Block my joists

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  #1  
Old 09-12-08, 02:16 PM
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Block my joists

In this thread:
http://forum.doityourself.com/showthread.php?t=359181

I was given the following advice:
Originally Posted by HeresJohnny View Post
Minimum requirement for a subfloor for ceramic tile is 5/8" tongue and groove. You have square edge. You can either add blocking between the joists at the plywood edges to support the edges if you have access from below, or add an additional layer of plywood (minimum 3/8"). You can use an isolation membrane over the additional plywood instead of cement board. That'll save you a little on floor height.

Are 2x4s sufficient to accomplish this, or do I mimic the joists themselves, or somewhere in between?

I presume the technique is to attach the blocking between the joists centered directly beneath the seam, then secure the subfloor to the blocking from above. Any specifics on fasteners?

And...
If I block my joists, does the isolation membrane still apply, or will I have to use backer on my blocked 5/8" ply?
 
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Old 09-12-08, 03:10 PM
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Are 2x4s sufficient to accomplish this, or do I mimic the joists themselves, or somewhere in between?
2X4'S are ok.

I presume the technique is to attach the blocking between the joists centered directly beneath the seam, then secure the subfloor to the blocking from above. Any specifics on fasteners?
You have it right. Deck screws are good for this.

And...
If I block my joists, does the isolation membrane still apply, or will I have to use backer on my blocked 5/8" ply?
Either or is good. Keep in my here with 5/8" plywood you are at the bare minimum. More plywood is always better.
 
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Old 09-12-08, 07:59 PM
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Great! I'll update my progress and add more questions here. I just didn't want to get too involved with a floor discussion in the Kitchen forum.

Stayed tuned...
 
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Old 10-08-08, 07:27 AM
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Follow-up: Are Gaps Needed?

My floor is coming along. I blocked the original sub floor and continued around each sub floor panel fastening them to the joists with deck screws. (The 48-year old nails were a little tired.)

On top of that, I installed an 5/8" ply underlayment. I staggered the panels (perpendicular to the subfloor) so that no seams lined up between the two layers. I applied construction adhesive and using 2 1/2" deck screws, fastened the underlayment through the sub floor to the joists. This floor is now probably stronger than any other part of the house.

My next step: lay out electric radiant elements and embed in SLC.

My next question: Do I need to create expansion gaps in the underlayment where the panels meet? I tried to keep them from butting against each other, but was only partially successful. If necessary, I could run a circular saw set at 5/8" depth along the seams to create a gap. And if I do so, should I tape over the gaps so that the SLC doesn't fill them? If so, will plain masking tape be sufficient?

There are other prep tasks for the SLC on my to-do list: primer the surface, create a perimeter "dam", pull my freaking hair out, etc. so if I need to make the cuts, it will have to be soon.

D.I.Y. is so F.U.N.
 
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Old 10-08-08, 08:25 AM
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My floor is coming along. I blocked the original sub floor and continued around each sub floor panel fastening them to the joists with deck screws. (The 48-year old nails were a little tired.)
You may have done more work than was needed. When you add a second layer of plywood, the blocking is not necessary, however it certainly wont hurt.

On top of that, I installed an 5/8" ply underlayment. I staggered the panels (perpendicular to the subfloor) so that no seams lined up between the two layers. I applied construction adhesive and using 2 1/2" deck screws, fastened the underlayment through the sub floor to the joists. This floor is now probably stronger than any other part of the house.
When you add a second layer of plywood, its actually best to screw the second layer to the subfloor rather than the joists. The screw pattern should be every 8" in the field and 6" around the edges. This actually helps to isolated joist movement from your tile installation. If you havent added screws in the field, you should do so as described above. 1 1/2" screws would be good.

Construction adhesive was not a good idea unless it was a full spread of the adhesive accross the entire floor (not just beads) and could cause voids between the 2 layers. It would have been best to just use screws. If you decide to use glue, a full spread wood glue like titebond II would be the way to go.

My next question: Do I need to create expansion gaps in the underlayment where the panels meet? I tried to keep them from butting against each other, but was only partially successful. If necessary, I could run a circular saw set at 5/8" depth along the seams to create a gap. And if I do so, should I tape over the gaps so that the SLC doesn't fill them? If so, will plain masking tape be sufficient?
Certainly wouldnt hurt. I'd also fill the gaps with a cheap flexible caulk.

Spend the necessary to time to learn about slc before you get into it. Here is a good article on slc.

http://johnbridge.com/vbulletin/showthread.php?t=1807
 
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