Siding and Other Exterior Surfaces


Artillery Fungus

I have black specks on my siding. What are they and how can get rid of them?

The specks may be spores from artillery fungus. When this fungus fruits it produces a small cup containing a clump of spores. When conditions are right the fruit points toward a bright light source and shoots out its spores with sufficient force to hurl them up to 20 feet, hence the name artillery fungus. If the light source is the sun the spores would fall short of the target and end up on the lawn or another surface where they would go unnoticed. However, the light source is often sunlight reflected off an automobile or siding on a house. In these cases the spores stick to the surface. When the spores land on a surface such as vinyl siding they attach themselves tightly to the surface leaving a tiny black spot. The problem usually occurs when wood chips are used as a landscape mulch. As the chips decay they provide an ideal habitat for artillery fungus.

Experts are not aware of any way of removing the spots with out mechanically scraping them off.


What is the best caulk to use with wood siding?

The most common type of caulk material used with wood siding is acrylic latex. Newer versions remain elastic longer and can be used at temperatures below 40 degrees Fahrenheit. They are paintable and easy to clean up. A drawback is that they can take longer to set and to cure. Silicone caulks remain elastic and perform well at very low temperature. However, they generally are not paintable and don’t adhere to some materials. Polyurethane caulks have the advantage of adhering to most materials. However, they need to be used quickly since the shelf life is short. They are also not readily paintable.

Caulking in Cold Weather

Can outside caulking be done in cold weather?

It is better to caulk when weather is warmer because most caulks go on easier. Caulks also bond better and are likely to stay put longer when applied during warmer weather. However, some caulks can be installed in cold weather. Check with retailers who handle a broad range of caulks. The February 1995 edition of the “Journal of Light Construction” had the following cold weather application tips:

    1. When applying caulk, keep it warm until the application time.
    2. Warm surfaces to be caulked with a hair dryer to melt any surface ice and remove moisture from the surface.
    3. Sand the contact surfaces if possible to improve bonding.

Cedar Deck Discoloration After Cleaning

Why does my cedar deck turn black within two weeks of cleaning?

Staff at the Forest Products Lab say that the condition sounds as if somebody used linseed oil on the deck at sometime. The oil is a tasty base for mold and mildew. Cleaning the deck washes off the surface mildew. The deck turns black again as the mildew regrows on the residual linseed oil in the wood. They suggest cleaning the deck with a good cleaner, one with bleach in it. Then, apply a wood preservative which contains a mildewcide to the deck. Better results are likely if you use a preservative that has some color to it, rather than a clear one.

Cleaning Lannon Stone

What is the best way to clean the lannon stone exterior of a home?

Lannon stone is a dolomite limestone which is fairly porous. Experts from several companies that supply such stone offered one caution, if your stone is any color but grey do not try to clean it yourself. The color is the result of weathering and is on the surface. It is likely to be affected by strong cleaners. If the stone is grey there are cleaners made specially for stone available at companies that sell stone. Buy one of these cleaners and follow the directions carefully. In general you wet the stone first then brush on the cleaner and let it work for a while. Before it dries rinse thoroughly. You might want to hire a restoration contractor since the cleaners can damage surrounding paint and other surfaces and since it may be difficult to produce a uniform color.

Controlling Mildew on Siding

How should we control the mildew on our wood siding?

Dark spots are often a sign of mildew on your wood siding. Mildew can be a sign of more serious moisture problems, such as excessive indoor humidity or a leaking roof. If you find soft or swollen siding in addition to the mildew, look for the underlying moisture problem before treating the mildew. Even without underlying moisture problems mildew can grow if there is moisture on the surface. Shade and high humidity can cause condensation on the siding providing the necessary moisture. Occasionally, hosing down the siding with water and a soft scrub brush will keep the food supply of dust and paint chalk down, reducing the chances of mold growth. It will probably make the siding look better as well.

Once mold develops, washing the surface with a bleach solution usually removes mildew. The Paint Quality Institute recommends a solution of three quarts water to one quart chlorine bleach. Use a garden sprayer to wet the siding with the bleach solution and allow it to remain on the siding for about half an hour, then rinse thoroughly. Be sure to protect landscape plants before applying the bleach solution and protect your eyes and skin.

