In order to offer high quality solutions in the manufacture of large parts for heavy industry and the wind energy sector, we explore the use of surface materials and coatings. Among these are intumescent paints, a type of coating that delays the spread of fire and helps maintain the structural integrity of parts.

In this article, we will explore in depth what intumescent paint is, how it is properly applied and how it differs from traditional fire-retardant paints.

What is intumescent paint?

Intumescent paint is a special coating that is applied to surfaces such as steel, wood or concrete. Its main characteristic is that, when exposed to high temperatures, it expands and forms an insulating layer that protects the substrate from heat and flames.

This intumescence process is due to the chemical components of the paint, which react to heat and release non-flammable gases. These gases create an insulating foam that can expand up to 50 times its original thickness, slowing heat transfer and preventing fire from spreading.

The purpose of intumescent products is to prevent the collapse of a building structure, which can occur if a load-bearing element reaches its critical state.

This type of paint must provide the fire resistance times set in regulation UNE 48287:2017 according to the type of structure and its use. These times can vary from 30 minutes to 240 minutes, depending on the requirements of the project and the applicable regulations.

Qué es y cómo se aplica pintura intumescente

How to apply intumescent paint 

The steel must be prepared to SA 2 ½ standard before being coated with a compatible primer. Intumescent coatings are preferably applied by spraying with an airless spray gun because of the quality and speed of the finish.

The dry film thickness and the amount of material required for a given fire resistance (R30, 60, 90, 120 or more) depends on several factors and is determined by:

  • Shape factor, also called massiveness or Hp/A: the shape factor is a ratio of the area of steel exposed to fire to 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 fireproofing material.
  • Exposure: this is the number of faces exposed to fire, depending on whether it is a column, beam, composite element, hollow section, etc.
  • Critical temperature: the lower the critical temperature, the faster the steel section will reach it, so the required thickness of intumescent material will be greater.
  • Fire resistance: the level of protection required (R60, R120, etc.).

During application it is necessary to frequently measure the thickness of the wet coating with a thickness gauge. To determine the dry thickness based on the wet thickness it is necessary to multiply the wet thickness by a specific number that varies according to the product.

Intumescent paints can also be applied in high humidity, semi-exposed or exposed conditions, if protected with specific coating, depending on climatic conditions.

Differences between intumescent paints and flame retardant paints 

Intumescent paint and fireproof paint are two types of coatings used to protect structures in case of fire. Although they look the same, they have important differences that we mention below:

Intumescent Paint Intumescent Paint
It expands forming a layer of carbonized foam. Acts as a physical barrier against fire
Used on metal structures to protect them and reduce heat transfer Can be applied on metal, wood, wall and ceiling surfaces
Helps to prolong the time available for evacuation Prevents the spread of flames and helps extinguish them


To sum up, intumescent paint expands and protects the metal, while fire-retardant paint prevents the spread of fire. As passive fire protection elements, both are essential for fire safety.

In the pictures you can see the application of intumescent paint on a steel structure and 22Tn of weight. The paint used was Steelguard 651 from PPG with a total thickness of over 3000µm applied in several coats of up to 700µm per coat and with a drying period between coats.

Recubrimiento de pinturas y metalizados para materiales metálicos