This article is a continuation of our common problems/ better solutions series at the PaintSource Network.
A common problem with painted exterior flooring is the use of oil based paint on wooden floor surfaces and decks. Unfortunately many national paint stores and builders warehouses continue to sell oil based floor enamel for exterior wood surfaces. This type of product is extremely hard, and will never withstand the expansion and contraction of exterior wood flooring. Even some acrylic floor enamels will be too hard or not breathable enough for certain construction designs. Extreme changes in moisture content and temperature of the wood cause hard coatings to be sheared from the surface as the wood expands, and the coating doesn't. Many times, new wood is extremely high in moisture content, and the wood surface is slick with mill-glaze. Primers (especially oil-based) are unable penetrate the surface of damp slick wood, and just lay on top with little adhesion. This also contributes to early paint failure.
Moisture entrapment also commonly occurs. Many times the wood is uncoated underneath, so moisture is drawn from the ground beneath the porch into the bare backside of flooring. This is the result of the non breathable nature of oil based products. Moisture trapped just beneath the coating surface fosters the growth of wood-decaying organisms. It also freezes in the winter months. The decay of this wood fiber leads to the release (peeling) of the paint film. Hairline cracks in the paint film, resulting from expansion and contraction of wood, allow further moisture intrusion, causing greater expansion of the wood, causing more cracks, allowing in more moisture, leading to rapid coating failure. If the floor is totally enclosed with no ventilation, our only choice is to use a solid color stain on properly prepared bare wood.
Sometimes we see only spot failure. Unfortunately, oil base paint never stops hardening. This is especially problematic on older coating systems that have been hardening to the point of eventual failure. Much of the paint that is currently intact, will eventually release. When we encounter a situation like this, we have two options. We can scrape the currently loose and peeling paint, and repair failed areas, and repeat this cycle every few years until the old hard underlying coating peels, or we can consider total coating removal. If lead is present in previous coatings, we need to consider chemical stripping as to not create a health hazard during coating removal and sanding.
For spot repair and repaint, we scrape off as much failed paint as possible, then sand with a dust-free palm sander (using 60 or 80 grit abrasive ) to blend in the bare areas. Final sand the remaining coating with 80 grit to leave a good profile for the coating. Prepare and prime the bare areas and recoat with an Acrylic Floor Enamel. Be aware that coating not removed now will continue to fail over time as any remaining old coating will always continue to harden. The second option involves total coating removal. There are several biodegradable strippers available. We also final sand the entire floor to remove any wood fiber damaged by trapped moisture, or the stripping process.
We have found very few good-performing floor paints for exterior wood floors. If the wood is already installed, and unprimed on the back, you have limited choices. If you absolutely want a solid painted finish, you could consider an acrylic solid stain like Enduradeck from California Coatings, or a solvent-based product like Sikkens Rubbol DEK, which is a flexible, breathable oil based wood floor coating (not a paint). It looks like paint, but performs like a stain--no film to peel. If you want to go back to natural wood, you have a variety of good options.
Each of your coatings options has distinct advantages and disadvantages depending on your specific requirements and whether you are recoating bare wood, or remaining paint. If you have failed paint, and choose not to strip the entire porch, you will need to sand the remaining coating so the new coating will adhere to it. Solid color stains are for uncoated wood only, so unless you get to completely bare wood, you should consider an acrylic floor paint , priming bare wood and existing paint with 2 different specialized primers. I hope this helps.