Dangers of Cement Asbestos Siding

How dangerous is it to have cement asbestos siding on a home?

This type of siding is often referred to as slate siding. The asbestos is typically well bound with the cement and not available to be breathed. So it doesn’t pose a particular health threat. If it doesn’t look good it can be painted quite easily. Hose it down to remove loose dirt and clean areas where mildew is present with a bleach solution. The siding can then be painted with a primer and top coated with a good quality latex paint.

If you keep the siding, keep in mind that should you sell in the future you may need to disclose to prospective buyers that the house contains asbestos.

Deck Cleaning

What is the best way to clean a wood deck?

You have several choices One choice is to use a chemical wash. According to article the April 1998 issue of “The Paint Dealer” there are three basic types. Chlorine based washes are very effective against mildew and other decay organisms. However, they can lighten the wood color, and cause a roughening of the surface. If not rinsed thoroughly the residue can eventually cause a greying of the surface. A detergent must be added to remove dirt. Sodium percarbonate products use oxygen bleach to remove mildew and reportedly avoid many of the disadvantages of chlorine-based products. The third type uses oxalic acid and is recommended for cedar and redwood decks in which water-soluble resins can discolor the surface. Since it is not effective at removing mildew it needs to be used in combination with one of the other type washes. Power washing is also an effective alternative to chemical deck washes. It can be effective in removing dirt, mildew and even previous coatings. However, if not used properly power washers can damage the wood surface, as well as adjacent windows, doors and siding.

Deck Sealing

What is the best finish for a wood deck?

Penetrating finishes are the best choice for decks according to researchers at the USDA Forest Product Laboratory. Film forming finishes such as paints and solid stains can trap moisture, which in turn causes blistering and peeling. They often crack from the swelling-shrinking cycles of the wood. They also tend to wear off in areas of heavy foot traffic and require much more preparation before recoating. Two types of penetrating sealers to consider are water repellent preservatives (WRP), which are clear and semi transparent stains which are pigmented but otherwise similar in composition. A good sealer should contain a solvent, a drying oil or sealer, a non drying oil such as paraffin and a mildew fighter. The solvent carries the oils into the wood. Many products use water as a solvent, however, the Forest Product Laboratory warns that some of these products do not provide the penetration that oil or solvent-based products provide. The clear products typically have to be renewed every year. The addition of pigment to the formula doubles or triples the time between applications. Even though semitransparent stains contain pigments they do not form a skin, which can peel.

Exterior Paint Selection

How can I decide which latex paint to use on my wood siding?

The term “latex” refers to several different inorganic binders or resins. Some are better than others for finishing exterior wood surfaces. The two most common are 100% acrylic resins and vinyl acrylic resins. According to a national resin supplier, acrylic resins are about twice as expensive as the vinyl acrylic resins. However, they have a number of advantages, so they are used in most top of the line paints. They adhere better, so they are less likely to peel and they are more water and dirt resistant so they are less likely to have mildew problems.Selecting the specific products from among various acrylic latex paints can be a challenge. One way is to go for the top of the line paint. Quality paint will be easier to apply and can last at least twice as long as low quality paint according to research reported by the Paint Quality Institute. Another way is to look for paints with a relatively high proportion of solids. In good quality paints from reputable companies, the solids are primarily binders and pigments. More solids in latex paint usually result in a thicker coat and more durability.

What type of paint is best for wood siding?

Paint experts at the USDA Forest Products Laboratory have found that in most cases, latex paints are the best bet for wood siding. They are more porous than oil-based paints, so they allow moisture trapped in siding to escape while effectively shedding water. Oil-based paints also become brittle as they age. Often, the paint becomes so hard that it cracks and chips. Oil paints also can also become yellow in areas that are protected from the bleaching effect of sunlight. Oil paints are more prone to mildew because the oils in them are usually plant -based and provide nutrients for mildew. Latex paints have two other major advantages. First, they use water as the carrier, so clean up is much easier. Spills can be cleaned up with a damp rag and brushes can be cleaned with soap and water. Secondly, they are more environmentally friendly because the manufacturing process generates less toxic waste and they release water when they dry instead of releasing mineral spirits.

Gray Stain on Siding

What would cause a gray stain where two pieces of steel siding meet?

