Box section steel for roof trusses

[cliveuk]

Can anyone  explain the difference between the Black and oily steel and the clean shiny stuff which is widely available in 6 metre lengths and which should we be using for roof construction, some of which will be on show and painted Black. Thanks.

[Excel]

Do you mean the oiled black steel compared to the galvanized steel which you refer to as shiny ?

[cliveuk]

10 minutes ago, Excel said:

Do you mean the oiled black steel compared to the galvanized steel which you refer to as shiny ?

Yes

 

[Excel]

5 minutes ago, cliveuk said:

Yes

 

So know you know then. The galvanised is generally in far less section sizes and on the thinner walled sections which you often see on Thai houses were the spans are minimal.

[Kwasaki]

1 hour ago, cliveuk said:

difference between the Black and oily steel and the clean shiny stuff

What does your architect drawing spec nominate, depends on what you need and how much.

[cliveuk]

14 hours ago, Excel said:

So know you know then. The galvanised is generally in far less section sizes and on the thinner walled sections which you often see on Thai houses were the spans are minimal.

Our local stockists have plenty of both, so one is galvanised and one isn't. Thats the only difference? I want some exposed Black steelwork so am I better with the galvanised and painting it or with the Black steel and cleaning it? Any idea?

[cliveuk]

12 hours ago, Kwasaki said:

What does your architect drawing spec nominate, depends on what you need and how much.

No architect involved, just trying to understand the materials.

[Excel]

4 minutes ago, cliveuk said:

Our local stockists have plenty of both, so one is galvanised and one isn't. Thats the only difference? I want some exposed Black steelwork so am I better with the galvanised and painting it or with the Black steel and cleaning it? Any idea?

As you want a black finish I would go for the black steel. Of course give it a good wipe prior to a primer, then your top coat(s)

[Kwasaki]

2 hours ago, cliveuk said:

Our local stockists have plenty of both, so one is galvanised and one isn't. Thats the only difference? I want some exposed Black steelwork so am I better with the galvanised and painting it or with the Black steel and cleaning it? Any idea?

Up to you steel amounts depend on costs. 

 

Welded joints on Galv section need primming and finish.

 

Untreated steel section needs all joints and surfacing primming and finish.

[sometimewoodworker]

9 hours ago, cliveuk said:

Our local stockists have plenty of both, so one is galvanised and one isn't. Thats the only difference? I want some exposed Black steelwork so am I better with the galvanised and painting it or with the Black steel and cleaning it? Any idea?

All steel needs treatment. galvanised Steel needs less protection Sir Humphrey Davy discovered this it 1824.
 

You will have to paint all your steel to provide and protect the black finish 

you will have fewer rust problems if you use galvanised steel.
You will have to take more care when welding 

[Excel]

3 minutes ago, sometimewoodworker said:

All steel needs treatment. galvanised Steel needs less protection Sir Humphrey Davy discovered this it 1824.
 

You will have to paint all your steel to provide and protect the black finish 

you will have fewer rust problems if you use galvanised steel.
You will have to take more care when welding 

When welding galvanised steel you need to ensure your welders have adequate protection as the zinc oxide fumes can be very dangerous especially in an enclosed space but quite often flu like  symptoms are a sign of inhalation of the fumes.  Also, and guess for simple Thai house builds, welds are not checked, but the zinc deposits can compromise the weld. Of course as I said no welds are checked in a Thai house build so no one is the wiser. We would never use pre-galvanised steel in major structures for that very reason but as I say for simplistic house builds then suspect no one cares, even if they know the hazards.