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joer308

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I have been using S-W P60 for most of my priming. However, there are times when I just want to prime a couple of small parts, not worth using the gun, so I bought some SEM rattle can primer.

I had great results with it till recently.

I m working on the roll over structure and primed the 4 pieces of F-01341, roll bar frame.

I t looked ok till the next day when the primer all flaked. I did the same prep I do on everything - scuff with fine scotch brite (gray), wipe with a degreaser (SX330 Acrli-Clean), let dry, prime.

So, then I wiped it down with Laquer thinner constantly changing cloth and removed all the primer. Then I wiped it down again the the SX330. Dried it very well, Prime.

Most 2 of the 4 pieces were ok, but 2 still had a little flaking, and I could scratch it off with my fingernail. I read a previous thread about this and thought I had it covered.

What's going on? Those frames seem like a different material?
 
I know I am not answering your question since I don't have much experience with the SEM rattle can primers but as I am building, I prep enough parts to be primed in one session and if there aren't enough parts, then I move to the next section to make more parts. This way with using the same primer (I am using Akzo epoxy primer) I can expect the same results and I have primed those rollbars in my previous build with no problem.
 
Bavafa said:
I know I am not answering your question since I don't have much experience with the SEM rattle can primers but as I am building, I prep enough parts to be primed in one session and if there aren't enough parts, then I move to the next section to make more parts. This way with using the same primer (I am using Akzo epoxy primer) I can expect the same results and I have primed those rollbars in my previous build with no problem.
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And that is exactly what I have been doing, just in the northeast in the winter, not many days that I can prime outside...
 
I used SEM primer and was generally happy. The process my paint store gave me was Scotch brite wet scrub with vinegar (mild etch); water rinse (if the water didn’t ‘sheet’ then clean with dawn, rinse again. Dry and spray. The only time I had trouble was when I decided the paint spray was too thin, and attempted to over-spray the mostly dry first coat. It all came off.
 
My guess is applying too heavy. Thin coats are the way to go. If you feel the need for more coverage apply a second thin coat after the first flashes off.
 
I use SEM primer, I did have it flake off the horizontal spars. My guess is it was fairly high humidity, haven’t had an issue since. I typically use Prekote and three light coats.
 
joer308 said:
I have been using S-W P60 for most of my priming. However, there are times when I just want to prime a couple of small parts, not worth using the gun, so I bought some SEM rattle can primer.

I had great results with it till recently.

I m working on the roll over structure and primed the 4 pieces of F-01341, roll bar frame.

I t looked ok till the next day when the primer all flaked. I did the same prep I do on everything - scuff with fine scotch brite (gray), wipe with a degreaser (SX330 Acrli-Clean), let dry, prime.

So, then I wiped it down with Laquer thinner constantly changing cloth and removed all the primer. Then I wiped it down again the the SX330. Dried it very well, Prime.

Most 2 of the 4 pieces were ok, but 2 still had a little flaking, and I could scratch it off with my fingernail. I read a previous thread about this and thought I had it covered.

What's going on? Those frames seem like a different material?
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A couple of comments on prep:
1) Degrease before scuffing otherwise scuffing will blend any grease into the abraded surface.
2) Scotch brite gray is SiC, silicon carbide, this abrasive grit can cause galvanic corrosion in aluminum. See AC 43.13--1B for guidance and use scotch brite maroon instead because the abrasive is AO aluminum oxide, compatible with aluminum. Maroon is equivalent to 320 grit and gray is around 600 grit so it is also too fine.

Lack of adhesion is most likely caused by inadequate prep i.e. not clean enough and not scuffed enough. Also check temperature and humidity before spraying - if outside of range can cause problems. Also ensure that paint has been agitated thoroughly and applied evenly.

Per the TDS

HANDLING AND APPLICATION
PREPARATION:
Clean surface thoroughly with SEM Solve or XXX Universal Surface Cleaner. Apply per directions. For overall
refinishing, sand with 180 grit paper. For spot repairs, sand with 320 grit paper. Blow off and clean again with SEM
Solve or XXX Universal Surface Cleaner.
APPLICATION:
Note:
Lifting may occur if too much Self Etching Primer is applied or if Self Etching Primer is painted over too soon. It
is not recommended to apply color directly to Self Etching Primer. Self Etching Primer should only be applied to
steel and aluminum.
AEROSOL
Agitate thoroughly before using.
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joer308 said:
I have been using S-W P60 for most of my priming. However, there are times when I just want to prime a couple of small parts, not worth using the gun, so I bought some SEM rattle can primer.

I had great results with it till recently.

I m working on the roll over structure and primed the 4 pieces of F-01341, roll bar frame.

I t looked ok till the next day when the primer all flaked. I did the same prep I do on everything - scuff with fine scotch brite (gray), wipe with a degreaser (SX330 Acrli-Clean), let dry, prime.

So, then I wiped it down with Laquer thinner constantly changing cloth and removed all the primer. Then I wiped it down again the the SX330. Dried it very well, Prime.

Most 2 of the 4 pieces were ok, but 2 still had a little flaking, and I could scratch it off with my fingernail. I read a previous thread about this and thought I had it covered.

What's going on? Those frames seem like a different material?
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Try some of this stuff as your last step, right before you prime. https://a.co/d/iZE79gO

61jjlomvXWL._AC_SL1200_.jpg
 
joer308 said:
. I did the same prep I do on everything - scuff with fine scotch brite (gray), wipe with a degreaser (SX330 Acrli-Clean), let dry, prime.
?
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sorry but that is WAYYY too fine for paint adhesion to a metal substrate. Steel needs sandpaper. Even a maroon pad is too fine on steel, even though it is marginally ok for aluminum (deeper scratches due to softer metal). The grey pads are for intercoat work not substrate prep.

Hit it with 220 or 180 grit and primer will grab much better. Yes, you will need a couple more coats to fill in the scratches.
 
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Try a different can, I had one during COVID that was garbage. Bought another can from the same place, same result. Bought a different can from a different supplier, same product, different lot, and had no issues.
 
I tried some automotive Self etch primer after following a tuber pre treat advice. It was bad!!! I'll accept the blame, but no more of that for me, solved my prime vs unprimed debate.

I want to take the SW paint class and then just follow all one system.

The rattle can I used had no specific directions on prep.
 
Years ago, I had occasional bad results priming. I traced it to using lacquer thinner, which can leave a residue, and switched to acetone. Lacquer thinner is a blend of solvents which may vary by manufacturer and even batch to batch and can contaminate paint. Acetone is a single chemical which evaporites residue free. For a final wipe or thinning the primer, acetone seems to work much better.
 
A couple observations:

1) SEM just totally HATES water of any kind. A humid day is probably enough to prevent adhesion.
2) There's something about that rollbar material that really made the primer not want to adhere to it. Its really interesting that you had the same experience. I'd try roughing it up with coarser sandpaper first. Thinking something like 320....

-G
 
georgemohr said:
A couple observations:

1) SEM just totally HATES water of any kind. A humid day is probably enough to prevent adhesion.
2) There's something about that rollbar material that really made the primer not want to adhere to it. Its really interesting that you had the same experience. I'd try roughing it up with coarser sandpaper first. Thinking something like 320....

-G
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Hey George, something IS different about that rollbar material, it just doesn’t look or feel like all the other bits.
…. I did it a third time, used maroon scotchbrite, clearned it twice with sx330, and it came out ok…
 
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