Painting steel beams

[canopy]

I will get steel beams for roof framing that will be welded together. I want to make sure the steel has long lasting protection. What is good for (1) removing the oil, (2) primer, and (3) is finish paint also needed / what type?

 

Adding to my confusion the welder, who is considered the best in the area, said to prime everything before welding and then prime again after but I was reading online paint should always be removed before welding.

 

[Fruit Trader]

Our work sheds have exposed steel trusses, we used following process to protect the steel.

 

Clean with turpentine dampened rag to remove mill black.
One coat of grey primer.
Welding.
Primer touched up around welds.
Two coats of Rust-Oleum.

 

Unless critical inspected welds don't worry about a little primer contamination in the weld.

[bankruatsteve]

Not a welder but my observation of stuff done on my home(s), they always prime before welding and sometimes even after.  A (long?) while back in this forum, someone said the red oxide primer binds well with the oil (IE: doesn't need clean first).  

[CGW]

The area that will be welded should be clean and grease free - for a "decent" weld, so it doesn't matter if the steel is primed before or after welding as with the quality of steel here and methods of welding you will never get a good weld, acceptable yes.

The important thing is, that most Thai's don't seem to grasp is after applying primer you need to seal the primer with a finish, primer breathes, useless for long term protection.

"A primer or undercoat is a preparatory coating put on materials before painting. Priming ensures better adhesion of paint to the surface, increases paint durability, and provides additional protection for the material being painted."

[sometimewoodworker]

3 hours ago, CGW said:

The area that will be welded should be clean and grease free - for a "decent" weld, so it doesn't matter if the steel is primed before or after welding as with the quality of steel here and methods of welding you will never get a good weld, acceptable yes.

Humm.

 

The quality of steel available here is equal to that anywhere if you pay enough. The quality of welding certainly can be good, Thailand's welders are one of the trades where professionalism is quite common.

 

Depending on the material used to weld and the method some needs to be squeaky clean with others not so much. If bright shiny steel were the only kind where you can get a good weld many farmers would be out of business.

 

That said, a clean unpainted surface is preferable if you can then get to it to paint, 

[canuckamuck]

I have started washing the steel with soap and water and then priming. I did use thinner and rags before, but you go through tons of thinner and rags, and even then I had some projects where the grease bled through the finish. Soap and water is actually easier, and way less toxic. looks cleaner when you're done too. Just get it good and dry right away.

Depending on the project, I prefer to prime and paint last, but if its stuff that is going to be hard to reach, I prime and paint before welding, but grind my weld locations before welding.  Then touch up with paint.

[leyali]

Why not use zinc coated steel bars. No cleaning no primer no painting.
Only clean where you welding with tinner and brush then paint or spray with zinc paint.
They also zinc coated inside the steel, so long life.


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[CGW]

48 minutes ago, sometimewoodworker said:

Humm.

 

The quality of steel available here is equal to that anywhere if you pay enough. The quality of welding certainly can be good, Thailand's welders are one of the trades where professionalism is quite common.

Exactly! you can get ABS stamped steel here, but OP is installing roof beams, the quality is just above tin cans ???? 

Thai welders can be very good worked with many certified 6g Thai welders, but if they were stick welding roof beams? their welding would be acceptable but you would never come close to 100% quality welds due to the poor quality steel and the steel being so thin, it would have to be welded with an alternative method if you were looking for "100%" welds, even then doubtful due to poor quality steel. Stick welding was never intended for thin steel, they have adapted here - it works and does the job cheaply, but from an engineering standpoint its crap! 

Ideally welding surface should be at a minimum ground, if you tried to bevel it ! there isn't enough steel. A bit of primer is going to make no difference.

 

You can buy pre assembled and zinc coated roof trusses now, far superior - downside is off course cost!

[eyecatcher]

IPS (ion plated) steel costs maybe 100bt a length more for a 4x2 box, and looks like stainless steel.

my neighbor used them on his office roof 4 years ago, no painting or anything, still nicely polished today.

[CGW]

1 hour ago, eyecatcher said:

IPS (ion plated) steel costs maybe 100bt a length more for a 4x2 box, and looks like stainless steel.

my neighbor used them on his office roof 4 years ago, no painting or anything, still nicely polished today.

Wouldn't welding destroy the coating?

[sometimewoodworker]

3 hours ago, CGW said:

Exactly! you can get ABS stamped steel here, but OP is installing roof beams, the quality is just above tin cans ???? 

Thai welders can be very good worked with many certified 6g Thai welders, but if they were stick welding roof beams? their welding would be acceptable but you would never come close to 100% quality welds due to the poor quality steel and the steel being so thin, it would have to be welded with an alternative method if you were looking for "100%" welds, even then doubtful due to poor quality steel. Stick welding was never intended for thin steel, they have adapted here - it works and does the job cheaply, but from an engineering standpoint its crap! 

Once again it depends on the quality of steel you buy for the job.

