Asphalt sided home in Two Harbors MN (C) Daniel FriedmanAluminum Siding Inspection, Defects, Diagnosis, Repair Advice
How to inspect, install, repair, clean or paint old aluminum siding

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Aluminum siding inspection, diagnosis, repair, cleaning or painting:

This article discusses the identification, history, and common defects observed in aluminum exterior building siding, such as weathering, paint loss, dents, and questions about the need for a vapor barrier behind asphalt siding and over building sheathing. Included are comments from several recognized building inspection and construction authorities.

Our page top photograph shows 1960's vintage (wideboard) aluminum building siding installed over peeling deteriorated wood clapboards on a pre-1900 home in Poughkeepsie, NY.

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Aluminum Siding History, Defects, Vapor Barriers, Inspection, and Diagnosis

Aluminum siding, narrow gauge, on a 1980's building; shrubs are too close to the wall (C) Daniel Friedman

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Article Contents

Aluminum siding, produced from aluminum coil stock and painted in a wide variety of colors, provided a durable exterior building cladding that resisted rust and rot. Aluminum siding in its earlier forms was typically produced in a (roughly) 6" wide clapboard stock, installed with a fiberboard backer to resist denting in some cases.

Aluminum & steel building siding was very popular and widely installed in North America from the 1940's into the 1970's. By the 1970's a narrow-width aluminum siding "board" stock (shown above) was in popular use in both smooth surface forms and in embossed designs resembling wood.

Because of the large amounts of energy used to produce aluminum siding and increasing raw materials costs, aluminum siding declined in popularity in the U.S. in the 1970's.

How to Identify Aluminum Building Siding

It's easy to distinguish between aluminum siding and vinyl siding products by careful visual inspection of the material edges or by observation of dents (aluminum) versus breaks or impact damage (vinyl).

But to distinguish between aluminum siding and it's steel look alike you may need a magnet (or you might see rust).

Aluminum Siding Inspection, Defects, & Maintenance Suggestions

Building siding in ground contact: risk of insect damage or rot & structural damage

Damaged aluminum siding (C) Daniel Friedman

Don't install any building siding down in contact with the soil or below the soil level (below left) - doing so is inviting a hidden termite or carpenter attack. On occasion we have inspected a building whose bottom course of siding was bulged outwards.

Knowing that it would have been virtually impossible to install the siding in that form, a good guess is that the building sills and or lower walls have been damaged by rot or insect pests.

Our siding photo at below left shows a roof gutter downspout spilling right by the aluminum siding that has been buried below ground level. Adding water increases the risk of hidden insect or rot damage.

This often hidden condition and the need for possibly costly building repairs can be verified by interior inspection or by removing some exterior siding at the wall bottom. This is not a defect peculiar to aluminum, vinyl, or other siding products - you can make this mistake with any wall cladding.

Buckling Aluminum Siding at Ground Level Means Big Trouble

Buckled siding at ground level indicates sill crushing (C) Daniel Friedman

The condition of building siding may be more than a cosmetic issue. For people interested in detecting hidden building damage the photo at left is one of the more important ones we've taken.

This aluminum siding photograph illustrates buckling aluminum siding at the wall bottom - not a defect in the siding material but a poor installation (buried in the ground) inviting insect and rot problems in the building structure.

The aluminum siding is buckled in the bottom two courses on this home but is intact on upper courses. The building, built over an inaccessible crawl space had suffered such extreme termite damage to its sills and lower wood-framed walls that the weight of the building above had crushed and buckled the aluminum siding.

An understanding of how siding is installed on buildings (from the bottom of the wall up) would lead an observer to realize that you couldn't install buckle siding in this fashion, the damage had to occur by a downwards movement of the structure (or an earth heave which was very unlikely in this pattern). Very extensive and costly sill and wall framing repairs were needed - an opinion confirmed when the lower siding segments were removed.

Aluminum Siding Details at Roof Abutments

Aluminum siding close to roof surface (C) Daniel Friedman

We cite the roof-siding abutment point as a common location of rot or insect damage. While wood siding too closet to the roof surface will generally rot, aluminum or vinyl don't suffer the same risk. However if proper step flashing was not installed under the roof shingles and against the wall under the siding, this same location becomes a roof or wall leak. I don't like to caulk this area - it's an unreliable repair. Notice that the installer omitted any J-channel at the siding bottom edge, perhaps figuring that it wasn't necessary. I'd take a closer look at the siding and flashing at the roof-wall abutment shown above.

Also notice how close that window sill and trim are to the roof surface? Expect to find rot at this location.

Comparing Aluminum Siding Wide and Narrow Widths

Our aluminum siding photo (below left) provides a close up of 1960's vintage aluminum siding that is losing its paint coating.

The right hand photo shows a nice algae growth on this shaded, aluminum-sided building wall that was covered with a narrow-gauge wood-pattern embossed aluminum siding product in the 1980's.

