Painting Exterior Woodwork (final)

Bob Yapp
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Joined: May 9th, 2011, 8:39 am

Painting Exterior Woodwork (final)

Postby Bob Yapp » August 19th, 2012, 1:22 pm

Author: Duffy Hoffman
Contributors: Bob Yapp
References:

Title of Treatment: Painting Exterior Woodwork
Class of Treatment: [x] Maintain, [ ] Stabilize, [ ] Repair, [ ] Upgrade, [ ] Exception
Type of Treatment: [ ] Traditional, [x] Modern

Condition to be treated: Exterior window casings, jambs and sills have deteriorating paint.

Description: Evaluate conditions and plan the work. Remove deteriorating paint down to sound paint or bare or clear wood. Prepare the surface and pre-treat bare wood. Prime with oil-based primer. Apply fillers, caulks or sealants. Apply two topcoats of paint.

This standard includes adding third-party products and materials to standard paint products. Three types of additives may be used here:

-- mildewcide to limit mildew and mold growth within the paint film
-- metallic salts drier to promote drying
-- "binder extenders" that enhance oil-based and waterborne acrylic paint adhesion, flexibility, durability and sheen

These additives should only be used by knowledgeable workers with at least 20 years experience using paint additive methods. Success with this method is highly dependent on the workers' judgement of surface conditions, weather conditions, paint products and the specific additive types, products and amounts used and drying times between coats.

Typical Procedure:

1. Evaluate existing coatings to determine type and extent of paint failure. If more than 16 mils (.016") of paint build up is present (about three complete paint jobs or 9 layers of primer and paint) consider removing all paint coatings. When multiple layers of paint coatings are this thick, water vapor cannot adequately pass through the coatings and may be trapped in the wood causing wood decay or paint peeling down to bare wood. Incompatibility between different types of paint, in multiple layers, also contributes to premature paint failure.
2. Remove deteriorated paint down to sound paint or the bare or clear wood substrate. If completely removing the paint, consider the following methods: wet hand scraping, infrared heaters; hot-air guns set below 640 degrees <I'll remove heat guns from this list for building safety and liability reasons--editor>; liquid chemical paint strippers (do not use chemical strippers containing methylene chloride, or caustic alkaline chemicals that require neutralizing).
3. Prepare the wood surface by removing all grey or loose wood cell fibers from the surface of the wood by scraping or sanding, exposing sound "bright" wood. These loose fibers appear gray in color and are caused by ultra-violet (UV) sun and water damage. Paint will not adhere well to these grey surfaces. Remove all old and failed caulking from all joints around all casing, window frame and sill. Sand wood surfaces smooth and clean surfaces and joints with a HEPA vacuum.
4. Evaluate existing woodwork conditions, complete all needed woodwork repairs and then continue with this paint procedure.
5. Apply a pre-treatment. Mix one part boiled linseed oil and one part paint thinner and add a mildewcide. Apply to all exterior wood surfaces. Allow to dry. This pre-treatment helps the primer adhere to the wood.
(Dry: "dry to touch" does note mean dry, Further drying or curing is usually needed and often takes a minimum of 24 hours.)
6. Add a binder extender of the penetrating oil type to each gallon of primer. A drier may also be added if needed. Brush apply the primer generously. This leaves a full coat of primer on substrate so vehicle and pigment do not separate and top coat will adhere better to the primer. Let dry, before top coats are applied.
7. Sand lightly between all coats, to knock off nibs and whiskers and to provide a tooth for the next coat. Clean and tack off dust.
8. Set and fill nails holes with putty or filler. Apply caulking or sealant to vertical and top joints all around the casing and frame to seal out draining water and limit air infiltration. Apply sealants to lap onto both sides of the joints enough for good adhesion. Be careful to not seal lower joints that may need to remain open to allow drainage of water from failing sealants above. Allow sealants to cure before applying finish coats. Visually and physically check joints to assure they are actually sealed.
9. Sand primer lightly with 100 grit sandpaper or use a carbide scraper to smooth lightly. This leaves a slight bit of roughness or tooth for finish coat to grab onto which creates a better bond for top coats. Vacuum, clean or tack all primed and sanded surfaces.
10. Select a 100% acrylic top coats which will flexible enough to move when the wood beneath contracts and expands. Add a binder extender by removing some paint from each can and put into a temporary container. Add the binder extender and a mildewcide to each gallon. Mix thoroughly and apply two finish coats to frame with a quality paint brush. Allow for enough drying time between coats.

