# Why Prime?

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#### Joekeyo

##### Well-Known Member
Many of us BARS did not prime our rockets on our first round of rocketry back in the 60's, 70's etc. I never noticed any paint flaking off or other problems that I would associate with not using primer.

My understanding is that the main purpose of primer is to help paint adhere to surfaces that it normally would not stick to very well. Metal comes to mind.

Paint sticks to paper and wood just fine. Some of our paper is covered with glassine, and the wood many have some CWF on it, but paint seems to stick to glassine well (see 1st paragraph). My CWF instructions mention painting, but not priming. I assume it is a paintable.

I use a light coat of primer to detect any grain that may have been missed after several coats of CWF. If it looks good, I paint. If it doesn't, then I sand it off and put on more applications of CWF. It's an inconvenient truth that paint does not cover, it colors. In fact sometimes it makes mistakes stand out. Thus, my techinque.

Other than this I am considering abandoning using primer on wood and paper (even with glassine) unless someone can come up with some good reason(s) to use it one these materials.

#### mbeels

##### Yes balsa
I think that the only reason I prime is to get a smoother finish. I can sand the primer to a better surface than I can CWF, bare cardboard, or wood. The primer helps fill in the CWF. Also, if I really want smooth, I can wet sand the primer and get a very good surface (but I don't always do this).

#### rharshberger

##### Well-Known Member
Many of us BARS did not prime our rockets on our first round of rocketry back in the 60's, 70's etc. I never noticed any paint flaking off or other problems that I would associate with not using primer.

My understanding is that the main purpose of primer is to help paint adhere to surfaces that it normally would not stick to very well. Metal comes to mind.

Paint sticks to paper and wood just fine. Some of our paper is covered with glassine, and the wood many have some CWF on it, but paint seems to stick to glassine well (see 1st paragraph). My CWF instructions mention painting, but not priming. I assume it is a paintable.

I use a light coat of primer to detect any grain that may have been missed after several coats of CWF. If it looks good, I paint. If it doesn't, then I sand it off and put on more applications of CWF. It's an inconvenient truth that paint does not cover, it colors. In fact sometimes it makes mistakes stand out. Thus, my techinque.

Other than this I am considering abandoning using primer on wood and paper (even with glassine) unless someone can come up with some good reason(s) to use it one these materials.
Glassine is paper aka super-calendared paper, that why paint sticks to it well. Primer is also to meant to fill minor imperfections and is much easier to sand than paint. Most of us as kids building rockets didn't have access to, primer also gives the surface a nice even color so that the paint hasca nice even colr as well. Most paints are not entirely opaque so differences in the substrate colors show as slight shade differences between the parts. A white nosecone, brown paper body tube and balsa colored fins would require more coats of paint to get all three to the same shade, or the rocket could be given a coat or two of smooth sanded primer (which is opaque) and less paint used.

#### Funkworks

##### Low Earth Orbit, obstructing Earth's view of Venus
The goal of priming and sanding is to tune the roughness and defect level to your liking.
(Edit: and to have a uniformly coloured canvas)
The goal of paint is only to have color.

If you use color only, you might end up with defects you can't repair.

It really just depends on your priorities. At first, I would've been fine with launching a raw paper towel roll, but now with killer alien viruses all over the place, I'd rather just stay home and practice nice finishes.

#### Joekeyo

##### Well-Known Member
I think this is a great conversation. Thank you for your informed opinions

My original post did say that I will be using primer to tune the roughness, so I concur. Based on my experience it takes more light paint to get good coverage on dark primer than on brown glassine. Specifically white paint on grey primer. Using a light colored primer could mitigate this. I expect this is due to the paint not being entirely opaque.

Good point about primer providing an uniform base. Back in the day, I did not fill the spiral on the BT. I do now. I think it is worth it to fill the unsightly spiral. After sanding off the CWF on the spiral, the tube is a far cry from being uniform in color.
.

##### Live to Build . . . . . . Build to Live
I've found that it's easier to "build up layers" of primer than it is paint. Because primer doesn't have a protective finish (satin, semi-gloss- gloss), primer seems to off-gas easier / better, which means less "paint herpes" issues.

