Steel welding & painting processes, working efficiently & reducing preparation

[mugget]

Seems like I'm well on my way & progressing with my welding projects, shouldn't be too long before I have some pieces completed.

I am using painted SHS and some black flat bar. I will be painting everything when all the welding is done. I just wanted to check on the best methods to reach this end with a minimal of doubling up on prep work etc.

Obviously I'll need to get out the flap disc and remove the paint from the SHS wherever it's being welded. But I'm just wondering if it's "best practice" to then use a zinc primer (weld through) do there isn't a bare metal section in the hole where the other piece of SHS joins up (if that makes sense)?

Or would you just leave it bare, weld it, then go ahead painting just like normal?

These pieces are going to be used in a vehicle fitout, so I guess you can say it's an "interior" use. But there may be occasional moisture if it's raining outside etc. (bringing wet tools & equipment into the cabinets etc.) I just want to make sure I do it right so that everything lasts a very long time, definitely don't want to be dealing with rust problems down the track.

A question on the black steel - I'll be removing the black finish at the weld points, but I'm not sure if it's okay to paint over the black finish? I sure hope so, otherwise that's a heck of a lot of work...

Cheers for any tips!

[Master Splinter]

The black finish is mill scale, and if you want to work to 100% best practice, it must be removed before painting to expose bright steel.

Otherwise, your best approach would be to skip any zinc-rich coatings, degrease it well, and spray on some epoxy based etch prime (etch prime and zinc rich paint don’t get along) followed by spraying on the industrial enamel of your choice.

Failing that, just slap on some Killrust or use that $9 tin of enamel that every man and their dog picked up from Aldi when they were on special.

[Michael G]

The industry way is to weld it up, black, blue it does not matter and then get it grit blasted. Prime within 10 to 12 hours (usually blasters can do this or get it done) and you should not have any problems. Grit blasting is not highly expensive either, so worth asking/ thinking about.

Michael

[mugget]

Ahhh... darn mill scale! Well at least I'm not using much of the flat bar.

Thanks Master Splinter. Okay, no zinc primer. I will have to check at the paint shop for a suitable primer. I was planning to finish it all in 2k, just because I have a stack of 2k clear already. I always get confused when people mention "epoxy primer"... is that just 2k primer? I have had a look around online, and I see people talk of "etch primer" and "epoxy primer" as two different products. Then again, a lot of that is probably just American terminology?

Good tip on the grit blasting & priming Michael. I had some motorbike parts powder coated not too long ago, it was quite a fair price (including sand blasting, priming etc.). I'll keep that in mind, in case I'm running short on time - otherwise I'm mad-keen to DIY this, I love spray painting! Haha

[KBs PensNmore]

Hi mugget,
I used to manufacture a product called "The Australian Chuckwagon", a storage unit in the back of 4WDs for campers, tradies, even our local Vet has several units. It was made from RHS rolled hollow section, Duragal 20 mm X 1.6 mm, zinc anneal sheet metal and black steel.
This was MIG welded together, ground off where required and then powder coated, never had a problem with the powder coating coming off. All they did was wipe it over with a cleaner, MEK I think it was, and then powder coated. We didn't sand the black steel unless it was very flaky or rusty. Found it was better to PC than try to paint it ourselves, cost versus time versus quality of finish. It was done in Notre Dame Ripple, having a lumpy effect finish, it didn't show grind marks etc.
If you already have the SHS, there should be no need to remove the paint for welding, it should arc through OK.
I used to do bar work using black pipe, also not sanded, just wiped over to remove dust, oils etc. Painted with Red Oxide undercoat and then 2 coats of enamel finish, usually black, sometime colour coded.
Kryn

[Master Splinter]

I think that most etch primers these days are epoxy based.

And you can get both 1k and 2k epoxies, as well as 1k epoxies that are 2k topcoat compatible. Just today I picked up a tin of 1k epoxy etch primer from Repco as it mentioned it was ok without topcoating for up to three months...which works out well for me as I am just starting to strip, de-rust and paint a trailer in industrial enamel.

Just make sure you have a good mask, as the zinc chromate primers are both toxic and carcinogenic (let alone the risk from 2k isocyanate hardeners).

[mugget]

Hhmmm... no need to hit the painted SHS with the flap disc before welding? I thought that MIG was fairly touchy with that? Stick welding I have heard is more robust. Maybe I'll give it a few tests on painted sections.

Well I checked out the paint & powder coating options today. 1k etch primer was recommended by the paint shop, no need to really worry about epoxy unless you need serious protection for full-time outdoor harsh conditions. I even used 1k etch on my van when I did some touch ups. If I wanted to paint this bench frame quickly in 1 session, I could spray the etch and leave it for 15 minutes, give it a light scuff and go ahead with the top coat. But the major drawback is that it still needs to be sanded/scuffed... no way around it. And that's a lot of fiddly work.

I did ask about epoxy primer and it is a fair bit more exxy...

If I take it to be powder coated there's no worries about leaving bare welds while I keep working on it (it will be indoors anyway). Only $95 and they will blast it, give it pre-treatment (iron phosphate), and powder coat. $115 for a fancy satin/flat/hammertone finish. 7-8 days turnaround and no from me. Yeah I think I will go with that option. I will have other things to paint so I still get to have my fun!

