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HomeHelpers: Deck stripper will remove sap from wood

Saturday, August 19, 2000

HomeHelpers is a home improvement column that tackles readers' problems with local experts. If you have a home-related problem or question or are an area contractor who can help answer readers' questions, write to: Kevin Kirkland, HomeHelpers, Pittsburgh Post-Gazette, 34 Boulevard of the Allies, Pittsburgh PA 15222 or send an e-mail to

Q: We have a 15-year-old deck built around and next to two 60-foot-tall pine trees. They provide shade and look nice, but they also drip sap on the deck. I've cleaned and stained the deck a few times but have never been able to completely remove the sap. And now that I'm using a darker stain, the white spots it leaves look really bad. What can I use to remove the sap this time?

-- E. Landis of Monroeville

James T. Hollihan, president of Doctor Deck Inc., replies:

Evergreens pose a variety of problems for decks. Pines drop pollen, dust and needles, which, if left alone, will cause black mold and mildew growth. Perhaps the hardest problem to deal with is tree sap, which can build up over time. All conventional deck cleaners on the market are ineffective at removing sap.

One method that is fast and effective is the use of turpentine. Use small amounts, only enough to soak the affected area. Then scrub with a stiff bristle broom or a wire brush, with the grain of the wood. If the sap is very thick, scrape off as much as possible first, using a putty knife or scraper blade. The drawbacks to this method are that turpentine can leave an oily spot of its own in the wood. Also, turpentine does not break down with water, and in large amounts it can harm plant and animal life.

The best method is to use an exterior deck stripper (e.g. Wolman's Deck Strip, Flood's Power Lift, etc.). This can be sprayed on large areas and involves less scrubbing. Simply brush stripper onto affected areas in the direction of the wood grain. Allow to stand for 10-15 minutes and hose off (pressure-cleaning is better). This stripper is deactivated by water, so runoff is safe for plants, grass and the environment.

The drawbacks to this method are that the stripper will burn skin, eyes, nose or throat if you come in contact with it. Always follow precautions on the label carefully. It also can leave the wood with a fuzzy look. These tiny fibers can be removed by light sanding just before a protective coating is applied.

When cleaning your deck, any stripping or problem areas should be done first. Then follow with a complete cleaning, using a deck brightener or pressure cleaner. This will give it an even look overall.

Some cleaning dos and don'ts

*Don't use bleach cleaners. They are not very effective and can leave white patches. Do use proxycarb cleaners.

*Don't use pressure cleaners above 2500 psi or below 1800 psi. Too high of pressure can damage wood; too low will not remove all discoloration.

*Use only coatings that meet or exceed federal water-repellency specification TTW-572B. If it's not mentioned on the can, it's not protecting your wood.

*Staining or painting pressure-treated lumber is not recommended on horizontal surfaces, such as decks. These coatings will soon fail.

*The cost of cleaning and sealing an average deck (250 to 300 square feet) is between $100 and $150 for do-it-yourselfers and approximately $300 to $400 for a professional. Special problems or stain removal can increase these costs.

*If you are having the job done for you, be sure to hire a professional. Ask questions and check references.

*Never pay for a job up front. If a retainer is asked for (on larger jobs), always get a receipt and pay no more than 50 percent of the total cost.

There are three basic sealant types on the market -- paraffin wax-based, oil-based and siloxane-based. Sap is the easiest to remove on decks sealed with wax-based sealers. These sealers also are generally easier to maintain and have a higher water-repellency rating.

Oil-based sealers give sufficient protection provided that water-repellency specifications are met. The problem with oil-based sealers is that they tend to hold more dirt and, therefore, need to be cleaned more often.

Siloxane-based sealers are new to the market and are not widely available at this time.

Doctor Deck Inc., which also cleans and seals fences, log homes, cedar roofs and natural wood siding, has five area offices and a do-it-yourself center that rents pressure washers and sells sealants and cleaning products. For more information, call 800-330-0512.


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