Deflect-O-Lator and Subfloor questions [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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11-24-2009, 09:02 AM
I used this tool but it seems to only account for deflection in one plane (Along the joist). It does not take into account the subfloor laid on top of it. Won't a sturdy subfloor "Help" or minimize the deflection? It most certainly impacts the deflection across the joist, won't it impact along the joist also?

Sub-floor height question:

I have some thin plywood in place now (Builder put in) and laid incorrectly (with the grain in the same direction as the joists). Rather than pull it up entirely, I plan to go over it perpendicular to the joists with something like 1/4" or 3/8" plywood. I then want to add in Suntouch Warmwire radiant floor heating, which will add in another 3/8" of floor height. The new floor will be about 3/4" higher than before, so what is the best way to handle that big of a transition?

My reason for asking is I have 2x10 constuction that is 16" OC (No idea how long joist span is). floor is over a garage and i am planning for a marble (travertine floor) and don't want it to crack.

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11-24-2009, 09:12 AM
The Deflect-o-lator doesn't consider the subfloor, just the joists. While there is some help when considering the subfloor thickness in evaluating the joists, we feel that the results the deflecto gives are conservative and more than adequate for judging a floor structure from long distance.

We recommend following the underlayment manufacturer's recommendations for subfloor thickness as a minimum .

Considering your floor, I think your plans are less than minimal. Even if the subfloor was 3/4", it is effectively only about 1/2" when installed with the face grain parallel to the joists. 3/8" plywood can help some, but cannot completely erase the twin mistakes of using too little plywood and installing it in the wrong orientation. I'd cut it out and install 3/4" plywood or OSB properly, then continue with your installation plans (assuming there is an underlayment in the mix).

Height transitions may be made using different matierals and practices, but you gotta give us some hints as to what's next to the tile area (unless you did in another thread someplace).

OK, you done snuck in and added the travertine part. Cut out the old plywood and replace with 3/4" Plywood or OSB with face grain (long direction of OSB) across the joists. Install at least 3/8" plywood or OSB on top of that, oriented the same way. Install your underlayment, then heat mat. If using Ditra, install the heat mat first, then Ditra.

Find out about the joist spans before you do anything else. Could save you a ton of work if the joists are not stiff enough for stone.

11-24-2009, 09:51 AM
The plywood is the subfloor in this case, so the current total thickness is very low (I have not measured but say 3/8").

So the recommendation is (If I understand correctly):
3/4" Subfloor (Plywood or OSB) - Laid perpendicular to joists
3/8 plywood underlayment -Laid perpendicular to joists (Overlap joints)
3/8" Radiant floor heating

Problem is that brings the floor up 1.5". (More if I use ditra)

The floor transition is a double door (6' wide) and is currently hardwood floor which is at the same level as the existing finsihed floor.

11-24-2009, 09:59 AM
You can make you second layer of subfloor as thin as 3/8" if you use Ditra as your underlayment.

What heat mat are you using that's 3/8" thick? Many mats are only 1/8" thick, and installed, not much thicker.

The hardwood floor is 3/4" thick, and the subfloor under it is 3/4"? As I see it, your stone floor will be about 1-3/4" to 1-7/8" thick, only 3/8" higher than the hardwood.

11-24-2009, 10:15 AM
I was planning on the Suntouch Warmwire system for the radiant floor.

11-24-2009, 10:21 AM
Consider a mat. It may be more expensive, but it will be thinner.

In any event, your floor will be 1/2" to 5/8" higher than the harwood if you use the Warmwire.

11-24-2009, 10:28 AM
My understanding about mats is that you need to begin and end at the same location, that is a bit of a challenge with my layout.

11-24-2009, 10:33 AM
Have you contacted the tech support folks at some of the mat manufacturers, such as Warmly Yours? Tell them your design constraints and let them configure a system around them.

If you have, forget I said anything, and go measure your joists.:D