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Old 10-28-2008, 08:38 PM   #1
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Existing sub-floor


Is there anyway to sure up my existing sub-floor. I don't see any mold or rot. The tiles that I removed were cracked. I also removed 5/8" press board. I'm replacing that with 1/2" Hardi backer. I'm also using thinset before applying the Hardi backer. The sub floor seems to be kind of soft or weak. Thank you for any advice you can give.

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Old 10-28-2008, 09:29 PM   #2
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Existing sub-floor


What's the subfloor made of? How thick, how many layers? What type, and size are the joists, their spacing? The reason could be the press board? What was this board? Were the tiles bonded direct to that? The new Hardie backer, nor any other tile backer, will add any strength to the floor.

Let's start with these few questions for now.

Jaz

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Old 10-28-2008, 09:56 PM   #3
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Existing sub-floor


The sub-floor is plywood, I don't know how thick it is. I don't know the size of the joists, I know they are larger than the average joists. I'm not sure of the spacing of the joists. I'm not sure what kind of board it was under the tile. It was some kind of press board. The tile was put on over the old linoleum. Will thinset help to make the sub-floor more sturdy?
Thanks!
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Old 10-28-2008, 10:57 PM   #4
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Existing sub-floor


You say you don't know the answers.....could you maybe find out? Or maybe we should just guess?

You mentioned you're going to do te work yourself? Maybe you should hire a professional?

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Old 10-29-2008, 05:39 AM   #5
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Existing sub-floor


the space between nail rows should help determine joist spacing. can you take a small piece of this plywood out without wrecking it?? Then you can see how thick it is, joist depth etc. Anything visible under stool etc?? How about drilling a very small hole. measure with a stiff wire down to ceiling below,(joist depth),,if thats the case,,and measure depth of plywood
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Old 10-29-2008, 08:42 AM   #6
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Existing sub-floor


Thanks JazMan, that was a real Jazzy answer. I guess I better do my homework.
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Old 10-29-2008, 08:46 AM   #7
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the space between nail rows should help determine joist spacing. can you take a small piece of this plywood out without wrecking it?? Then you can see how thick it is, joist depth etc. Anything visible under stool etc?? How about drilling a very small hole. measure with a stiff wire down to ceiling below,(joist depth),,if thats the case,,and measure depth of plywood
Thanks, that sound like a good idea. I'll do that and come back with a better idea of what I;m working with.
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Old 10-29-2008, 09:04 AM   #8
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Existing sub-floor


I did some checking and found that the joists are 1-3/4" and they are 10" apart. They screwed the subfloor down across the joists. I thought they were supposed to screw it along the joist. Am I right or wrong?
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Old 10-29-2008, 11:06 AM   #9
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Existing sub-floor


That's impossible! The joists are either' 2x8 2x10 or 2x12. Typical spacing is 16". We also need to know the length of the span.

I agree you need to do some more research. Been watching those DIY tv shows have you?

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Old 10-29-2008, 12:25 PM   #10
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Originally Posted by JazMan View Post
That's impossible! The joists are either' 2x8 2x10 or 2x12. Typical spacing is 16". We also need to know the length of the span.

I agree you need to do some more research. Been watching those DIY tv shows have you?

Jaz
JazMan, just so you know the 2"x10" is literally 1-3/4" x 10" but i'm sure they round it off to make it easier for some people to grasp the concept. Typical or not the joists are 10" apart. Thanks for your replies, I can handle it from here. PS. Did you notice the name of the chatroom?
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Old 10-29-2008, 12:59 PM   #11
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Existing sub-floor


If your measurements are correct (and I assume they are, unlike some...), it sounds like the floor is well-supported. I'm not sure what you're describing about the plywood. Typically, plywood is designed to carry load along it's length vs. width, so it should be set so the the long side of the plywood runs perpendicular to the joists. If it's not, it might sag between the joists when you put load on it. If this is the case, you can help it out by putting down another layer in the correct direction. I like Advantec, but it might not work for you.

