Question

Does priming and painting OSB help prevent offgassing?

Asked by Kevin Hanrahan
Smyrna, TN

I have OSB walls in my new workshop. What should I do?

Answer

Amy Green

Answered by Amy Green

New York, NY

[box], LLC

March 12, 2010

There are some companies out there such as the Architectural Coatings + Design Center based out of Los Angeles, who sell sealants specifically to stop off gassing from OSB and protect indoor air quality.

However, sealing or painting OSB to stop off gassing isn’t necessary when you look into the OSB process and how OSB factories handle off gassing and curing at the plant which stop off gassing by the time it reaches your construction site.

According to the Structural Board Association Representing OSB, “There is no measurable off gassing from the finished [OSB] panel.” You can read more about their studies of OSB in their Technical Bulletin in this pdf which touches on other sustainable aspects of OSB such as

  • using Aspen as a rapidly renewable resource for OSB production
  • OSB production is resource efficient as it uses all parts of the tree, and
  • sustainable farming practices OSB companies follow for production.

As for Volatile Organic Compounds (VOC)’s in OSB, OSB companies must follow stringent guides, greatly limiting the VOC’s they emit into the air. The two most common resins for binding OSB are polymeric diphenyl methane di-isocyanate (MDI) resin and phenolic resin. During the pressing operation, the resulting gases are driven off and collected in a venting system. The collected gases either go to the energy system as part of the under fire air supply, are incinerated in a regenerative thermal oxidizer (RTO) or treated with a bio-filter.

MDI is actually formaldehyde free, which is the main carcinogenic off gassing concern people usually have, so that isn’t a concern with most OSB.  However these are not the most eco-friendly of resins, and MDI is a poison when inhaled.  The factories do stand by the study above from the Structural Board Association, that once OSB leaves the factory, the panel isn’t off gassing (read more about MDI at The Toxics Use Reduction Institute.) 

Fortunately, the resins in OSB are designed to completely cure in the hot press process at the plant, and after the process, SBA mills hot stack panels for at least 48 hours after trimming to allow gases to dissipate, and current findings are that the OSB panels will only very minimally off gas after that, doing so only when coming in contact with high heat and cutting, such as when they are cut on site during construction or demolition. So if you’re doing construction or demolition with the OSB, make sure to wear a mask and gloves to protect against fumes when cutting, and be sure to vent the area with a fan or other blower system to remove fumes from the space after cutting.

However, if the OSB has already been in use for some time, findings are that there really is no reason to paint or otherwise seal it to protect from VOC’s and off gassing as it shouldn’t be off gassing unless cutting is involved.

Furthermore, the Eastern Laboratory in Québec and the Minnesota Natural Resources Research Institute (MNRRI) in Duluth, MN have determined that there are no additional VOCs released from OSB when it is burned or placed in a landfill than what is released from solid wood, so there aren’t additional off gassing worries with disposal.

My recommendation if the OSB is existing, let it be. If it’s existing and you’re cutting it, then follow the protection and venting recommendations. However, if you haven’t selected the product yet, look into the newer types of OSB, called "new-generation" OSB panels, which use isocyanate resins that do not contain formaldehyde and are considered non-volatile when cured.

Companies such as Lousiana Pacific carry these OSB panels and they’ll allow you to select a resource efficient material with no off gassing.

 

For more information:

Read Ian MacLeod's Q&A "I'm concerned about toxic offgassing from OSB subflooring and roofing. Are safer products available?"

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