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Siding of Wood – A Lasting Stain Free Finish


Have you ever seen brown stains mysteriously appear on a painted piece of wood siding? Or have you seen the color of a piece of stained redwood or cedar change color or deepen after it has been exposed to the weather? If so, you may have witnessed extractive bleeding stains. These stains originate inside a piece of wood, not from some outside source.

Extractive Chemicals

Many people know that redwood and cedar are excellent woods to use for siding. The reason stems from their durability. They simply resist rot and decay for long periods of time, even when exposed to large quantities of moisture.

The reason these woods perform well under moist conditions has to do with natural preservatives that all woods contain. All woods contain pigments, resin, oil and tannin. These are present in differing percentages depending upon the species of the wood. These are all chemical compounds and act as natural preservatives. Redwood and cedar, however, have large quantities of these chemicals.

Some of these preservatives can be dissolved in water. When this happens, they are extracted from the wood.

In the case of redwood and cedar, the water soluble extractive chemicals usually have a brownish color. A brown stain usually results on a painted or stained surface when water, laden with some of these chemicals, runs across or drips onto an adjacent surface. In many cases, the water evaporates and leaves the brown chemicals behind.

Redwood or cedar which is left untreated will usually darken in color with age. This is partially due to the fact that some of these extractive chemicals are drawn to the surface by water vapor or water that has soaked into the wood. Water vapor in the air can soak into a piece of untreated wood. This water can dissolve small amounts of the chemicals and pigments. Then, sunlight or wind may draw the water to the surface. The water, once again, evaporates and leaves the chemicals at the surface.

Iron Fasteners = Stains

Extractive chemicals, especially those in redwood and cedar, can chemically attack iron. These chemicals corrode the iron and cause a particular black or blue-black stain. These stains can penetrate deeply into the wood and be very difficult to remove. The best solution to the problem is prevention.

When installing redwood and cedar siding and trim, use only double dipped hot galvanized nails or, better yet, use stainless steel nails. Stainless steel offers the best protection, as it is unaffected by the tannins in redwood and cedar. It is possible to chip off the zinc coating of galvanized nails when striking them with a hammer.

Pay particular attention to other metal connectors that you may use in constructing redwood decks or cedar arbors. Purchase the highest quality metal connectors possible, especially if you intend to apply a clear finish or semi-transparent stain.

Minimizing Stains

The best prevention in avoiding stains caused by extractive chemicals is to cut off the water which dissolves the chemicals. This is not that difficult to do. It simply involves encapsulating or surrounding each piece of exterior wood with a coating which water cannot penetrate.

Note that I said surround. This means that the front, back sides, and edges of each piece of wood need to be coated or sealed. This sounds hard and time consuming but it is really not that hard to do.

Painters often refer to this process of completely sealing wood as backpriming. Painters have known for years that paint finishes failed, often with flaking or blistering effects, because of water soaking into wood. When given the opportunity and the financial incentive, painters would 'prime the back' of each piece of wood with paint. This would stop wood from absorbing water from behind. The really good painters would also paint the ends of each piece of wood. This, of course, is where water most easily enters a piece of wood.

Making it Fast & Easy

Backpriming is rarely done. There are several reasons:

  • Some builders and painters don't realize what it is.
  • Some builders and painters don't care.
  • Some builders and painters think it takes too long.

The end result of all these scenarios, if you have redwood or cedar siding or trim, may possibly be stains from the extractive chemicals.

Backpriming is not that difficult to do and, believe it or not, it can actually save you money in the long run. Savings can and will be achieved by longer lasting paint or stain jobs that require little preparation other than washing. Wood which has been backprimed rarely, if ever, has finish problems such as peeling or blistering.

My painter and I developed a system which really worked well. We simply spread out some tarps outside in good weather and set up my saw horses. On top of the saw horses, we would set a long 2 x 10 or 2 x 12. Beneath this board was a scrap piece of plywood that spanned the sawhorses. The plywood acted as a table upon which to set the paint roller pan, roller and brushes. The large 2 x 10(12) was the table upon which the siding or trim boards were painted.

Without the 2 x 10(12), siding set across saw horses acts something like a wet noodle. It is very limp. Anyway, by using a paint roller sized for the siding and trim boards, you can apply paint or stain very rapidly.

My painter would roll the paint on all surfaces of each piece of siding or trim. On the side which was to be exposed, he would do one extra thing. After the paint was applied with a roller, he would take a paint brush and walk very rapidly down the board, never lifting the brush. He would make as many passes as necessary to convert the orange peel texture created by the roller to a brush texture.

The siding or trim board was then set aside to dry. We always painted the shorter lengths first, so that they could be leaned against a wall beneath the void space of each successively longer piece of trim or siding.

When priming new wood, always make sure the wood is dry. Remember, if you backprime wet wood, you will definitely have a problem. Just as soon as that wood is installed and the sun hits it, the trapped moisture will work its way to the surface and cause the finish to fail. Make sure that wood siding and trim stays dry while in storage before it gets painted.

To achieve a really first class paint job, often three coats need to be applied on new wood. If you decide to do this, give serious consideration to applying your second coat of paint 'on the ground' as just described. My painter clearly demonstrated that he could paint more square feet faster on the ground than by constantly moving ladders around a house.

Preprimed Wood

Several wood siding manufacturers offer preprimed wood siding and trim. My experience with these products has been somewhat unfavorable. The primer that was used always seemed to be very thin and always required another coat of primer once it was on the jobsite.

There is a possibility that within the past two years the quality of the paint has improved. But even if it has not, it still may be worth purchasing, as this wood will have a tough time getting wet during shipping and handling.

Sealing Cut Ends

The best backpriming job can be torpedoed by an uninformed carpenter. Just because a painter seals the ends of a piece of wood doesn't mean they will stay that way. Just about every piece of wood siding or trim gets cut to size.

These cuts expose what is called end grain. This is the same grain that is exposed when you initially cut down a tree or saw a log into firewood lengths. End grain exposes the channels through which sap and other nutrients travel up a tree. After a tree is cut down and dried, these channels still exist. In fact, they readily look for water and soak it up like a sponge. This is the primary reason you frequently see paint peel from wood siding or trim at or near its end.

For these reasons, you must make sure, or instruct, your carpenter that he or she must seal the ends of all cut pieces of wood before they are installed. Remember, it is impossible to seal this end cut once another piece of wood has been butted against it.

I always used to keep a paint can and a brush on my cutting table. After I cut a piece of wood and checked it for proper fit, I would then dab some paint or stain on this fresh end cut. Yes, this did take a an extra minute per cut, but I can take you to some of my jobs where the paint finish hasn't peeled for 15 years. You make the decision. Is it worth it or not?


Backpriming is the key to a long lasting, stain-free siding finish. Invest in this process and you will reap large dividends. Good luck on your project!

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