Water Level Controls and Devices. A water column is used on a steam boiler to reduce the turbulence and fluctuation of the water level so the gage glass can provide a steady, accurate water level reading. The use of a water column is not mandatory.
Preparation. Verify the paint is completely dry. Never use varnish to seal acrylic paint if it is even slightly wet. Dust the surface of the dry paint gently with a clean cotton rag or paper towel. Rinse a jar or cup with water to remove any dust particles. Read the label on your varnish to find the correct water-to-varnish ratio. Mix the varnish with water in the jar or cup.
Is there a paint/sealant that is used to seal old A/C ducts and clean them up? A. A/C ducts can certainly be painted successfully to improve the appearance; you may notice some reduction in noise level when the A/C is running, too. But to seal leaks, a quality caulk (sealant) should be used. To Seal them: use a quality latex acrylic or siliconized acrylic caulk at the seams and joints.