Resources

Crucial Facts - Intumescent Paint

Primer and Pre Application

The condition of the primer/substrate of the steel to be fire-rated is of critical importance to the overall fire performance of the Intumescent system.
We have carried out extensive testing that shows whilst the intumescent paint may actually adhere to dirty steel and degraded primer, failure will occur when a fire is present.
We have confirmed that a high standard of preparation and surface condition is required to ensure:

• Adhesion to the substrate
• Long term durability and stability
• Performance in a fire

Climate Conditions

The ambient environment is also an underappreciated aspect of intumescent paint applications. Humidity, dew point and temperature etc. all play an important part in the success of a paint system.
These factors are stipulated on ALL manufacturers’ technical literature.

Film Build Thickness

The thickness of the applied intumescent coating is the most important part of the performance criteria for fire resistance.
We are concerned as to the lack of data currently supplied for Intumescent painting contracts, especially in regards to an “information rich” Producer Statement.
Even though architectural specifications call for such details, this is often not realised.
WFT (wet film thickness) measurements are useful indicators of DFT (dry film thickness); however, there are many factors that may cause a critical variance in the final DFT.
In order to get an accurate reading of the applied coatings a special electronic meter must be used, this ensures precise DFT measurements.

Topseal

All too often intumescent paints are being applied in unsuitable environments without topcoats. This is a dangerous practise, and contrary to most technical data from various suppliers.
Intumescent paint is prone to deterioration from airborne moisture. This damage may not be seen at all, but will invariably affect the fire performance of the coating.

The only possible situation suitable for application without topseal is a C1 environment using the following classification system based on ISO 12944-2.

TABLE 1 - CORROSIVITY OF ENVIRONMENTS (ISO 12944-2:1998)
Corrosivity Category		Steel Loss	Exterior	Interior
C1	Very low	≤10 g/m2 (≤1.3µm)	-	Heated buildings/neutral atmospheres.
C2	Low	10-200 g/m2 (1.3-25µm)	Rural areas, low pollution, dry.	Unheated buildings, possible condensation
C3	Medium	200-400 g/m2 (25-50µm)	Urban and industrial atmospheres Moderate SO2 pollution Moderate coastal	Production rooms with high humidity and air pollution
C4	High	400-650 g/m2 (50-80µm)	Industrial and coastal.	Chemical processing plants Swimming pools
C5-I	Very high industrial	650-1500 g/m2 (80-200µm)	Industry with high humidity and aggressive atmosphere	Permanent condensation and high pollution
C5-M	Very high marine	650-1500 g/m2 (80-200µm)	Marine coastal, offshore High salinity	Permanent condensation and high pollution

Summary

There are many vital factors to consider when using intumescent paint on structural steel.
It is therefore very important to remember that intumescent paint is used to provide a function, rather than just “stick, stay, and look good”.
A philosophy of “If a job is worth doing, it is worth doing well/right” is the best approach to such a critical performance coating.