Probably a stupid question but.... Metal prep for primer

[chunkytfg]

As someone who's only worked on car bodywork previous to this time round I'm not used to buying steel raw with the black finish on it.

What do I need to do to it to prep it properly for paint? Specifically Jotun 87?

Ive already spent far too much on flap discs sanding and entire garden gait to make it fully shiny prior to primer but with the impending priming of a 4m wide garden gate I'm not sure I can face doing the whole thing so thoroughly again nor can my bank account for how many fap discs it takes!

Is it needed to flap disc the whole thing completely to remove all evidence of the black finish or is it okay to paint over it following a once over to degrease it? Or somewhere in-between?

 

[brightspark]

get it galved and painted . best shotblasted

 

[ajlelectronics]

Is it needed to flap disc the whole thing completely to remove all evidence of the black finish or is it okay to paint over it following a once over to degrease it? Or somewhere in-between?

I wouldn't take it back to bright metal. Clean and degrease, then 80 grit abrade it if that is what the TDS calls for.

 

[chunkytfg]

get it galved and painted

If only.

No way to transport it and budget is not exactly overflowing.

 

[brightspark]

best get all the mill scale of it one way or another before painting if you want it to last. needs roughing up not smooth , knotted wire wheel in an angle grinder will do it

 

[chunkytfg]

I wouldn't take it back to bright metal. Clean and degrease, then 80 grit abrade it if that is what the TDS calls for.

TDs says to prep to St 2 (ISO 8501-1) which looks like basically a clean and degrease with light sand to a matt finish.

 

[ajlelectronics]

TDs says to prep to St 2 (ISO 8501-1) which looks like basically a clean and degrease with light sand to a matt finish.

The TDS overrules anything that you might read elsewhere, in my opinion.

 

[chunkytfg]

just realised I put this in the wrong section!

@mods. any chance of moving it to the correct place?

 

[dave h 2]

This is about factory black primer on motor body panels and not the black mill scale that you get angle iron etc which as it comes straight from the rolling mill red hot and is very much raw steel

 

[ajlelectronics]

This is about factory black primer on motor body panels and not the black mill scale that you get angle iron etc which as it comes straight from the rolling mill red hot and is very much raw steel

That stuff is a nightmare and pickles easily (experience of old Ford panels). Based on that experience, I would want it back to bare steel.

 

[brightspark]

This is about factory black primer on motor body panels and not the black mill scale that you get angle iron etc which as it comes straight from the rolling mill red hot and is very much raw steel

he says doing gates so its mill scale

 

[chunkytfg]

he says doing gates so its mill scale

Yeah just standard 50x50 box section type steel. My previous experience was pre primed car panels so you had to sand back to metal to get a suitable weldable surface followed by a quick etc prime and away you went with however you wanted to paint it

 

[brightspark]

best if you can remove the mill scale and rough the surface up if u want a pucker job to last if not just rough up a bit and clean the oil and filth off and prime

 

[chunkytfg]

Okay so I guess my next question is which is the best way to remove it? Poly discs dont seem to want to touch it, flap discs last seemly no time at all and grinding discs seem like overkill!

do the flexible backing pads that take velcro sanding sheets work best?

 

[ajlelectronics]

Okay so I guess my next question is which is the best way to remove it? Poly discs dont seem to want to touch it, fall discs last seemly no time at all and riding discs seem like overkill!

do the flexible backing pads that take velcro sanding sheets work best?

I'm getting confused now. If it is panel paint, fetch it off with thinners or stripper. If it is mill scale, clean, abrade and clean it again as per TDS.

 

[chunkytfg]

I'm getting confused now. If it is panel paint, fetch it off with thinners or stripper. If it is mill scale, clean, abrade and clean it again as per TDS.

Sorry my auto correct is having a field day today.

It's nothing more than mill scale that needs removing. The black coating that normal lengths of metal box section come covered in.

 

[brightspark]

a knotted cup wire wheel on an angle grinder will rip it off fast

 

[chunkytfg]

I know the TDS keeps getting mentioned and I understand that but I'm trying to figure out if I need it back to shiny bright steel or is it sufficient to clean it and then scuff it up?

 

[chunkytfg]

a knotted wire wheel on an angle grinder will rip it off fast

thank you. I'll try that

 

[brightspark]

https://www.screwfix.com/p/titan-multi-material-wire-brush-100mm-3-93-/191PR?tc=RB4&gad_source=1&gad_campaignid=22609681624&gclid=Cj0KCQjw097CBhDIARIsAJ3-nxffnN1Co97DFNVkoX3j6vmW3N0owUmaERG9tLzdMcVffRPCY91YRSoaAkzvEALw_wcB&gclsrc=aw.ds

they hold up well and last ages