subfloor--fir or spruce, does it matter? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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09-16-2001, 11:03 PM
we are installing 13x13 tiles in a room 14x26 previously done with 3/4 osb we are going to use 5/8 spruce for the subfloor, we were told that the spruce was not as moisture resistant as the fir and that the tiles would probably lift, what do you think? help?

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John Bridge
09-17-2001, 05:43 AM
Hi Georgie,

Fir is a little stronger, but spruce will work fine. You will need cement backer board over either, though.

There will be others along to explain it further. I'm on my way to work. Hang tight.


John Bridge
09-17-2001, 04:44 PM
Hey, somebody please jump in and tell Georgie about cement backer board.

Rob Z
09-17-2001, 05:27 PM
Hi Georgie

Fir is indeed more stable and water resistant than pine or spruce. The only way I would advise anyone to set tile over a plywood floor is to use Schluter DITRA on top of the plywood and under the tile.

You can read about Ditra at

Whether you use Ditra or cement board, we need to know what the joist size, span, and spacing is under you floor.

Also, do you have a Home Depot or Lowes in your area? HD usually stocks Durock and Wonderboard. Lowes (here in VA) usualy stocks Hardibacker.

We'll wait to hear back from you.


09-17-2001, 05:55 PM
Hi Georgie,

Yes,plywood has been promoted as an underlayment for ceramic tile.However,amongst the boys here(who only encourage high quality installations)it is not recommended.

Please don't listen to what the guy at the hardware store is not an acceptable method for a long term installation.Years ago I actually did a few jobs over exterior grade spruce,but it is a hit or miss venture.May fail in two weeks,two years or perhaps never.Why gamble with a tile installation though?

The Schluter product that was mentioned is an excellent solution and underlayment that has many technical advantages over other substrates.Look into that and forget about directly bonding to plywood.

The locations of the pros on the forum here range from Australia,Canada(B.C. to Ontario),Continental U.S.(from FL. to CA.)and it is safe to say that they are unanimous on the plywood subject.

09-17-2001, 06:35 PM
Hi Rob, I believe the joists are 16" spaced. Is the biggest concern movement or moisture? I have been reading that no less than 1 1/4 inch thickness of subfloor is needed. The room we are doing is a livingroom without much traffic.
I live in Canada and the nearest supply centre is Totem.

Rob Z
09-17-2001, 08:06 PM
Hi Georgie

I must confess that I don't know much about Canada, so don't know if where you live is a place with lots of product selection.

The concern is actually BOTH movement (we call it deflection in the tile business) and moisture.

Moisture that gets in the plywood subfloor causes the wood to swell. Fir is more stable than spruce or pine, meaning it doesn't swell, warp, check, split etc as much as a less stable species of wood.

Ron summarized it correctly when he said going over plywood is a hit or miss type of gamble.

Ditra has some properties that have been engineered into the product that cement board can't provide.

Cement board is an excellant choice, when properly installed over a good substrate, and gives a good masonary surface to bond the tile to and just plain makes the floor feel more solid.

We need to also know how big the joists are (example: 2 x 10's ) and the span (distance from one side of the joist to the other, or from supported end to supported end).

I'll check back in later.


PS To all my Canadian friends: even though I don't know much about your country, I hope to come and visit someday! The closest I've been is seeing some of the Canadian teams play the Capitals here in Washington, DC.

John Bridge
09-18-2001, 05:37 AM

We have Canadian members, Ron and Bri in the Toronto area, Harry in Barrie. Tileprof in Vancouver, B.C. Did I miss anyone?

Someone should be able to help you find materials.

09-19-2001, 06:17 PM
Hi Georgie,

When I was in Calgary I visited the Totem supply stores.Similar to Home Depot and Revy,but I preferred Totem.They carried my favourite thin-set mortar there:Flextile 52 for about $20/bag.

So yeah,Totem is a good source for the materials you'll need.Just don't rely on them for tile advice.