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BANGKOK 24 May 2019 19:58
canopy

Painting steel beams

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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.

 

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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.

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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).  

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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."

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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, 

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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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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!

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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.

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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?

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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.

E2041554.jpg.88adf40057e4dce2e760bb7b4fdb05ae.jpg

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 

IMG_7249.PNG.5635d654b45e2009df54d28cc67517c8.PNG

 

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.E4043471.jpg.87277a423cd7c67d29416a43c4c6df70.jpg

 

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.

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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.

 

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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 🙂 

 

E2041554.jpg.88adf40057e4dce2e760bb7b4fdb05ae.jpg

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Posted (edited)
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 by sometimewoodworker
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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

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