OBS to Concrete as a subfloor

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Old 12-12-16, 04:12 PM
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OBS to Concrete as a subfloor

Just purchased a condo for the ex. 2nd floor in a apartment complex gone condo.
The sub floor is concrete. I imagine it's concrete over some type of wood base? Just not sure. Anyone have experience with this type of building?

Here's the thing. It had wall to wall berber that I ripped up. Expected wood subfloor, found concrete. There are a lot of cracks in the concrete. 1/4" wide by several feet long. I'm assuming they are not structural or my floor would be part of the downstairs neighbors floor.

She can't have new carpet with her asthma.
There is plenty of room for flooring. The door threshold is 2 inches above the concrete. There is also a slider to the deck with just over an inch of clearance. Yeah, the concrete is not exactly level. A couple mild dips as well.

So, I purchased 700 sq ft of solid bamboo flooring. 3/8 inch thick. Tongue and groove, not click lock.

I have installed many wood floors over the years but never over concrete.
I'm thinking 3/4 T&G OSB secured to the concrete and then use my floor nailer to nail (or staple) it down. How should I secure the OSB to the concrete? Hilti type power nailer? Construction adhesive? Thin set mortar?
Should I use 2 layers of 1/2 inch OSB or plywood layered in opposing directions?

Any other advice would be greatly appreciated!
Thanks.
Mike
 
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Old 12-12-16, 04:30 PM
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Most likely what you are seeing is Gypcrete instead of regular concrete. It is a normal layering in commercial buildings where tile/carpet will be laid. You can skim over the scratches and use the recommended barrier and install the flooring. I would have purchased click lock for the ease of installation and less mess using glue. You won't be nailing the 3/8". It may be time to reconsider the installation method to click lock.

Before we get too deep, post a few pictures of the floor, and if possible pull a floor vent and give us a picture of the layering in the opening. http://www.doityourself.com/forum/el...your-post.html
 
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Old 12-12-16, 05:08 PM
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Gypcrete, lightweight concrete. Ok. makes sense.
There are no floor vents to get a cross section view. All air handling is through the ceiling.
Did a bit of googling. Found it's recommended to use a floating plywood sub floor if nailing down the floor.
But you say not to nail it? Because it's 3/8? Installation instructions state to nail or staple or glue as second choice.
I sure as hell don't want to FTU.
But I do want a solid feeling under foot.
 
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Old 12-12-16, 06:21 PM
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Do you have access to a 3/8" nailer? That will be a big question. Glue would be my last choice. It is messy and more time consuming. I was saying not to nail to the gypcrete. You will need another layer on top of it, and if the consensus is to float it and nail the flooring to it, then that is what I would do.

I hate to beat a dead horse, but in the quest of trying to keep your workload and materials down, using a vapor barrier over the gypcrete and exchanging your flooring for click lock this would zoom. Your plan will require cutting and fitting plywood, then acquiring a nail gun for narrow flooring, then laying it on top of the plywood.
 
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Old 12-13-16, 04:29 AM
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Air nailer access? Yes, but my nailer is for standard 3/4 flooring. Purchased at harbor freight 3 years ago for less than $100. Used it to nail a couple thousand sq feet of oak, SYP and fir. It still works.
Based on reviews I'm planning to buy a freeman mini nailer for $83 at HD.
If it makes it through the entire condo, I'll be happy.
So yeah, time and materials is a factor, but the ex deserves the best I can do for her. I want her to step directly from the hall to the floor without stepping down an inch and a half and I want it to feel like wood underfoot.
The biggest issue so far is removing the crappy vinyl floor in the kitchen and bath. Someone used some seriously sticky glue. Any experience with the HD rental compact floor stripper? The pole scraper is slow going.
Thanks for the tip that the concrete is gypcrete. probably just an 1.5" or so thick.
So, I guess the real question is to secure the 3/4 " OSB to the gyp or float it? If securing, what's the best method? Construction adhesive, glue or mortar?
Thinking my rotary hammer drill and concrete screws is out of the question. Would hate to drill into the neighbors ceiling.
Then use cleats or staples to secure the flooring?
Thanks.
 
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