Deck Fence and other wood pressure washing

Approximately 1/2 the homes in the Georgia have a wooden deck, siding, fencing, or roof. Without protection wood will rapidly deteriorate from the following elements:
1.Water. Water is absorbed into the wood and washes out the natural wood resins and color. Freezing/thaw cycles can splinter and crack the wood. Also water promotes algae, mold, and mildew growth and rotting.
2.Sun Light. Ultraviolet (UV) rays bleaches the wood fibers and breaks down the cell structure.
3.Mold, Mildew, Algae, and Fungus. Wood and moisture are a natural food source for mold, mildew, algae, and fungus. This generally causes a black, green or gray discoloration.
4.Contamination. Contamination comes in the form of food, dirt, atmospheric pollution, etc. This is a good food source for Mold, Mildew, Algae, and Fungus.

Wood in poor condition reduces the value of a home. Proper cared for wood adds to the value and appearance of a home. There is more than one way to clean and seal a deck. We will examine the most popular techniques and point out some of the advantages and disadvantages of each. You will have to choose the technique that you prefer.

Preparing a Deck for Cleaning
1.Inspect the site and assemble the necessary items such as:
•Scaffolding, man lifts, or swing stages for higher jobs.
•Pressure Washer with variable pressure wand (ST-54) and 15, 25, & 40 degree nozzles. Cold Water Pressure Washers with 6 to 13 horsepower gasoline engines are the most popular. Hot High Pressure Washers with 12 to 20 horsepower gasoline engines are also used.
•150 Feet of High Pressure Hose.
•Two 100 Sections of Garden Hose.
•Leaf blower.
•Chemical applicators: Pump up Garden Sprayer, Flojet or Shurflo sprayers with pressure regulators, or Airless Sprayers.
•Three 5 gallon plastic mixing buckets..
•Respirator with cartridges for caustic and acid chemicals.
•Hard Hat with a face shield.
•Deck Repair Items: hammer, nails, rotary sander, screws, cordless drill with screw driver attachment for Phillips head screws, broom.
•Yard Sign with your company name, and phone number on it
•10 or 12 gauge electric extension cords, duct tape.
•For fuzzy (furring) removal: steel or bronze wool, sand paper, kitchen scrubber, steel brush, or pool brush.
•Camera for before and after photos of the deck for your portfolio and customer satisfaction. Sometime the customers forget just how bad his deck was!
2.You should remove all furniture, flower pots, barbecue grills etc. from the deck.
3.Clean the dirt off the deck surface by sweeping or blowing with a leaf blower.
4.Repair any structural damage to the deck. This includes: replacing or hammering in nails, tightening loose screws, bolts, or spindles, and replacing deteriorated wood as necessary.
5.Carefully inspect the area to be cleaned for electrical outlets, switches, lighting fixtures, telephone jacks or any type of electrical appliances that might be subjected to water damage or cause injury to the person doing the cleaning. NOTE: Electricity and water in close proximity is very dangerous. Shorting of electrical circuitry through the introduction of water to an electrified area can cause injury or death! BE CAREFUL ! If you find any electrical outlets or wiring in the immediate area you should be certain that the power is turned off at the breaker box and that the proper lock out , tag out procedures are followed. Next you should cover any electrical outlets, lighting fixtures, telephone jacks or anything that can’t be moved and might be damaged by water or cause injury to the person doing the cleaning if it comes in contact with water. Duct tape, electricians tape and plastic sheeting are often used to cover these items with.
6.The next thing you should do is cover any plants or shrubs around the deck with 2 to 4 mil clear plastic sheeting to prevent incidental damage by high pressure spray or chemical. Clear plastic works best because it doesn’t allow as much heat buildup and you can better see the plants and water pools that may build up in the plastic.Instead of plastic sheeting some Contract Cleaners use a water spray from a garden hose or their high pressure washers to protect things. Dilution is the solution to the over-spray. Paint drop cloths and paint shields are also used.Also some contractors use old bed sheets where the climate is hot. They can be purchased for pennies on the dollar from uniform shops or linen companies.


