Tile Underlayment


  #1  
Old 02-06-03, 10:02 AM
kstevens
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Question Tile Underlayment

My husband and I are slowly remodeling our house. We live in Maine, Cold winters and Better than Average Summers. We are currently doing the Mud Room/Entry. I really want to tile the floor in the Mudroom. We gutted this and are going to start from scratch, it is a really old house. The Mudroom is above a concrete Basement. To this point, we have pulled up the Subfloor and are down to the joists. The question I have to start with What if the 2X10 joists are not 16 on center? I measured and they are 24oc. I have read numerous posts and everyone says they have to be 16 oc. Is there anything we can do or do we have any options so that I can have Tile in the Mudroom? The room measures 8x8 and has doors at both ends.
Thanks for any suggestions or answers.
 
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Old 02-06-03, 05:55 PM
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Your floor joists DO NOT HAVE TO BE 16" ON CENTER.

But there are some things you will need to do and to adhere to rigidly.

Since you are down to the floor joists you are in good shape so far.

You will need to install two layers of plywood. The first layer should be 23/32" (3/4") exterior glue T&G ply fastened to the floor joists. Face-grain should run perpendicular to the floor joists. Follow plywood manufacturers recommendations for installation.

The second layer should also be 23/32" (3/4") exterior glue plywood installed with 1/8" gaps between the sheets. These fasteners SHOULD NOT penetrate the structural floor joists and should lap previous seems by 1/2.

There are dryset thinset mortar tile adhesive products that will allow you to install your tile directly to the plywood. I personally would not do this. I would also add 1/4 cement board bedded in thinset.

NOW....
There is one other method that will work. And that method is to use a product called DITRA made by Schluter Systems. If DITRA is used, you could reduce the second plywood underlayment requirement to 3/8" ply installed in the same fashion as above. You could then replace the cement board with the DITRA. This method would saveabout 1/4" in height if height is an issue.

The second method would be my preference.
 
  #3  
Old 02-07-03, 04:31 AM
TileguyTodd
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I dont think i would reduce that plywood requirement for 24 " OC Bud. Schluters figures are for 16" OC.
Lets get right down to it and find out what kind of a span we are looking at. I realize the room is 8x8 but what is the longest Span of the joists and what are the joists? Douglas fir?? Look for a stamp on the joist. If there is no stamp then it may have been a locally milled product and up in your country that probobly means spruce.Bud get this info and punch it into the deflectolator(you know where it is)I would do it,but i am headed for Cabo this afternoon and will be gone for a week.Lets make sure we can get that floor to meet l/360 specs.if not,we may need to do some structural work like adding(or sistering) the joists in your tile area.
Span is going to be a big key here.
 
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Old 02-07-03, 01:49 PM
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My concerns are that maybe too much change in elevation of the final floor is a problem besides the reduction in plywood is TCA.
 
 

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