CERTIFIED INTUMESCENCE
Passive fire protection for metal structures, certified and complying with the most demanding regulations.
How Intumescent Paints Work
Intumescence is a reactive coating that swells as a result of exposure to heat, increasing in volume and decreasing in density. Specifically, an intumescent paint is a coating that reacts to heat by swelling in a controlled manner to several times its original thickness producing a carbonaceous foam, formed by a large number of small bubbles that act as an insulating layer that protects the substrate.
The purpose of intumescent products is to prevent the collapse of a building’s structure, which can occur if a load-bearing element reaches its critical state. For steel, this is linked to the critical temperature, which is defined as the temperature at which the load capacity equals the effect of the applied loads (so the load element would be very close to collapse). The critical temperature of steel can vary between 350ºC and 750ºC, depending mainly on the load scheme, but in most cases it is between 500ºC and 620ºC. For concrete, the critical state is linked to the critical temperature of the rebar (usually between 350°C and 500°C) and the range of a temperature of 500°C inside the concrete element. For wood, it is linked to the residual section of the loading element after combustion.
Read more about intumescent paints:
Application of Intumescent Paints on Steel – Preparation Tips
Intumescent paints are always part of a system. For steel work, the system includes an anti-corrosion primer and (in certain cases) a finishing coating.
- The purpose of the primer is to ensure adhesion to the substrate in the cold state, to protect against corrosion and to ensure the adhesion of the carbonaceous foam formed during exposure to fire.
- The purpose of the finishing coating is: an aesthetic function and, in the case of a specific aggressive atmosphere, a sealing function that prevents early degradation and inactivation of the intumescent layer, resistance to weather and end-use conditions.
Steel must be prepared to the SA 2 1/2 standard before being coated with a compatible primer or, if already painted with a compatible primer, it must be cleaned (free of grease, oil, dirt, rust, or other contaminants that may inhibit bonding).
The primers that are compatible with Promat products are:
- Acrylic
- Short or medium alkyds in oil
- Two-component epoxies
- Zinc silicate (inorganic zinc)
- Zinc-rich epoxy (containing about 80% epso from metallic zinc powder)
- Zinc-rich epoxy (containing about 96% epso from metallic zinc powder)
- Polybutadiene (Promat® TY-ROX)
For concrete and wood, preparation depends on the physical condition of the support. For more information contact our technical department.
Intumescent coatings are preferably applied by airless spray gun due to the quality and speed of their finish.
Intumescent paint applied by spray, brush or roller.
Finish coating applied by spray, brush or roller (if necessary).
Primer approved with international certification or by Promat. Please contact our technical department.
Structural Steel Column or Beam- Clean, dry and free of oil, dust, loose scale or rust and any other condition that prevents good adhesion and blasting in accordance with appropriate international standards.
The dry film thickness of intumescent paints
The thickness of the dry film and the amount of material required for a given fire resistance (R30, 60, 90, 120 or more) depends on several factors.
The dry film thickness of intumescent products is determined by:
- Form factor (also called massiveness or Hp/A). The form factor is a ratio of the area of the steel exposed to fire and the volume of the steel section. The higher the form factor, the faster the steel section heats up, and therefore, the greater the required thickness of flame retardant material.
- Exposure: this is the number of faces exposed to fire, depending on whether it is a column, a beam, a composite element, hollow section, etc.
- Critical temperature: The lower the critical temperature, the faster the steel section will reach it, so the thickness of intumescent material required will be higher.
- Fire resistance: the level of protection required (R60, R120, etc.)
- Certifications and Standards: Different standards and certifications can give different thicknesses for the same protection.
When to Measure Wet Film and Dry Film Thickness
During application, it is necessary to measure the thickness of the wet layer frequently with a thickness gauge.
To determine dry thickness based on wet thickness it is necessary to multiply wet thickness by a specific number that differs from product to product. For Promat products the value is between 0.68 and 0.7 (see the corresponding data sheets for more information).
The maximum thickness that can be applied in each layer varies from product to product (see the corresponding technical sheets) as well as the related consumption.
After drying, the thickness of the dry film should be measured using the corresponding gauge. An electromagnetic induction instrument with a statistical function to store readings and give an average is very useful. Where dry film readings include a primer coat and/or top coat, these coatings should be taken into account and subtracted from the total reading.
