TECHNICAL BULLETIN
We have all heard the term “Pre-finished Metal Siding.” It has been said over the years that these surfaces never need to be painted. Although the factory coatings on these surfaces are typically very hard, providing an abrasion resistant surface, they do have a tendency to chalk and erode, leading to fading of color and a loss of gloss. In extreme cases, the underlying metal can be exposed and rusting may occur. Ultimately, they too must be maintained and restored. If your siding is suffering from this fate, Diamond Vogel has the solution.
The good news is that metal siding is one of the best surfaces to repaint. The process of repainting pre-finished metal siding is a little different than it is for other types of exterior surfaces.
Surface Preparation
As with all exterior painting projects, proper surface preparation is the key to restoring your metal siding. Begin by thoroughly cleaning your siding of all loose dirt, chalk, and other contaminants. Cleaning of the surface can be done by hand washing with warm, soapy water or with the use of a high-pressure washer (2500 psi minimum). Pay close attention to the chalk that may be on the surface. Chances are the original coating on the siding has chalked quite badly. Test for chalk by rubbing your hand on the siding, checking for a transfer of chalk onto your hand. Chalk must be completely removed prior to painting. The use of a household detergent or a pre-paint cleaner will aid in the cleaning process. Be sure to rinse the surface thoroughly, not allowing detergent to dry on the surface.
Areas such as eaves, soffits, and ceilings usually degrade less than surfaces exposed directly to the sun and elements; they often have accumulations of dirt and mildew. These areas should also be power washed to remove any contaminants. If mildew is present, it should be removed with a solution of 3 parts water and 1 part bleach. Allow the solution to remain on the surface for 10 minutes, followed by rinsing with plain water and allow the surface to dry prior to coating.
Remove all loose coatings and rust by scraping, sanding, or other abrading method. Dull glossy, slick, and/or
non porous surfaces with sandpaper. Spot prime bare areas with a rust inhibitive primer such as Diamond Vogel’s CoteAll Multi-Purpose Alkyd Primer, Iron Prime 600 Fast Dry Universal Primer. Pay special attention to the type of metal substrate.
There are many different types of factory applied coatings used on metal siding. Most generally weather down to a surface that will allow repaint coatings to adhere tenaciously. Since it is not possible to judge the ability of a coating to adhere to a surface by observation, it is always a good practice to try a test patch to ensure the results will be as expected.
Finishing Systems
The painting system used on these surfaces is dependent on the effectiveness of the cleaning process. The use of a primer may not always be necessary. When severe surface oxidation or severe chalking is present and cannot be completely removed during the cleaning process, the use of a solvent-thinned primer, such as Diamond Vogel’s CoteAll Multi-Purpose Alkyd Primer or Iron Prime 600 Fast Dry Universal Primer, is recommended.
An acrylic latex topcoat such as Diamond Vogel's Palisade Ultra Premium Exterior Acrylic Latex, Durango Acrylic Latex Exterior Finish, EverCryl Exterior Acrylic Latex Finish, or Vers-Acryl 222 Acrylic Maintenance Semi-Gloss are recommended for long-term durability to these surfaces. Two coats are recommended for optimal performance.
Steel doors, door frames and hand rails should be cleaned, then primed with a rust-inhibitive solvent based metal primer, followed by a variety of topcoats. These areas are subjected to a great deal of wear and abrasion, so care should be taken when choosing a finish coat.
For further information on painting metal buildings, contact your Diamond Vogel representative.