second orthirdgrowthtreestendtohavelessheartwoodandconsequentlyextractives. Sidingsandtrimmanufacturedfrom oldertreescontaingreaterquantitiesofwater-soluble extractives. from larger, close-grained lumber buthigh-grade, Water-soluble extractives arefoundintheheartwoodofmostspecies, to 30%. The totalextractive content ofwoodmayrange fromlessthan1%up species amongbuildersandhomeownersalike. ot o-ealcbitebuh ao Problem-Solver Cabot non-metallicbristlebrush. a soft, Cure moisturecaninfiltrate theopenendgrain ofthewoodatthosepoints. improperly, oraredone Ifcaulking andendprimingarenotdone, suchaswheresidingabutswindowordoorframes. materials, gutter problems(orlackofgutters)andopenjointsinsiding Problemareascanincluderoofleaks, penetration. Diffused discoloration can usuallybeattributedtoaporousorthincoatingwhich iseitherinsufficientorinadequatetopreventwater irrigationandhighhumidity. condensation, dew, These externalsourcesincluderain, source. Extractive problemscommonlyoccurwheninteriorhumiditylevelsexceed50%. typical ofnewconstruction. bathingorgeneral high-moisturevapor levels hottubs, cooking, suchashumidifiers, material fromaninteriorsource, itindicatesthatmoistureisenteringtheuntreatedbackofsiding whichoftenoccurswithlapsiding, pattern, The Problem eanwto h ufc o 01 iue.Lgtysrbsubr tis thenrinse withclearwater. Lightlyscrubstubbornstains, remain wetonthesurfacefor 10-15minutes. Applyusingagarden-typesprayer andallowsolution to will easilyremove unsightlydiscoloration stains. with water, hnetatvsd per theycansometimesberemoved bycleaningwithawarm water detergentsolutionand When extractives doappear, T Extractive discoloration inadiffusedpatternwouldindicatemoistureisenteringthewoodsurfacefromanexternal
extractives are fo are extractives nisaeawtrslbe eds-rw iclrto asdb h fet fmitr n ulgt While reddish-browndiscoloration causedbytheeffectsofmoistureandsunlight. annins areawater-soluble,
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f f eteial betoal,thisdiscoloration doesnotharmthesidingorpaint/stain aesthetically objectionable, otn.Hwvr fcnetain ttewo ufc r iheog,theextractives ifconcentrations atthewoodsurfacearehighenough, However, coating. a nefr ihpoe eerto,absorptionand/ordryingpropertiesofany may interferewithproperpenetration, future finish. The Cause tannins aredissolvedbymoistureandthendrawn tothesurfaceofstainedor ane odvatesnadhdottcpesr omss.The presenceofmoisture painted woodviathesunandhydrostaticpressure(osmosis). usually occursaftertheinstallationandpaintingofsidingcanoriginatefrom netrssac otesdn aeil accountingforthepopularityofthesewood insect-resistance tothesidingmaterial, densityanddecay- taste, odor, impart thefavorable propertiesofnatural color, These water-soluble extractives Mahogany andIpe. Redwood, Eastern White Cedar, w xrciebedn sntpito ti alr.Whenextractive discoloration occurs, Extractive bleedingisnotpaintorstainfailure. trslbe The mostpopularwoodspeciesinthiscategoryare Western RedCedar, ater-soluble. S taining woodsarethosewhichcontain Tannic Acid andotherextractives thatare Not aStainorPaintFailure Extractive Bleeding: ® W o rgtnr#03cnetae mixedina1:4ratio ood Brightener#8003concentrate, (Continued onback)
TECHNICAL BULLETIN #2 EXTRACTIVE BLEEDING Extractive Bleeding (Continued from front)
Prevention To prevent extractive discoloration by water-soluble tannins, it is important that the siding to be stained has a moisture content below 15%. Prior to siding installation, all faces of the lumber should be stained. The prestaining or prepriming of the siding material will ensure the moisture content of the lumber is stabilized, reducing wood swelling and shrinkage while improving siding durability. Clear water-repellent finishes, semi-transparent and semi-solid stains do not offer reliable protection from extractive discoloration. Oil-based solid color stains produce thin films, providing more protection than clear or semi-transparent stains. Since all water-based latex stains or paints use water as a carrier, they can actually create extractive discoloration problems. The most important step in preventing wood tannin discoloration is the application of a high-quality oil or alkyd based, stain-blocking primer. Cabot Problem-Solver® Primers #8111 and 8022 contain polymerized, natural, linseed oil modified with alkyd resin to provide a continuous film impervious to moisture, especially when applied to all faces of the lumber. Acrylic latex stain-blocking primers often require two coats to be effective. However, there is no guarantee when it comes to the prevention of extractive discoloration. Proper construction techniques, combined with the use of high quality coatings correctly applied, are your best assurances against the occurrence or recurrence of extractive discoloration.
Hints for Preventing Extractive Bleeding
* Only stain/paint wood with a moisture content below 15%.
* Use proper construction techniques: -Adequate overhangs of two or more feet. -Proper flashing above windows, doors and at wall and roof intersections.
U M W O O D M I C E A R * Caulk correctly. Use high performance, paintable exterior caulks R E P with either acrylic or silicone acrylic, butyl, polysulfide or a polyurethane base. Avoid “bargain” or pure silicone caulks.
S I N C E 1 8 7 7 * Ventilate internal moisture. Use dehumidifiers and ventilation fans in bathrooms and kitchens. In northern climates, install a vapor barrier behind the drywall on the warm side of the wall. Cabot® Newburyport, MA 01950 * Use a high quality oil or alkyd-based, stain-blocking primer, Tel.: 800-US-STAIN applied to all faces of the siding lumber. Fax: 1-800-998-3299
* Apply primer and stain or paint at proper spread rates. Visit the Cabot Home Page at: cabotstain.com
#71-0002 — updated 2/08