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Ferrocement Educational Forum  |  Ferrocement Discussions  |  General Discussion  |  Topic: Ferrocement over plywood for a floor? « previous next »
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Author Topic: Ferrocement over plywood for a floor?  (Read 2098 times)
nathan
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« on: January 01, 2013, 05:37:22 PM »

My bathroom floor needs replacing.  I need the new floor to be stiff.  It is currently two layers of plywood,   5/8 plus 3/8 I think and the tile has cracks.  I am wondering if I could put down 5/8 plywood and then a layer of ferrocement.  Does this seem like a good idea?  Would it be stiffer?

I can't make the floor much thicker, can I make a layer of ferrocement 3/8 or 1/2 inch thick?  What metal should I use and would the overlap at the seams make tile impossible?

Thanks,

Nathan
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Paul Sarnstrom
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« Reply #1 on: January 02, 2013, 08:23:05 AM »

Hello Nathan,

The short answer to your question is no, a thin layer of ferrocement will not make your floor stiffer. FC in and of itself is flexible. This is especially true for a layer of FC that is not tied to anything along the edges.

If the existing subfloor is two layers of plywood, 5/8" and 3/8" and you are okay with a 1" thick subfloor, then I'd take up the existing subfloor and replace it with a layer of 1" plywood. When you have removed the existing subfloor then you also need to check and see that the initial cause of cracking is not due to a cracked or other wise moving floor joist. Check that there is sufficient blocking betwen the joists, sufficient that is to prevent any lateral movement of the joists. If the joists are rock solid and you have 1" of plywood it should be plenty stiff for setting tile.

Although it is not generally done, you could use some wire mesh like expanded metal mesh [stucco lath] in a thin layer of mortar and then do your tile bedding mortar on top of that. This would help with crack resistance but you need to address the subfloor issue first.

Paul
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Paul Sarnstrom
nathan
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« Reply #2 on: January 02, 2013, 04:59:49 PM »

Thanks Paul, I'm planning to sister the joists, glued and screwed and braced.  I want to make some water tanks and a small shed so I'm looking for little things I can learn something on.  I will find a different project.

Thanks,

Nathan
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Paul Sarnstrom
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« Reply #3 on: January 02, 2013, 06:13:44 PM »

Hi Nathan,

Yeah, that should do it. Usually tile floors don't crack unless the substrate is flexing or shifting. If you do the joists right everything else should come together with the floor.

Paul
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Paul Sarnstrom
philb
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Posts: 203


« Reply #4 on: January 05, 2013, 11:44:49 PM »

Nathan,
I would suggest an alternative-
Use backer board to lay the tile with pressure treated plywood underneath. That is, after insuring the joists are good and sturdy and do not move You can use "X" bracing or a piece of wood such as a 2X12 between the joists. The backerboard is available at Home Depot and Lowes. This will expand and contract more closer to tile.
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