Cleaning can be done with chemicals, scrubbing with a brush and rinsing with a water hose (homeowner technique) or power washing with a pressure washer (Professional Contractor Technique). We will examine each of the items in detail.

Cleaning & Brightening Chemicals:

Chlorine Based Bleach. Bleach is the most popular chemical used to clean and brighten a deck. About 1/2 of the professional contract cleaners use this chemical. However its use is very controversial. Bleach is a fair cleaner and a good mildewcide as it kills non-vascular mildew growth. Bleach works better if mixed with a good detergent. Start out using 1 part bleach with 3 parts water, or add 25% bleach to your detergent.

Lignin is natural component the holds wood fibers together. Bleach (Sodium Hypochlorite) is used in the production of paper to break down the Lignin. Excessive bleach will do the same thing to a deck. If this happens the wood fibers will appear loose which you can push up with your fingernail. This may also be visible and appear as fuzzies. This is not to be confused with fuzzies that appear after pressure washing with too much pressure.

Additional information on bleach can be found on the Clorox website at

Phosphoric Acid: Removes the gray of aged tannins on unfinished decks. Used to neutralize the surface after using a Sodium Hydroxide Cleaner.

Oxalic Acid: Good for removing tannin and rust stains. Used primarily on redwood. It is not very good on mildew or dirt. Used to neutralize the surface after using a Sodium Hydroxide Cleaner. Mix 2 to 8 ounces of oxalic acid to 1 gallon of water.

TSP (Trisodium Phosphate): Commonly sold in hardware stores for deck cleaning. Mainly a consumer product. Mix 1 cup of TSP with 1 gallon of water.

Citric Acid. A mild acid good for using on fine decks made from hard woods. Not as harsh as Oxalic Acid. Used to neutralize the surface after using a Sodium Hydroxide Cleaner. Mix 2 to 8 ounces of citric acid to 1 gallon of water.

Sodium Hydroxide (high caustic cleaners). These are popular with Professional Contract Cleaners. The chemical does most of the cleaning and very low pressure (300 to 1,000) can be used for pressure washing. The surface needs to be neutralize with a weak solution of citric, phosphoric, or oxalic acid because caustic cleaners promote fiber degradation, wood rot, and darken the wood. Citric, phosphoric, or oxalic acid will brighten the wood. Cedar or redwood may be turned black from the cleaning process but will return to the natural color after neutralization. This product is stable and has a long shelf life. (Example: DSR-50).

Disodium Peroxydicarbonate Oxygen Based Bleach: An environmental friendly oxidizer. A good bleach and brightening for wood surfaces. Do not use on new wood. This product is not very stable has to be used within 6 hours of mixing a powder with water. (Example: DSR-49).

Cleaning Pressure:

PSI (pounds per square in of pressure): The PSI for pressure washings decks (wood) varies from 300 to 3,000 PSI at 3 to 6 GPM for Professional Deck Cleaners. Too much pressure will cause the wood to furr. If this happens you will need to sand with fine sandpaper or steel wool to knock off the furred surface. A lot of Deck Contract Cleaners use a variable pressure wand (like the ST-54 61″ Double Lance Wand) so that they can adjust the pressure as necessary. Using low pressure and letting the chemical (like DSR-50 or DSR-49 Deck & Siding Restorer) do the work will avoid furring the deck. Hint: use the underside of the deck to test the PSI. You should start out with as low as pressure as possible then increase the pressure as necessary.

Another way to lower the pressure is to change the spray nozzle to larger size. This will decrease the pressure and will work on any pressure washer.

Some Contract Cleaners use heavy concentrations of either Chlorine Based Bleach, Oxygen-Based Bleach, or Sodium Hydroxide based cleaner and use only garden hose pressure to clean the surface.

