Most paints are flammable if they are exposed to a flame. However, there are some paints that are specifically used to slow the spread of fire. These are known as intumescent paints. But where should you use them, how do they work and how do they differ from fire retardant paints?
Generally, intumescent paints are used on timber and steel, although they can be used on walls and ceilings, too. Take guidance from your local building control officer, since he/she has final say, and will normally check and satisfy his/herself that things have been undertaken correctly. 'If the building inspector is in doubt, they normally ask for proof of compliance - in other words, it's up to the building owner to prove he/she has undertaken the job correctly. Someone from the suppliers or the manufacturers could also visit and confirm the job has been done right,' says Gary Bryant of Envirograf, a company that has made intumescent and fire retardant products for the past 28 years.
As a rule, you'll need to use intumescent paint on doors that aren't fire doors if you are renovating a house (if they are fire doors, you can use normal paint) and have added a third storey. 'When a third storey, like an attic conversion, is added to a dwelling, they will require all suitable rooms off the evacuation route in case of fire to be fire doors - normally FD20 standard,' continues Gary. 'Suitable rooms would include bedrooms, the lounge, dining rooms and kitchens. It is not required toilets and bathrooms. Under normal circumstances, and subject to the building control officer, these materials are only applied to the risk side of the door, which is normally the room side of the door.'
These paints work by changing their nature from a decorative paint into an intumescent (or, "expanded") layer of carbonaceous char, which forms when the coating is subjected to heat. This layer can be 50 times the thickness of the initial coat, and is formed as the paint is heated to around 100 degrees centigrade and above. As the fire progresses and time passes this layer of char grows thicker thus increasing the insulation provided.
'Intumescent paint should always be applied to a certain loading. For example, apply at 12m sq per litre or 8m sq per litre. The thickness of the paint determines the amount of protection the application will give. For instance, timber 35mm thick requiring 30 minutes protection would need two coats at 8m sq per litre. In the event of a fire, the material will expand and continues to expand to maybe 20 to 30mm in depth, creating a black carbon barrier. The thickness of the paint applied will determine how long the expansion continues for and hence how long the protection continues for. The carbon layer acts as a heat insulator against the penetration of the heat source.'
'Normally used in rooms where there are large areas of wood, fire proof paint is more economical than intumescent paint,' says Gary.
'Once a flame is applied, the surface will slightly carbonise and stop the spread of the initial flame. However, if the source of the flame is continuous, it may burn through the paint into the substrate and continue to burn the substrate.'
'The products are safe to use - they are all water-based, and application is easy to achieve without complications - your average jobbing builders or competent DIYers can apply these products without problem,' says Gary Bryant. 'And, providing the substrate is sound, they can be applied over most existing finishes.'
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