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Old 12-22-2013, 03:48 PM   #1
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Rebuild from Subfloor up to support ceramic tile


I have demo'd my half-bath, to the studs. Previous assistance was provided and details are in the following thread:
Advice: half of floor raised by concrete

Now I am looking for assistance in how to rebuild the flooring to support ceramic tile. Please comment on my plans to handle this.

The situation is that part of the old subfloor is rotten, the space is about 3'x7', with 2 joists (16" on center) running down the middle of the room lengthwise.

I'll probably rent a saw with a blade that can go right up against the wall, in order to remove the existing subfloor. There will most likely not be joists or support along the walls that I can attach the new plywood to, so I will have to add that lengthwise just under the wall; as well as adding blocking between the joists along the short ends of the room.

In order for the floor to be stiff enough to install ceramic tile; I will replace the old subfloor with 2 layers of 5/8 inch exterior grade plywood (2nd layer laid perpendicular to the first).

I'll lay down DITRA on the top layer, before the tile.

Please comment and let me know if you think this is the way I should go -

Thanks,
Rich

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Old 12-22-2013, 05:28 PM   #2
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Rebuild from Subfloor up to support ceramic tile


How thick is the bad subfloor? How extensive is the rotten spot?

I ask these questions because removing the entire subfloor may be more workthan necessary. Often patching in tha bad spot and then overlaying a 1/2" sheet of BC ply is the best solution.

The old subfloor can be removed---but supporting the edges is fairly advanced carpentry----whatever you choose,we can help---

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Old 12-22-2013, 05:51 PM   #3
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Rebuild from Subfloor up to support ceramic tile


I haven't taken up any flooring/plywood so far, so I don't know how thick it is.
However I have almost fallen through in the spot outlined in red in the photo.
The floor joists run from the top of the picture to the bottom.
Since there was no resistance to going through this layer, I doubt there is anything under this layer - or if there is, the layer below is in even worse shape.

Rebuild from Subfloor up to support ceramic tile-img_20131219_123448_small.jpg

What is the best way to find out what is 'below'?

Rich
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Old 12-22-2013, 06:39 PM   #4
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Rebuild from Subfloor up to support ceramic tile


Your first instinct was correct---that subfloor needs to be removed----

I use a Sawsall with the blade mounted upside down---long blade---press it against the wall and bend the blade slightly---then make a shallow skim cut---just cutting the ply--DO NOT make a plunge cut----you might hit plumbing,electrical,heating--

when it's gone,post a picture--we will help you block and replace the subfloor.
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Old 12-22-2013, 07:39 PM   #5
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Rebuild from Subfloor up to support ceramic tile


IMO. set your skillsaw 3/4" deep, cut around the red area, staying 1-1/2" away from wall (guard distance to blade) first, remove that to see the joists/wiring/plumbing. Then do as Mike said- if possible/clear areas. Though it does appear massive rot possible delamination. Either of the walls bearing?

Gary
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Old 12-22-2013, 07:45 PM   #6
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Rebuild from Subfloor up to support ceramic tile


i would use a circular saw set to 1/2" and cut out a section. then pry out that piece.
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Old 12-23-2013, 12:39 PM   #7
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Rebuild from Subfloor up to support ceramic tile


Thanks for the encouragement guys!

I like the idea of taking out a bit in the middle right where the worst damage is to take a looksee.

I've got a reciprocating saw I can use as Mike suggests - so no need to rent something.

Gary - yes both 'long' walls are load bearing. One being the exterior wall. There is a header over the door in the interior wall that is made of 2 2x8's, 26" span.

The flooring 4'x8' is laid lenghtwise, right to left, so we only see half of the panel in this room... I'll see how that is supported when I can see into the crawlspace.

I don't really want to leave the floor open for long... that's for sure.

Rich
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Old 12-23-2013, 03:52 PM   #8
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Rebuild from Subfloor up to support ceramic tile


Depending on the condition of the old floor at the edges,it is often easier to cut the subfloor out using a skill saw and leave an inch and a half around the perimeter---

then add 2x4 blocking to the remaining 'flange' and use that to support the new sheeting---
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Old 01-03-2014, 05:57 PM   #9
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So here we are again, after the holidays - hope yours was the best.

I've pulled up half the subfloor, and intend to add 2x4's between the joists to provide both support as well as places to screw down the plywood around the perimeter. The red squares in the picture indicate where I plan to add them.
Rebuild from Subfloor up to support ceramic tile-img_20140103_184130_small.jpg
I will nail the 2x4's to the joists and the sill, level with the top of the joists... then screw them in as well - using the nails to hold things still until I can get the screws in.

Then the 1st panel screwed down to the joists and the 2x4's... and the 2nd panel screwed down to the 1st panel (avoiding the joists and 2x4's).

With the pipes sticking out of the walls at both ends of the room, I may have trouble putting in the panels in one piece. I may have to end up cutting the panels into 2 pieces, offsetting the cut for each layer so they aren't aligned together.

Am I on the right path? Missing anything?

