Protecting the structural steel in the event of a fire is an important consideration in the civil industry. The vermiculite spray is often used as fireproofing for internal and semi-exposed elements mainly of steel structures, concrete slab steel plate collaborating and hollow-core slabs.
But the chemical chosen for the fireproofing should have fire resistance as required for the building while it should be ensured that no toxic or hazardous fumes are released during the fire and no health hazards during or after application to the structure.
What is Vermiculite?
It is a hydrous phyllosilicate mineral undergoes significant expansion when heated.
Generally, a monolithic coating is adopted with a mixture of vermiculite and Portland cement to withstand the fire. This is more preferred due to low density which will not add extra dead load to the structure and high durability. Also, the damage or crack to this layer is minimal during any mechanical impact.
A top coating shall be applied to the structural element before the application of the vermiculite spray for the proper bondage in between.
Properties of the vermiculite spray shall be as follows,
- Colour – Off-white
- Initial set – 2 to 6 hours at 20 degree Celsius and 50% RH
- Density – 400km/m3
- Compressive strength – 560kPa
- Thermal conductivity – 0.0095W/mK at 20C
- pH value – 12.0 – 12.5
The required thickness for the application of vermiculite spray shall be calculated at the site according to the structural member sizes and the fire rating required based on manufacturer guidelines. The below figure shows confirming the thickness of the application with a needle penetration gauge.
A mesh reinforcement shall be placed in between the coating and the structural element in the following cases,
- The depth of the web exceeds 325mm
- The dimension between the flanges exceeds 650mm
- Circular sections with the diameter greater than 325mm
- Hollow sections with a single face exceeding 325mm
- The substrate that is subjective to excessive vibrations