Cold Water Washers are normally used as heat will expand and cause the wood to absorb too much water. However, in heavy grease or oil and sealant stripping situations heat may be required.


Sometimes sanding is required. Use a 10,000 rpm orbital sander starting with 40 grit paper and finishing with 80 to 100 grit paper. Caution: 140 grit sand paper will produce a finish too fine for the wood sealer to penetrate. Do not sand rough sawed lumber. Note: you cannot sand wet wood.

Cleaning Unsealed Decks:
1.Soak the area to be cleaned with water. This has three purposes: 1) it wets down the area around the deck and will help protect plants and grass from the cleaning chemicals, 2) damp wood will keep the cleaners on the surface of the wood where the cleaning needs to take place and not be soaked into the wood and 3) it cools the wood so the cleaners do not evaporate as fast, this is important especially on a hot day.
2.Apply the cleaning solution. This is normally done with one of the following: a pump up garden type sprayer, a brush with a 5 foot handle, or a pumping system with a Flojet or Shurflo pump with low pressure hose and trigger gun. With a Flojet or Shurflo pump you should use a pump with a pressure regulator rather than a pressure switch for better pressure and flow control.
3.Allow the solution to soak for 10 to 20 minutes but not so long as to dry out before washing. If it does dry you can reactivate the cleaner by spraying water on it or reapplying the chemical.
4.Pressure wash with as little pressure possible. You will need enough pressure to remove the dead wood but not so much pressure as to furr the wood (300 to 1,500 psi). Test the underside of the deck to test for the correct pressure. Pressure wash with the wood grain and feather the end of each pass. Normally you never wash across the grain of the wood or use a zero degrees rotating nozzle as this may splinter the wood
5.If you used a sodium hydroxide cleaner, neutralization will be required as these cleaners darken the wood. Mild acids brighten the wood. If the wood is not neutralized it will turn very dark and maybe even black. Just apply a mild acid to return a bright natural color. Typical mild acids are Phosphoric, Oxalic, and Citric.
6.After cleaning, do a thorough job of rinsing (everything you might have gotten overspray on) with your pressure washer or a garden hose. Any excess chemical will normally dry white.
7.After the deck is cleaned it needs to dry 24 to 48 hours before sealing. Try to choose a time when it is not going to rain for at least 12 hours. Several sealers can be applied to damp wood but you will obtain a better job is you wait for at least 24 hours.

Cleaning a Previously Sealed Deck:

If you are sealing over a previous failed finished you will need to remove the old finish first. Sodium Hydroxide Based Strippers will remove most oil stains and sealants (DSR-50). Testing is required with strength and dwell time because of the variation in the quality of the old sealant plus degradation due to time and weather. You need to use the stripper as weak as possible and you can increase dwell time by covering the stripper with plastic sheeting. It is not unusual when removing stains for it to take two or three cleanings.

When using harsh chemicals expect some furring and sanding may be required. This problem is worst on softwoods like cedar and pine. Follow directions carefully.

Removing Fuzzies:

Fuzzies can become a problem at anytime, even with low pressure. The sun UV rays kill the outer layer of wood and this is what turns a deck gray. When washing is done this outer layer of dead wood is what is removed. Sometimes this results in the furring of the wood called fuzzies. It’s like the wood has grown a lot of short hairs. It is caused by tearing of the wood fibers. If left alone over time they will generally go away in 2 or 3 weeks.

Some homeowners object to this appearance. They can be removed by light sanding, a kitchen scrubber, pool brush, steel brush, bronze wool or steel wool. Note: Bronze wool will not leave rust spots as steel wool does from steel particles left over in the wood.

