Author Topic: Concrete or cement over plywood subfloor  (Read 14413 times)

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alcowboy

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Concrete or cement over plywood subfloor
« on: June 08, 2009, 06:04:12 AM »
I know this is way off subject but I need your help.

I am building a screen house to learn some of the building techniques here. I have the floor joists, rim boards, and the beam down the center. The building is 10x15 - 4x4 PT posts with 2x6 framed to the outside perimeter bolted to the posts. There is a double 2x6 beam down the center running the 15 foot length. The floor joists are attached with Simpson Stongties running the 10 foot width at 16 inch on center and each is about 4'9" or 4'11" in length. I plan on putting a 3/4" plywood and on top of that pour a 1 inch thick cement slab. Can this be done or would it not work/adhere or even be too heavy? I have thought of driving nails randomly just below the 1 inch grade to hold the cement to the floor or placing cattle panel wire (thick wire).

 ???

Offline n74tg

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Re: Concrete or cement over plywood subfloor
« Reply #1 on: June 08, 2009, 06:36:40 AM »
If your center beam is supported by columns I can't see why the floor couldn't support the weight of the concrete.  I would however, be worried about undesirable reactions between the curing concrete and the top of the plywood subfloor.  So, I think I would at least put down something waterproof between concrete and subfloor.

Now, that being said, why do you want to put concrete over the plywood?
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alcowboy

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Re: Concrete or cement over plywood subfloor
« Reply #2 on: June 08, 2009, 06:56:31 AM »
I knew that question was going to come up.  :)

Here is my reasoning. Screen house, exposed to weather, don't really want to work with tile or should I say hoping for a cost savings versus tile flooring, IE: backer board, grout, tile, etc., and lastly ease of cleaning and less maintenance.

I thought maybe 1-2 inches thick?????? What if I were to tack tar paper to the plywood subfloor prior to pouring the cement?

Offline MountainDon

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Re: Concrete or cement over plywood subfloor
« Reply #3 on: June 08, 2009, 07:07:53 AM »
or an application such as a screen house, exposed to weather, I believe the desire to have a concrete dloor would be better met with using a poured concrete slab. Poured with a drainage slope to a drain pipe would take care of any water.  We went with PT planks and it has worked fine for us through a few years now; rain, snow etc.


As for tile, that would be a nice floor if made with outdoor rated floor tile. Most, ceramic tile is too porous for outdoor use. Outdoor tile is usually porcelain tile; much harder and will not absorb moisture that when frozen will cause problems.


Just because something has been done and has not failed, doesn’t mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

alcowboy

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Re: Concrete or cement over plywood subfloor
« Reply #4 on: June 08, 2009, 07:20:21 AM »
Too late for poured slab. Plus it would have been SO MUCH more effort. the ground was not level and I did not want to spend the time grading it.  :-\

Trying to weigh my options here.

  • Wood floor - in long run, more maintenance in my opinion.
  • Tile - An option but weighing this cost against cement over the playwood.
  • Cement - easier to work with than tile, but again, questioning.

These are my reasonings. I am still questioning and hunting for answers.

Offline John_M

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Re: Concrete or cement over plywood subfloor
« Reply #5 on: June 08, 2009, 08:09:32 AM »
What about pressure treated lumber covered with and indoor/outdoor carpet?
...life is short...enjoy the ride!!

alcowboy

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Re: Concrete or cement over plywood subfloor
« Reply #6 on: June 08, 2009, 08:11:25 AM »
No indoor/outdoor carpet. Too messy.

Offline rocking23nf

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Re: Concrete or cement over plywood subfloor
« Reply #7 on: June 08, 2009, 08:58:48 AM »
maybe painted wood is your best bet.

maybe you can seal the openings during winter to minimize damage in the off season?



Offline John_M

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Re: Concrete or cement over plywood subfloor
« Reply #8 on: June 08, 2009, 10:36:29 AM »
No indoor/outdoor carpet. Too messy.

 ???
...life is short...enjoy the ride!!

