Q. The length of a ridge drywall seam in our home needs to be repaired before we repaint. What would be the best way to do this?
MIKE York, Maine
A. Looks like you have a failure of the ridge seam paper tape. A common failure at this location is called “joint ridging’’ or “beading,’’ but I can’t tell from the photo whether or not that’s what you have. Joint ridging is a uniform fine line of deformation that occurs at gypsum board joints. (Drywall is a gypsum plaster board.) Factors that contribute to this are:
■ Wood shrinkage
■ Poor workmanship
Any of the above can cause this. The common denominator is compression of the edges or ends of the finished gypsum boards.
Your photo shows a clear failure of the paper seam tape, and you may be able to remove this and redo it with mesh tape. Problems can arise when the initial layer of mud dries before the paper tape can be fully imbedded into it. This is common if the taping is done on a hot summer day. Over time, the tape separates from the wall. Poor application is probably the most common cause of tape failure.
Note: In order to repair drywall seams, the gypsum board system should be allowed to stabilize. You should wait to make repairs until after one complete heating/cooling cycle. When you do this repair, ensure that the room is warm and dry.
■ Lightly sand down the ridge, taking care not to damage the embedded joint-reinforcing tape.
■ If you find that just the tape failed, use a utility knife to remove it, extending a foot past the damage.
■ Sand the area smooth, stopping just short of the drywall surface. Do not sand away the drywall paper.
■ Retape. I like self-adhesive fiberglass mesh tape.
■ Fill the surface over the joint with topping or all-purpose compound, feathering as wide as necessary to create an essentially flat surface.
■ Allow the compound to dry for at least 24 hours.
■ Apply a second coat, if needed.
■ After the compound is dry, you can lightly sand it to feather the edges and remove trowel marks.
■ Apply primer and paint the entire (yup, the entire) ceiling.
Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to email@example.com or tweet them to @robertrobillard. Subscribe to our free real estate newsletter at pages.email.bostonglobe.com/AddressSignUp.