Galvanized steel vs. regular steel

[EVENKEEL]

I know if I get a quote for a job building a porch area with materials included they will use cheapest materials like galvanized. I did a 6Mx7M car port and I went with builder to pick out the steel and paid labor separate.

 

I haven't priced the galvanized steel, and strength of build is more a consideration than price of materials.

 

 

[Woof999]

I'm not an expert by any stretch, but galvanised steel is there for rust protection primarily, not for strength. Personally I'd be going with concrete column to closer match the architecture of the house, depending on what that is.

[novacova]

For strength use steal, protect it with two part epoxy paint. Before applying paint, etch with muriatic acid.

[brianthainess]

13 minutes ago, Woof999 said:

I'm not an expert by any stretch, but galvanised steel is there for rust protection primarily, not for strength. Personally I'd be going with concrete column to closer match the architecture of the house, depending on what that is.

Galvanized is just as strong but here it is cold galv. coating and needs 2 coats of sliver gloss paint, on top, it will never rust. can always bolt direct to concrete base.

 

 

[OneMoreFarang]

As far as I know there are special rules when and how to paint galvanized steel. 

But you don't have to paint it.

So, if you want to paint it, better do some research.

 

The following is a good site to get an overview of available materials and cost:

https://www.onestockhome.com/en

 

[Ralf001]

5 minutes ago, OneMoreFarang said:

As far as I know there are special rules when and how to paint galvanized steel. 

But you don't have to paint it.

So, if you want to paint it, better do some research.

 

The following is a good site to get an overview of available materials and cost:

https://www.onestockhome.com/en

 

 

Best not weld it if painting aint on the plans.

[Dante99]

53 minutes ago, EVENKEEL said:

they will use cheapest materials like galvanized.

why is galvanized the cheapest, it is additional coating that must increase the cost

 

I think you may be confusing two different weights of steel with the lighter weight galvanized.

 

Nominal dimensioned steel here is sold in different weights for the same dimensions.  More weight more strength.

[Ralf001]

1 minute ago, Dante99 said:

why is galvanized the cheapest, it is additional coating that must increase the cost

 

I think you may be confusing two different weights of steel with the lighter weight galvanized.

 

Nominal dimensioned steel here is sold in different weights for the same dimensions.  More weight more strength.

 

Steel basically has the same density.

 

Different weights would be to do with wall thickness.

[brianthainess]

5 minutes ago, OneMoreFarang said:

As far as I know there are special rules when and how to paint galvanized steel. 

But you don't have to paint it.

So, if you want to paint it, better do some research.

 

The following is a good site to get an overview of available materials and cost:

https://www.onestockhome.com/en

 

I watched them build my house with galv, they used as I said oil based silver gloss, no special paints, or etching needed, goes on like water almost, I had never seen it done before and googled it, yes they were absolutely correct. and Have used it myself on many occasions, it never rusts. 

[sometimewoodworker]

55 minutes ago, EVENKEEL said:

I know if I get a quote for a job building a porch area with materials included they will use cheapest materials like galvanized. I did a 6Mx7M car port and I went with builder to pick out the steel and paid labor separate.

 

I haven't priced the galvanized steel, and strength of build is more a consideration than price of materials.

 

 

As has been mentioned there is zero difference in strength between the same grade and thickness of galvanised vs mild steel.

However if it’s going to be welded take proper safety precautions as zinc smoke is toxic.

The thicker the steel the longer it will last before rust compromises the strength. Also though galvanised will have a much longer life before it rusts it will eventually rust once the zinc has been depleted.

[LS24]

24 minutes ago, brianthainess said:

Galvanized is just as strong but here it is cold galv. coating and needs 2 coats of sliver gloss paint, on top, it will never rust. can always bolt direct to concrete base.

 

 

Hi Brian, I just want to expand on what you have said. In general, you are correct. But cold galz comes in a lot of different varieties. and has some drawbacks.

 

OP, you need to ask the question of what the "G" rating is of the galv steel. You want a minimum of G275 (275 grams of zinc galv per metre squared of surface. That is the SI metric which most of Thailand should use. But they may use imperial like they do with plumbing for some reason.

 

One thing to watch out for is the internal of the post. I have seen far too many posts rust out from the inside to the outside. Make sure the base of the posts and weled with a cap and a flange to bolt to the floor. Brian's photo looks to have an angle bracket to bolt to the ground and a bolts to the post. Unsure if there is an end cap.

 

An end cap that covers the bottom of the post and extends out to bolt through into the ground is a much better method for a variety of reasons.

 

If water will get access to the top opf the post, make sure that is also capped.

[impulse]

If you're in Bangkok, there's a huge metals market just west and southwest of Hua Lamphong train/MRT station.  Blocks and blocks and dozens (hundreds?) of shops of all kinds of metals and structural steel.  I used to wander around there for hours.  Lots of tools, welders, screen, profiles, etc.

 

I'd suggest galvanized for anywhere you can't slap on a coat of paint, like penetrating concrete, etc.  But make sure the thickness is adequate.  For example, my handy Chinese reference books shows 4.0, 5.0 and 6.0 mm thickness available in 100mm square steel tube.  Some sizes, the choices are between 1.2mm and 5 mm for the same outside dimension, with half a dozen different thicknesses. Caveat emptor if you bid it out.

