Thin film applied Intumescent paint is a fire protective intumescent coating designed to insulate structural steel and prevent the temperature of the steel from rising to a critical point at which structural failure becomes possible.
Although Intumescent paint provides an appearance similar to that of a paint finish that at ambient temperatures remain stable, in a fire situation the increase in temperature causes a chemical reaction.
This reaction causes the intumescent paint to expand to many times its original thickness. This provides an insulating foam-like coating or "char" which protects the substrate. Solvent or water based intumescent paints may be applied by airless spray, roller or brush and have the ability to protect steelwork for 30, 60, 90 and 120 minutes in a fire.
Protecting timber structures
Timber structures are more susceptible to the surface spread of flame and heat propagation. Intumescents are designed to reduce heat propagation, and reduce the spread of flame.
How do intumescents work?
The expansion process is caused by the interaction of three precisely formulated components:
- Carbon supplier: polyols as starch, pentaerythritol
- Acid source: ammonium polyphosphate
- Expanding agent: melamine
NOTE: These components are bound in a solvent or water-borne polymeric binder. Other components are added to improve the paint properties, enable easy application, enhance build and achieve faster drying.
Typical intumescent process
As heat is applied the chemical reaction begins:
- The heat begins to soften the polymeric binder
- It also causes an organic acid to be released from the Ammonia Polyphosphate
- Carbonisation of the polyols begins
- As the blowing agent (melamine) decomposes, gas is produced which swells the molten mixture
- Finally, the foamed char solidifies, through a cross-linking reaction, to maintain the insulation
In an ideal situation, intumescent can expand to around 100 times its original thickness. To achieve this requires careful selection of formulation components and precise matching of processes involved. Any secondary casings that may be applied after intumescent coating must allow for this expansion to ensure the paint can operate correctly
Advantages of using intumescent paint
The main advantage of using intumescent paint over other methods of structural fire protection is the aesthetically pleasing finish it gives to steelwork once coated
Other advantages are:
- Fast application
- Easy to cover complex details
- Easy post protection fixings to steelwork
A quick guide to intumescent coatings
When selecting a subcontractor to tender for an intumescent paint package you should consider providing the following information.
- The period of protection
- The primer data sheet
- The environment on completion
- The Type of floor decking
Professionally produced paperwork is more likely to result in a professional job. Insist on a loading sheet with the tender for fair comparison, the manufacturers name at the top of the sheets to show that the calculations have been produced with reliable software.
Important factors to note are:
- Not all intumescent coatings are compatible with all primers. A primer data sheet should be part of your tender enquiry document package. Insist on a copy of the primer compatibility from the paint manufacturer.
- Environment – the end environment information is required for choice of base coat. Leisure pools, wash down areas and external works require a solvent basecoat recommended by the manufacturer. You cannot rely on the top seal to give you the full environmental protection.
- Decking type is important as this can save you money and also speed up the works. Bison beams keep the top flange covered so a three sided application reduces the paint loadings and your costs. The use of some super hollow rib decking can cost you money. Trapezoidal decking with large profiles should be avoided as these leave a lot of the top flange exposed. The smaller dovetail profile requires no extra loading.
- WFT or Wet Film Thickness tests are carried out with a comb, marks will show in the intumescent paint coating. DFT or Dry Film Thickness tests are carried out with an electromagnetic gauge.
- The least expensive intumescent is a water based product. When using this product car should be taken to programme your work once the building is watertight. Solvent based materials with withstand weathering for up to three months. No intumescent can be applied to wet steel.
- Galvanised steel requires degreasing and a mordant wash. The steel should darken considerably. Some solvent based materials do not need a primer after this process. All water based materials require a primer after preparation. A top seal will be required for decorative areas. Sharp colours may require two coats. Food halls and wash down areas will require a top seal for hygiene reasons. Leisure pools including adjacent rooms will require a two pack top seal to prevent chlorine damage.
A quick guide to intumescent coatings
To protect your company, use a FIRAS registered sub-contractor. If this is not possible consider asking for an independent inspection towards the end of the contract. The documented report can go in your O&M manual as part of you inspection procedure.