It is unlikely that this stain is from the siding itself. When the siding is properly installed, there are no raw edges to cause stains. If there were, the stains would be rust-colored instead of gray.

The logical source of the stain is either dirt collecting on the siding or some colored liquid leaking from some material behind or above the siding, such as building paper. If it is dirt, wash the area above the siding and the stained area with a solution of one-half cup of laundry detergent, one-half cup of trisodium phosphate and one gallon of water. An alternative to trisodium phosphate is automatic dishwasher powder. Use a soft brush to apply the solution and then rinse with clear water. If this does not remove the stain, add a quart of chlorine bleach to the washing solution. The bleach will kill any mildew.

If the stain returns quickly, then you should check for the source of the staining. It may be a leak in the roof or plumbing or condensation from inside the house.

Lightening Wood Siding

Is there a way to lighten wood siding that has been stained a dark color?

There is no good way to do it. The color is in the surface of the wood. It is possible that treating the surface with mineral spirits might remove some of the color. You could test this approach on an inconspicuous section of siding. Even if it worked it would be tedious and would require care in handling the residual mineral spirits. The only other possibility is to mechanical remove the surface of the wood by sanding. It would be difficult to do this and achieve an even effect.

Low Maintenance Siding

What is the best choice in low maintenance siding?

The answer is not simple. Much of the decision is based on personal preference. Vinyl and Aluminum are the two most common choices for maintenance free siding. Vinyl has been gaining in popularity in recent years and is a little cheaper. The color goes all the way through vinyl siding so it can’t wear off. On the other hand, the color on aluminum siding is similar to automobile paint and will eventually need to be renewed. However, painting aluminum siding is easy. The fact that you can repaint it means that you have the option of changing colors. Aluminum siding can dent, vinyl siding doesn’t dent but it can break if hit hard enough. Individual sheets of either type of siding can be replaced however matching the color could be a problem.

Orange Stain on Cedar Siding

What would cause an orange stain on an area of cedar siding?

One possibility is that there is some water leakage in the area of the stain. The water leakage is causing what is known as extractive bleed. Resins in the wood are dissolved by the water and then flow to the surface. I suggest you begin by checking for leaks in the roof or from other sources within the house. Once you have removed the source of the discoloration, you can treat the stained area with a stain blocking sealer and repaint. The USDA Forest Products Laboratory web site is a good source for answers to wood finishing questions.

Painting Asphalt Siding

Can the asphalt siding on a home be successfully painted?

Painting asphalt siding is not recommended. Solvent based paints may dissolve some of the asphalt in the siding and cause discoloration of the paint. Standard latex paints may not bond well and quickly become brittle. One paint manufacturer Indicated that a vinyl modified urethane paint might work. The paint the technician had in mind was made specifically for metal.

Peeling Paint

Why would the paint on the east side of a house continue to peel when paint elsewhere on the house does not?

If the paint is peeling in large sheets and peeling back to bare wood it may mean that the siding is being wetted from the inside. In an older home, the problem is probably caused by water vapor escaping from inside the home. One indication that this might be the case is that your windows steam up in the winter. The solution is to decrease indoor humidity by running exhaust fans. The fans will be more effective if you open a window on the other side of the house. For more information about this and other paint problems, visit The USDA Forest Products Laboratory web site is a good source for answers to wood finishing questions.

Permanent Marker on Aluminum Siding

How can writing done with a permanent marker be removed from aluminum siding?

Try alcohol first because it won’t hurt the paint. Other solvents — such as acetone — remove the marker, but probably also will remove paint. If alcohol doesn’t work, consider buying some matching high-quality paint and repainting the area. Start with a stain blocking sealer and cover with a high-quality acrylic latex paint. Aluminum siding accepts paint extremely well, and the paint should last many years.

Powder on Brown Paint

What would cause a powdery, frost-like coating on a recently applied dark brown exterior paint?

According to a paint expert at the National Forest Products Laboratory here in Madison this frost effect occasionally occurs particularly on dark color paints. One source of the problem is that a filler such as calcium carbonate used to make the paint easier to spread migrates to the surface leaving the white residue. Another is that inexpensive resins were used in the paint and the resins degraded and came to the surface. These problems are most common with low cost paints. They can happen with any color paint but are most noticeable on the darker colors. He recommended going to a lighter shade of paint or using a better quality paint.

