GRAIN CONSIDERATIONS

Wood has either flat or vertical grain. The pith side of flat grain lumber has a greater tendency toward grain-raising. Where possible, it is best to apply flat grain wood with the bark side exposed to weather

The bark side of flat grain lumber can be determined by looking at the end of the piece. The annual rings appear as concentric arcs-convex to the bark side and concave to the pith side.

EXTERIOR FINISHING

BACK SEALING: (BACKPRIMING) preventing moisture from entering the back of siding and trim is the most important step to insure a long lasting finish. If you don’t backseal, moisture enters the back of the product and works it’s way through the face. This pushes the finish off the face and adds to cupping, splitting, and bleeding problems. Skip this step and you can cut your finish life in half!

GRAIN: Vertical grain products shrink in width 1/2 as much as flat grain products. the more the product moves, the shorter the finish life. Although V.G. is not always available, use it whenever possible.

ROUGH OR SMOOTH: The rough or resawn side will take more stain than the smooth. That is why the finish lasts significantly longer on the rough side.

WEATHERING: Contrary to common opinion, the “Forest Products Lab” has determined, through extensive testing, that the longer you expose siding unfinished, the shorter the expected service life. Finish it ASAP ! Light sanding of smooth face products prior to finishing is recommended to allow proper adhesion.

EXTERIOR FINISHES

CLEAR SEALERS :  Ultraviolet (U.V.) rays damage wood more than water. Clear sealers have little or no effective protection from these rays, even if it says so on the can. Expect a service life as low as 3 months to 1 to 2 years max! Stay away from it.

SEMI-TRANSPARENT:  These contain solids in the pigment that block some of the U.V. but let the grain of the wood show through.  They last a little longer (2-4 years max) , then you must clean the siding and restain.  The maintenance needed with this product is the “ trade off “ for a “ natural “ look.

SOLID STAIN : These block most U.V. rays.  Although softer than paint, they do reduce the chance of cracking and peeling greatly.  Priming with an oil or alkyd primer is highly recommended before you solid stain.  This gives you a solid foundation for your finish coat.  One coat of primer plus one coat of stain is much better than two coats of just stain.  Service life is 4 to 10 years.

PAINT : This provides the most protection.  Back and face priming is essential.  Paint tends to get hard and inflexible over time and cracking and peeling occur.  If it is done right, it lasts a long time.  If not, it can be a problem.

LATEX VS, OIL: For primer, oil or alkyd is the only way to go.  They seal the wood well and provide a good foundation for the finish coat.  Avoid latex primers.  For solid  stain and paint, we lean toward latex, but either is fine.  Latex resists mildew better ( mildew actually thrives on linseed oil ).  It is also more “ colorfast “ than oil and resists fading better.  Alkyd oil primer with a solid latex stain over it is one of the best “ systems “ available.

WEATHERING STAINS :  These products contain bleaches to speed up the weathering process and a little gray stain to hide the transitional stages.  They leave a more natural nonuniform look that some people prefer.  One re-application after a few years is a good idea.

BUY QUALITY :  You cut the cost of producing finishes by reducing the percentage of the expensive ingredients that make a product long-lasting.  Generally ,the less a product costs, the shorter the service life.  Don’t skimp or you’;; pay in the end!  Products should contain mildewcide.

 GENERAL DO’S & DON’TS :

 Do not use lacquers, varnishes, or any similar film forming products as they eventually crack and break down and are hard to refinish.

 Do not use a spray system.  Brushing is the only way to really get the finish into the wood.

 Prestained or preprimed products generally work well because they are done under controlled conditions. However, the results on solids are a lot better than on semitransparents.  You should always do a finish top coat on the job after installation.

 You wouldn’t wax your car without washing it first, would you ?  Exterior wood gets dirty quickly and should by cleaned before any finishing begins.

 A surface sheen or glaze created in milling a smooth face can hinder finish penetration.  Light sanding prior to finishing will break this glaze and enhance finish performance.

 Follow finish manufacturers directions explicitly especially as regards to temperature and  weather considerations.

INTERIOR FINISHING       

 LOCATION : Exposure to moisture and temperature changes are the most critical factors.  Humid areas such as bathrooms and indoor pools are much better served with a vertical grain product to prevent grain raise and prolong finish life.  Saunas and steam rooms should always be vertical grain.  Finishes should not be used in these areas.

PREPARATION :  Finish limber suitable for exterior use is not in the finished state for interior use.  Nicks, scratches and surface defects should be removed by sanding.  Mill glaze should also be sanded off for proper penetration of the finish.

FINISHES :  Why finish?  Wood left unfinished will discolor.  Sealing the wood will allow it to maintain a good appearance.

OIL FINISHES :  These work by penetrating the fibers  of wood and give a “ matte “ finish.  They are available in clear, clear-tint and colors.  Areas subjected to sunlight should use semitransparent to block ultra-violet rays.  Clear finish will yellow from exposure to sunlight.  Oil finishes are not appropriate for high abrasion areas such as floors or water collection areas.

POLYURETHANE : These finishes bond to and coal the fibers instead of penetrating.  Three coats are usually necessary with light sanding in between.  It is offered in satin and gloss with the gloss being the more durable finish.  If a satin finish is desired in a high use area such as a floor, it is best to use the gloss poly and then polish it to a satin sheen with fine (#00) steel wool after the last coat.  Most are oil based, but there are some water based new to the market.

