Painting steel beams

[canopy]

Yes it is both a roof and a floor. Top will be outdoors with ceramic floor tiles.

Edited May 1, 2019 by canopy

[CGW]

1 hour ago, canopy said:

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.

 

Full weld and grind off - especially if you are in a humid place, welders and rods are cheap, corrosion can turn out to be very expensive.

[Fruit Trader]

No need to complicate this straightforward job. Clean and prime the steel get your top welding guy in action then coat the result with quality paint of chosen color.

 

Example shown at post #11 photo 2.

[mogandave]

Yes it is both a roof and a floor. Top will be outdoors with ceramic floor tiles.

What at you using for a sub-floor under the tile?

What’s supporting the roof/floor?

He may not want to weld the top as it can/will bow the joists down. More welding will mean more bowing.

How big is this? Are we welding in the air or on the ground?

[canopy]

Size 8x8M including eaves. Sub floor is cement board. Steel beams supported by load bearing q-con block walls with ring beam. Welding in the air.

 

Is it perhaps best as suggested to weld the sides and not weld the top and bottom?

 

[mogandave]

Size 8x8M including eaves. Sub floor is cement board. Steel beams supported by load bearing q-con block walls with ring beam. Welding in the air.
 
Is it perhaps best as suggested to weld the sides and not weld the top and bottom?
 

I wouldn’t, they’re really not doing anything anyway

[CGW]

2 hours ago, canopy said:

Is it perhaps best as suggested to weld the sides and not weld the top and bottom?

Consider this, if you are not going to weld the top and bottom you are leaving the inside exposed to the "elements" without a full weld, so little point going to a lot of trouble coating the outside to a good standard when the inside has nothing to protect it, if it is welded decently it will not distort, try bending a piece of oblong tubing with just a little localised heat, not going to happen, on that note - hope the job goes well - I will "butt" out as you are getting conflicting advice and have enough to sort out.

[mogandave]

Consider this, if you are not going to weld the top and bottom you are leaving the inside exposed to the "elements" without a full weld, so little point going to a lot of trouble coating the outside to a good standard when the inside has nothing to protect it, if it is welded decently it will not distort, try bending a piece of oblong tubing with just a little localised heat, not going to happen, on that note - hope the job goes well - I will "butt" out as you are getting conflicting advice and have enough to sort out.

My concern with fully welded is that water will have no way of draining, water will become trapped and cause the tubing to rust out.

A little localized heat is nothing like laying down 8” of weld on 18” (or whatever) centers. That said, with a little planning welding top and bottom the distortion could be minimized.

I agree completely that fully welded and water-tight would be better, I just don’t see that happening. We’re talking 24” of weld on each joint, that includes 16” vertical and 4” overhead, using a buzz-box while hanging from the joist 10’ in the air.

Unless I’m missing something, these pieces are adding no support to the structure, except perhaps where the edges of the cement panels butt together. They are merely “blocking” the joists.

[CGW]

1 hour ago, mogandave said:

My concern with fully welded is that water will have no way of draining, water will become trapped and cause the tubing to rust out.

Without oxygen rust cannot form "if" there was water trapped, which is unlikely - it would be unable to "oxidise" due to no oxygen, if fully welded.

1 hour ago, mogandave said:

I agree completely that fully welded and water-tight would be better, I just don’t see that happening. We’re talking 24” of weld on each joint, that includes 16” vertical and 4” overhead, using a buzz-box while hanging from the joist 10’ in the air.

Having spent 45 years joining pieces of steel together this job would be routine and happen many times in the average day on projects I have been on, are my expectations too high that it can be done here? Any reasonable welder should be able to run a bead around these joints, yes I know this is Thailand but there are some good welders around, shipyards are all quite now, must be possible to find someone capable? Probably not as easy as it sounds I know.

A "welder" would know how to weld without distorting tube, it is important that the steel butts up - meaning it is correctly cut and fitted, you don't want to be filling in huge gaps & creating a lot of heat as that can cause distortion. 

