Fire retardant coatings, when correctly applied, are a crucial line of defense in building safety. Yet applying too much or too little of these coatings can introduce real and sometimes hidden risks to both people and property. Let’s look at the specific problems that can occur when installers don’t hit the mark on application thickness; proving that attention to detail is a must on every project.
What Happens When There’s Too Much or Too Little Fire-Retardant Coating?
Restricted Char Expansion Reduces Fire Protection
Intumescent coatings work by expanding into a protective char layer during a fire. Over-applying the coating, or installing it where there isn’t enough room for expansion, can stop the coating from forming this vital char. When a coating is applied too thickly under closely spaced substrates, the result is less effective insulation and weaker fire protection for structural steel and other surfaces. Industry safety authorities have documented cases where restricted expansion compromised the entire fireproofing strategy.
Cracking and Delamination from Uneven or Thick Layers
When fire retardant coatings are applied in uneven or overly thick layers, the surface can crack, peel, or even fall off over time. Improper curing, especially during cold or humid weather, makes the film brittle and prone to separating from the substrate. Facilities that have experienced this problem often face costly rework and increased risk until repairs are made.
Failing to Meet Fire Resistance Ratings
Under-applying intumescent coatings is a frequent cause of buildings failing inspection. Coatings that don’t reach their tested minimum thickness simply can’t deliver their promised fire resistance. Real-world fire investigations have found cases where under-specified or improperly applied coatings left structures exposed, resulting in property damage and higher insurance risk.
Unnecessary Costs and Wasted Material
More isn’t always better. Applying more coating than required increases project costs and can result in wasteful material use. Not only does this impact the project budget, but over-application can also create films that expand unevenly, reducing the effectiveness of the fire protection itself.
Moisture Trapping Leads to Long-Term Damage
Thick layers that are not properly cured can trap moisture, especially in humid environments or when weather conditions aren’t ideal. Trapped moisture can degrade both the coating’s adhesion and its ability to form a stable char, undermining the long-term durability of the entire fire protection system.
Hidden Weak Points in Thin or Patchy Films
Relying only on thickness measurements can create a false sense of security. Thin or unevenly applied films may pass basic tests but still leave hidden weak spots; areas where adhesion, porosity, or density aren’t up to standard. These weaknesses can go undetected until the system is needed most: during a fire.
Proper fire-retardant coating application means hitting the manufacturer’s recommended thickness, allowing for proper curing, and keeping records to prove compliance. At IFTI, we support this through detailed applicator training and quality control—helping contractors, code officials, and owners avoid costly rework, failed inspections, and safety risks. If you want to ensure your next project delivers both compliance and peace of mind, talk to our team about our Certified Applicator Program or visit our Paint to Protect contact page.