I'm considering using 1×3 strapping before applying my new drywall ceiling (after doing some more work on them the other night and realizing it may be the best option). The ceiling joists are exposed and the walls at the top have a gap from about 1/2-3/4" from using a utility knife during tear down. I'm not overly concerned with gap in excess of 1/2" because taping and mudding will hide it, plus I'm adding crown with backing at the end.
What I want to do before installing the strapping is to ensure the joists are in the same plane with one another. I don't have a laser level, but I do have a 4' bubble level and some string. My thinking was I could run some string at various intervals across the joists, having it flat against the first and last joists and checking that it's tight against all the other joists. I could then confirm by measuring from the joists that cause the gaps (meaning they are the lowest) to the floor.
Any suggests on another way (without laser level) to achieve these?
Best Answer
Your plan for using builder's string is good, but don't set the string tight. That opens you up to cumulative contact error. You'll end up with a soup bowl for a ceiling.
Instead, put a spacer of a convenient thickness under the string at the outside. I've often used a scrap of 1x or 2x lumber (3/4" and 1-1/2", respectively). Then you'd measure the gap at intervals, either by setting a series of lines across the room, or by swinging a single line from a corner across to various points along the opposing wall.
If you find high or low spots, here are a couple remedies...
For low spots, sister blocks or strips to the joist as needed, or use shims under your strapping. You can still screw your strapping to the joist, so these don't need to be thick enough for screws. They just act as a spacer.
For high spots, chalk a line from end to end on one side of the joist, anchoring at the bottom corner. Use a circular saw or power planer to remove the hump (sag).
Note that level isn't really what's important here. No one can see a mild slope in a ceiling. Flat is your priority.