask for it at a 'chain' auto supply such as Auto Zone or O'Reilly the often inept employees most likely will look at you with bewilderment though. At chains, be prepared to look at the ingredients yourself in the Radiator/Head Gasket sealant chemicals; this stuff is most often marketed now for "Head Gasket Repair"...K&W Block Seal is one product that has it as the major ingredient.
If you go to an independent NAPA/Carquest or local "unbranded" auto supply, the parts people tend to be more knowledgeable and most likely can direct you to the product you want.

Independent non-chain pharmacies USED to stock pure Sodium Silicate in bottles; if you can actually FIND an independent/olde-tyme pharmacy/drug store, you may find it there as well.
Nowadays just finding an independent pharmacy is a major task in itself in many areas of the country.

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When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL, if you have to ask what is "NORMAL" , you probably aren't !
Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, CHAOS, and HAVOC !