Technically speaking, a properly dried finish means that enough solvents have been removed from the finish to allow good coalescence.
• Oil based finishes have slow solvents and anti-skinning agents that have to come out of the coat before oxygen can start reacting with the oil to dry and cure the film.
• Water based finishes require all the water to come out so the hardeners and catalysts can react with the finish. If not removed, most of the hardeners and catalyst will react with the water leaving the system soft.
Now that you know what technically needs to happen for each system to cure properly, is it possible to create ideal conditions so that a perfect finish is achieved every time? While that question is not easily answered, one thing could make all the difference in the finishing process - ventilation. Ventilation is the most important factor in drying any floor finish. Other factors have an influence, but they are only significant when used along with ventilation.
Good vs. Too Good
When applying finish, it is important to have good ventilation - but be sure that it's not too good. If there is too much air movement, the top of the finish will dry quickly, trapping solvent gasses beneath the flashed over surface - resulting in a hazy look or a soft finish that scratches easily.
By closing up the site, the solvent and water evaporating from the finish surface can quickly saturate a small layer of air just above the surface. If this saturated layer is not moved away, it has nowhere to go except back down into the finish - oftentimes softening the top layer.
The same is true when working in an enclosed room or space with limited air circulation. A window that is open only a crack will more than likely not provide the type of ventilation needed.
Mike Sundell, president of Basic, recalls first hand a "trapping the gasses" situation on a gym that was being coated. The crew completing the floor applied the first coat and went to lunch. They shut the job site down tight to avoid contamination of dust and to keep unwanted visitors away. When Mike arrived, he opened the door to take a look and was shocked. At first, he thought there was something wrong with the lights. He then realized that as the finish gassed off, a fog cloud had formed above the floor. After nearly an hour of drying, the floor was as wet as when it was coated. After opening all the doors and turning on the exhaust fans to get the airflow going strong, the floor was dry enough to walk on in about 10 minutes - and it was saved from potential problems down the road.
Whether you use solvent based systems or water based systems, removing the solvents and water from the floor, room and building are essential to developing hard, long wearing, surfaces for the customers.
Remembering these simple steps will help ensure the best possible results:
1. Little or no airflow during the application process.
Too much air movement can cause the top of the finish to flash dry, trapping solvents - resulting in a slower drying and curing process.
2. Let the finish sit for about 30 minutes before starting the airflow process.
This allows the finish to not only continue gassing off the solvents, but to flow and level. If you start a flow of air over wet finish, it can leave waves in the surface.
3. Don't blow in on the job -- ventilate the solvent and/or water out of the room or building.
It is possible to put dust from outside into the wet finish - definitely not a good move at the end of a job. In high humidity conditions, it is important to remove the water and solvents from the room or building so the finish will dry hard and smooth.
4. Use aggressive airflow to start drying and curing process of finish coat.
As the finish gasses off, you must remove the gas from the room to keep it from settling back down on the finish coat. The first 4 hours are the most important in the life of a finish - that's why you need to get aggressive in the drying process.