 

My roof beams are certainly not just above tin can thickness or quality.

in this picture they are tacked in place before being cut to final length. They have all been primed as it's a lot easier to do at ground level rather than 4 ~ 7 metres up.

 

 

 Neither is the steel I used in this building 

 

Nore is it Crap from an engineering standpoint as if it were my 1 tonne under slung crane would have dropped on my head quite some time ago.

 

Yes you can buy thin walled, low quality steel profiles and yes they are cheap and not at all easy to stick weld however the skill of many of the Thai welders is such that they can produce perfect stick welds in that material. Certainly MIG would be easier and TIG even more so but they are either outrageously expensive or slow.

 

Do you know the steel that "canopy" is going to use? I don't and he hasn't said yet.

[sometimewoodworker]

9 hours ago, canopy said:

Adding to my confusion the welder, who is considered the best in the area, said to prime everything before welding and then prime again after but I was reading online paint should always be removed before welding.

Your welder will almost certainly be using E6013 2.5mm rods and they are perfectly capable of welding through the standard primer.

 

He has outlined the normal way of construction here there are millions of buildings built exactly like that.  An amateur will find it quite difficult to weld perfectly through the primer, not so the Thai professional.

 

What you will have read online will not have addressed the real world small house structural welding. It will have been either newly out of school welders, fabrication welders, or others where the subsequent welds are far more critically inspected, because of the places they are used, than is needed here. So in those cases because the slightest inclusion or porosity will be a fail (probably correctly so) they will have said that the weld area must be perfectly clean.

 

 

I would do as as he says prime, weld, descale, and prime. Then add some colour of oil based topcoat.

 

[CGW]

2 hours ago, sometimewoodworker said:

Thai welders is such that they can produce perfect stick welds in that material.

Nonsense, we obviously come from different backgrounds and use different standards, after 50 years in the industry starting as a time served Fabricator/welder and finishing as a project manager for 750 million dollars offshore units, I have gleamed some knowledge of steel, welding procedures & paint systems.

What do you classify as a "perfect" weld"? is the weld I have circled "perfect" it looks like bird@rap, its not even straight, at least there's plenty of it, shame its not evenly distributed ???? 

 

[sometimewoodworker]

1 hour ago, CGW said:

What do you classify as a "perfect" weld"? is the weld I have circled "perfect" it looks like bird@rap, its not even straight, at least there's plenty of it, shame its not evenly distributed ???? 

That isn't welded????. There are two tack welds holding it in position before it's cut to length, and as to being straight, you maybe correct or it could be the camera angle, it is a compound angle cut so it is the way it needs to be.

 

As I mentioned the kind of work you were involved in has little relationship to the kind of work in house construction here, apart from the point that they both involve melting steel.

 

An analogy would be the tables I build and ones you buy from Ikea, the are both tables but mine are constructed with expansion joints and wood the Ikea ones are made of paper (MDF) or sawdust (chipboard) covered with textured plastic or microns thin veneer and screwed together, in the correct place they both do the job they are designed for, with reasonable care mine will still usable in 50 years plus, with the same care the Ikea ones may last 5 to 10 years. Deeply scratch the surface of mine and it can be sanded and refinished again and again, do the same to the Ikea one and it's time to buy a new top.

 

There is nothing wrong with the Ikea furniture, it's built to a price and does the job it's made for and it does it adequately.

Edited April 18, 2019 by sometimewoodworker

[eyecatcher]

13 hours ago, CGW said:

Wouldn't welding destroy the coating?

then in that case you treat it thereafter with a matching product such as galvafroid which they use when putting together galvanised steel

[sometimewoodworker]

10 hours ago, sometimewoodworker said:

That isn't welded????. There are two tack welds holding it in position before it's cut to length, and as to being straight, you maybe correct or it could be the camera angle, it is a compound angle cut so it is the way it needs to be.

[CGW]

14 hours ago, sometimewoodworker said:

As I mentioned the kind of work you were involved in has little relationship to the kind of work in house construction here, apart from the point that they both involve melting steel.

I don't believe you ever did mention the above, but regardless, point taken - the fundamentals involved remain the same, though off course standards vary, which is fine as long as the end result is "fit for purpose" you were the one who questioned my original statement, which is correct, I could quantify further as to why - I was trying not to ramble on - but won't bore you any further!  ???? 

[shaemus]

Why not use galvanised Steel?

 

You can buy it from lots of places now. Inc global house. saves you alot of prep work.

 

As for welding it. same process, just remove the galv coating with an angle grinder/ flap wheel. and weld as normal.

then coat with a zinc based paint (tubro brand). i used a mig welder for my trusses. it puts much less heat into the metal, each joint is fully welded and then sealed. 

 

depending on where you live will dictate the availability. there is a lipped c channel availailable from Global @2.3mm wall thickness in various formats, this particular sytle has a strengthening pressing in the side wall.