Application is a two step process - first a sealer followed by the polyurethane.  It is good for large areas as it does not require multiple coats.  Polyurethane does yellow when exposed to ultraviolet light and should only be used on smooth wood.

 If you follow the above finish recommendations, most finish problems will be avoided.  However, if a problem occurs here are some possible solutions.

 FINISH PROBLEMS             

SYMPTOM :  Blistering, cracking and peeling.

SOLUTION ; If the failure is due to inadequate surface preparation, the finish should be removed and the surface prepared in accordance with manufacturer’s recommendations.  If moisture must be determined and eliminated.

SYMPTOM :  Clear finishes :  Bleaching, fading, mottled appearance.

SOLUTION : Remove the old finish by sanding or briskly brushing the deteriorated areas.  Where the finish film is strong, use a varnish remover.  Once the finish has been removed, the color may be restored and stains  removed by applying the oxalic acid solution described  in the Appendix.  Reminder:  Do not use steel wool or ferrous metal brushes to remove old finish.

SYMPTOM : Mildew stains.  Mildew can grow on unprotected wood.  It has a tendency to appear on siding in fan-shaped patterns with dark growth at the top and wider lighter colored spores spreading in a fan below.  Mildew occurs more frequently in shady moist areas.

SOLUTION :  To remove a mild case of mildew, scrub with a mild cleanser or detergent.  Next, rinse with a household bleach to kill surviving spores.  Lastly, rinse with water.

For severe mildew infestations, scrub with a stiff bristle brush using a solution of one cup or trisodium phosphate,, one cup of liquid household bleach and one gallon of warm water.  Rinse thoroughly.  If necessary, follow with an application of 4 ounces of oxalic acid crystals dissolved in one gallon of warm water in a non-metallic container.  Apply evenly with a soft brush.  When wood dries, rinse with water.

If refinishing is necessary, remove the existing finish.  Scrub the surface clean using warm water, a mild detergent and a household bleach.  Protection against recurrence of mildew growth can be provided by using a finish containing mildewed.

One product, which contains tributyl tin oxide ( TBTO ), is commonly used and can be obtained in paint stores.  Follow manufacturer’s  recommendations.

SYMPTOM ; Sticker stains.  Sticker stains are not considered a defect.  They are permitted in all grades under the standards.

SOLUTION :  Sticker stains can be minimized by washing with trisodium  phosphate ( TSP ) or the oxalic acid solution described in the Appendix.

If the wood is left unfinished, sticker stains usually blend in with the rest of the wood through natural weathering within a year.

SYMPTOM : Red or brown stains on exterior lumber.  Moisture migration and evaporation may leave extractive residue on the surface.

SOLUTION :  Determine and eliminate the source of moisture.  Fresh stains may be removed by washing with mild detergent and water.  Older, more stubborn stains may be reduced by the application of the oxalic acid solution described in Appendix A.  Note: Oxalic acid can be hazardous, so follow recommended practices and see comments in Appendix A.  Mildew is sometimes mistaken for extractive bleeding.  Bleeding tends to follow the grain of the wood and mildew frequently takes the form of dark spots.

SYMPTOM : Dark stains around nail heads.  Nails weren’t stainless steel or aluminum.

SOLUTION :  The only complete solution would be the extraction of the corrosive nails and this is  seldom feasible.  To remove nail stains, treat the siding with oxalic acid as described in Appendix A, unless the siding is to be painted.  Oxalic acid has a tendency to lighten color; so for a uniform appearance, the whole face of the boards may need to be treated rather than just a section.  If a small section of a large surface is being treated, feather out the area surrounding the stain with samller amounts of oxalic acid.

SYMPTOM : Moss and algae growth.

SOLUTION :  Moss and algae can be removed from smooth surfaced wood structures by scrubbing the affected areas with a solution of trisodium phosphate ( TSP ) and warm water.  The most effective tool to use is a stainless steel wire brush.  Do not use a ferrous wire brush which might leave corrosive metal particles.

Garden stores sell a variety of preparations for preventing or controlling the regrowth of moss by killing the residual spores.

For consistent control, a moss killer must be applied at intervals of 1-2 years.

APPENDIX
A.  OXALIC ACID TREATMENT

A solution of 4 ounces of oxalic acid per gallon of water is quite effective in reducing many types of discoloration’s and will also restore weather-darkened wood to a reddish tan.

This solution should be applied t bare wood.  Because oxalic acid will tend to lighten and brighten wood’s color, it should by applied to the whole face of the boards.  If a small section of a particularly large surface is being treated, feather out the area surrounding the stain with smaller amounts of the solution, much as one would treat a spot in dry cleaning to prevent formation of a ring around the spot being removed.  The oxalic acid should be allowed to dry completely, and then be thoroughly flushed of f with water and allowed to dry again.  Following this, the desired finish system may be applied.

Prepare oxalic acid solution in a plastic, glass or enamel container.  Wear rubber gloves and eye protection.  Oxalic acid is poisonous and should not be applied by sprayer or allowed to drip on plants.  It is not dangerous when properly handled.

B.  DISCOLORED FINISH - CLEANING

Frequently, soot and dirt are the cause of badly darkened natural finish.  This discoloration can be removed by washing the surface with a solution of water and a mild household detergent.  An effective solution can be made by mixing one cup of trisodium phosphate (TSP) in a gallon of water.  TSP is generally available at drug stores, hardware stores, paint stores, and home centers.  Scrubbing may be necessary where discoloration is heavy.  After the initial treatment is dry, you may want to follow with the oxalic acid treatment ( see above ) to brighten up the finish.