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How-To

Back-Blocking Butted Drywall Seams

Use this technique to minimize ridging between butted joints.

By Myron R. Ferguson
Article Image

Throughout this drywall guide, I have stressed the importance of trying to avoid butted seams between the untapered ends of panels. If, however, you have to have butted joints, make sure to keep them away from the center of the wall or ceiling and take time to feather the taped joints carefully. No matter how careful a job you do, however, the joints may still be visible after the room is painted. I’m embarrassed to say that I found this out when I returned to a job to take some photos for an article. What had looked like a perfect job on the day I finished had developed slight ridges at the center of the butted joints. The deformation, known in the trade as “ridging,” was visible only in certain lighting, but it was enough to bother me.

Ridging

Building materials expand and contract as the temperature and humidity inside a building change. As the building materials move, tension builds up against the drywall panels. The tension is relieved as the panels bend outward, usually at a joint.

Ridging can occur in regular tapered-edge seams, but it is much more common in butted end joints. After the ridging has stopped, typically in six months to a year, the ridged joint can be blended into the surrounding area by applying joint compound to both sides of the ridge and feathering it into the panel surface. There is, however, a way to minimize ridging in the first place: by back-blocking the butted seam.

 

WORK SMART: If ridging occurs on a finished wall, wait six months before refinishing the area. After six months, the area should have moved as much as it is going to move.

 

Back-blocking

Back-blocking is designed to minimize ridging by placing butt joints between framing members. The drywall is hung perpendicular to the framing members, so that the butt ends can be reinforced along the back of each panel, behind the joint. The panel seams can be reinforced by installing a drywall panel behind the seam (see the drawing below). But commercial products designed for back-blocking are much easier to use. For more on this process, see “Back-Blocking the Easy Way.”

 

The Benefits of Back-blocking

  • Finishes butt seams flat and smooth, simplifying the installation of counters, trim, and cabinets.
  • Produces finished seams that are the same width as beveled-edge seams.
  • Takes less time and materials to finish them than typical butted seams.
  • Allows the joint to float between the framing, virtually eliminating cracking and ridging.
  • Eliminates callbacks.

 

Back-Block with Drywall

 

Back-blocking the Easy Way

When butted seams on nontapered ends are inevitable, position them between framing and use a back-blocking device to recess the joint automatically.

Attach the back-blocking
Attach the back-blocking: After installing the first panel so that it ends between the studs, attach a back-blocking device (in this case, a product called RockSplicer; available from www.wilcotools.com) behind the seam you’re creating.

Seams recess automatically
Seams recess automatically: Here you can see the screw is set back from the edge to reduce damage to the drywall core. The raised edge of the RockSplicer helps recess the seam.

Attach the second panel
Attach the second panel: The butted edge of the second panel is screwed through the drywall into the back-blocker. And because it falls between framing members, it’s unlikely to crack or ridge.

A durable seam
A durable seam: The design of the back-blocker pulls the seam in, creating a recess and making it easier to conceal at the taping and finishing stage.

 

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