So what does primer really do?

[Justin Horne]

Hi.
I always prime my rockets, after i didn't on the first one, and i can tell. But what exactly does primer do? I've always been told that the primer gets the surface ready, but what's it do? I mean, if the primer sticks to the surface, why can't the paint?

Well, thanks.

 

[Elapid]

helps give an even-colored surface so the paint is more uniform, and primer also is easier to sand than paint is, so it saves work when trying for that perfect finish!

 

[DJ Delorie]

All paint is about compromise - color vs texture vs durability etc.

Primer is formulated to stick, sacrificing everything else. Sandable primer is formulated to stick and dry fast and brittle so it can be quickly and easily sanded.

Paint is formulated for color and texture, sacrificing stickiness. Primer happens to be one of the things it sticks well to.

So, the purpose of primer is to create an ideal surface for the paint.

 

[BlueNinja]

And it's really handy to put a different color of primer than your BT! I didn't prime my Initiator and when I tried to scrape the paint off a crimp i couldn't tell where the paint ended and the tube began... with primer I would have had a point where when I saw white beyond the gray, that's where to stop.

 

[DJ Delorie]

I suppose if you alternated primer colors, you'd know when you've got all the grain filled because the last color comes off evenly ;-)

 

[DynaSoar]

Originally posted by Justin Horne
Hi.
I always prime my rockets, after i didn't on the first one, and i can tell. But what exactly does primer do? I've always been told that the primer gets the surface ready, but what's it do? I mean, if the primer sticks to the surface, why can't the paint?

Well, thanks.

Primer sticks to the surface AND to the next layer of paint. The next layer can bond to it better than it can to paper, glass, etc. If it could bond just as well, then it'd be primer. And it'd have a primer-like finish, ie., not very good. Without primer, the top layer can peel if it doesn't bond well enough. This is often seen on high impact styrene plastic nose cones and fins.

 

[lalligood]

Originally posted by DJ Delorie
All paint is about compromise - color vs texture vs durability etc.

Primer is formulated to stick, sacrificing everything else. Sandable primer is formulated to stick and dry fast and brittle so it can be quickly and easily sanded.

Paint is formulated for color and texture, sacrificing stickiness. Primer happens to be one of the things it sticks well to.

So, the purpose of primer is to create an ideal surface for the paint.

Another benefit of primer is to create a consistent colored base regardless of the materials underneath--particularly for lighter colors. For instance, if you sprayed bright yellow paint directly onto a white plastic nosecone & natural paper/glassine tubes, you would see a shade or 2 difference (the body tube being darker) between the parts. Perhaps after *several* coats you might be able to get them to match up. But with even a single coat of primer, that difference would be *greatly* reduced--in fact, probably all but eliminated

HTH,

 

[Stymye]

what Lalli and elapid says,

it gives the the various surfaces,filled fins,plastic cone, paper tube an even finish , texture,and color, so your paint doesn't have uneven shadng , texture, or gloss to it.

it's not necesarily for paint to stick

 

[Micromeister]

I think the question should really be WHY do we use primers?

What holds paint to the ANY surface? Surface tension..(the absence of air). This helps explain how we can remove an entire sheet of dried paint film for a fingernail or Glass window. Without getting into the chemistry, paints are forumlated to (Cross-link) bond to the surrounding microscopic platelets of pigment/vehicle forming a continuous film sheet. However they do NOT stick to the surface to which they are applied. The only HOLD paint has is that surface tension on the microscopic scratches and imperfections in the surface to which they are applied. Hense the reason we should always sand the surface to be painted before applying any coating. Sanding gives whatever base material being painted some (tooth) for the paint or primer to hold on to.
Most primers have chemical additives that "etch" the surface to which they are applied, adding to the HOLD on the sanded surface. This HOLD and the surface tension create a better bond than any paint could ever achieve. After primers are applied they can be sanded, filled and overcoated with paints to give the mirror like shine we are striving for.
The long and short of it... We have to start out Dead Flat(with primers) to end up High Gloss
Class over..pay the fee at the door
hope this helps