Prefinished Siding- How It Works

The Story Behind Prefinished Siding- How It Works

As people noticed us cleaning brick and stone in the downtown areas, we started getting calls from people with aluminum siding who wanted to know if we could clean it.  We found that in some cases we could and in others the paint was simply worn out and the siding needed to be repainted.  It seems that when Reynolds, Alcoa or whoever had come out with aluminum siding and told us it was forever they were mostly truthful.  The part they didn’t share was that the painted finish isn’t. 

Paint has a “natural” aging process.  It starts off with whatever sheen it has (full gloss, semi gloss, satin, etc.) and over time “flattens” out.  That is to say it changes to a flat sheen or loses all of it gloss (assuming it had some to start with!).   The next stage is to start chalking.  The solids (pigment, fillers, etc.- see glossary) in the paint begin to slough off.  Over time it continues to wash off until you get to a point where there is virtually no paint left and the grey aluminum is showing through.  Some paint manufacturers actually touted this- they claimed there paint was self cleaning!  Pretty clever way to convince someone your paint is wonderful while it wears out!

Where your siding is at in this aging process will determine the likelihood of cleaning alone being an acceptable approach for restoring the finish.  When you rub your finger on the aluminum siding or trim if it leaves either no paint or a light chalky coating on your finger there is a good chance cleaning it alone will work.  If on the other hand (or finger!) the chalk is so thick you can barely see your skin through the chalk, more than likely, after all of this loose chalking paint is removed, the aluminum will show through.  It should be noted, that from the perspective of the pressure washing equipment, dirt and chalk are the same, it cannot differentiate between them, so if it is removing one it is also removing the other! 

Depending on the color of the paint on the siding the dark grey aluminum showing through may or may not be objectionable.  On white siding, if the chalk is heavy, the siding may look worse after it is cleaned than it did before.  That is the bad news.  The good news is that all chalk or dirt must be removed from any painted surface before it can be properly repainted.  Paint sticks incredibly well to dirt or chalk.  The problem is that dirt and chalk don’t stick to much of anything well.  Consequently, if you paint over dirt or chalk the paint will peel still attached to the layer of dirt that separated from the surface below.

In some cases, as long as the siding still looks presentable the fact that the paint is chalking doesn’t necessarily matter in others it is more problematic.  If you have painted siding or trim (regardless wood or aluminum) that is above a natural finished surface (i.e. brick or stone), when it rains the chalking paint will run down with the rain water and over a period of time stain the finish below.  The classic example is the aluminum siding on the gable ends of a red brick, Cape Cod style home.  It is common to see white stains coming from the siding on the red brick.  For more information on this see Paint Removal- Chalking Paint.

Another noteworthy point about chalking paint is that what is a problem in one area may not be a problem in a different area and vice versa.  That is to say if the paint is in reasonable condition on the siding, it doesn’t mean it won’t be a problem on the corner pieces, fascia, trim pieces, etc. (or the other way around).  In fact very often the paint directly under the drip edge of the siding may still be sound (because it doesn’t get exposed to as much “weather” as the rest of the “board”) while the paint on the rest of each row or course of siding is all but gone.  This is related to inconsistencies in the amount of weather exposure, as well as in the thickness and or quality of the original baked enamel finish which was applied to the respective pieces.  Pieces with thicker, high quality finishes exposed to less weathering will most certainly exhibit less chalking that to components with the opposite characteristics.

While you may think you don’t want to ever touch or see a can of paint for the outside of your home, and opt to go for some other style of “prefinished” siding, buyer beware!  As vinyl siding became more popular we started getting calls for cleaning this as well.  Vinyl siding generally cleans up pretty well and doesn’t have some of the issues found with aluminum siding.  Contrary however to what the manufacturers would have you believe it is not without limitation.  Although it does generally clean up well the pigments utilized in the vinyl are not immune to the damaging effects of UV exposure.  Not too much of a concern with lighter colors or white, the darker colors in this writer’s opinion have a tendency to fade or “wash” out and we have yet to find a way to cost effectively restore the original appearance, short of, dare we mention- paint?

In the end, we suspect that we will find similar limitations with other exterior finishes as well (whether they are currently on the market or yet to be developed!).  The damaging effects of UV light are hard to avoid and as of this writing we have yet to see a product that, across the color spectrum, will withstand prolonged, long term exposure, without degradation of the finished appearance.  What the consumer needs to do to restore the original color, sheen or look, and the cost for doing so, become the questions to be answered.

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