I just wondering about some sections that I'm going to weld in, the tube will be closed on both sections (if I weld it properly!). Not sure if I should go ahead and drill holes on the underside of the SHS, otherwise it could pop or something when it's put into the powder coat oven? Might have to check on that tomorrow.

[KBs PensNmore]

Hhmmm... no need to hit the painted SHS with the flap disc before welding? I thought that MIG was fairly touchy with that? Stick welding I have heard is more robust. Maybe I'll give it a few tests on painted sections.

Well I checked out the paint & powder coating options today. 1k etch primer was recommended by the paint shop, no need to really worry about epoxy unless you need serious protection for full-time outdoor harsh conditions. I even used 1k etch on my van when I did some touch ups. If I wanted to paint this bench frame quickly in 1 session, I could spray the etch and leave it for 15 minutes, give it a light scuff and go ahead with the top coat. But the major drawback is that it still needs to be sanded/scuffed... no way around it. And that's a lot of fiddly work.

I did ask about epoxy primer and it is a fair bit more exxy...

If I take it to be powder coated there's no worries about leaving bare welds while I keep working on it (it will be indoors anyway). Only $95 and they will blast it, give it pre-treatment (iron phosphate), and powder coat. $115 for a fancy satin/flat/hammertone finish. 7-8 days turnaround and no from me. Yeah I think I will go with that option. I will have other things to paint so I still get to have my fun!

I just wondering about some sections that I'm going to weld in, the tube will be closed on both sections (if I weld it properly!). Not sure if I should go ahead and drill holes on the underside of the SHS, otherwise it could pop or something when it's put into the powder coat oven? Might have to check on that tomorrow.

Hi mugget, No need to drill holes etc on blanked tubes, the metal doesn't get that hot in the oven, not like galvanising which will float in the bath, if it's sealed.
Kryn

[Master Splinter]

Tidy up the welds with a flap disk, rub the whole thing down with prepsol, slap on a coating of hammerite, and call it job done!

[Legion]

Don't weld through paint unless you have a strong fan blowing the fumes away. And even then, don't. It stinks and I hate to think what the fumes might do to you. Even an inch away it stinks. It probably sucks to weld too.

I've been using lanolin spray to prevent rust on welds before I get around to painting. Works well, just needs a bit of degreasing prep work. I use a biodegradable orange spray followed by sugar soap (which also "etches" a bit) right before priming.

[LordBug]

You can MIG through paint and other contaminants, not so much on lower settings but definitely easily on higher.
It's not nice, as Legion said horrible smoke, and sometimes a small bit will persist and show up in the weld in the form of pimples. But, if you just need to have it held in place temporarily or similar unimportant task, it's nothing to stress about.

Good habits are the best habits, but knowing the shortcuts can teach you what to look out for and not to do

[Legion]

Further to my last post, the lanolin spray you can weld through if you have to. It smells exactly as you'd expect burnt sheep grease to smell and I doubt it's anywhere near as bad as paint or galv. Best to clean it off though and it's a damn sight easier to clean off than paint or mill scale deep in a corner that you forgot to grind away. So you can prep your work for welding (grind it to bare metal) and then spray with lanolin and it's good for a looong while exposed to the weather. Then at weld time, quick degrease and you're good to go.

I've even tigged through it a few times for fun and it has almost no noticeable bad effects to weld quality. Fairly safe and easy to apply and remove. Magic stuff.

[mugget]

Cheers all. Yeah the paint smells bad enough when grinding or flapping (flap disc'ing?).

Good habits are the best habits, but knowing the shortcuts can teach you what to look out for and not to do

I like that! That's pretty much how I like to approach things as well, always trying to do things the "proper" way. But then if the situation calls for it I'm happy to do things in "dodgy" ways as well. Haha

Thanks to all for the tips and advice, everything is coming along quickly now...



I'll post up photos in a new thread once it's all done!

[soundman]

on the matter of epoxy primers .

The word epoxy confuses people ... it sort of brings up visions of araldite and two pack paint.

There are many single pack epoxies and its more common than you might think.

Wattyl Super etch is a single part epoxy bassed etching primer undercoat it contains zircon as a corrosion inhibiter and is good under pretty much anything.

Watty Kilrust is an epoxy bassed top coat .... its is an enamel because it contains ground glass ( or similar) as a filler.

Normal "enamel" ( correct me if I am wrong) is basicly an oil based varnish type resin ( like old school varnish) with pigments and ground glass as a filler.

While Superetch is a thinners bassed product, wattyl make a more or less identical formular but turps bassed under the killrust brand.

Other manufacturers will have a similar family of products.

cheers

[Legion]

I like the killrust paint system. But I've had similar results with the primer as I did with metalshield - the primer sprays great the first time but if I try to use it again a few months later it's gone off. I thin it but it's like spraying spiderwebs. Comes out already dry in big tendrils and absolutely covers my spray area with thick cobwebs and nothing ends up on the job.

Anyone recommend a better primer system that means I can buy 4L cans and use a bit at a time?