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-   -   Primer instead of sanding sealer, what kind of primer? (http://www.oldrocketforum.com/showthread.php?t=15843)

clhug 03-12-2016 05:06 PM

Primer instead of sanding sealer, what kind of primer?
 
I'm getting back into building rockets after probably at least 20 years since my last one. (Still got several I build over 20 years ago though!)

I notice the instructions are saying to use primer instead of sanding sealer. I've done several searches both here and general Google about this with pros and cons both ways.

Anyway, that's not really my question. I haven't been able to find anything to specifically answer my question..

My question is really, is there any special kind of primer I should use? Is there a modeler's primer? Or just any regular Krylon or Rust-o-leum primer from the hardware store?

Thanks!

chrism 03-12-2016 05:35 PM

Some builders choose to use a high fill auto primer to completely fill the grain. Others use Elmer's Carpenter wood filler thinned with water to fill the grain, others use the old fashioned sanding sealer, and others paper the fins.

mikemech 03-12-2016 05:53 PM

And some of us just want to fly and don't really care about spirals or grain.

ghrocketman 03-12-2016 10:26 PM

I fill grain the old fashioned way-the best way-with good old fashioned DOPE.
3-4 coats of Aero Gloss Balsa Fillercoat with sanding between coats 2/3/4.
I apply the first two coats 'wet' right over the top of each other; both sides of one fin then move to next fin until they have the initial two coats. Wait 2 hours or more, then sand, apply coat 3, wait 2 hours or more then sand and decide if a 4th coat is needed. Let final coat dry overnight, sand then apply two coats of Aero Gloss Sanding Sealer with sanding between coats.
This is time consuming but you get Balsa fins/cones/transitions with a completely filled smooth surface that is top-coat ready for your choice of color finish.
I usually use vintage Aero Gloss colored Dope as the color topcoat from a spray gun as I have a vintage stock of quarts, pints, and half-pints of all the Pactra colors that rivals most 80's hobby shops.
If using basswood for fin stock ONE coat of Balsa Fillercoat followed by one coat of Sanding Sealer is usually plenty.
Finishing with Dope is time consuming, but ALWAYS rivals all other finishing systems other than extremely costly Automotive Urethane (with catalyst/hardener) finishing systems.
If you can find old stock of two-part Petit Hobby-Poxy or K&B Super Poxy topcoat, that also rivals Dope.

clhug 03-15-2016 07:08 PM

Thanks for all the feedback, but most of it is really overkill for me. I'd really like to get back to the original basic question.

Yes, back when I built rockets regularly as a kid, I finished all balsa parts using coats of Aerogloss, sanding between coats. That's what I expected to keep doing when I recently started building again, so I was a bit surprised when the instructions in the kits I bought recently said to use primer paint instead of aerogloss. So I thought I'd give the primer a try.

I'm not a perfectionist by any means. I'm not going to put the time and effort in that some have described using various suggested methods. For me, I'm either sticking with the aerogloss, or going to try just regular spray in a can primer.

So going back to the original question, if I want to do the primer, can I just use regular Krylon or Rust-o-leum primer in a spray can, or is there is a specific modeler primer paint I should look for? I looked on the Testors paint rack at the hobby shop and didn't see a primer. The instructions don't give any detail about any specific primer.

Actually, now that I think about it more, even beyond the primer, what about just the regular spray paint? I've always used Testors paint. Is there a reason to prefer this vs. just regular Krylon or Rust-o-leum spray paint? I'm sure it's cheaper (probably the same price for 2 or 3 times the size of spray can)? Certain colors I'm guessing I can probably really only find in the model spray paint, but for basic black, white, red, blue, green, would just Krylon or Rust-o-leum do fine?

Thanks again!

bernomatic 03-15-2016 07:17 PM

Well I don't know about do fine. some will swear by one or other, but yes, Krylon and Rustoleum work to very well. Rustoleum filler primer works all right for covering and being sandable.

One thing is for sure, ask ten YORF'ers and you'll get eleven answers about what is best. :chuckle:

bernomatic 03-15-2016 07:27 PM

and btw, don't limit yourself to spray primers, I've had good luck with Rustoleum painter's touch Ultra Cover in the quart can. It just needs to be thinned a touch.


LeeR 03-15-2016 08:10 PM

clhug,

You can buy cheap primer that does a respectable job of filling grain on balsa, and seams on body tubes. While I like filler/primers like Duplicolor, I've had good results using Walmart brand cheap primer, called HomeShades. It's about $1.33 a can last time I bought it. Dries pretty quickly, and sands easily. If you cannot find this one, try Rustoleum Filler/Primer, which works well, it just costs a bit more. Some cheap primers do not sand well, and gum up your sandpaper., so you may have to experiment if you must buy an unknown brand.

Spray it on pretty heavy, and do maybe 3 coats to have a heavy build. If you get a run here and there, no worries, since you need to sand most of it off! The key is to leave primer in the balsa grain and body seams, and not have a thick primer coating on the entire surface. If you do this the grain and seams will never disappear, you'll just see less distinct impressions. Don't sand too deeply though, or you'll tear up the balsa or the cardboard. When you start to see traces of balsa and cardboard peeking thru the primer, you are getting close to the point where you should stop, and prime again. You may have to do this prime/sand cycle several times, depending on the depth of grain and seams. You final cost can be lighter than fill coats, such that you have a uniformly colored, smooth surface for your color topcoats.

kevinj 03-16-2016 09:02 AM

Get a primer that is compatible with your finish coats. Usually I get the primer made by the same company as the paint. Look for "sandable" or "high fill" primers.

kj

samb 03-16-2016 10:38 AM

2 Attachment(s)
Welcome back to the hobby !


Quote:
Originally Posted by clhug
...

My question is really, is there any special kind of primer I should use?


No. BUT... as you can tell from the responses, alot of people like filler or high-build primer, especially if you forego sanding sealer or some other filler on the wood parts.

Quote:
Originally Posted by clhug
Is there a modeler's primer?


Not that I know of.

Quote:
Originally Posted by clhug
Or just any regular Krylon or Rust-o-leum primer from the hardware store?


That'll work. Two popular cans are:


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