Sealing Equipment:

Additional items for your equipment check list for sealing are:
1.Airless Sprayer: Airless Paint Sprayers, Pump Up Garden Type Sprayers, Flojet or Shurflo pump sprayers with pressure regulators.
2.Hand Applicators: Natural bristle brush for clear sealers, sponge roller, and hand stain or paint pads.
3.Shields: Drop cloths, 2 to 4 mil plastic sheeting. card board shields.
4.Appropriate sealer or paint, paint strainers, hot box, paint trays, paint thinners. · Paper towels, and rags.
5.For Lattice: Roller with 1 inch or longer nap.

Sealing the Color and Brightness In:

The first and most important step in sealing any deck is to choose the proper sealer. There are many different sealers on the market. The best one to use is the one that will afford the maximum protection for the minimum cost. There are many companies who claim that their product will deliver what you need. Experience has taught us that a large percentage of these claims are false. Purchase advisedly, see the references at the end of this article. About the only product that most Contract Cleaners will agree on is that “Thompsons” is not a product of choice!

A good sealer will have UV protection, mold and mildew resistant, and a life of several years.

After cleaning the surface to be sealed and allowing sufficient drying time (at least 24 hours) you are now ready to apply the protective coating. We recommend the use of an airless spray rig, paint brush, and a roller for material application. Apply properly and read the manufacturer instructions carefully.

You can spray the majority of the area to be coated and use the brush or hand paint pad to pick up runs, smooth out puddles and cut in around areas where you can’t spray. You will also need a shield to keep the over-spray from getting on the house and other immovable objects around the deck.

Begin by shielding all areas with plastic sheeting or tarps that your do not want overspray on. This includes the side of the house, windows, grass, and shrubs. Next place tarps, plastic sheeting, or cardboard under the rails, spindles, etc. Now you are ready to apply sealer to railing. Mop or brush up any runs IMMEDIATELY as these spots will dry darker than the rest of the deck. If you get sealer spots on the floor of the deck and do not immediately mop them up with a rag you will have a spotty deck. Once these spots dry it is nearly impossible to get them out.

Next seal the floor with an airless or roller. Apply the sealer so that you are always applying sealer to damp sealer. Do not apply sealer to dried sealer as this may leave a demarcation line. After applying with an airless back brush to get better penetration and smooth out any puddles.

The wood grain in knots is different from the rest of the wood and normally will dry shinier than the rest of the deck. However with time these shiny spots will begin to blend in with the rest of the deck. Inform your customer to expect this to happen.

Sealed decks can normally be walked on in 3 to 4 hours, but it will take 24 to 48 hours for the deck to completely dry.

Next thoroughly clean the area where you’ve been working, replace the deck furniture that you moved in the beginning and make a final check around the area before presenting your bill to the customer.

Sealing Hints:
1.When sealing mix all the batches together in one container if possible to insure color uniformity and consistency. Especially important if you are using old left over sealer with new.
2.To get easier flow the sealer some Contractors construct a Hot Box with an electric light bulb to slightly raise the temperature of their sealer.
3.Try to keep an even flow so that you never apply sealer over dried sealer. Always try to apply sealer to wet or damp sealer.
4.If spraying always brush out the runs or puddles promptly.
5.Two coats are better than one heavy coat for better penetration.
6.Color test a deck in hidden place to determine exact color. Expect slight color variation between different boards on a deck.
7.You can test a deck sealer to see if it is still working by pouring a cup of water on a deck and see if it is absorbed into the wood or if the surface darkens due to the absorption of moisture.
8.Doing handrails, and spindles with stain pads by hand and beams and deck floor with a roller may be faster than using an airless sprayer. You’ll have no overspray and a cardboard shield can be put under these items to catch drips.
9.Sealers will generally cover 100 to 250 Sq. Ft per gallon. Older surfaces may require two coats. The coverage for the second coat will about 50% greater than the first coat. Also the second coat will give a more even appearance and reduce the discoloration around knots.
10.Lattice: Apply with a roller with a 1 inch or longer nap, then finish up with a brush or hand stain pad.
11.When choosing a sealer pick one that will not be ruined if a sudden unexpected rain occurs. This has cost a lot of contract cleaners dearly.
12.Apply sealers only when it is above 60° F and will not rain for at least 12 hours.

