Need to paint RSJ ?

Ted10

Was on site at the weekend and someone mentioned that they heard that you should paint any RSJ's to prevent the rust on them coming through the plaster. Anyone know if that's correct or is it one of those tall tales ?

Mellor

RSJs are normally painted as fire protection.

Ted10

What is the type of paint I should look for, any particular brand name ?

Mellor

Its intumesceant paint, its a fireproofing paint that expands in firm, insulationg the RSJ and allowing extra time before it fails. Not sure of a brand name. Steel doesn't do very well in fire, timber actually survives longer. Speak to who ever designed/sized the RSJ, it may be factory applied or not required.

Ted10

Thanks for that, on a bit of a steep learning curve.

Qwerty?

I don't think people bother with fireproofing paint on RSJ's in houses, as it's too expensive.

The rust bleeding through the plaster shoudn't be a problem, because you generally cover the RSJ in :-
plywood and then plasterboard
or
plywood and then expanded mesh.

Mellor

Qwerty? wrote: »

I don't think people bother with fireproofing paint on RSJ's in houses, as it's too expensive.

The rust bleeding through the plaster shoudn't be a problem, because you generally cover the RSJ in :-
plywood and then plasterboard
or
plywood and then expanded mesh.

True, but the OP didn't mention what the RSJ was for. Thats why I suggested he find out from the engineer if it was needed. He could give advice specfic to the exact RSJ.

The reason I mentioned it was because the OP was told about a reson RSJs are painted, fireproofing is the common reason, not rust. If the beam is downstand (likely in a house) it will be boxed in ply as you said.

sinnerboy

always inumescent paint - in case future works ( such as insertion of recessed lighting ) creates a path for a fire to attack the beam .

google "fireseal" for more info

Mellor

sinnerboy wrote: »

always inumescent paint - in case future works ( such as insertion of recessed lighting ) creates a path for a fire to attack the beam .

google "fireseal" for more info

We still have no details on the beam so, there may not be a reason to fireproof.

If future works could expose beam then it should be painted if in needs fireproofing, but there are ways to ensure that future work doesn't expose beam, therefore not requiring paint.
Basically the beam (if requiring fireproofing) needs 30 mins protection, painting is the easiest, but there are other options, such as boxing it in fully and sepatately from other areas such as floor.

Ted10

The beam will be used to support the hollow core floor. It'll be over a span in the kitchen and we are going to enclose it in an archway which will be slabbed.

archtech

You could encase the beam with a fire rated "plasterboard" type product. However ensure that the encasing is not penetrated by wiring, downlighters etc.For a dwelling 30 minutes fire resistance is generally sufficient.

sinnerboy

Ted10 wrote: »

The beam will be used to support the hollow core floor. It'll be over a span in the kitchen and we are going to enclose it in an archway which will be slabbed.

100% MUST be fireproofed . by paint or by other means as described

Mellor

Ageed, A beam supporting a floor must be fireproofed, always. There are few acceptions in domestic construction, but this is a must, 30 mins please