Progress in restoring the south wall: Crack prevention

UNLIKE MOST BUILDING WALLS, our sanctuary’s long walls are made of two different materials: concrete (along the bottom), and a wood frame that is covered with gypsum lath and plaster. This has been a problem for the portion of the south wall that is exposed to the (sometimes blazing) sun, as compounded by re-radiation from the adjacent asphalt parking lot. In reaction to the daily heating-and-cooling cycles, the two parts of our wall respond differently: they expand and contract at different rates. Little wonder, then, that over the past 25 years, a horizontal crack developed along the seam between the two parts of the wall, running about 70' long.

1/10/23:  Horizontal crack at the seam of the concrete wall and the frame wall
also showing moisture damage from water intrusion
(As usual, click/tap on an image to enlarge it.)

As you probably know, the wall is in the process of reconstruction, as part of the interior painting project. Below the jump, this post explains the steps that we have taken to prevent that crack from reappearing.

The drywall subcontractor and I have collaborated to produce the following plan that we believe will create a flexible joint between the two parts of the wall — to allow for expansion and contraction along the seam.

1.  Attach a metal edging strip along the bottom of the frame wall, at the level of the sill plate. 

7/28/23

2.  Affix drywall to the concrete foundation wall (in place of the damaged plaster that was cleanly scraped away), but cut it a bit short — so as to leave a small gap beneath the metal strip. 

7/28/23

3.  Tape over the joint and apply drywall mud as needed to make a smooth wall surface. (Not shown.)

4.  Sand down the surface as needed to expose the metal edge. Run a drywall knife along the wall underneath that edge, in order to create a clean, straight, thin gap beneath it. (This allows for expansion and contraction over time.)

8/4/23

5.  Fill in the gap under the metal strip with a bead of flexible caulk. Then paint the wall.

8/11/23

The result is an unobtrusive line. It is even less likely to be noticed when the seats are eventually replaced along the wall.