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What the Heck Is Moisture Bagging?

Photo From catchlightpainting

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I had no idea either, until I moved to New England from San Francisco and encountered a multitude of paint failures that are unique to old wood houses and Old Man Winter.

The above photo is of an elevation on the Fitch Inn in Bedford, the start of Paul Revere’s famous ride. The clapboards in question are not original to the structure but nonetheless exhibit the classic bagging or blistering that occurs when interior moisture transpiration through the sidewall meets and is trapped by an impervious coating.  The solution is simple enough; once the wood is dry and conditions warm enough to paint, scrape, feather sand then prime and touch up.  We’ll be extra careful feather sanding as the cedar clapboards will no doubt be softer than those we worked with on the original elevation.

The original elevations of the Inn we stripped with Paintshavers 2 years ago and this coating is tight as a drum.

This above photo from the same building but of a recent renovation shows tannin bleed through the paint coating; the distinct demarcation of the stain also reveals the use of fingerjointed trim.  Again, a simple solution; after cleaning and sanding the door casing, we will prime with a stain-blocking coating then refinish.  It used to be that only oil or alcohol based primers could seal these water soluble stains; but the new generation of effective water-based primer/sealers make this a simpler fix.

We’re huge fans of the boffins and chemists who keep coming up with water-based coatings that outperform their more toxic and polluting solvent-borne counterparts!

Learn more about our wood restoration services here.

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