Preparing Siding for Paint

How do you prepare wood siding for repainting?

If the existing paint is peeling severely, you need to determine the cause before repainting. Preparation involves washing the surface to remove loose dirt, chalking and stains. If surface mold exists, treat it with a dilute bleach solution (one cup of household bleach to one gallon of water) and rinse well. Add some powdered automatic dish washing detergent to the bleach water to remove stubborn mold stains. Research from the USDA Forest Products Laboratory indicates that it is critical to carefully sand any bare wood. Just a few days of exposure of bare wood to sunlight changes the surface so that paint will not bond well. The longer it is exposed, the worse the problem is. It is, therefore, critical to sand off a thin layer of the exposed wood, about one millimeter, before painting wood that has been exposed. It is also important to carefully feather the edges of old paint surfaces where they meet bare wood. Not only will the paint job look better, but if abrupt edges are present, it is likely that the thickness of the paint layer will be thin at that point and you may have a premature failure. There is an important caution about sanding. If you are working on a house built before 1978, the existing paint may contain lead. Sanding lead paint can be hazardous. The USDA Forest Products Laboratory web site is a good source for answers to wood finishing questions.

Preserving Natural Cedar Finish

What is the best way to preserve the original color of cedar siding?

Some of the new cedar tone stains may approximate the warm tan color that is associated with cedar. Usually the sun will open the surface of the wood so that some water will be absorbed. This can lead to other changes in color as various funguses and other organisms take up residency.

In case this is happening, first clean the siding with bleach water [1 cup bleach to 1 gallon water] and then rinse it before applying stain.

Pressure Treated Lumber

What do you recommend for use in place of treated wood?

Because of concern about arsenic leaching from CCA pressure treated wood is no longer available for residential uses such as decks and landscaping. Two alternative preservatives, copper azole and alkaline copper quaternary (ACQ), are commonly used in pressure treated wood available today. According to the USDA Forest Products Laboratory, wood treated with these alternatives should function pretty much the way the older product did. However, it may require special fasteners because of greater corrosion potential. It also may be somewhat more expensive. This leads to another important difference. CCA treated wood usually came in one retention rate. So the same lumber could be used above and at grade. Now different grades are avaialble so it is important to look at the end label to be sure you are getting lumber suitable for the exposure you have in mind. See the related link for more details. Alternatives types of wood may be worth considering. There are a number of naturally decay resistant woods available. Perhaps the most familiar are redwood and various species of cedar. However, the “Wood Handbook” produced by the USDA Forest Products Laboratory lists many other species that are “resistant or very resistant” to decay. It is generally only the heartwood, not the sapwood that is decay resistant. Since much of today’s lumber comes from second growth trees that contain a high proportion of sapwood, species alone does not guarantee decay resistance. Sapwood is usually more open in grain and lighter in color. The “Wood Handbook” is available online at  Search for the Wood Handbook to get the entire pdf or individual chapters. “‘Decay resistant’ does not mean maintenance free. Any type of wood used outdoors needs protection from ultraviolet light damage and from water. They need to be sealed with paint or a penetrating water repellent UV blocking finish. 

With the concern about arsenic leaching from pressure treated wood what can we do with existing pressure treated wood in our yard?

There are several things that you can do to reduce the risks that you and your family may encounter from existing CCA pressure treated wood structures. First, be sure that children wash their hands after playing on pressure treated wood play structures and discourage them from playing in dirt at the base of any pressure treated structure.Second, consider coating the structure with a semi transparent stain or other water repellent. According to preliminary work at the U.S. Forest Products Laboratory in Madison, Wisconsin, this can reduce the leaching of arsenic dramatically. Sealing the wood is something that you should be doing anyway to extend its life. While pressure treated wood is decay resistant it is subject to damage from ultraviolet light and from water. Applying a penetrating stain or water repellent can reduce this damage. These coatings need to be renewed every few years to be effective. While paints and varnish will reduce arsenic leaching even more efficiently, they have the disadvantage of cracking with time and requiring sanding when they are prepared for recoating. The sanding may release arsenic. 

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Protecting Logs

When reassembling an old log house how can the logs be protected?

