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Ask the Carpenter: Is it OK to use exterior paint inside?

Ask the Expert Home Improvement
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Q. After paying to have my children’s bedroom painted, I noticed — too late — that he used white exterior paint on the walls and ceiling. Do I need to remove it before applying regular semi-gloss interior paint for safety reasons?

BETTY WOODS

A. If you’re comparing a latex interior paint against a latex exterior paint, some solvents and chemicals in them may differ. The chemistry behind today’s paint components defines them for their intended use, and both manufacturers and professional painters recommend you use each can as labeled: interior paints inside and exterior paints outside.

Exterior paints often contain fungicides, UV-protective additives, and mildewcides. A higher volume of acrylics in the exterior paint could cause a lingering odor that may be unhealthy in enclosed areas.

Bottom line, paints perform best when we use them as they’re intended. Over time, the gases leach out and do not affect performance. Regardless, you do not have to remove the paint: Just sand it, or degloss the sheen, so that the new interior semigloss has a good surface to which to adhere.

Note: Indoor water-based paints, including latex, are designed to contain the lowest levels of volatile organic compounds. VOCs are used as solvents in the paint and off-gas at room temperature. Look for interior paints with low to no VOC levels. Not all exterior paints meet the same VOC requirements.

VOCs are linked to short-term and long-term health problems, from headaches and dizziness to respiratory disease and liver damage. They may also be associated with certain cancers.

 

Q. My wife and I recently bought a renovated home in which a porch was converted into a mudroom/entryway. It’s great, and we really like having it, but we’re trying to figure out whether it’s possible to add insulation without tearing down the walls.

I’ve done research and read a few articles about boring drill holes in the exterior siding and then blowing in spray foam or something similar, but I’m not sure whether that’s a good idea or how much it would cost. Can you provide some guidance?

MATT H.

A. I reached out to my insulation contractor, who advised me to use a cellulose material in this type of application, not foam, because there will be no voids in most cases and yield the same R value at a much lower cost.

The cost can vary greatly from contractor to contractor. I suggest you contact Mass Save (866-527-7283, www.masssave.com) for an audit and rebate incentives.

Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to homerepair@globe.com or tweet them to @robertrobillard. Subscribe to our newsletter at pages.email.bostonglobe.com/AddressSignUp