Another point to consider for the OP, are they going to weld up the ends of the tubing to "airtight" them, if not then it makes no difference if they are only partially welded.

[canopy]

As far as the ends, not many are exposed and the few that are will have steel plates face welded shut. So all things equal it sounds best to weld all sides so it is all sealed up. However, in this case the roof is pitched slightly for drainage (1/4 inch per foot) and so the beams need to pretty dead on a plane without bowing up or down. Side to side bow is no problem. So really the only question is this: is welding the top/bottom going to risk bowing up or down? The welder thinks welding the top would bow them. He has 20 some years of experience, but I don't think he has worked with 8 inch stuff before. Beams are 3/16 inch thick.

 

Edited May 2, 2019 by canopy

[sometimewoodworker]

5 minutes ago, canopy said:

As far as the ends, not many are exposed and the few that are will have steel plates face welded shut. So all things equal it sounds best to weld all sides so it is all sealed up. However, in this case the roof is pitched slightly for drainage and so the beams need to pretty dead on a plane without bowing up or down. Side to side bow is no problem. So really the only question is this: is welding the top/bottom going to risk bowing up or down? The welder thinks welding the top would bow them. He has 20 some years of experience, but I don't think he has worked with 8 inch stuff before. Beams are 3/16 inch thick.

 

The welding process certainly can cause the metal being welded to bend if too much heat and weld metal is added in one spot too quickly, as when it cools the shrinkage will bend anything, the size of the piece being welded 8" is quite small. This is why gas shielded MIG is preferable as you can start and stop easily so giving time for your work piece to cool near the weld.

 

I know that I couldn't do the weld without distortion but my  neighbour who is a welder certainly can and has for everything he has done for me.

 

So your welder doesn't have the correct experience to do what you want, the answer is change what you want or change the person doing it.

[mogandave]

Having spent 45 years joining pieces of steel together this job would be routine and happen many times in the average day on projects I have been on, are my expectations too high that it can be done here? Any reasonable welder should be able to run a bead around these joints, yes I know this is Thailand but there are some good welders around, shipyards are all quite now, must be possible to find someone capable? Probably not as easy as it sounds I know.
A "welder" would know how to weld without distorting tube, it is important that the steel butts up - meaning it is correctly cut and fitted, you don't want to be filling in huge gaps & creating a lot of heat as that can cause distortion. 
Another point to consider for the OP, are they going to weld up the ends of the tubing to "airtight" them, if not then it makes no difference if they are only partially welded.

I assume it’s safe to assume we’ll charge the structure with nitrogen to evacuate all the oxygen, yes?

In any event, laying 24” of weld per joint (48” per component) to effectively block the joists seems a little overkill to me. I would likely just stitch-weld the sides and be done with it...

[VocalNeal]

Any unwelded seams can be caulked with Silicone? All Thais know how to quirt that stuff around?

[CGW]

1 hour ago, sometimewoodworker said:

So your welder doesn't have the correct experience to do what you want, the answer is change what you want or change the person doing it.

My thoughts exactly, your paying him to do a job. If he can't convince you he can do the job without distortion he is not the right man for the job.

 

30 minutes ago, mogandave said:

assume it’s safe to assume we’ll charge the structure with nitrogen to evacuate all the oxygen, yes?

Why,  once the oxygen is used up it cant be replaced, why the poor attempt at sarcasm?

 

30 minutes ago, mogandave said:

In any event, laying 24” of weld per joint (48” per component) to effectively block the joists seems a little overkill to me. I would likely just stitch-weld the sides and be done with it.

Thats your prerogative, just trying to help out the OP not convince you, my view is rods and welders are cheap, sure you can seal after with silicone, second best option in my opinion, you already have a welder on-site.

Edited May 2, 2019 by CGW

[mogandave]

You really think my sarcasm was a poor attempt? I thought it was pretty good.

So now we’re welding plates on the ends of all the rafters an calking all the welds, rather than just making sure it drains, sweet.

[VocalNeal]

My silicone idea was a bit tongue in cheek. 

