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TinaB 03-14-2012 02:33 PM

Is this enough subflooring support?
About to install 3/8" thick, 12 x 12 granite tile to a kitchen floor that has a hardwood floor already. There is an 1/2" subflkoor of plywood. If I leave the 5/8" thick hardwood flooring on the floor, plus the orginial sub-flooring will that be enough support for my 12 x 12 granite tiles. The floor is very level, but i was wondering would I have to seal the hardwood before applying mastick for the tile. Or would it be better to place backerboard on the hardwood flooring then the tile.

juvi427 03-14-2012 02:59 PM

Are you using some sort of cement board to mount the tiles on? Rhino board or something like that. Not sure if that adds to the support of the floor, or the weight that needs to be supported..?

TinaB 03-14-2012 03:17 PM

I have looked at using cement backerboard, 1/4" thick, but every time I add another layer it adds to the 'step-up' from the floor that is still there...for living room will remain hardwood, but now there is this 1/2 " step-up to enter the granite tiled floor of the kitchen.

juvi427 03-14-2012 06:43 PM

I would move the old hardwood, keep the subfloor and use cement board. The mortar for the tile needs something to stick to. Not sure how it works with mastic?

TinaB 03-14-2012 07:14 PM

Well, those were exactlly my thoughts as well until I started doing research on stone tiles and everyone was making such a important deal out of having sub-flooring that could handle the load of granite and cement board. All these 'experts' were saying to go under neath the house and place more support if I were going to replace the wood with cement board and granite. They thought that the granite would weigh way over the amount that the orginial floor was designed for.
So, that's when I thought I would come to DIY.

JetSwet 03-14-2012 07:52 PM

You have plenty of subfloor from joists up no need to add any more and cement board is not for structure only as a filler to protect your subfloor if tile rails.

TinaB 03-14-2012 08:27 PM

So, you opine is that any house that has 5/8" thick hardwood flooring has a sub-flooring that will be more than enough for 3/8" thich granite floor tile? If this is so, I'll cut the hardwood out with a toe-kick saw and go with 1/4" thick backerboard, then the mastick and then the 3/8", 12 x 12 granite
Any waterproofing that needs to be done to the plywood sub-flooring?

JazMan 03-14-2012 08:35 PM


This is one of those threads where I'd like to throw this espresso cup at my screen. Just about everything suggested so far is wrong. :yes: The only semi-logical post is your #5 earlier today. The rest is JUNK!.


framer52 03-14-2012 08:35 PM


Thinset is your friend, not mastic.

As far as the subfloor is concerned i believe you said you had 1/2". that is not sufficient.

Would I count a hardwood floor over that, no. i would remove and install a 3/4" T&G plywood product . Then thinset 1/4" cement board, then the tile.

Remember, thinset, not mastic!

JetSwet 03-15-2012 05:53 AM

My fault for reading the post wrong, thought it was 1/2" and 5/8 of subflooring didn't see the word hard wood floor.

Regardless 1/2" won't support cement board or anything else for that matter.
So either take the 1/2" up and put 3/4" down or put another 1/2" on top.

oh'mike 03-15-2012 05:59 AM

Let's start at the beginning ---floor joists---

How big---how far apart--what is the unsupported length?(foundation wall to beam.

What you need for a sub floor starts with your floor joists and their spacing.

The hardwood will have to be removed in any case.

TinaB 03-15-2012 07:43 AM

I'm going under the house this morning with a tape measure and flashlight. Since we are talking about kitchen area here, surely the builders allowed for weights of large appliances, i.e. Refrig., stove and cabinet units.
Be back before you know it.
Ears are open

TinaB 03-15-2012 10:13 AM

Is this enough support?
Went into crawlspace under the kitchen

Have joists that measure 7" x 1 - 1/2 with 15" spacing
The loadbearing joist that these attach to is 3 'sistered 9" x 1-1/2"
How can I make this stronger?

TinaB 03-15-2012 10:34 AM

'Is this enough subflooring support?'
Also...need to know where I can measure the exact subflooring thickness. I have looked under HAVAC grids, but were too covered with vent material. Any suggestions with out drilling a hole in the floor?

mnp13 03-15-2012 10:46 AM


Originally Posted by oh'mike (Post 877986)
Let's start at the beginning ---floor joists---

How big---how far apart--what is the unsupported length?(foundation wall to beam.

What you need for a sub floor starts with your floor joists and their spacing.

The hardwood will have to be removed in any case.

That is the FIRST thing that I thought when I was reading the original post. What's on the floor has nothing at all to do with what you can put on the floor. It all depends on what is supporting the floor from underneath.

And please please please don't ruin a hardwood floor by putting tile over it. There are many people out there who will be more than happy to remove the entire floor for you if they can keep the wood that you don't seem to want/care about anyway. (I'm still short on the wood I need for my house, if you're nearby I'll come over and do it! lol ) That will take care of some of the height issue. And whom ever told you that you could attach tile of any kind directly to a wood plank floor knows nothing at all about tile. Wood expands and contracts year round, those tiles would have been popping off endlessly.

Oh - and the Deflectolator is your friend!

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