Replies

1. 
   calvin | Jul 13, 2019 12:16pm | #1

   Joe,
   Plaster sticks up and beyond the lath so you have to use a narrower joist than what’s there. But you already knew that. I put in in the reply as not everyone does.

   I can only add that deep throated clamps help hold it in place while you predrill, use lags and a clutched drill motor, snug up with a ratchet.

   I’ve only done it this way once because of the pristine 150 y.o. ceiling below.....

   Some use steel plate.

   Or you might take a chance and do what I found years ago after removing the flooring in an 1875 commercial store. 24 ft span, 3 x 12+ joists 12”oc. They scabbed long lengths of full 1 by from low on the bearing end to high in the middle of the span. A geezer way older than I at the time offered that “that’s the they did it then” to stiffen the span.

   Doubt it was the pool hall that it was at the time we worked on it.

   Then there’s the commercial exchange building in Findlay, Ohio.
   It had constant runs of rough 2 by TALL joists with 1” standing blocks nailed in between. By constant I mean the 1” blocks every foot or so is what made the on center layout..........hence, 1 inch centers. This was the first floor over the basement.

   Some buildings I’ve worked on where car dealerships in cities. These had several floors of showrooms. 2 by flooring over 6 o.c. BIG floor joists. The cars went up by elevators. There plastered high ceilings were pretty darn pristine. How much did those early 20th century cars weigh anyhow?

2. 
   CBJoe | Jul 13, 2019 12:33pm | #2

   Hi Calvin, What i have is Rock-Lath, so I don't have any issues with the mortar/plaster sticking above the surface. So i'll have no issues sistering a standard 2x6.

1. 
   calvin | Jul 13, 2019 01:39pm | #3

   I’d better read closer, didn’t even see the rock lath and sorry for all the bs later as well.

   If you need to tip your sister into place, cut (rip) opposing bevels on each edge of the joist, or rip it once a bit narrower than the existing.

   The rest of the pertinent fastening stuff from above applies.

   Over 45 yrs of uncovering surprises in how things were put together got the better of me. Moderate impact driving through a clamped sister should not damage the plaster provided the sister doesn’t try to correct a curve, hump or bump in the existing joist . No contact with the plaster backer below is what you want.

1. 
   CBJoe | Jul 13, 2019 01:44pm | #4

   Thanks for the insight. The full floor is up and I should be able to slide the 2x6 straight into the outer end bearing support. I hand't thought about the stress if the new corrects a curve...almost think that will be very likely. Hopefully not much

1. 
   calvin | Jul 13, 2019 05:46pm | #5

   Joe,
   You shouldn’t have a problem if your new framing is narrower than the original. Any deflection in the old won’t be changed unless it dips more than your new one will allow w/o pushing against the rock lath.

   And if this damn site would allow it, I would have edited my previous post to say about the top and bottom beveled edge......parallel rips so you relieve the edges enabling you to tip it into place.

   Best of luck on your project!