How do I know what’s galvanized metal and what isn’t?
Galvanized metal is used for a variety of items in both high-rise condominiums and townhome complexes. You can find galvanized metal used for perimeter fencing, roof flashings, gutters and cladding. Take a hard look at the metal on your site, does it have a mottled silver grey appearance? That is your galvanized metal.
What exactly is galvanized metal?
In layman’s terms “galvanized metal” is metal that has gone through a chemical process to keep it from corroding. The principal method of making steel resist corrosion is to alloy it with zinc. When steel is submerged in melted zinc the chemical reaction permanently bonds the zinc to the steel through galvanization. Therefore, the zinc isn’t a sealer like paint; it doesn’t just coat the steel, it becomes a barrier between the metal and the environment. The zinc actually, permanently, becomes part of the metal.
Ok, now that I know what galvanized metal is, why is the paint on my pre-finished galvanized metal perimeter fence failing?
There can be several reasons why the fence coating is failing. 1/ If the fence is pre-finished, the issue most likely originated at the manufacture’s level. 2/ If the fence has been recoated, the issue is more likely to be associated with the level of preparation and the products used during the repaint. 3/ In some cases, both scenarios are at play.
I’m just getting more confused. I have three paint contractors bidding on this project but each of them has a different idea on how best to approach the issue and the pricing is all over the map. How do I know how to correct the problem?
Not to worry, even seasoned paint contractors have made uneducated decisions regarding galvanized metal. Just remember, there are three things that should always be at the forefront of any galvanized metal coating project – CPA – Clean, Prime and always use Acrylics.
Clean – the most important and first step when dealing with galvanized metal.
New galvanized metal is coated with a thin coat of oil. This must be removed with a high quality water soluble cleaner before it can be painted. If left untreated, exposure to the elements will cause the protective zinc coating on the metal to oxidize.
The oxidized material is called white rust and resembles white powder that must be removed prior to coating. This requires wire brushing and washing to ensure the metal is residue free. If left uncoated the zinc barrier will eventually be depleted, allowing the metal to rust.
Painted galvanized metal must have all loose and failing paint removed. In many cases, due to the level of oxidation, much of the existing coating must be removed before any cleaning can take place.
NEVER USE OIL BASED CLEANERS INCLUDING THINNERS!
Primer – Yes… primer is necessary!
Use only 100% Acrylic and only primer recommended for use on galvanized metal. Never use an oil based primer. There is also a significant distinction between interior and exterior primers; always ask your contractor for specific information about the coating system to be used. Paint stores are happy to provide data sheets for any of their products.
Acrylic – When applying any coating directly to galvanized metal always use acrylics. Oil based rust primers and paint work great on regular steel or over top of a good primer but are a disaster when used directly on galvanized metal. Oil or alkyd products will initially adhere to the galvanized metal, but will eventually fail. A process called “saponifcation” will occur when the zinc chemically reacts with the alkyd binder of the paint or primer. With this process a soapy film will be created and the paint will peel.
Now that I have a better idea of the process involved, what can I make of the three quotes? They vary in price and specificity.
Ask for specific information of all three contractors—preparation techniques, primer, finish coat and cleaner data. It’s important to keep in mind that when one contractor’s price is significantly lower than another’s the price is most likely an indicator of what they are NOT doing. Properly dealing with galvanized metal substrates is not a simple exercise. One way to help cut through any confusion is to call your local commercial paint store (ie: Sherwin Williams or ICI). Their sales reps are always willing to verify or write out a paint specification for you.
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