 

There is an old way of starting a fire in your enemy's house. Bunch some rags up, soak them in an accelerant , tie it to the back of a rat, light it and throw it in a window. 

 

So using the same logic one could bundle up some rags, tie to something appropriate and soak in primmer and pull it through the box section beams.

 

Me? I would have just got Somchai to build it and it would probably out live me.

[CGW]

28 minutes ago, mogandave said:

You really think my sarcasm was a poor attempt? I thought it was pretty good.

Truthfully, I thought it was ignorant and ill informed ???? 

[mogandave]

Truthfully, I thought it was ignorant and ill informed [emoji846] 

Oh dude, now you’ve hurt my feeeeeeeelinggggggs....

[mogandave]

Getting back to the Space Shuttle....


(Is that better?)

[CGW]

11 minutes ago, mogandave said:

Oh dude, now you’ve hurt my feeeeeeeelinggggggs....

 

Good! - You can only imagine how wounded I felt ???? 

[canopy]

Note once the structure is complete the beams will be completely covered and not visible from the inside or the outside. They won't get wet. I like the advice here to weld all the way around each beam. But since the welder has warned me it will warp I feel I must accept his limitations and will seal with silicone.

 

I had a chance to look at primer. I saw TOA rusttech someone mentioned is top notch. It's epoxy based and costs 1500 baht a gallon. I filed that one away if I ever need something extremely durable it sounds real good; they show it used to paint chains. Since this job will primer before weld I doubt epoxy would be desirable. All else I saw was lots of red oxide or grey primer with the grey being a bit more expensive.

 

[JimShortz]

Lots of good advice here, but there is a big case of "how far do you need to go?". Do you plan to live forever?

My advice is to not try to be too different to what your workers are used to, but insist on decent wall thickness steel. So, my tuppenth is to:
 

• listen to the guy about warping (box section is surprisingly easily warped by stick welding - has caused me many headaches)
• Buy steel of wall thickness 2.3mm (perhaps 2.0mm for battens), not the common 1.6mm that many use. The thin stuff is a pig to weld and you get holes easily; also rusts away easily.
• Unless it is very oily just paint with red oxide before welding, then at welds afterwards. For very oily steel you may need to wipe first, but it does just mix fine with the red oxide; save your effort for something meaningful!
• put a roof on top, box it underneath and leave for many, many years - decent thickness steel, in the dry, lasts for many decades this way. Why do more? Go with the flow...

I understand about multi-layered paint, clean surfaces, seam welding, etc, but it is not a ship, and the above will outlast anyone old enough to be reading this on Thaivisa, and quite probably their chiildren too! ????

[Chazar]

On 4/18/2019 at 2:19 PM, Fruit Trader said:

One coat of grey primer.

Found the grey to be way inferior to the red  oxide and if I was the  OP I'd  use galvanised  steel right from the off.

[Chazar]

On 4/26/2019 at 10:27 AM, shaemus said:

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

I  just weld two c  channels  together .

[mogandave]

I  just weld two c  channels  together .

What is the benefit of welding two c-channels together?

[canopy]

Any comments on the quality of this weld? The good, the bad, the ugly. Just anything.

 

[mogandave]

It is not ideal.

How does the back look?

[bankruatsteve]

7 minutes ago, mogandave said:

It is not ideal.

How does the back look?

I'm not a welder but I've observed lots of welds and that one appears to have a LOT more weld than should be necessary.  (?)

[mogandave]

I'm not a welder but I've observed lots of welds and that one appears to have a LOT more weld than should be necessary.  (?)

It depends on what the weld is doing.

I think there was talk earlier in the thread about fully welding tubing, when the welds were (apparently) not really doing anything but holding the tubing in place.

The volume of weld depends on what the weld has to support.

An inch of good weld is much better than six inches of crappy weld.,

[canopy]

It is 4x8 inch tubing and some of the welds are structural holding up a 2nd floor. If the welds fails, the floor breaks to the detriment of those on both floors. All the welds look just like this. Since there are no building inspectors in Thailand this is my only chance of gauging the safety aspects of the work performed.