Damaged aluminum siding (C) Daniel Friedman Damaged aluminum siding (C) Daniel Friedman

Cause & Evaluation of Paint loss on aluminum siding

Paint loss from 1960's era wide aluminum siding (C) Daniel Friedman

Watch out: some versions of aluminum siding (especially from the 1960's) included a paint coating that weathered, chalked, and even washed off entirely, leaving a bare aluminum surface (photos below). Besides the obvious appearance of aluminum siding that has lost its paint - shown above, even aluminum siding that has retained its white color (or other color in later siding products) may be chalky and in poor condition. Chalking paint or paint loss on siding is caused by aging of the paint or to put it more technically: binders have been lost from the paint coating, leaving pigment that can wash or wipe away. More about the mechanisms involved in paint failure is

Check for chalking in the paint surface

A simple field-test of the condition of the surface of older aluminum siding is to wipe a finger across the siding surface - perhaps it's best to choose an unobtrusive spot so you don't leave an ugly smear. If your finger comes away white with oxidized paint you have an idea that the surface is deteriorating. As the photographs below show, paint loss on older, typically wide-board aluminum siding, can be so extreme that the silver aluminum below is exposed.

Damaged aluminum siding (C) Daniel Friedman

The painted coating on some aluminum siding can also be "pulled" off of aluminum siding by some fungal growths (artillery fungus) and by vines (photo below).

Damaged aluminum siding (C) Daniel Friedman Damaged aluminum siding (C) Daniel Friedman

Our aluminum siding photo (above at left) shows a close up of a fungal growth on an embossed aluminum siding product. The mold growth on this siding is not a product defect, it is the result of site conditions - moisture and shade, as is the green and black algae shown on the siding in a photo earlier in this article.

How to Clean or Paint Aluminum Siding

Damaged aluminum siding (C) Daniel Friedman

Step 1: clean the aluminum siding

Aluminum siding (and other siding products) can be cleaned by power washing or by hand scrubbing. Don't be upset if scrubbing the weathered aluminum siding causes more paint-loss. That's part of proper surface preparation in that your new paint will bond better and last longer if installed on a sound, secure, surface. Painting over dirt or chalked paint surfaces may not give a lasting paint job. .

Watch out: don't spray your power washer "up" under any building siding product or you risk blowing water into the building walls, causing a mold or water damage problem.

Watch out: also don't use solvents such as acetone, lacquer thinner, or mineral spirits to clean aluminum siding in preparation for painting. Not only are some of these solvents dangerous to handle, a run of acetone or lacquer thinner down a painted wall can leave a dissolved run-pattern that telegraphs through the new paint job. If you already made this mistake, when the wall surface is dry, sand it lightly with 200 grit emery paper or finer. We only use a solvent, such as mineral spirits, if road tar or roof cement asphalt has been splashed onto the to-be-painted aluminum surface.

You can paint bald and balding aluminum siding but without proper surface preparation such as power-washing, the paint job won't be durable. And power-washing to clean siding or to prepare it for painting can itself cause trouble if the power-washer is not handled properly. Spraying "up" against the lower edges of aluminum (or vinyl) siding forces water into the building wall system and can in the worst cases soak building wall insulation or cause a costly mold contamination problem. Don't do that.

Step 2: Choose the primer and paint for aluminum siding

With careful surface preparation and selection of a paint or primer + top coat paint specifically recommended by its manufacturer for aluminum siding, it is possible to re-paint weathered aluminum siding - of course we then have converted a "no maintenance" material into one that will require occasional repainting.

Aluminum building siding damaged by rain splash-up on a patio (C) Daniel Friedman Aluminum building siding damaged by rain splash-up on a patio (C) Daniel Friedman

The siding above is installed down to ground contact at a stone patio, offering an inviting path to termites or carpenter ants who may enter the building wall or floor framing. The dirt and debris on the siding tells us that there is considerable rain splash-up onto these walls, adding wet conditions and increasing the risk of insect damage, leaks, or rot. In fact extensive termite damage was found in the floors of this building.

At above right you can see peeling paint on the lower course of siding as well as efforts to seal the siding-to-patio joint with exterior caulk. Painting did not help to protect this building.

Following surface scrubbing and cleaning, select the paint for your aluminum siding by asking your local paint store for product suggestions.

Step 3: Apply primer, let dry, apply top coat(s) of paint on the aluminum siding

Be sure that the surfaces to be painted are not only clean of loose paint and soil but that they are dry, that you are painting in warm but not hot weather, and that rain is not expected for at least 24-hours.

Professional house painters like to spray the paint onto the walls - making the covering of the under-lip of the siding far easier and faster than using a roller or brush. I've used a combination of spray and roller and brush to both get the paint onto the wall and, where surfaces are irregular (more common on wood siding) brush it well into the surface. Spraying paint on top of even a small amount of debris is going to mean a short paint job life. Spraying too much paint on the wall means runs and sags in the paint job: it's better to spray two thin coats than one thick coat. If you spray too much paint on the wall, quickly brush out the run or sag with a fine-bristle brush.

Steel Building Siding

Steel building siding was sold based on advantages similar to aluminum siding (see Aluminum siding) but with disadvantages of heavier weight, more difficult to install (harder to cut and trim), and vulnerable to rust. Steel siding was never as popular in North America as aluminum nor its later replacement - vinyl.

Photos and notes on steel siding are wanted - CONTACT US.

Below: corrugated steel siding on a medical center in Oxaca, Mexico. This building, located in the highlands above Pluma de Hidalgo, serves as a medical center.

Corrugated steel siding (C) Daniel Friedman Oxaca


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