Materials:
• Primer, oil-based boiled linseed with alkyd resin type
• sealant or caulking, acrylic
• Putty, linseed oil or exterior filler
• Sand paper, or sanding sponge
• Paint, waterborne ("latex"), 100% acrylic topcoat
• Mineral spirits, 100% (not containing water)
• Mildewcide additive
• Binder extender, oil-based, penetrating product additive <product: Penetrol, this product name will be removed--editor>
• Binder extender, acrylic, waterborne additive <product: FlowTrol, this product name will be removed--editor>
• Japan drier additive

Quality of Results

Best Work: All surfaces have three full coats. All paint and caulking looks and feels smooth, is visually consistent. No gaps at joints, except lower draining joints.

Inadequate Work: Rough surfaces, open joints, holidays (unpainted spots).

redrocketracer3garner
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Re: Painting Exterior Woodwork (draft)

Postby redrocketracer3garner » November 2nd, 2012, 9:37 am

Would like to see a note about painting at least 1/16" of paint on the glass (exterior & interior).

Bob Yapp
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Joined: May 9th, 2011, 8:39 am

Re: Painting Exterior Woodwork (draft)

Postby Bob Yapp » November 2nd, 2012, 11:15 am

Hi David, I think your comment about painting onto the glass 1/16" is a good one and it is covered in a Standard about painting windows. This one is about the exterior trim around the window opening.

The only problem I see with doing this on both sides of the glass is that if done on the interior side, the sight line to the molded profiles is not clean. I've always painted just the wood and the bedding material on the interior side so we have a crisp paint line. I also underputty by 1/16" on the exterior so that when the paint comes onto the glass, it cannot be seen from the inside of the window. We're open to your thoughts on this.

John, I think we would be hard pressed to find a window artisan not using a heat gun for inside corners and detail work. The 640 degree limit is critical and so maybe instead of eliminating it we should be clear that a quality, adjustable, heat gun should be used. Test the settings and actually measure temperature with a thermometer to assure the proper setting for 640 dgrees maximum. The EPA is allowing them to 1,100 degrees which is absurd. On the other hand, I don't use one for exterior trim, I use wet carbide scraping for these tough detail spots.

davidjgarner
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Re: Painting Exterior Woodwork (draft)

Postby davidjgarner » November 5th, 2012, 11:36 am

We paint to the glass on both sides of glass. Painting on the interior, we believe, doesn't allow too much moisture/condensation to settle into the the rabbet.

johnleeke
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Re: Painting Exterior Woodwork (draft)

Postby johnleeke » November 8th, 2012, 9:53 am

OK, I'll shift these painting onto the glass panes over to the painting glass discussions.
John
Standards Co-Founder
Standards Editor

http://www.HistoricHomeWorks.com

johnleeke
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Re: Painting Exterior Woodwork (draft)

Postby johnleeke » November 8th, 2012, 10:33 am

Bob,

I agree with wet carbide scraping for detail paint removal, and will included that in the standard above.

I agree with your comments about hot-air guns, the types to use, how to adjust them, etc.

Research: decayed wood can ignite at 302F. (Reference: "Firepoint" magazine - Journal of Australian Fire Investigators, http://www.tcforensic.com.au/docs/article10.html)

Personally, I really don't like to see or even think about using hot-air guns right on the building, because so many building fires are started that way. (Reference: Heat Guns start fires in Historic Buildings, http://historichomeworks.com/forum/viewtopic.php?t=482) I have personal experience on this. I, myself, started a building fire back in the 1970s using a hot air gun for paint removal from a window. We, and the fire department, caught up with it quick enough to limit the damage to just a couple square feet of the wall, but it scared the heck out of me, and I have never put a hot-air gun to a building since, nor allowed it on any of my projects. I do sometimes (rarely) use a hot-air gun for paint removal from removed building parts working in the shop, where the situation is more controlled.

Many local fire chiefs recommend against the use of hot-air guns for building paint removal, and some localities have regulations against it.
John
Standards Co-Founder
Standards Editor

http://www.HistoricHomeWorks.com

johnleeke
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Re: Painting Exterior Woodwork (draft)

Postby johnleeke » November 8th, 2012, 10:35 am

This discussion on paint removal could become a separate standard for paint removal.
John
Standards Co-Founder
Standards Editor

http://www.HistoricHomeWorks.com

davidjgarner
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Re: Painting Exterior Woodwork (draft)

Postby davidjgarner » November 14th, 2012, 4:40 pm

Please consider a mention of painting exterior woodwork within the limits per manufactures tech specs e.g. temperature, humidity, and wind. Recently I’ve (a sub contractor) have been asked to paint exterior woodwork when the substrate was 40 degrees for less than 2 hours ... GC under time schedule you know. Anyway, I sense the outcome of that paint application will be poor adhesion, however, it may not show up until next summer. Time will tell, eh?


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