Mill Glaze:

Mill Glaze is a hard surface that is formed on Cedar and Redwood during the process of milling the lumber. Most manufacturers of protective coatings will not warranty their products if this glaze is not removed. You can test to see if Mill Glaze is present by simply putting a few drops of water on the wood surface. If the water is not readily absorbed into the wood Mill Glaze is probably present. Sanding, aging, and chemicals have been successful in removing Mill Glaze. After removing the Mill Glaze you should retest to be sure it is removed. Sodium Hydroxide Based Deck & Siding Restorer Plus Strippers will remove most Mill Glazes (example: DSR-50).

Mill Glaze (on New Redwood and Cedar)

By: R. Sam Williams and Mark Kanebe
Wood Finishing Research
USDA Forest Service
Forest Products Laboratory
One Gifford Pinchot Drive
Madison, Wisconsin 53705-2398
October, 1995

A condition known as mill glaze (also called planer’s glaze) can occur on smooth flat-grained western red cedar siding and occasionally on other species, such as redwood. There is controversy over the exact cause of this condition, but it seems to be a result of using dull planer blades and is exacerbated by the difficult-to-plane flat-grained surface of the lumber. In vertical-grained wood, the early wood/latewood bands are perpendicular to the surface. Because of this perpendicular orientation, vertical-grained lumber is easier to plane, even with dull tooling. Planning causes two distinct changes to the surface of the lumber– it burnishes the surface and crushes some of the wood cells.

During the planking or milling process, overheating of flat-grained siding may bring more water-soluble extractive to the surface, creating a hard, varnish-like glaze. Excess water-soluble extractives can also form on the surface during kiln drying. As these extractives age, particularly in direct sunlight, they become insoluble and difficult to remove. If these extractives occur prior to final planning or sanding of the lumber, the final surface preparation usually removes them. The wood surface can be tested for this glaze by carefully placing a few drops of water on the surface prior to finishing. If the water beads and resists soaking into the wood, the surface probably has mill glaze. Light sanding of the surface will remove this glaze.

The second factor usually found with the glazing on flat-grained wood is crushed early wood on the pith-side of lumber. Dull planer blades tend to burnish the surface and crush the less dense early wood bands directly beneath the more dense latewood bands at the surface. Later, when these boards are exposed to weather, the crushed early wood absorbs moisture and rebounds, causing the surface latewood bands to rise.

These two surface defects act in concert to cause flaking of the finish parallel to the grain. The pith-side of flat-grained lumber finished with a single coat of oil-based solid-color stain is particularly susceptible to his type of finish failure.

Sanding will remove the extractives build-up, but it is not likely to remove all the crushed wood and subsequent wetting will continue to cause the surface to deform. Exposing the wood siding to the weather for a short period may help to condition the surface. One or more wetting and drying cycles are necessary to remove these planer-induced stresses in the wood. However, wood should not be exposed to the sunlight for more than 2 weeks before application of a film-forming finish, because this exposure decreases the adhesion of the coating.

The simplest and best solution to the problem of mill glaze, when using flat-grained bevel siding, is to install the siding rough side out. The rough side is the side of choice for application of penetrating semitransparent stains. Solid-color stains form a film and will give a much longer service life when applied to the rough-sawn side. In addition to the lack of mill glaze, the rough side has two other advantages. The film build on the rough side will be greater, and the film will have greater mechanical adhesion or “bite”. The best film build is obtained by brush application. If the finish is applied by roller or spray, it is advisable to back-brush the stain immediately following application to even out the finish and work it into the surface of the wood, thus avoiding bridging, gap formation, and lap marks. If the flat-grained siding must be installed smooth side out, remove the planning stresses by wetting the surface, then allow 4 to 5 days for the surface to dry before finishing. Scuff sand the surface of the wood with 50-80 grit sandpaper prior to finishing.

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