Hardibacker Subfloor Requirement


  #1  
Old 05-21-03, 09:39 AM
Nascar Fan
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Hardibacker Subfloor Requirement

I would like to install 12x12 ceramic floor tile in several adjoining rooms. My subfloor is 5/8" exterior grade plywood on 16" centers. I have read that your subfloor should be at least 1 1/4" thick before installing the Hardibacker.

I have also read that it would be ok to install 1/4" or 1/2" Hardibacker over 5/8" or 3/4" subfloor thickness.

It seems strange to me the 1 1/4" subfloor is the correct way. That would mean you would have to make a lot of adjustments to adjoining rooms if you wanted the baseboards to line up.

Which is right? (Please, please, please, tell me that it is ok if I install 1/4" Hardibacker over my 5/8" subfloor-with proper thinset mortar underneath it of course)
 
  #2  
Old 05-21-03, 01:20 PM
ee3
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IT is suggested to have 19/32" min. with 16" oc. However your substrate must meet 1/360 ---what is your joist spacing ,depth, length??
 
  #3  
Old 05-22-03, 06:18 AM
Nascar Fan
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Hi ee3,

I have no idea what L/360 is. Can you explain that and how to make sure to meet the requirement?

This is a basement home.

The joists are 16" oc (14 3/4" space between the joists).

The joists are 1 1/2 x 7 1/4. The length of the joist under the dining room is 11'. Then there is a 7 3/4" beam (supported by posts). The joist on the other side of the beam is 14' and this is the area under the living room. There are also areas in between the joists that have braces for extra support.

The interior length of the dining and living room where we would like to tile is 25'.

I am not sure if the information I just gave you is what you want to know, but any information/advise is greatly appreciated.
 
  #4  
Old 05-22-03, 07:28 AM
floorman
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what you have is 2x8 joists on 16 centers that is not eneough to accept ceramic tile without falure in the future.The last thing you want is to have to tear this out because you did'nt beef up the sub floor BEFORE you laid the tile in the first place.Alot of people like to throw out the deflection thing the l/360 for whatever reason,in a perfect world thats a consideration but unless you want to re-build the entire joist system then you need to work from the top and you do that by beefing up the ply-wood sub-floor thats already down,if it were me i would put another layer of3/8 cdx plywood[they are sheets glued together] glued with construction adhesive then screwed every 2 inches on the seams and every 4 to 6 in the field then you're 1/2 rock put in to manufacturers recommendations.do not skimp on the subfloor it will come back to haunt you trust me.You can deal with the base boards later
 

Last edited by floorman; 05-22-03 at 07:43 AM.
  #5  
Old 05-22-03, 07:59 AM
Nascar Fan
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Thanks Floorman,

I am glad I asked these questions BEFORE I started buying materials. If I wanted to lay tile in a smaller area (5x9 or 5.5x5.5) such as the kitchen and adjoining laundry room, will I also need to follow your previous suggestion?

I may need to re-consider what type of flooring to replace the old carpet with.

Thanks again for your advise.
 
  #6  
Old 05-22-03, 08:20 AM
floorman
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yea ,what you want to accomplish is to cut down on the movement of the floor as much as possible.realistically you are not going to rebuild the joists in you're home thats where the L/360 stuff comes in it's the amount you're floor sags or moves when pressure is applied from the top.So what you want to do is to add to the top,the only other concern would be the beam,do you know the span of the joist between the beam? the longer the span the you need to be concerened about the weight that you are adding to the floor above which is about 3 or 4 puonds per square foot,you can also add a liquid latex to the grout to help with the bonding to the tile to cut down or eliminate the cracking that may occure in the grout
 
  #7  
Old 05-22-03, 08:24 AM
Nascar Fan
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Floorman,

Off the top of my head I do not know the span, but with all this information you have given me, I think I will look into a different type of flooring altogether.............maybe hardwood floors.

I am trying to stay away from carpet as much as possible in the higher traffic areas.

Got any suggestions?
 
  #8  
Old 05-22-03, 11:02 AM
ee3
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The for what ever reason, is depending on yor joist system you may not need to add the extra layer of ply wood. Floor joist like roof joist can come with differant loads, and spans in mind. There are differant requirments depending on what you have.. If your joist don,t bow over a certain limit you are Ok for tile.- ie:with a 10' span you can have the floor bow 21/64". this measurement is takin in the center of the span under live and dead loads expected.Also depending on joist spacing may require additional ply wood. The TCA has details for 16",19.2" AND 24" spacing. If you joist are strong enough one layer of ply is ok with 16"o.c. spacing,with cement board on top.I do agree with floor man that more is better, but it may not be needed>
 
 

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