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Frequently Asked Questions
Q. Why is thin-film intumescent not really suitable for external use?
A. Thin-film intumescent depends on the top coat as a protective coating to the intumescent basecoat. Once this has been broken through, the intumescent is open to attack from the elements. Even solvent-based intumescent relies on the top coating for this kind of protection. Conversely, epoxy intumescent was developed for the rigours of the offshore industry … thus, it is inherently weather resistant without any decorative top coat.
Q. Do I need to shot-blast and prime the column surface to SA 21/2 offsite before the casting can be installed?
A. No that’s not necessary. Providing the surface has had any mill scale or flaking rust removed by wire brushing, followed by a surface-tolerant primer (this can be applied by brush or roller on site).
Q. Can cast epoxy intumescent be used to fire protect I-Sections?
A. Yes it can. However the requirement should be based on the need to offer definition to the section in a decorative environment. It does not make economic sense to cast the material onto an I-section if it is to be hidden behind a suspended ceiling. The castings are made to fit the profile and offer good definition to the I-section (see detail photo). There will be four castings per section on a four-sided detail (these are then mechanically fixed and glued together).
An alternative is to use a box section to give a different impression to the one actually created by the structural steelwork. Interact can cast their epoxy intumescent to give the impression of underlying features that aren’t really there. For example, a standard tapered beam can be made to look like a boxed I-section, giving the structure a feeling of greater robustness.
Q. Is it OK to dispense with fire protecting the steel if a circular hollow section is under 169 mm diameter, only a one hour period is stipulated, and I intend to concrete fill the column anyway?
A. The most popular reason for concrete-filling a hollow section is to enhance the fire protection properties of the structure. All the published tests carried out to date have used a minimum diameter of 168.7 circular hollow section; 140 square hollow section; or 200x100 rectangular hollow section.
The reasoning behind this limit is the ability to compact the concrete to the required strength (refer to structural engineers requirement). It should also be noted that two holes must be drilled into the section every four metres—or at floor junctions—whichever is the more frequent. This is to allow steam generated by the heat flux to escape—and therefore prevent the hollow section from splitting prematurely. Concrete is a low conductor of heat. The steel section will therefore heat up at a faster rate than when unfilled, resulting in an increased reliance on the concrete fill to withstand the full design load of the building.
The greater the section size, the easier it is to concrete fill to the required strength. Thin-film intumescent coatings can reduce the heat transfer through to the steel for a limited period of time by increasing the insulation to the external exposure of the steel column. But again, there is no data below 169 mm for the reasons stated above.
If you require further information on this, please contact Interact direct.
Q. With Interactive Columns, what treatment is advisable where the column meets the floor?
A. Where possible, you should take the castings into the tanking area under the surface of the floor as they may not abut correctly with the surface top coat. Also, there might be settlement that would lower the level and so reveal the primer of the unprotected part of the column (this area may be attacked by fine abrasions and/or chemicals). If the column casting is extended below the surface, the tanking will protect against such occurrence.
Q. With Interactive Columns, what extra treatment might be needed at the head of the column?
A. Where possible, the casting should be cut to the profile of the abutting steel beam and taken to the underside of the floor or abutting the fire protection board soffit.
Q. We are in a country which suffers from high humidity. The requirements of many secondary application—and in particular Intumescent coatings—is that the humidity must be below 85%. How does the humidity affect your product?
A. Interactive Columns are a cured product and not affected by humidity. The application of the adhesive is under the casting and therefore also protected, in the main, by the casting. When applying wet materials to steel columns, it is impossible to control the environment as any protection may make contact with the surface and ruin the finish.
As Interactive Column casings are already cured, local environmental control is easy and economical. Typically, a polythene sleeve can be put around the steel and dry air pumped into the void. There will therefore be no effect from high humidity or rain during the initial curing stage of 12 hours in temperatures around 24°C. The sleeve can then be removed and the material left to finish curing in the normal environment. Like all wet materials, it is imperative that the material does not get wet. Interactive Columns can be put on at any time using this type of control.
Q.The steel to receive your epoxy intumescent casting has thin film overspray on it. The subcontractor has rejected the condition even though they are both intumescent materials—and have the same purpose (to expand in a fire and offer insulation to the steel). So, why is this?
A. There are a number of reasons why the steel has to be free of such overspray.
1) Warranty: Nobody has tested a fire protection system using two different intumescent materials and, therefore, cannot confirm how they would react. All fire protection systems are tested in a certain way. Variation from the test criteria will make the system invalid. The epoxy intumescent may pull the thin film away from the steel, causing de-lamination at a critical time of the fire.
2) Adhesion: All materials have different adhesion properties. If the thin film intumescent has a weaker bond with the primer than an epoxy intumescent, the epoxy intumescent will pull the thin film away from the primed surface. It does so because epoxy intumescent generally shrinks by 1%. While the primer bond to the steel can hold this, it is unlikely that the any thin film would do the same. The result would be a system that is hollow and may fall away in a fire.
3) Casting Size: The castings are made to fit a specific size of steel. The additional coating on the steel section may interfere with the fitting of the casting, thus affecting the aesthetics and resulting in additional cost of installation.
4) Best Practice: All trades should leave their work suitable for following trades to carry out their work without additional costs.
Q. How can I specify Interact's products through NBS?
A. Specification clauses can be found on Update 45 of the National Building Specification and can be specified in NBS Section M61, clauses 110, 115 and 120, with the details in the NBS Plus manufacturers guidance window.