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This article desribes and illustrates common building exterior & interior painting mistakes, describes how to diagnose paint failures on buildings, and outlines a procedure for diagnostic field inspection & lab testing of failed painted surfaces. We include photographs of paint failures on buildings and more photos of forensic paint laboratory examination of samples of failed paint useful to assist in diagnosing the probable cause of each type of paint failure. Our page top photo shows a horrible paint job on a building exterior: the painter simply painted over loose, alligatored paint.
For a description of proper painting procedures see PAINT SURFACE PREPARATION. For a detailed guide to selecting and using exterior paints and stains, readers should also see PAINT & STAIN GUIDE, EXTERIOR. Also see PAINT FALURE, DIAGNOSIS, CURE, PREVENTION and PAINTING MISTAKES for details of paint failure cause, diagnosis, cure and prevention. Odors from paints and low-VOC or zero-VOC paints are also discussed at ODOR DIAGNOSIS CHECKLIST, PROCEDURE. Also see VOCs VOLATILE ORGANIC COMPOUNDS.
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Experts representing paint manufacturers see many field failures of painted surfaces, often arising from a common cause. But getting a clear answer from these professionals can be tricky: the painting contractor is their customer, not the building owner. Therefore, while most paint failures are due to poor surface preparation or painting in improper conditions of temperature or moisture, the "expert" may be reluctant to say so.
Importantly, other paint failures are due to construction errors, building ventilation or vapor barrier errors, building leaks, or improper maintenance. It is important to understand why a paint failure occurred before re-painting a building. Otherwise the expense of a new paint job may be wasted.
"Improper or inadequate surface preparation is by far the most common cause of house paint failures such as blistering, peeling and staining. If the new paint is separating from the old coat of paint, it is most likely due to chalking or some contaminant on the old paint that prevents the new paint from penetrating and binding to the old painted surface.
If the peeling failure is down to the bare wood, it is most likely that the problem is a result of too much moisture within the wall, forcing itself out, taking the entire paint film with it."
"Over 65% of all paint failures can be attributed to poor or improper surface preparation. Two of the major causes of paint failure on exterior wood surfaces are either moisture passing through the substrate from the interior, or exterior sources of moisture getting behind the paint film. Temperature and humidity have major effects upon drying and ultimately upon the characteristics of the paint film. These effects will always determine the actual appearance and performance of the paint itself.
Paint should be applied at temperatures of 70o F, (21o C), ideally, plus or minus 20o F (12o C) - unless product specifications state otherwise. A surface should not be painted if its temperature is within 5o F of the dew point or the relative humidity is above 85%." -- PPG Exterior Failures.
The follow sections of this document form a checklist of building and site conditions leading to paint failures (such as peeling paint,
blistering paint, chalking paint, cracking or alligatoring paint, or bleeding and stains through paint--terms defined below). The focus is
on failures of painted wood surfaces on building exteriors but the paint failure diagnostic procedure can be
generalized to other surfaces inside and out.
BAD PAINTING SURFACE PREPARATION - 26 Painting Mistakes That Mean a Bad Paint Job with a Short Life - causes of early paint job failure
Frequently Asked Questions (FAQs)
Question: how to remove mold from a wood tree sculpture & prevent mold re-growth?
This may be unusual, but I'm a sculptor. Part of my output is expressed using lime wood branches, clippings. I've noticed that mold has appreared from the cut ends of these branches and cuttings. Can I retard this or reradicate it using a spray/chemical? I'd appreciate any advice or someone to whom reference can be made. Yours sincerely, I.C. 6/8/2013
Thank you for the interesting question about mold growth on wood branches used in a sculpture - it helps us realize where we need to work on making our text more clear or more complete. A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with mold growth on art and artifacts as well as diagnosing the probable cause of that mold; but I can say that the species of wood, in this case limewood or perhaps wood from the Linden tree. Indeed limewood has a long history of use in artworks, having been used for the carving of painted icons, apparently because of its resistance to cracking and the ease of sanding it smooth.
I don't have a full picture of just what you're making or what mold you're dealing with nor its extent; so my advice is a bit general.
In most simple terms the proper course of action is to
1. remove the problem mold - clean the surface; depending on the sensitivity of your wood and sculpture, simple household cleaner would perhaps suffice; for cosmetic reasons you may need to use a more aggressive or oxidizing cleaner, even bleach - but obviously you won't do that if your work would itself be damaged;
If your work is sensitive or fragile you'll want to chat with an art conservator for some specific recommendations; often we can find success using gentle means to clean and remove stains from wood. (I am an aerobiologist interested in mold in artwork but not an expert conservator, as you'll read at some of the references in links I include below);
2. protect the wood against new mold growth - if your project permits, when the wood is thoroughly dry, if you seal it to resist moisture uptake it will be more mold resistant. Parmetol, a wood preservativerecommended by the manufacturer was used as a fungicidal additive to paint on the Blue Poplar wood sculpture in Amsterdam, by artist Mari Shields [per our discussion in 2010] I'm not sure it was entirely successful. 
Watch out; if you don't clean adequately, or if you seal damp wood, or if your sealant is exposed to weather, there is a risk of new mold growth beneath the sealant - a condition that then could be harder to clean; I discuss this problem at - PAINTING MISTAKES
3. identify & fix the cause of the mold growth - such as wood sculpture in a damp or wet area or if outdoors, in a shaded wet area. Those conditions need to be addresses too if you expect to avoid a recurrent mold problem on your work.
You may be surprised as well but this is not the first such request I've received from a sculptor on exactly this topic; wood is a natural meal for many species of mold. If the wood is wet and thus absorbs water the risk of mold growth is significant. Mari Shields a sculptor in Amsterdam was faced with similar problems of mold growth on a large wooden tree sculpture that was exhibited outdoors; some of her work can be see at http://www.marishields.com/ - and she may have other suggestions for you.
These articles may also be of interest to you
Please keep me posted on how things progress, and send along photos if you can. Such added details can help us understand what's happening and often permit some useful further comment. What we both learn may help me help someone else./P>
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