New primer over (unknown) old?

PaulStrickland · #1 12-12-2009, 03:24 PM

I purchased what I thought was a new tailkit from a private party, and was pleased to see that some work had been done to start the HS - about 90% of the deburring! The issue is that he primed the spars prematurely.

Now that I have match drilled & deburred the ribs & brackets, it occurs to me that the thing really should be re-primed. I have no idea what primer was used originally though.

Is there a primer that's safe to use over unknown primer?

Phil · #2 12-12-2009, 08:03 PM

You should post up a photo and see if someone might recognize the color of it and maybe narrow it down to 2-3 choices for you.

I would say that it's no big deal though. I'd just clean the parts by wiping on some PPG DX-330 with a paper towel. Keep wiping it with a fresh paper towel until the towel comes back free of dirt and oil. (I'd expect a little primer color on the rag though, because it's wiping off the top layer of the primer)

Then I'd shoot it with the primer. I'm using Dupont VariPrime, but you can use what ever you decide. There are plenty of good choices out there.

Phil

MrNomad · #3 12-12-2009, 11:09 PM

One of the problems with painting over unknown and older surfaces is the lack of adhesion. It's important for subsequent layers to adhere to what's already there else the top coat will peel. At 200 mph, you'd be amazed what lousy adhesion will do.

The last post was correct. Clean it thoroughly so no grit is left on the surface. Using DX330, wipe in one direction only, and wear rubber gloves because DX330 is not good for your skin.

Prepping a surface for primer or paint is not like waxing your Honda. Your rag should accumulate dirt and then be discarded when it's full. Pour the cleaner onto the rag rather than allow the rag to deposit trash back into the can.

Personally, I would scuff sand the old stuff so the new primer has something to bite into. Wet sand with 3M 320 grit paper should help. You won't get a great chemical adhesion due to the age of the primer but you should get a mechanical bond.

After a final wipe with DX330, use a tack cloth to pick up any final particles. Once again, wipe in one direction only.

Most good paint shops can tell you what's already there and make a good recommendation. Study the process, try to work in as clean an environment as possible, and my all means, wear a good respirator or better yet, wear a fresh air respirator that draws in air from outside the booth.

Read the labels. Allow the chemistry to scare the *&^%$ out of you so you protect your hands and lungs. You only get two of each.

PCHunt · #4 12-12-2009, 11:29 PM

What's the reason for only wiping in one direction

. Just curious, as I am not a painter.

Phil · #5 12-13-2009, 08:11 AM

It pushes all the debris in the same direction and to the same edge. So you end up cleaning the 'upstream' portion of the swipe first and pushing the dirt 'downstream'.

Keeps you from swirling debris/oil over areas that have already been cleaned.

MrNomad · #6 12-13-2009, 08:52 AM

Phil has it right!! Look at the rag after wiping. You should see quite an accumulation of dirt. Experiment, run the used rag the other way. You have now left dirt all over the job which will not look good on your fuse.

Ditto for holding a rag over the opening of your $40 gallon of Prep Sol (aka DX330) and turning it over to wet the rag. Every time you do that you dump whatever trash was on the rag back into the gallon.

Woe be unto the next fellow who uses the cleaner to prep his surface and gets your leftover primer on his job.

PaulStrickland · #7 12-13-2009, 09:58 AM

Thanks guys - looks like a pretty simple solution. I'll clean & then shoot with some Napa 7222 - the one with zinc chromate. I'm primarily looking for corrosion protection on the interior mating pieces without mixing & cleanup. Once it's time to look at the exterior, I'll take a 200mph-appropriate approach & get more messy

hevansrv7a · #8 12-13-2009, 04:39 PM

Quote:

Originally Posted by PaulStrickland

Thanks guys - looks like a pretty simple solution. I'll clean & then shoot with some Napa 7222 - the one with zinc chromate. I'm primarily looking for corrosion protection on the interior mating pieces without mixing & cleanup. Once it's time to look at the exterior, I'll take a 200mph-appropriate approach & get more messy

You imply you are doing this to parts that have not yet been joined. If not so, then you need to re-think this. IMHO. If you cannot get between already joined parts then perhaps you'd be better off leaving it alone.

If this is only about mating surfaces, then why re-prime? The essential role of primer between mating surfaces is just to prevent galvanic corrosion and just about anything will do that - or so I've been told. For a layer under final paint - where it shows - that's a different issue. Ditto if the primer will be the final coat, like in some interior surfaces.