How have I screwed up this primer?

[julianf]

Epoxy primer -

You can see at the bottom left of the second photo that the coat is thin, but some areas were much thicker and suffered just the same.

I sanded the steel and sprayed down one part with thinner, but not the others. But all parts are the same with the error. I still suspect improper cleaning.

I sprayed an alloy part also. Same error. Maybe a little less so, but still there.

Lechler product, mixed as per sheet.

 

[The_Yellow_Ardvark]

Silicon impurities on the surface?

 

[Munkul]

I'd say silicon too.

It's a right barsteward to get off, too. Back down to bare metal if possible. Etch primer might help, I know it did for me one time on a car, anyway.

 

[awemawson]

Probably Silicone rather than Silicon.

 

[Barking Mat]

A second coat?

 

[Alan Reynolds]

That is surface contamination. Looks like silicone as others have said. I've seen it just keep on "fish eyeing" even after cleaning. Even touching the panel with your fingers can cause problems. Try using acetone to clean off the rubbed down panel then a tack cloth. If you don't clean the dust off, any dust containing silicone can cause little pinholes. I had one panel that still fish eyed even after going to bare metal a couple of times. Horrible stuff once it's in the metal.

 

[Ruffian]

Could be solvent pop also.

But either way not degreased properly.

 

[julianf]

Ok, so I've been out, and stripped back to bare metal using thinners.

I then recoated, and the job looks just the same!

Air from the compressor is going through a 3 stage to a belt pack, with a small line from the belt to the gun.

I've not used this pipe in ages, but I can't think it's the issue. It's never been used with auto oilers or anything but won't have always been used with the 3stage filter either.

This coat is no better than the last, but I'm tempted to let it harden off and then see if I can't sort it out.

I can be certain that the contamination is not comming from the metal, as the amount of thinner etc I used to take off the previous coat will certainly have cleaned up the surface good and proper.

 

[mr haynes]

Do you have a filter on the gun?
Hose could be the problem

 

[julianf]

Do you have a filter on the gun?
Hose could be the problem

No filter on gun.

What would I need?

But I'm also thinking I should buy a new hose.

I actually keep one just for the 3stage to air fed connection, so I know that's clean. But the whip one has been knocking about for ages, and, indeed, this is the first time I've used it for ages too.

 

[mr haynes]

there's the disposable kind like this
https://www.ebay.co.uk/itm/Starchem...058403?hash=item1ed422a223:g:0JQAAOSwc2FaJ~9N

 

[mr haynes]

cheapy reg combo

https://www.ebay.co.uk/itm/Air-Pres...noa=1&pg=2047675&_trksid=p2047675.c101224.m-1

 

[julianf]

I have in mind that maybe I purchased one of the second units some time back and have never used it!

I think I'll need to check my emails for invoices and, if I did, it will be time to go on a hunt.

(It may have just been the reg though, not the filter)

Again though, I've been careful with the other pipe so it may be simple enough just to add a small length to my next paint order and hopefully sort it that way?

 

[julianf]

...no, it seems the one I have (somwhere!) is just the needle valve / gauge, not the filter.

 

[mr haynes]

I'd be tempted first to do a little mix and do a small test spray on something known to be spotless.
My initial thoughts were in line with the others suggesting silicone contamination
i used to use the disposables, many moons ago, even with my knackered ringed wee compressor and had no contaminant issue

 

[julianf]

I just can't see how the job can still be dirty if I've painted it, then used enough paper and thinner to wipe away all of the failed layer of paint?

I mean if I've done enough wiping to remove a layer of paint, but there is still contaminants, I kind of have no hope!

I'm not really even saying there isn't. I mean somthing is going wrong. But my logic just does not work that I can managed to wipe away a whole layer of paint off a job, but still leave a problem chemical behind. On a previously sanded bit of metal.

I reckon it's got to be hose, or user error.

 

[mr haynes]

If hose is the problem you should get the same result on a different surface, hence my test suggestion before spending any money.
Either way, i think the filter on the gun is probably a good idea for multi use hoses
Other possible entry for contaminant is mixing cups, stick etc, something else to consider

 

[julianf]

Mixing -

New cup from middle of the stack.
Fluids pulled up using 10mm out of date medical syringes. The ones that you break out of their own 'sterile' packs.
Mixed with the screwdriver I use for my resin based printing inks. Which is probably one of the cleanest things in our place!

I think what I'll do today is, instead of the old small hose, use my normal long hose that I use for evreything else.

It gets constant use and is always connected via a trap, so, whilst it's not had a restricted life (like the one I use for the air fed mask) it's been blown through constantly with clean air.

I'll do that in a few hours and see if the result is better.

I didn't strip last night's work, so it will be over the top of whatever is there now.

 

[carbon]

As you are connecting through a three stage filter it shouldn’t need a filter to the spraygun but one could be connected in the outlet from the belt regulator. I only use one airline for my air fed mask and it doesn’t get used for anything else. This air line is the only one I have that has euro style couplings so no chance of it being connected anywhere else.

 

[tom2207]

oil from your compressor , would be my guess , separate oil separator and reg needed ,
providing every thing has been cleaned well , and youve drained your compressor recently for water .
How olds your compressor , has it run a life time driving air tools etc.