#### Spitfire222

##### Well-Known Member
I've found that it's easier to "build up layers" of primer than it is paint. Because primer doesn't have a protective finish (satin, semi-gloss- gloss), primer seems to off-gas easier / better, which means less "paint herpes" issues.
Not to mention there are specific "filler primers" with the express purpose of being a mild filler of imperfections, and that are easily dry or wet sandable to get a decent finish with a minimal effort.

#### neil_w

##### Slowly reviving
My priming regimen varies with my mood.

Filler/primer: almost (but not quite!) always. Main purpose is final stage of filling/smoothing grain and other rough spots. After sanding there's not much left, so I don't think it serves all that much purpose as a base layer for paint. I try (not always successfully) to leave enough on plastic parts to serve as primer; definitely good to have something there to enhance adhesion to plastic.

Regular white primer: Sometimes. As mentioned above, it does provide a consistent color base for whatever's going on top of it. I usually prime when I'm applying light colors. That said, I've done some rockets in white Rusto 2x without primer underneath with good results. Of course Rusto 2x is advertised as painter/primer in one, so that is no doubt part of it. When I do use primer, *usually* I will apply it in the same session as my top coat: one or two light coats of primer, about 10 minutes apart, followed by two or three top coats, also 10 minutes apart. All is finished within the 1 hour recoat window.

Why do I not sand the primer before applying topcoat? Well, in my experience with Rusto 2x, it doesn't help that much. Most effective time to sand 2x is just before final heavy topcoat. What my routine has become, mostly is: Apply full topcoat. When dry, evaluate: if not smooth (about 50% of the time), wet-sand and then reapply one heavy coat. That final coat is usually very good. But because I hate painting, I will only do it if I'm really unhappy with the first topcoat.

#### mikec

##### Well-Known Member
I've spent some time wondering why I was using primer also, especially with the newer supposedly paint+primer Rusto paints.

One reason is that some colors (reds, oranges and yellows, and fluorescents for sure) look drab over anything but white primer.

I'm pretty lazy with regard to finishes but the primer step is so easy even I usually do it.

#### neil_w

##### Slowly reviving
I'm pretty lazy with regard to finishes but the primer step is so easy even I usually do it.
It is definitely true that primer is very easy to apply and relatively (!) foolproof compared to topcoats (especially gloss).

#### mbeels

##### Yes balsa
When I do use primer, *usually* I will apply it in the same session as my top coat: one or two light coats of primer, about 10 minutes apart, followed by two or three top coats, also 10 minutes apart. All is finished within the 1 hour recoat window.
I had never considered that was possible. I always waited days (out of habit). I do tend to spot sand parts of the primer coat, even if I don't wet sand the entire thing. But good to know that a single session prime + paint is possible.

Lately I've been brush painting a household exterior latex primer and I'm happy with the results. Some light sanding with 400 grit eliminate the brush strokes, and it fills moderately well (not as well as a true filler - primer, though).

#### neil_w

##### Slowly reviving
I had never considered that was possible. I always waited days (out of habit). I do tend to spot sand parts of the primer coat, even if I don't wet sand the entire thing. But good to know that a single session prime + paint is possible.
The only reason I felt confident to try it was the Rustoleum told me it works. And I reasked the question several different ways to make sure we were talking about the same thing.

That said: I don't have a large enough sample size to be able to really specify how it might behave differently this way vs. letting the primer dry first.

#### dr wogz

##### Fly caster
I think as well, that paint properties / compositions have changed over the past few years.

The rattle cans of the 70's, 80's, 90's were solvent based, VOC laden clouds of colour. The paint stuck, covered, and was "on" when sprayed.

fast-forward to better health understanding, municipally demanded changes, and the all mighty \$ for lower cost ingredients has changed paint to be low VOC, easily removed from buildings & sub-ways, and generally "good" for the environment.. So, having a primer to act as an 'in between' layer for good adhesion makes sense..

(Of course, it also ensures said rattle can company can sell you 2 cans as opposed just tone one can of colour..)

for the record, I prime & paint. I didn't used to, but I find I get a better result when I do..