Offline Redoverfarm

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Re: Concrete or cement over plywood subfloor
« Reply #9 on: June 08, 2009, 11:08:40 AM »
Anything less than 2" thick is asking for trouble.  Even if you were able to accomplish it I would go with the recommendations of a drain centered and pitch the concrete to it if it is going to be exposed to the elements.  If it is not pitched the water will collect against the side members and eventiually rot them at the top of the concrete.   

Offline JRR

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Re: Concrete or cement over plywood subfloor
« Reply #10 on: June 08, 2009, 11:45:01 AM »
You could lay strips of roofing felt, or metal flashing strips, on top of the joists ... followed by regular decking.  I like to paint my deck boards with Behr latex.  Space the decking, as usual, to allow easy drying.  Apply some black poly sealer at all board-to-joists connections.  You've got a pretty good floor at this point that should last a long while.  

Then, if you just must have concrete ... I would consider laying on large concrete pavers to the decking.  A resilient poly sealer bed should be used atop the decking ... much like laying regular tile.  Generous gaps between pavers should be installed ... don't try to dam back the water, let it flow thru.

Will it work? ... dunno ... just thinking out loud.

Offline MountainDon

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Re: Concrete or cement over plywood subfloor
« Reply #11 on: June 08, 2009, 12:41:27 PM »
concrete pavers... reminded we that's what we did in a corner of our gazebo where the wood burning chiminea sits. We packed them tightly though to prevent ember fall through.


Just because something has been done and has not failed, doesn’t mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline n74tg

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Re: Concrete or cement over plywood subfloor
« Reply #12 on: June 08, 2009, 06:10:18 PM »
I don't know how "well" this would work, but check out this alternative.

http://www.backwoodshome.com/articles2/lee92.html
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Offline Retiredpoor

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Re: Concrete or cement over plywood subfloor
« Reply #13 on: June 08, 2009, 06:33:52 PM »
What about self levelling concrete? In most cases this material is much stronger than regular concrete and you can pour some types up to 1 in.....

i searched and found this link but there are plenty more

http://www.edisoncoatings.com/html/Self_Leveling_Concrete_Floor_T/self_leveling_concrete_floor_t.htm

Offline MikeT

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Re: Concrete or cement over plywood subfloor
« Reply #14 on: June 08, 2009, 08:53:19 PM »
Remember that Forever Floor?  Maybe it would work here too?

http://www.backwoodshome.com/articles2/lee92.html

Offline rocking23nf

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Re: Concrete or cement over plywood subfloor
« Reply #15 on: June 09, 2009, 10:04:03 AM »
I dont know if self leveling cement will work because when you walk on wood, it moves, so I would think the concrete would crack.

Offline rwanders

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Re: Concrete or cement over plywood subfloor
« Reply #16 on: June 09, 2009, 07:48:33 PM »
When used as you describe, "lightweight concrete" is usually specified----it uses lightweight aggregate that is also a smaller diameter allowing thinner pours. Any concrete company usually offers this option. It is also self leveling.
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Offline glenn kangiser

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Re: Concrete or cement over plywood subfloor
« Reply #17 on: June 10, 2009, 05:23:08 AM »
The apartments I am working on now have 1 1/2 inch concrete over OSB throughout.  They put down #15 felt over the OSB.

They put fibermesh in the concrete gfor reinforcement.

There are a few cracks.  That is going to be the finished floor - polished or stained.
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Offline John Raabe

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Re: Concrete or cement over plywood subfloor
« Reply #18 on: June 10, 2009, 09:36:07 AM »
What Glenn mentions is often done, especially for hydronic heating systems which run tubing through the pour.

Most builders go to a deeper joist to carry the extra weight and add more stiffness.
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Offline glenn kangiser

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Re: Concrete or cement over plywood subfloor
« Reply #19 on: June 10, 2009, 10:34:10 PM »
These are on engineered TJI's or similar.
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Offline poppy

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Re: Concrete or cement over plywood subfloor
« Reply #20 on: June 11, 2009, 08:17:22 AM »
What about forgetting the plywood all together; put down screening and then composite decking?