 

Structural engineers will calculate the size and thickness you need, but that's a tough option in Thailand.  Back in the nanny states, you'd need that stamped calculation from a PE to get a building permit...

 

Edit:  I'd add that there is hot rolled and cold rolled structural steel, but I'm not claiming to be an expert on the differences.  My brain has leaked a lot since I worked with them in my shops in China.

 

[freeworld]

21 minutes ago, Dante99 said:

why is galvanized the cheapest, it is additional coating that must increase the cost

 

I think you may be confusing two different weights of steel with the lighter weight galvanized.

 

Nominal dimensioned steel here is sold in different weights for the same dimensions.  More weight more strength.

Galvanized is not cheapest, it depends on the design and section selected for the structure, galvanising is the protective coating and also adds to the weight of the structure.

 

There are different thicknesses of galvanizing and a special process to prepare the metal/steel before galvanising.

 

Here are some advantages and disadvantages of galvanised coating.

 

https://www.mechanicaleducation.com/galvanizing-advantages-and-disadvantages/

[brianthainess]

2 minutes ago, LS24 said:

I have seen far too many posts rust out from the inside to the outside.

Sorry should have said it is 'C' section, so no 'inside' to rust, I prefer to work with "C" section as it can be just  be easily bolted, tek screwed together, as my garage is, no welding whatsoever. Plus it can always be moved if necessary. the rust you see in the foreground is from leaving an unpainted piece of steel on it. 

 

[VocalNeal]

1 hour ago, EVENKEEL said:

• Gender:Male
• Location:By the sea

 

 

How close by the sea? Painting is likely more important than the "type" of steel.🤔

[Ralf001]

1 hour ago, LS24 said:

.

 

One thing to watch out for is the internal of the post. I have seen far too many posts rust out from the inside to the outside. Make sure the base of the posts and weled with a cap and a flange to bolt to the floor. Brian's photo looks to have an angle bracket to bolt to the ground and a bolts to the post. Unsure if there is an end cap.

 

 

 

Welding removes the galv coating so make sure the post is capped well other it will rust like a champ from the inside out !

[itsari]

Galvanized steel is 20 to 25 percent more than non galvanized steel . 

[Artisi]

2 hours ago, sometimewoodworker said:

As has been mentioned there is zero difference in strength between the same grade and thickness of galvanised vs mild steel.

However if it’s going to be welded take proper safety precautions as zinc smoke is toxic.

The thicker the steel the longer it will last before rust compromises the strength. Also though galvanised will have a much longer life before it rusts it will eventually rust once the zinc has been depleted.

Don't think the OP will still be around and interested in  rust after the zinc has been depleted. 

[EVENKEEL]

7 hours ago, VocalNeal said:

 

How close by the sea? Painting is likely more important than the "type" of steel.🤔

1 km close, I built outside car port here with steel, primed and ends capped on the supports, just minimal rust.

[EVENKEEL]

Thanks for the answers, I'll just over size everything like I usually do. Some technical answers are beyond me. I just simply thought galvanized was popular because it was cheap which isn't true. So, I'll see what I choose.

[AndyAndyAndy]

There are three levels.

 

 1. You buy material and build it yourself.

 

2. You buy material and pay workers just to put it together. This is what 99% of thais are doing. You are paying only their daily rate.

 

3. You let them buy material and pay for the result. This is what is considered very stupid in Thai society. Because they will choose cheapest of the cheap garbage possible and take shortcuts and their secret tricks how to make 1'' pole work even if it requires 4''. Then they add their own margin on bought material and pretend they payed for 4''. Yeah, nobody does this.

 

Welding & concrete are my hobbies so very often I'm going 1. Sometimes, like putting down ceramic tiles, my skills are not good enough so I'm going 2. I never went 3 and I don't know anybody in my surroundings who would go 3.

[Lacessit]

12 hours ago, EVENKEEL said:

I know if I get a quote for a job building a porch area with materials included they will use cheapest materials like galvanized. I did a 6Mx7M car port and I went with builder to pick out the steel and paid labor separate.

 

I haven't priced the galvanized steel, and strength of build is more a consideration than price of materials.

 

 

In terms of cost from low to high, the order is:

Cold-rolled uncoated

Galvanised

Zinc-aluminium alloy.

Pre-painted e.g. Colorbond.

 

Galvanised is a bit tricky cost-wise, as the price depends on the coating thickness as well as the steel thickness. The thicker the zinc coating, the longer the sacrificial protection will last. Coating thickness can vary from 50 g/sqm to 400 g/sqm.

 

Galvanised gives better cut edge protection than zinc/aluminium alloy. Zinc/aluminium is mainly used in roofing applications, with 0.35 mm being a fairly standard thickness.

 

Post-painting is usually unnecessary unless the environment is quite humid, or welding operations are involved. In dry environments, galvanised will last for over 100 years.

 

If painting over galvanised, an etch primer should be applied first. These have phosphoric acid and/or zinc phosphate as passivating compounds. Painting would be recommended for a marine environment.