#### Joekeyo

##### Well-Known Member
Mood, lazy. I like these words. Does it have to be perfect? Cost-benefit analysis also comes to mind. Do I really want to spend more of my precious time to add yet another coat of freakin' CWF? The answer is probably yes, if I want it closer to perfect.

I am currently working on an Estes Sprint look-alike. This rocket was originally developed as a competition model. In that spirit I am trying to make it as aerodynamic as possible. Right now my time may not be quite as precious as during the last era, so adding yet another coat should be no big deal.

One of the things that spurred me onto thinking about the validity (cost-benefit) of primer was this article. https://rocketn00b.blogspot.com/2016/11/the-weight-of-paint.html Four parts. I thought it was well worth the read. He might be a noob, but he has some good insights. If you are lazy, like me, the bottom line is that paint comprised about 1/4 of the weight of the rocket and that he could not overcome the altitude lost from paint weight gain by making the finish smoother.

#### Joekeyo

##### Well-Known Member
I think as well, that paint properties / compositions have changed over the past few years.
I expect this might be true for decals. They sure seem a harder to work with these days. I don't think it's me. Back then I was much more impatient (flyitis) and klutzy.

#### Funkworks

##### Low Earth Orbit, obstructing Earth's view of Venus
Not to mention there are specific "filler primers" with the express purpose of being a mild filler of imperfections, and that are easily dry or wet sandable to get a decent finish with a minimal effort.
Yes I like these (I use the Duplicolor one), because - and I'm still not sure if this is normal - when I use it, it actually sprays liquid droplets and makes a total wet mess on the rocket, but it dries quickly and sands very well so I end up with a real smooth finish. I just like the contrast between the initial mess and final sanded surface.

##### Well-Known Member
I've found that it's easier to "build up layers" of primer than it is paint. Because primer doesn't have a protective finish (satin, semi-gloss- gloss), primer seems to off-gas easier / better, which means less "paint herpes" issues.
That, plus each layer of primer tends to deposit a significantly thicker layer of paint (vs. layer enamel).
If you need to fill uneven grainy balsa wood surfaces, or paper tube spirals, spraying primer is a more efficient way of accomplishing that goal.

Yes I like these (I use the Duplicolor one), because - and I'm still not sure if this is normal - when I use it, it actually sprays liquid droplets and makes a total wet mess on the rocket, but it dries quickly and sands very well so I end up with a real smooth finish.
+1 for Duplicolor line of automotive paints / acrylic lacquers (from AutoZone or Amazon).
I'm toying with Tamiya paints right now, and they seam to work consistently and reliably as well, but yet more expensive.

#### SCIGS30

##### Well-Known Member
Back in the day I don't think I used primer, but paint was different. Now with EPA regulations paints have changed and primer helps with adhesion.

#### Exactimator

##### Well-Known Member
I've spent some time wondering why I was using primer also, especially with the newer supposedly paint+primer Rusto paints.

One reason is that some colors (reds, oranges and yellows, and fluorescents for sure) look drab over anything but white primer.

I'm pretty lazy with regard to finishes but the primer step is so easy even I usually do it.
I have the same attitude. If I can get colored fiberglass I do that and skip the painting step. When I DO paint I prime. I wanted to paint a rocket burnt orange, and instead of finding a burnt orange topcoat I just used black primer. It got me close enough. I don't worry too much about finish since my rockets get scratched during travel to and from the launch, from the rail, and when it lands.

#### BABAR

##### Builds Rockets for NASA
Regular white primer: Sometimes. As mentioned above, it does provide a consistent color base for whatever's going on top of it. I usually prime when I'm applying light colors. That said, I've done some rockets in white Rusto 2x without primer underneath with good results. Of course Rusto 2x is advertised as painter/primer in one, so that is no doubt part of it. When I do use primer, *usually* I will apply it in the same session as my top coat: one or two light coats of primer, about 10 minutes apart, followed by two or three top coats, also 10 minutes apart. All is finished within the 1 hour recoat window.
Just confirming/clarifying

You are saying in one sitting you can put on a coat of primer, do another coat in 10 minutes, and then 10 minutes later you can put on your final color coat?