A scientist at the U.S. Department of Agriculture’s Forest Products Laboratory, located here in Madison recommends using a water repellent preservative on the side of each log that will be exposed to the outdoors as it is installed.

You should try to get as much of the product into the wood as possible. Water repellent preservatives contain varying amounts of wax. You usually cannot paint over those with higher wax contents. A product with a high wax content would be best for your situation. Coat only the outer side of each log because you are using a high-wax product and may wish to finish the interior surface with paint or some other product.

To prevent insect damage, keep the logs dry and discard any logs that display evidence of rot. Any treatment for existing decay would only be effective in the short term. Separate the bottom layer of logs from moisture by beginning with a pressure-treated plate or some other barrier that will not allow moisture to be absorbed up into the logs.

Removing Asbestos Siding

What precautions are needed when removing cement asbestos siding?

From the Wisconsin Department of Natural Resources:
What you need to know about renovation & demolition – A regulatory summary for contractors and building owners (December 2010)

Asbestos Program for Demolition and Renovation Projects

Removing Bug Stains

How can bug stains be removed from vinyl siding?

Extension Entomologist Phil Pelliteri has seen similar problems. However, in many cases what looks like insects spots are actually fungal spores from a fungus growing in nearby wood chips. In cases where the spots are actually spider and insect excretion the home usually has light colored siding and has security lights that make the siding very bright at night thus attracting insects and spiders. He did not encourage the use of any type of insecticide but encourages you to correct the causes. The fungal spores and the insect spots both include proteins so that enzyme laundry products may be effective in removing them. Be sure the product you select is effective in the water temperature you will be using it; some work only in hot water. For stubborn spots the Vinyl Siding Institute recommends lacquer thinner. This will actually remove a little of the vinyl and is not something you would want to use to wash the entire structure.

Removing Eggs from Brick

How can the residue of eggs thrown against a brick house be removed?

Egg is a mixture of proteins and fats. I suggest you try a laundry detergent containing enzymes. Avoid detergents with added bleach. Mix the detergent with very warm water and scrub the surface. If this doesn’t work, make a poultice by mixing the detergent solution with a filler such as talc, powdered silica or bentonite until you have a thick paste that can be applied with a trowel onto the stained area. Cover with plastic and let it stand for at least an hour. The poultice and plastic will keep the area wet long enough to dissolve the egg. The same approach should work for dried egg on other exterior surfaces.

Removing Ivy

What is the best way to remove ivy from the wall of a brick home?

The best plan is to cut the ivy away. According to the Brick Institute of America, this is safer than pulling it away. Pulling away may pull away mortar and loose bricks as well. Chemicals may stain the bricks or mortar. Immediately after removing the ivy use a stiff brush and laundry detergent to remove the pads that hold the ivy to the masonry. If you let them dry they will be nearly impossible to remove. Some types of vines have rootlike anchors that burrow into the mortar. These will eventual dry up and disappear once the vine is removed.

Removing Lead Paint

Is there a safe way to remove lead-based paint from the exterior of a home?

Lead is a serious environmental health hazard particularly for young children. Recent research suggests that even low levels of lead in the blood can have serious effects such as mental retardation. Paint on houses built before 1980 is likely to contain lead.

A Bulletin developed jointly by UW-Extension and the Wisconsin Bureau of Public Health “Maintaining Your Home-Lead- based Paint Hazards (3628) gives advise on dealing with lead paint removal safely and lists people to contact for lead paint testing and advise. The brochure is available at county University of Wisconsin Extension offices and county health departments.

Removing Paint from Vinyl Siding

How can we remove paint spilled on vinyl siding?

According to the Vinyl Siding Institute here is what you do:

    1. Lift off with a plastic or dull metal scraper any that comes off easily.
    2. Dampen a clean cloth with paint thinner and gently rub off the remaining paint.
    3. If paint thinner doesn’t remove the paint use dry cleaning fluid.
    4. Rinse area with clear water after removing stain.

Avoid scraping or heavy rubbing since it may make the surface shiny.

Sealing Exterior Masonry

What is the best type of sealer to use on the walls of our brick home?