 

One poster here suggested muriatic acid ( i.e. hydrochloric acid ). That creates a corrosion cell unless completely removed, and is bad news for any crevices.

 

 

[Yellowtail]

Galvanized C-channel is a good choice. Thicker is generally better than thinner.

 

Hot-rolled steel is cheaper than cold rolled, and it's likely all you can get anyway. 

 

Galvanized is better for most every application unless you want smooth, shiny painted finish. 

 

A lot of people love rectangular tubing, and it looks better, but it is more difficult to work with, more expensive and much more susceptible to rust. It is also generally not available in galvanized. 

, 

The corrosion issue with tubing is not water getting into the tubing, but water not draining. It's not easy to paint the inside of the tubing, and welding caps on the end of tubing can exasperate the problem if there are no drain holes. That's why they always rust out at the bottom. 

[sometimewoodworker]

33 minutes ago, Yellowtail said:

A lot of people love rectangular tubing, and it looks better, but it is more difficult to work with, more expensive and much more susceptible to rust. It is also generally not available in galvanized. 

I’m not sure about availability anywhere other than in my area but galvanised rectangular and square tubing is stocked by all the local steel suppliers, in fact the village store only carries galvanised tube, round, square and rectangular, it is special order for uncoated. Angle though is all uncoated.

 

So it may well be area specific.

[Yellowtail]

42 minutes ago, sometimewoodworker said:

I’m not sure about availability anywhere other than in my area but galvanised rectangular and square tubing is stocked by all the local steel suppliers, in fact the village store only carries galvanised tube, round, square and rectangular, it is special order for uncoated. Angle though is all uncoated.

 

So it may well be area specific.

Is it welded seam? I've seen the real light gage formed-seam stuff in galvanized, but not welded. 

 

Steel tubing is typically rolled from coil and the seam is either formed or welded in process. C-Channel and formed seam tubing can rolled from galvanized coil, but it would not make sense for welded seam. I think welded seam would have to be galvanized in lengths, like they do structural. 

 

 

 

 

[sometimewoodworker]

12 hours ago, Yellowtail said:

Is it welded seam?

Yes this one is 1.2mm and probably not hot galvanised,  it’s on both surfaces 

 

The 4” other square section is not welded there is no join. I don’t know the forming process. It is also 1.2mm wall, it is probably cold rolled from the marks on the pipe.

 

[Yellowtail]

52 minutes ago, sometimewoodworker said:

Yes this one is 1.2mm and probably not hot galvanised,  it’s on both surfaces 

 

The 4” other square section is not welded there is no join. I don’t know the forming process. It is also 1.2mm wall, it is probably cold rolled from the marks on the pipe.

 

 

I'd bet that the tubing in the photo was made by hot-rolled sheet that has been slit into coil, and then rollformed into shape. The welding would typically be done in between two of the final stations prior to the cutoff. 

 

I can't really see the coating, but if it's coated inside and out, and the coating was not burned off the weld, then I would bet it was coated after cutoff. 

 

If the coating looks like it's been burned off, or burned off and the seam recoated on the outside it was probably rollformed from galvanized coil. 

 

If it is galvanized, and there any spangle, it's hot-dip. If it does not have any spangle, it could be either hot-dip or electro-galvanized. If there is no spangle and its smooth and shiny, it's probably electo. 

 

I'm a bit confused by: "The 4” other square section is not welded there is no join. I don’t know the forming process. It is also 1.2mm wall, it is probably cold rolled from the marks on the pipe."  1.2mm wall thinness seems a bit thin for 4" seemless. 

[Ralf001]

6 minutes ago, Yellowtail said:

 

I'd bet that the tubing in the photo was made by hot-rolled sheet that has been slit into coil, and then rollformed into shape. The welding would typically be done in between two of the final stations prior to the cutoff. 

 

I can't really see the coating, but if it's coated inside and out, and the coating was not burned off the weld, then I would bet it was coated after cutoff. 

 

If the coating looks like it's been burned off, or burned off and the seam recoated on the outside it was probably rollformed from galvanized coil. 

 

If it is galvanized, and there any spangle, it's hot-dip. If it does not have any spangle, it could be either hot-dip or electro-galvanized. If there is no spangle and its smooth and shiny, it's probably electo. 

 

I'm a bit confused by: "The 4” other square section is not welded there is no join. I don’t know the forming process. It is also 1.2mm wall, it is probably cold rolled from the marks on the pipe."  1.2mm wall thinness seems a bit thin for 4" seemless. 

 

 

there will be next to zero chance it was gal dipped before cut to length.

There  will be zero chance is was formed from Gal coil.

 

[Yellowtail]

31 minutes ago, Ralf001 said:

 

 

there will be next to zero chance it was gal dipped before cut to length.

There  will be zero chance is was formed from Gal coil.

 

If the weld was burned off, it was rolled from galvanized coil. 

 

If a metal center has a bunch odd coil from drop or mistakes, why would they not roll it into tubing to get rid of it. 

[Ralf001]

1 minute ago, Yellowtail said:

If the weld was burned off, it was rolled from galvanized coil. 

 

 

 

It wont be.