 

When i did my structure i wanted to get galv I beam / H beam. Not possible where i am. so i just bought some standard steel (zubb) and wet snadblasted them, removed the flash rust with a flap disc. then painted with Jotun primer 2 coats and then a polyurethane top coat also Jotun. my workers though i was mental, but they had never encountered painting like it. normally they would just slap red oxide primer ontop of the half cleaned mill oil. 

 

Shaemus

[canopy]

Would love to go galvanized but I need 8 inch deep beams due to the spacing, spans and loads involved. I have been told galvanized isn't available in this size so will unfortunately go the laborious route of de-oiling, primer and finish coat.

 

[shaemus]

5 hours ago, canopy said:

Would love to go galvanized but I need 8 inch deep beams due to the spacing, spans and loads involved. I have been told galvanized isn't available in this size so will unfortunately go the laborious route of de-oiling, primer and finish coat.

 

what format of Beam, I beam H beam, C channel. there are galvanising factories around. where do you live?

have you looked at the lysght (bluescope) steel range of purlins etc ?, that is all galv and better than most you can buy locally. The cost of what you want to do with black steel will add up considerably if done properly. http://www.bluescope.co.th/segment-type/building-construction-en/ you might want to get a purlin catalogue from australian website to check you requirements and then speak to blue scope to see what they have. 

 

 

to answer one of your original questions, remove the oil with thinners and lots of rags (buy some chemical proof gloves as it is not very good for humans)

 

the jotun paint i mentioned you can buy from global house. i have also seen the brand International for sale on marine websites here in thailand,  i used a two part polyurethane as a mid coat twice then used a colour to finish .

 

i dont know what your design is or the spans etc. but you could use black steel for the base then glav on top. for rafters etc

 

As for the welding. you can buy a gasless Jasic mig welder and wire here in thailand. unless you builders are at expert level they will not be able to perform (good) weld using stick on the thinner metal.  i had all my trusses made for me by a contractor in Khon Kaen, and i just craned them up and bolted them togther. some were welded on site. the structure i made is well over engineered  but it wont rust, i will never have to paint it and it wont fall down whilst i am alive. the whole structure 100M2 took about 5 days. then i had to install the insulation and mesh my self . then the roof sheet. and guttering all of which is colorbond from Australia (nicer colors than than the Thai pallet)

 

Pm if you want to chat 

 

Shaemus

[mogandave]

The TOA “RustTech” is the best primer I have used, although once mixed, it only has a 60 minute pot-life...

Galvanizing would be best, and there’re companies that will hot-dip for you. If you’re MIG welding, running CO2 will burn the zinc off saving you the hassle of grinding.

[CGW]

23 hours ago, mogandave said:

running CO2 will burn the zinc off saving you the hassle of grinding.

fairly sure from what I remember it actually melts & causes porosity in the weld. (due to lower melting point than steel.) 

Edited April 30, 2019 by CGW

[mogandave]

fairly sure from what I remember it actually melts & causes porosity in the weld. (due to lower melting point than steel.) 

Perhaps is you’re welding on the Space Shuttle, but generally speaking, using CO2 the zinc will just burn off.

Welded galvanized in the HVAC industry for 18 years and have product installed and inspected all over the world.

[canopy]

There seems to be some folks here with considerable welding knowledge so if I might ask one thing. The beams will be laid out in a welded grid to support a flat roof. The top of the beams needs to be a flush surface with no weld bead sticking up. The welder said he will weld sides and bottom but not top. He said while he could weld the top and grind off the bead it's not a good idea because the beams could warp and go out of plane. Note these are 4x8 inch beams. This makes me uneasy. Doesn't sound as strong and any water that happens to get in there, say during construction, has no way out.

 

[mogandave]

There seems to be some folks here with considerable welding knowledge so if I might ask one thing. The beams will be laid out in a welded grid to support a flat roof. The top of the beams needs to be a flush surface with no weld bead sticking up. The welder said he will weld sides and bottom but not top. He said while he could weld the top and grind off the bead it's not a good idea because the beams could warp and go out of plane. Note these are 4x8 inch beams. This makes me uneasy. Doesn't sound as strong and any water that happens to get in there, say during construction, has no way out.
 

The drawing looks like rectangular tubing, is that correct?

Have you already purchased the material?

[canopy]

Yes & yes

[mogandave]

I would not weld the bottom either as welding the bottom will trap water. I would actually space it out such that I had a 1-3mm gap.

You might want to dip the ends in ZRC or some other cold galvanizing compound after cutting, but prior to assembly.

I would not have used tubing, I would have gone with C-channel.

Tubing will look better though.

[canopy]

I originally was going to use c-channel. There were pluses and minuses each way but at the end of the day tubing came in the most ideal dimensions for the project. c-channel would have meant running pairs of 3x8 inch beams to properly support the flooring. For future reference what do you see as the benefits of c-channel?

 

[mogandave]

You can get it GA
You can paint the inside
It doesn’t trap water
It’s generally cheaper

[mogandave]

I thought is was a roof, not a floor, or is it both?