Steel Purlins - shot blasted and primed??

[Moggaman]

Hi 

I have 2 12m long 203x102x 23 UB as purlins on my roof build as i  have a room in roof scenario. Are the beams required to be shot blasted and primed or can they be left raw. 

Also, i have 2 No 203 x 203 x 46 UC in the house holding up hollowcore..again do this need to be shot blasted and primed?

My engineer was like '' it would be no harm'???

Any thoughts.

[Gus Potter]

Hello Moggaman.

 

Working on the basis that your purlins are supported somewhere along the span? maybe a splice? below is part of a steel spec.

 

"All steelwork is to be fabricated by a CE approved fabricator and comply with the BS EN 1090 series requirements. Site welding is not permitted. It is the Contractor's responsibility to check all steelwork dimensions prior to manufacture."

 

"Shot blast to grade SA2.5 and painted with a zinc rich primer. Nominal DFT 80 microns."

 

Shot blasting comes in varying degrees of "cleaning", SA2.5 is a common one for domestic applications. The primer spec gives your local fabricator a bit of play as to what they can use.. the tins of paint are actually drums of paint so they can "use up a drum" on your job. DFT means nominal dry film thickness.. in other words it looks like paint not just a sniff.

 

It's worth doing as a matter of good practice and can help protect vulnerable parts like the welds and bolts / fixings. In summary, if your steel is in an indoor, heated and fully protected and non aggresive environment then strictly speaking no need for painting / treatments. If it is running over a bathroom and you may have moisture? Would I leave the steel raw on my own house? No.

 

The primer can get rubbed a bit as it's quite soft so don't panic if you see a few bits scuffed off. Last thought, it often comes in two colours, red or grey if that matters?

 

 

 

Edited June 22, 2021 by Gus Potter

[saveasteading]

Agreed as above, having built with steel for decades I can say this.

in a wet or damp environment you need serious protection, galvanised and painted with special stuff. swimming pools look good with just factory galavanising, special paint,  or the 'right' plastic coating.

In an utterly dry environment, just like a warehouse say, it will never rust, and primer finish  looks good still after 30 years.

 

However , in an enclosed space where potentially there could be damp, I would protect it. Spec's will say sand blast and prime and so on.

In reality, a coat of bitumen will stick and protect it, as will single coat paints (Hammerite/Ruberoid etc). expensive but worth it.

 

in your case, I don't know the circumstances. If the steels are on show then of course paint in a suitable colour. If hidden, bitumen, but up to you.