Need details on sistering joists with plywood [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile

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rjh959
02-08-2017, 09:01 AM
Hi guys,
I plan to sister up some 8" joists with 3/4"ply on both sides and had a few questions. What type of nails to use and the spacing of them?
thanks
-Ray

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cx
02-08-2017, 09:06 AM
It would help if we knew more about your joist structure and intent, Ray, but if you're doing this sistering to reduce joist deflection I'd strongly recommend you not use plywood for that purpose.

My opinion; worth price charged.

rjh959
02-08-2017, 10:03 AM
Sorry about that. I plan to lay tile in my 12'x10' kitchen in a house built in 1949. The span of the 8" joists are just over 11'. The joist width varies from 1.5-2". Based on the age, size, span, I will probably have some deflection issues since I would like to lay 12" tile. Would sistering them with 2x8's be better for deflection?
thanks
-Ray

cx
02-08-2017, 10:06 AM
Substantially better.

rjh959
02-08-2017, 10:15 AM
thanks, I was afraid of that. gotta luv the interweb. many sites/posts say both methods are equally effective...
What nail type and spacing would you recommend?

cx
02-08-2017, 10:55 AM
The difference is that with plywood you are limited to 8-foot lengths unless you buy specialty material. You also get no more than 3/5ths of the total thickness oriented the correct direction for your purpose even if you get very good 5-ply material.

I do not recommend nailing at all for sistering. I prefer construction adhesive and screws that allow the sisters and joists to be pulled together tightly enough for a good glue bond.

You must sister a minimum of the center two-thirds of the unsupported span to do any good in deflection reduction.

My opinion; worth price charged.

rjh959
02-08-2017, 11:08 AM
I plan to remove the subfloor and will have full access from above to drop in sisters that are full length. Could you recommend a screw type and spacing?

HooKooDoo Ku
02-08-2017, 12:02 PM
Exact screws and spacing won't really mater as the main bond should be the glue. So the main purpose of the screws is to pull the two boards of wood tight together so that the glue can form a good bond.

When I installed some sisters, I used glue and 1/4" bolts (with fender washers) spaced 2' apart.

cx
02-08-2017, 12:31 PM
My usual is 2 1/2 or 3-inch deck screws and PL Premium adhesive. I'll generally use three screws on a 2x8 in a row angled from top to bottom and the rows about 16" apart. I pre-drill whichever side the screws will enter first.

My opinion; worth price charged.

Carbidetooth
02-08-2017, 12:35 PM
And for sure, not drywall screws! Drywall only for those, it's illegal otherwise.







OK, maybe not illegal, but perhaps is should be...