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02-28-2017, 01:09 PM
Planning to install wood grain tile in the second floor of my house. I hired a company to remove carpet in the bedrooms and tile flooring in the bathrooms on the 2nd floor of my house.

There is paint over-spray, from where the original painted wall was sprayed, onto the plywood substrate. I planned to use a belt sander to remove the paint or install 1/2" plywood or backer board onto the existing plywood and install the Ditra and tile.

Problem is that I noticed the floor-joists measure 24" on center, not 16" or less.

Is this going to be a possible structural problem? What is the BEST solution to do this job correctly? Ideas please..!

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02-28-2017, 01:18 PM
Aside from the spacing you need to check the unsupported span of the joists and their size to calculate deflection.
Just an FYI but cement board does nothing to strengthen a floor, it is merely a backer to adhere tile.
What do you have now for ply? Tounge and groove? Thickness?

02-28-2017, 02:07 PM
I need to pull up one of the current plywood pieces and see it's thickness. Also, I am not sure of the unsupported joist length and beam width.
I will check both. I am in the process of hiring a structural engineer to come over and give me their thoughts on what I will need.

02-28-2017, 02:18 PM
If you have any hvac vents in the floor you can pull the cover and check that way with less effort. You may have yo pull a nail or two that is holding the duct work there.

02-28-2017, 02:26 PM
The plywood that was installed is 3/4". Joists are 24" OC. Cannot tell what the unsupported span is, but the greatest distance between any 2 walls is 14' in the Master Bdrm.

02-28-2017, 02:28 PM
So far, I think the best plan is to install 1/2" - 3/4" plywood over the existing floor to strengthen it for the tile install... just not sure about the support issue on the floor and walls..

02-28-2017, 04:09 PM
Welcome, Jeff. :)

You need to determine what you have for a joist system. If you have no access at all you can drill a hole or two with a three or four-inch hole saw and look down in there to get a look. Easy enough to patch later.

At 24" spacing I'd expect you to see engineered joists of some sort. That may make it more difficult to determine your actual design deflection, but it will almost always ensure that the floor meets building code of L/360 or better.

You will then need to install a second layer of at least nominal 1/2-inch exterior glue plywood over what you have, then your tiling substrate of choice.

My opinion; worth price charged.

03-01-2017, 03:48 PM
After removing a plywood panel upstairs... the floor joists are 24" OC and 2'x12" manufactured joists.
That being the case, I feel the 1/2" exterior plywood install should be sufficient. Would 3/4" ext plywood be overkill?

Do you recommend any type of levelling solution between the existing plywood and the additional plywood install?

03-01-2017, 04:26 PM
Nothing between the layers, if you plan to use a SLU or pourable underlayment that will go over your 2nd layer of ply.

03-01-2017, 10:14 PM
Unless you're going to remove the base layer and make the existing joists all perfectly in level plane, any leveling must be done on top of the final plywood layer. It's somewhat unusual to have engineered joists and then not have them straight. Is there a load bearing wall under there that might be jacking the things up?