Painting over steelwork protected by intumescent paint

[Demontim]

One of our buildings is currently undergoing a significant refit. Prior to the refurbishment, both floors had a suspended ceiling or mf ceiling.  The structural steel beams spanning the width were painted with intumescent paint. 

The current arrangement has exposed these steel beams on both floors and they have been over sprayed with the same ?grey? paint as the rest of the soffits.  I am not sure what paint was specified, but from my recollection, if you over spray anything that previously had intumescent paint, you lose the fire retardant properties. 

It maybe that paints have developed nowadays for this not to be an issue, but would welcome any input as to whether or not the fire integrity has been affected.

[wee brian]

you need to check compatibility, some are, some aren't. You might first need to get an expert in to identify what's been used. The ASFP might be able to help with that.

[Fire Monkey]

There are fire resistant paints and fire retardant paints - these are different products I understand. There are two classes I understand - class 1 and class 0.

Some products may require a primer to be applied to the steels first. Also some products may require more than one application.

I would presume if you cover a fire resisting material with one that is not that the product may spread the fire defeating the purpose of the original product - I suppose it would be like a clean fire escape route compartment that was lined with posters. You may need to reapply a new fire resisting product?

Have a look at BS476 or http://www.checkmatefire.com/downloads/ASFPOnSiteIntumescent.pdf

[Mike Buckley]

No the purpose of the intumescent paint on the steel work is to protect the steel work from the effects of fire. In particular to reduce the heating of  the steel work.

Whilst steel does not melt at the temperatures you can expect in a normal fire c. 1000-12000 degrees C it will lose its structural strength at about 500 degrees C. Hence why you often seem the steel beams draped across the pillars and floor following a major factory fire.

The purpose of the intumescent paint is not to prevent the surface spread of flame par se however it will probably do that quite well anyway.

[Demontim]

No the purpose of the intumescent paint on the steel work is to protect the steel work from the effects of fire. In particular to reduce the heating of  the steel work.

Agreed Mike.

My concern is whether the over-painting will impact upon the intumescent material's effectiveness i.e. will it potentially reduce responsiveness (time and or restrict intumescence)?

[Fishy]

Paints intended to improve fire resistance and paints intended to improve reaction-to-fire (e.g. Class 1 or Class 0) are different beasts, and good performance as regards one doesn't necessarily mean good performance as regards the other.

As regards over-painting, there isn't an all-encompassing answer - some manufacturers have tested their systems over-painted with 'standard' paints and will support such painting; some have (and will) not.  If the paint can be identified, then the supplier/manufacturer should be able to advise on compatibility.  If it cannot be identified, then it would be safest to assume that some degree of diminution of the fire resistant properties would have been caused by the over-painting.

If necessary, ASFP might be able to recommend specialists that could come up with a more definitive answer in this particular case (www.asfp.org.uk)

[Demontim]

After tracking back through the O&M's and then contacting the manufacturers of both products, the matter has been satisfactorily resolved.

Thanks for the input everyone.