strong joists


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Old 10-06-06, 01:42 PM
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Question strong joists

hello all, i want to put ceramic tile down in the kitchen, butwas wondering if the floor joists are strong enough. i ripped up the floor to the planking, and have to replace about 4-5 of them due to water damage. uppon inspection from the basement the joists seem un affected. they are 2x8 16" oc with a 12' span. should i sister them or just leave wellenough allone. thanks
 
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Old 10-06-06, 02:33 PM
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2x8's 16 oc with 12' span will not support a ceramic tile installation. You either have to shorten the 12' span to about 10' or less by putting a support wall below or you could sister the joists.

Youll need to put a minimum of 1/2" plywood over the planking before you put down any cement board or membrane.

Saw your other question about how to put the plywood down so here goes. Make sure the planking is secured real good to the joists. Put in some extra screws if necessary. Screw the plywood to the planking only, avoiding the joists as much as possible. The idea is to limit the transfer of the joist movement to the upper layers of the floor as much as possible. Avoiding the joists will do this. Screw the ply every 8" in the field and every 6" at the edges. Leave a 1/8" gap between plywood sheets.

Your other question also touched on a mud floor vs cement board. If you can afford the height the mud floor is always better. There is no better underlayment for ceramic tile than a mud floor. Keep in mind that a mud floor will add about 1 1/4" to the height of the floor. It sounds like you tore out quite a few layers of plywood to get where you are so maybe you can afford this height.
 
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Old 10-07-06, 06:14 PM
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Talking

oh boy do i have some work ahead of me......ok ill start by sistering them joists. i saw this new stuff durabond i believe...... better than anything for bond strength. that n some nails and we will be golden. i can afford 1 1/2-1 3/4" inch for the height of the floor,then i would'nt be able to open door...lol. that would kinda cause a problem huh.
thank you for your help, and motavation.
Maria
 
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Old 10-07-06, 07:10 PM
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I would sister the joists. Add 3/4" tounge and groove exterior grade ply. Then another 1/2" ext. grade ply then 1/4" cementboard uderlayment. This would end up being around 1 3/4" from the joist to the top of the installed tile. If the door wont clear the new height it's pretty easy to cut a small amount off the bottom. I have to do it all the time.
 
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Old 10-10-06, 08:08 PM
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A layer of 1/2 plywood over the planking, then 1/4" cement board would be fine.

Man with another layer of 3/4, then 1/2 then cement board they'll be hittin there heads on the ceiling.
 
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Old 10-10-06, 08:23 PM
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I am talking about total layers from the joists. 3/4" directly to the joists then 1/2". That would give you 1 1/4" total substrate which would give you the recommended 1 1/8" I was assuming that all the planking was to be removed which it certainly should be. Sorry I should have started off by saying it might be a good idea to strip down to the bones then sister etc. I wouldn't trust the old "planking" not to pull up or sponge I would replace it with plywood
 
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Old 10-10-06, 09:07 PM
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sorry i am dubble posting.......
hello again all, i finnaly got the floor down to the planking, sistered the joists. when i was repairing the planking that had rotted there was one small section...4"wide and 9"long that the builders never put in place due to the sink drain pipe. my question is if im putting 3/4 tng plywood down with 1/2" 2nd layer ply then 1/2" wonderboard for ceramic tile should i repace that section? i kinda understand why it was never placed in the first place, but will such a small area create a weak spot? its under where the cabinits will be and will have no traffic on it. thanks. ps sorry for the dumb question.
but now that i see to remove all planking.........i have with the old planks 2 1/4" space to fill. i must thank all for the replies ty ty ty (: i reeeealy am clueless. ask me to diagnose and treat a heart attack (god forbid) no problem but demoing a kitchen whew boy.
 
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Old 10-10-06, 09:44 PM
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If you are used to studying medical texts (seems your a doctor if diagnosing heart attacks) then a bit of study might be warranted for taking on this task. Between the prep work and the actual laying of the tile there is a bit to it. Think of it scientifically instead of something overwhelming and you might gain a better perspective on it.
 
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Old 10-11-06, 12:36 PM
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not doctor....just a lowly Paramedic. ( ;
 
 

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