According to the Brick Institute of America, you should choose a product from a major manufacturer with a track record. Choose a solvent based sealer that has not less than 5% solids. Check the label of the percent effectiveness as a water repellent and for its breathability. You are looking for a sealer that keeps out liquid water but allows water vapor to easily escape. Before you apply the sealer carefully check the mortar joints and do any re pointing that is necessary. Also remove any stains and fungal growth. Apply two heavy coats and be prepared to re coat every 3 to 7 years. The Institute recommends only using a sealer if the surface is clearly deteriorating not for preventive purposes.

Spots on Hardboard Siding

What is the cause of dark spots on hardboard siding?

The first step is to do a simple test. Apply a little household bleach to one of the stained areas. If the stain disappears, then it was mold. In that case, the American Hardboard Association recommends that you clean the surface with a combination of bleach water (1 quart per gallon and 2/3 cups of trisodium phosphate). Scrub with a soft brush and than rinse carefully. Avoid splashing the solution on yourself or shrubbery.

If bleach does not remove the stain then it may be a wax bleeding through the siding. This sometimes occurs when moisture from inside the building is being forced through the siding. You can remove the wax with hot soapy water applied with a scrub brush or by steam cleaning.

Staining Painted Cedar Siding

Can cedar siding that has previously been painted be stained?

If the house has been painted it is generally not advisable to try stain. The paint will block the stain from penetrating. Even if there doesn’t appear to be a paint film there may be enough pigment in the wood surface to interfere with the stain and to give a blotchy appearance.

Temperature for Applying House Paint

How warm must it be to apply house paint?

Most latex paints need at least 24 hours at temperatures above 50 degrees F. to cure properly. With cooler temperatures, the paint can turn to powder rather than forming a protective film. Newer paints may have lower curing temperatures.

Treating Cedar Shakes

Do new cedar shakes have to be treated in some way?

While cedar is naturally water- and decay-resistant, in our climate it benefits from a little help. Without a sealer the shakes are likely to weather unevenly on different parts of the house. So it’s a good idea to give the shakes some extra protection with a water-repellant preservative. You may also want to add a pigment to the sealer to block ultraviolet light, which damages wood. Select a pigment close to the color the cedar will become after weathering. Some new sealers contain UV blockers, but I have not seen evidence that these are long-lasting.

Using Latex Over Oil Paint

Our house has been painted with oil paint. Can we change to latex paint when we paint it this time?

A latex paint is probably a good choice for your home. According to the paint experts at the U.S.D.A. Forest Products Laboratory, it is not a problem to put latex paint over oil-based paint provided the surface is properly prepared. Oil-based paint is often quite chalky so you need to be sure that you have removed the chalk before proceeding. Applying a primer meant for chalky surfaces is one way to do this but carefully cleaning of the surface to remove chalk is also important. One way to test whether you have removed enough chalk is to apply the primer to a small area; let it dry overnight then apply an adhesive bandage to it and pull it away quickly. If the paint comes with it, you need more cleaning or to use an oil based primer. Once you have successfully primed the house, you can apply your latex paint. You should not have to worry about the priming when you repaint in the future.

Vines on Wood Siding

Will vines growing on the wood siding of a home cause damage?

Vines climbing on walls can cause two problems. First, they can lead to moisture build-up on the wall, which can result in decay and mildew. They also usually attach themselves to walls, and these attachments are very difficult to remove if you ever get rid of the vine. If you like the look of vine on a building, you may consider using a trellis that would keep vines 12 inches or more away from the siding.

When to Prime Siding

When does siding need priming before repainting?

Primers are formulated to help top coats adhere better. If existing paint is intact and has been carefully washed, it isn’t absolutely necessary to prime. According to the Paint Quality Institute, water based primers are fine in most cases. There are three exceptions. 1)The existing surface is highly chalked and you don’t want to take the effort to clean it before painting. 2) There are four or more coats of oil based paint already on the surface. 3)You are painting over wood that is colored like redwood or cedar. These woods may have extractives in them that will bleed through latex primers and discolor the top coat. Some new latex primers may be formulated to block these extractive stains just as well as the oil based primers. Read the can and ask a knowledgeable dealer to check a particular product you are considering. Also, check how long you have after applying the primer before you apply the top coats. If the primer is left exposed too long, paint applied over it may not adhere properly.

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