#### neil_w

##### Slowly reviving
You are saying in one sitting you can put on a coat of primer, do another coat in 10 minutes, and then 10 minutes later you can put on your final color coat?
Yes, as officially approved by Rustoleum. I know, sounds crazy. Seems to work, though, as long you don't want to sand the primer as part of your process. That's how I did the Skywriter yellow.

#### rharshberger

##### Well-Known Member
Yes, as officially approved by Rustoleum. I know, sounds crazy. Seems to work, though, as long you don't want to sand the primer as part of your process. That's how I did the Skywriter yellow.
iirc it also requires the paint and primer being the same brand and type ie Rusteum Industrial or Heavy Duty (whichever its called) or similar. I used Rusto Industrial (Lowes) primer and paint on my kids swing set, shot the primer 2 coats and 20ish minutes later the color coats 2ish coats, then reassembled the swing about 2-3 hours later.

#### Jim Hinton

##### Well-Known Member
Hi Folks;
One of the main reasons I like primer is that it makes it much easier to see surface imperfections. Some things that don't show up on the bare surface are immediately visible under primer.

Jim

#### KenECoyote

##### Well-Known Member
Hi Folks;
One of the main reasons I like primer is that it makes it much easier to see surface imperfections. Some things that don't show up on the bare surface are immediately visible under primer.

Jim
I was going to say the same thing!

I've been using primer for years now and love it. Recently I felt lazy and just did final color and it just wasn't very good tbh. Have been using Rusto Filler/Primer (usu found in Walmart auto section too) and Rusto 2X almost exclusively. YMMV

#### Philip Tiberius D.

##### Old Fashioned 2.5oz Rye/H2O 8 drops Orange Bitters
I have problems with some primer “clogging” my sandpaper (there’s a joke there somewhere), Rusto 2X in Grey very, very rarely does this. I purchased some Dupli-color to try. Searching for the Golden Squirrel ....

#### Jim Hinton

##### Well-Known Member
I have problems with some primer “clogging” my sandpaper (there’s a joke there somewhere), Rusto 2X in Grey very, very rarely does this. I purchased some Dupli-color to try. Searching for the Golden Squirrel ....
The Dupli-color sands out really nice from my experience. Some primers are less prone to clog paper with long dry times. I've had less clogging after waiting about a week to sand. The Dupli-Color dries real quick and seems to be immediately sandable. Just a little hard to find.

Jim

#### Philip Tiberius D.

##### Old Fashioned 2.5oz Rye/H2O 8 drops Orange Bitters
It is hard to find, I had to order it off Amazon - you think Tulsa would have a supplier and probably does I just need to dig.

#### SCIGS30

##### Well-Known Member
Yes, as officially approved by Rustoleum. I know, sounds crazy. Seems to work, though, as long you don't want to sand the primer as part of your process. That's how I did the Skywriter yellow.
I do the same thing, I prime then apply the top coat the same session with no issues. I dont use filler primers so I normally dont sand the primer coat.

#### Hooked On Rockets

##### Well-Known Member

Unprimed.....

Primed, and sanded, and primed, and sanded......
THEN painted.
BTW, this is not color-sanded or buffed out, this is just as I sprayed it (yes knowing how to paint is definitely crucial to making all the prep work worth doing all the work).

The orange is Krylon "Farm Implement" in Husqvarna Orange, A VERY good paint with the good spray tip and a reasonable recoat time...within 2 hours or after 48.....

The black is Dupli-Color Gloss Acrylic Lacquer.
Again, no buffing or color sanding etc.

One rocket (orange) deserves that, the first one (red) didn't.

It's all about what effort makes you happy with your finished product.

SS

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#### Greg Furtman

##### Well-Known Member
I have problems with some primer “clogging” my sandpaper (there’s a joke there somewhere), Rusto 2X in Grey very, very rarely does this. I purchased some Dupli-color to try. Searching for the Golden Squirrel ....
Philip, I've been using 3M ScotchBrite #7414NA for sanding my primer coats. It's like 3D sandpaper, and when it starts getting clogged I can throw it in some solvent to clean it up & use again.