Primer

From the LUNAR List

I have a question for any and/or all of you out there. What is a good primer to use that will fill things like the weave on fiberglass cloth epoxied to an airframe? I'm not too keen on adding another layer of finish-cure epoxy on and sanding that smooth. I've heard terms used (such as in a PML catalog) "scratch filling primer". I'm not sure the Model Master grey primer I thin down to use in my airbrush will do it without ten or twenty coats. That stuff works great on PML quantum tubes and G-10 fiberglass fins, but for the 'glassed cardboard airframe I have, I need something better. Any ideas?

Geoff

Geoff, I just use the automotive sandable primer in a spray can with the same chemistry as the paint I am going to use and get good results on most paper tubes. I have not used it on fiberglass, but it should work fine. Be really careful of the chemistry. If you try to mix laquer and enamel paints you will get terrible results, unless you wanted a model that looks like it has lizard skin.

Bill

The Model Master primer is a very-low-fill primer. It's mostly for use on plastic models where you need to fill the scratches left after that rough as a cob 400 grit sandpaper.

Of things currently available at hobby shops, I suggest K&B UltraPoxy primer. It's outrageously expensive, but a little goes a long way. It's a 2-part item, so you need the primer, the primer catalyst, and some K&B SuperPoxy thinner. A 1:1:1 mix of partA:partB:thinner will go through my Paasche "VL" airbrush with a #5 tip with no problem. It's kind of weird stuff - it comes out glossy. But it sands pretty well. Any normal hobby paint should go over it OK. I've used all three brands of dope over it with no problem. It is very heavy, but there aren't a lot of light ways to fill up epoxy weave divots.

The UltraPoxy paint works well too. It's not as expensive at it first appears - it covers so well that little is needed,

The key to any sort of filling is waiting long enough after you apply it. Wait at least a couple of days with the Ultrapoxy, and preferably longer, to let it do as much shrinking as possible before sanding. Catalyzed primers can be sanded much more quickly than any air-drying product. I would recommend at least a week for any air-drying product.

Brett

Hey Geoff,

There is a product out there called Elmer's Finishing Wood Filler that can be found at Home Depot. Great stuff. I use it all the time for filling in the fiberglass weave on rockets, works like a champ and sticks like crazy to most surfaces. Here's what I do: -Stir some water into the FWF until the consistency is like packaged cake frosting or pancake batter. -brush this coating over the part and allow to dry -using some kind of a backer on the sandpaper I sand the part smooth. Just using your hand allows the paper to follow the contours of the divots rather than smoothing them out. -dust, prime, touch up filler as necessary, reprime, and paint.

The best primer I've found is one manufactured by Zynolite called Kilstain - Stain Killer. It's relatively inexpensive and it builds like crazy. Dries to recoat in a couple of hours depending on the film thickness you installed. For white rockets I've been applying this primer until I get the opacity I want then I install a coat or two of Mop-n-glo to give it a sheen. I do this for black rockets to come to think of it but I use plain old flat black for that.

Good luck

Bob

Go to "wildrocketry.com" and check out Kerry's Yank Black BrantX project. ?Day 8 (second page of article) tells about "Smooth Prime". Can spray it on fiberglass and requires less sanding with superior filling (even light glass weave). Sounds like what your looking for.

Mark

Geoff, I use an Automotive primer, Nason Surface Primer 421-30 gray. It is a water based primer that is thick and will need to be thinned with water to spray. Fills excellently, dries fast and sands very easily. Also being water based it is environment friendly.

Mark