on Paint and Coatings Sam Williams Madison, Wisconsin WoodWorks Webinar 23 August 2010 Learning Objectives

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1 Wood Properties and Their Effects on Paint and Coatings Sam Williams Forest Products Laboratory (Retired) Madison, Wisconsin WoodWorks Webinar 23 August 2010 Wood Products Council is a Registered Provider with The American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non-aia members are available on request. This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation. Learning Objectives Effects of wood species, anatomy, and manufacturing processes on finish performance Explain appearance grades of wood Matching finishes to wood surface properties to maximize service life Your wood and painted wood can perform well for centuries. For example

2 Wood Finishing Research at the Forest Products Laboratory Madison, Wisconsin Your wood and painted wood can can perform well for centuries. I wonder if vinyl siding will last that long???? For example Stav church Norway, 14 th century North America 1700s

3 Wood and wood products Lumber Paper products Composites wood/wood wood/plastic They all come from trees! Wisconsin 1800s Wood and wood-based products are Anisotropic properties differ with different grain angles Hydrophilic dimensional change is caused by changes in relative e humidity and water absorption, not temperature Porous water and water vapor move easily through wood Grain orientation Tangential Flat-grained (Flat-sawn) Radial Vertical-grained (Edge-grained) grained) (Quarter sawn) Longitudinal End-grained

4 a, vertical grain b, vertical grain/with pith c, flat grain Raised grain on pith side Notice the difference in the cell density on either side of fthe latewood band Re-sawn bevel siding Vertical grain siding Both pieces are the same Flat-grained siding The re-sawing gives boards with completely different properties One board, smooth bark-side saw-textured pith side One board, smooth pith side saw-textured bark-side vertical grain Flat grain

5 Vertical-grained siding Both sides are the same Saw-textured is vertical-grained Planed side is vertical-grained Cutting bevel siding Flat-grained siding The surfaces are different Planed surface before wetting Bark side Pith side Grain raise following wetting End-grain view, before wetting Matched end-grain, after wetting Raised grain, end-grain view

6 Extractives Only about 5 % by weight Great effect on properties Cross grain cracking in the juvenile wood Color Light stability Paintability Decay resistance Gluability Insect resistance Flammability Water repellency Metal corrosion Health hazards Poor performance of wood, wood composites, and finishes on wood products In general, two causes WATER SUNLIGHT Some softwoods contain pitch

7 Where is the flashing? Not here! Not here! Flashing is installed above window but the siding is installed wrong! No gap between the siding and the flashing Suddarth s Rules There are three simple rules that must be strictly followed for Three rules for Good Wood Design 1. Keep wood dry GOOD WOOD DESIGN

8 Three rules for Good Wood Design 1. Keep wood dry 2. Don t let wood get wet Three rules for Good Wood Design 1. Keep wood dry 2. Don t let wood get wet 3. Always keep water away from wood Problems In general, two sources WATER SUNLIGHT Weathering or Wood Photodegradation by sunlight (UV radiation) Leaching, hydrolysis, shrinking and swelling by water Discoloration and degradation by micro-organisms organisms

10 Weathering causes erosion of the wood surface The amount of erosion depends on Wood species (density) Grain angle Weather conditions Angle of exposure to the sun Loss of wood from surface: 100 years vertical-grained i wood exposed at 90 degrees facing south in a temperate climate 6 mm (1/4 ) most softwoods 10 mm (3/8 ) western redcedar 3 mm (hardwoods)

11 Effects of short-term term weathering of wood before painting ( weeks) On long-term paint performance (3-20 years)

12 Appearance grades of wood The cedars eastern red cedar southern redcedar Alaska cedar Atlantic white-cedar Port-Orford-cedar incense-cedar cedar western redcedar northern white-cedar Juniperus virginiana Juniperus silicicola Chamaecyparis nootkatensis Chamaecyparis thyoides Chamaecyparis lawsoniana Libocedrus decurrens Thuja plicata Thuja occidentalis (also called eastern white cedar)

13 Getting the best match of Finish properties p and Wood properties Wood properties Finish performance Smooth vertical grain Saw-textured vertical grain Smooth flat grain Saw-textured flat grain Knotty grades Finger-jointed grades Water-Repellent Preservatives Traditional formulation Resin 8 to 12 % Wax 05to1% 0.5 Preservative about 0.5% Solvent/cosolvents l t Organic solvent New formulations Water emulsions, cosolvents Water Traditional use included d siding New formulations are primarily for decks

14 Water-repellent preservatives Saw-textured only VG or FG Knotty or clear Deck finishes Saw-textured or smooth VG or FG Knotty or clear Oil-based semitransparent stains Saw-textured only VG or FG Knotty grades, use dark color New formulations tend to be high in solids They may not penetrate as well as traditional finishes Lap mark

15 Other Stains Latex Semitransparent (water-borne, forms a thin film) Solid Color (forms a film, much like a paint) Solvent-borne, Oil-based Water-borne, Latex Bleaching Solid-color stains These are really paints Wood must be primed and sufficient coats must be applied to get a film- build of 4-6 mils If smooth planed, They work best on vertical-grained lumber If saw-textured, Flat-grained or vertical-grained lumber Paints, Two general categories Solvent-borne, Alkyd-based (oil) Water-borne, Latex-based (acrylic) (vinyl acrylic) Paints They perform best on vertical grain lumber or siding Saw-textured or smooth-planed (20+ years for 3 coats on saw- textured) t Use darker colors on knotty or fingerjointed lumber or siding

16 Varnish Do not use traditional varnishes The new formulations having transparent pigments perform better Use saw-textured wood Design and exposure are extremely important Discoloration of wood and finishes Extractive ti bleed Mildew Check out the FPL Website Iron staining fs fed

17 Mildew, Aureobasidium pullulans Combined effects leaching of extractives weathering mildew growth No decay.yet!!! Mildew removal Be careful with household bleach and commercial cleaners Many cleaners pulp the wood The more gentle, the better Commercial cleaners, active ingredients Mildew Sodium/calcium hypochlorite Sodium percarbonate Pulp surface, remove old finish Sodium/potassium hydroxide Remove iron stain, brighten surface Oxalic acid Corrosion of fasteners

18 Iron stain extractives bleed Removal of iron stain oxalic acid 3-4 ounces Water 1 gallon Note: Oxalic acid is toxic Wood the 200+ year siding Good design keep the water out Quality siding paint ASAP Compatible wood/paint keep the water out Installation keep the water out Maintenance keep the water out Courtesy of the Rohm and Haas Paint Quality Institute Courtesy of the Rohm and Haas Paint Quality Institute

19 Sam s contact information Sam Williams and Associates LLC rsamwill@gmail.com

Wood Properties Important to Exterior Coating Performance

Wood Properties Important to Exterior Coating Performance American Coatings Association Mar 18, 2010 Christopher G. Hunt US Forest Service, Forest Products Laboratory 2 Good Wood LASTS! 3 How To Get Great