If the plywood is in the right direction, anything 5/8 thick or more would be fine if the joists are that close together (although Jazz's comment is correct, they are usually on 16's).

I guess I should have asked at first, why do you feel it's soft?
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Old 10-29-2008, 02:04 PM   #12
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If your measurements are correct (and I assume they are, unlike some...), it sounds like the floor is well-supported. I'm not sure what you're describing about the plywood. Typically, plywood is designed to carry load along it's length vs. width, so it should be set so the the long side of the plywood runs perpendicular to the joists. If it's not, it might sag between the joists when you put load on it. If this is the case, you can help it out by putting down another layer in the correct direction. I like Advantec, but it might not work for you.

If the plywood is in the right direction, anything 5/8 thick or more would be fine if the joists are that close together (although Jazz's comment is correct, they are usually on 16's).

I guess I should have asked at first, why do you feel it's soft?

Thanks for the hand. I remeasured and the joists are definitely 10" apart. The way the plywood is laid down, the seam is across the joists not the length of the joist. So it's where the plywood meets plywood that there is nothing to screw it down to, that is where it seems to be weak and flexible.
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Old 10-29-2008, 04:01 PM   #13
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Existing sub-floor


Oh! That usually means the subfloor plywood isn't tongue and groove, so one sheet flexes a little when you step on the crack? If that's the only place it flexes or seems weak, I think you would probably be OK just using 1/2-inch Hardi-backer, especially if you use mortar to hold it down along with screws, staples, or whatever. If you just cant stand it, I've seen people bridge under the plywood joints from underneath. You could take short pieces of 2x6 and screw them in between the joists, then screw the plywood into the bridge.

That's kind of unusual to have the joists that close together. It usually indicates that the original builder was doing that to compensate for a marginally long span or planning on a heavy load on the floor (such as tile, etc). I usually don't span more than 10-12 feet on 2x10's on 16" centers(I'm sure somebody on here will say even less) for a normal load floor, so if they put them on 12" centers (10.5 inches between), and the span doesn't exceed 12' more or less, I think you should be fine on load-bearing.
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Old 10-29-2008, 07:39 PM   #14
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Originally Posted by o_jay66 View Post
Oh! That usually means the subfloor plywood isn't tongue and groove, so one sheet flexes a little when you step on the crack? If that's the only place it flexes or seems weak, I think you would probably be OK just using 1/2-inch Hardi-backer, especially if you use mortar to hold it down along with screws, staples, or whatever. If you just cant stand it, I've seen people bridge under the plywood joints from underneath. You could take short pieces of 2x6 and screw them in between the joists, then screw the plywood into the bridge.

That's kind of unusual to have the joists that close together. It usually indicates that the original builder was doing that to compensate for a marginally long span or planning on a heavy load on the floor (such as tile, etc). I usually don't span more than 10-12 feet on 2x10's on 16" centers(I'm sure somebody on here will say even less) for a normal load floor, so if they put them on 12" centers (10.5 inches between), and the span doesn't exceed 12' more or less, I think you should be fine on load-bearing.
Ya, that's the only place where it seems slightly flexible. I think I'll just use that subfloor and put 1/2" hardie backer and hope for the best. And yes I'm going to use thinset under and over the hardie backer, then tile. Thanks alot for your patience and expertise.
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Old 10-29-2008, 09:02 PM   #15
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Existing sub-floor


Divine,

In post #9, I said "That's impossible" because you said in post #8 your joists were 1 3/4". I offered the size joists come in, and you misunderstood the entire thing. You still haven't understood the importance of measuring the unsupported span of the joists.

You have been given some bad advice by jay66, I know he thinks he's helping, but he obviously isn't an expert when it comes to tile installation and subfloors. He sounds like a hardworking handyman to me.

The only reason I am trying to correct what has been written here is to help the hundreds or thousands of others that may read this thread for their own projects.

As for you....you can do it anyway you feel like doing it, and as you stated...."hope for the best".

Jaz

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