Recently I had to make a hole in a lath-and-plaster ceiling for an attic fan. Of course the location of the opening was determined by what looked good from below, rather than by the joist spacing. The existing ceiling was in good shape, and I wanted to keep it that way. Needless to say, cutting the hole involved sawing through a large swath of plaster — well away from the joists and without their solid backing. I’d rather spend a little effort in the beginning of a project to reduce a lot of time-consuming repairs later on in the job, so I tried this improvisation.
First I marked the placement of the fan hole on the ceiling, and then I drilled four small holes at the corners. This let me clearly see from the attic what was going to need support for the upcoming cut.
Next I mixed up a batch of molding plaster (plaster of Paris) and poured two lines of the mix along the crosscut path that the sawblade would have to take to get through the lath and plaster. While the plaster was still wet, I laid 1x4s flat on top of the mix, as shown in the sketch.
Since the hole would need some picture-molding trim on the face of the plaster below, I went ahead before I cut the hole and installed this trim with screws that went through the plaster into the 1x4s. This captured the plaster in a clamping action between the trim and the 1x4s. Then I cut the plaster, lath and joists with a reciprocating saw.
—James E. Power, Lawrence, KS
Edited and illustrated by Charles Miller
From Fine Homebuilding #18
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To the FH / Taunton team: This is a good tip, but it should be updated. We now know that attic fans are a bad idea: a serious fire hazard. You could change the description to an attic ladder, and add a new drawing.
Mark Hays
Do you think it is a good idea to NOT put in headers to support those dangling ceiling joists?
Cutting into plaster, and lath is always tricky.
Whether it be in ceilings, or walls, I always take the time to draw my layout, score with a utility knife, and then screw into the plaster, and every lath outside of my cut line so that the vibrations from the recip saw doesn't shatter the plaster back into the field.
... And yes, headers are a must!
How does the plaster of Paris help?
Wouldn’t it be better to header it off and frame it correctly first. Then just cut out the opening with a skill saw or die grinder ?
1984 issue.