Rich
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Old 01-03-2014, 08:13 PM   #10
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Rebuild from Subfloor up to support ceramic tile


Looks like a good plan---
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Old 01-03-2014, 08:28 PM   #11
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Rebuild from Subfloor up to support ceramic tile


Rich,

In which direction do you plan to install the subfloor sheet? And then the underlayment over the subfloor?

You need more blocking than what is shown. You have to block/sister along the perimeter walls. That would be the east & west walls as oriented in the photo. You do not need the center row of blocking shown, but won't hurt to keep them too.

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Old 01-04-2014, 10:36 AM   #12
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Rebuild from Subfloor up to support ceramic tile


Jaz,

You are probably right in regards to the blocking/sisters. I was trying to avoid adding them along the perimeter walls. However, when I used pieces of the 4x8 sheets of plywood left over from cutting them to size for the room - as temp walk support in the area where I removed the old sheeting... even two layers still sag with my weight.

I'll probably 'box' in the area around the ducting, as the old subfloor was not supported along the perimeter at that point - it was actually cut away a couple of inches to clear the duct... which will have to be done again with the new - at least for the first layer.

As for which direction to lay the layers... It would be nice to lay each layer perpendicular to each other - but I'm not sure I can do that. (I am using plywood, not OSB, so it's built that way anyway.) I've already had two panels cut to the (approx) 3'x7' size.

Due to the pipes coming from the walls on both sides and the drain from the floor - I'm not sure I can simply slide the sheet into place (or even get the whole sheet into the room through the 24" entrance). So I may have to cut the panels further to get them into the room and to lay them around the pipes. I was thinking of cutting one layer on the toilet side, just outside the drain, so 12" or so from that wall. Then cutting the next layer 12" or so in from the other wall to avoid the sink pipes.

Both layers would be panels (as a whole) laid in the same direction.

Rich
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Old 01-04-2014, 11:07 AM   #13
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Rebuild from Subfloor up to support ceramic tile


Rich,

The sheets must be installed with the face grain perpendicular to the joists. So, the grain goes across them like this <------> as pictured. Plywood and OSB is stronger in this orientation.

Therefore you will install each layer in at least 2 pieces. The top layer, (underlayment) also goes in the same direction. You just offset the joints both ways, I suggest about 2 ft. +-. Actually because it's a small room you'll probably only be able to offset in one direction. The smallest piece of subfloor should be no smaller than 32", so it will be supported by 3 joists.

Do not glue the 2nd to the subfloor, just nails or screws into the sub with fasteners just long enough to go through the sub. and not penetrate the joists.

Jaz
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Old 01-05-2014, 12:56 PM   #14
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Jaz,

Thanks - that is exactly what I needed to know.

Can I put flexible silicone sealer in the crevices between the panels in the first layer, and between the panels and the wall studs... to limit air flow from the crawlspace?

Can I also do that on the 2nd layer? or would that interfere with adding the Ditra?

I intend to use spray foam in the void where the plumbing in the wall goes through the floor as well, to limit air flow.

How much height do you think will be added by the install of 'thinset/Ditra/thinset/tile'? I think the Ditra itself adds about 1/4"? I'm trying to see if the existing toilet drain is at a height that will 'fit' - or if it needs to be re-engineered to fit the new floor height.

OH- the offset of joints between panels, 1st to 2nd layer... If I don't remove the toilet drain, I'll need to cut the hole for the drain in the subfloor to fit the lower (vertical) section of the pipe - not the width of the top flange... So I would need a small section of plywood behind the drain, across all joists, width from the wall behind the toilet to the front of the toilet drain (about 15"). Then maybe 2 additional sections of plywood to cover the rest of the floor.

The 2nd layer would then only be offset by the width of the drain pipe - if this makes sense? Here is a quick diagram. This makes the offset only the width of the drain pipe. Is that OK?
Rebuild from Subfloor up to support ceramic tile-capture.jpg

Thanks for your help.
Rich

Last edited by rdarlin2; 01-05-2014 at 02:27 PM.
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Old 01-05-2014, 02:04 PM   #15
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Rebuild from Subfloor up to support ceramic tile


Rich,

I don't see a problem with sealing the subfloor seams and perimeter. Are you not using t&g subfloor? It's ok to use square edge since you're installing a second sheet, but t&g is better or you can install blocking under the seams to support the edges.

The underlayment in installed using ring shank nails and gapped 1/8" between sheets, 1/4" at perimeter. The underlayment is oriented in the same direction as the subfloor, but seams are offset as much as possible from the subfloor seams. Be sure the crawlspace has a vapor barrier on the ground per local codes.

Quote:
Originally Posted by Rich
How much height do you think will be added by the install of 'thinset/Ditra/thinset/tile'?
I don't recall you telling us how thick the tiles are. Assuming they're about 9-10mm. you can figure 7/16 to 1/2" for the tiles. But, some cheapo tiles are thinner than 9 mm, some are 7mm. (.276").

Quote:
I think the Ditra itself adds about 1/4"?
Wrong. Regular Ditra is 1/8" before and after installation. The thin set adds nothing due to the way the back is designed. Ditra XL is 5/16" thick.

Where will the bottom of the flange be in relations to the finished floor?

Jaz

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