Rust on Steels

[Johnny Jekyll]

I have 4 steels on my project (2 x UC23 and 2 x UC30). The UC23's are at mid-floor level. The UC30's are at eaves roof level.

I purchased them with oxide paint already applied, about a month ago. The plan is to install them and then cover in the 30 mins fire proof paint in situ (all specified and agreed).

I am noticing bits of rust coming through the oxide paint (see photo). I presume this is where they were perhaps a little rusty and just painted over before being delivered.

Do I need to strip them back completely to bare metal and start again?

Thanks.

[Johnny Jekyll]

Hi guys, any comments on post above thanks?

[Mr Punter]

The intumescent paints tend to go fairly mouldy unless they are covered.  Best to give a quick brush of loose rust and a couple of coats of quality red oxide before you start with the intumescent.

[Conor]

Just lightly rub the area and prime. Intumescent paint can be quite tricky to apply, so it's worth getting a well prepared surface for it.

[markc]

A few scabs are no problem for intumescent painter often erected bare or holding primer steel and it would be intumescent painted later

Edited October 14, 2021 by markc

[Johnny Jekyll]

The intumescent paint is water based, so I'm worried that may encourage the rust.

Or would that take hundreds of years and I just shouldn't worry about it?

And simply it clean back and paint as you say?

[markc]

1 hour ago, Johnny Jekyll said:

The intumescent paint is water based, so I'm worried that may encourage the rust.

Or would that take hundreds of years and I just shouldn't worry about it?

And simply it clean back and paint as you say?

If you have any doubts, wire brush and prime, but unless this steel is going to be outside or in a humid location then you have nothing to worry about … for a few hundred years at least

[saveasteading]

steel doesn't rust without water and oxygen. paint prevents that if it is adhering, even primer will suffice in normal indoor conditions,

I would rub down the flaky bits, gently rub any flaking rust bits off, but not through to shiny metal, then put a coat of primer on the exposed steel.

then intumescent away.
I assume you have the intumescent base coat and also a finish coat.

 

it is horrible to put on as thick as it is required. Sometimes best to work out the volume of paint you need, then keep recoating til all gone. then seal.

[Lorenz]

Reminds me of a weld, if you wire brush if off before painting it would show up if it was, which I hope is unlikely. Condensation is the thing indoors.

[Johnny Jekyll]

The paint has been specified through computer model for the size of steels by the paint company so all good there.

Can't thank everyone enough for all the advice. First self build and learning something new every day.

[saveasteading]

2 hours ago, Johnny Jekyll said:

The paint has been specified through computer model for the size of steels by the paint company

 

Sorry to nag: I have seen many a steel with insufficient thickness and some left-over paint, because the painter said he didn't need it all. It is usually very much thicker than normal paint.

Also many where there is no seal coat. The working intumescent stuff is soft and gets mucky, so make sure you have the finish coat too.

 

On the other hand, the paint company likes to sell paint. If the steel is already enclosed on one or more sides the amount of paint reduces, and they dont always bother to mask. A heavy enough steel doesn't need extra protection at all.

Edited October 14, 2021 by saveasteading