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Subfloor over concrete


darinstarr's Avatar
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03-29-06, 10:48 AM   #1  
darinstarr
Subfloor over concrete

Hello,

I need to install a new floor in an attached workshop. The current floor is a level slab on-grade. Ultimately I will be installing ceramic tile flooring.

A few questions-

-I've read that poly film or felt paper should be placed over the slab prior to any framing. Is one recommended over the other for any reason?

-Should I frame the perimeter of the room, then install joists @ 16" oc inside that perimeter?

-What size lumber should be used?

-My room is 13x13 (162"x162" to be exact) For convenience I was going to use 8' boards met in the center, cut to size. I would place a beam in the center where they meet - what method should be used to fasten to that beam?

Thanks for your help with these fairly silly questions. If anyone knows of a relevant book that would help, I'd appreciate any recommendation.

-Darin

 
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03-30-06, 08:03 AM   #2  
There's no better floor for ceramic than a slab. Why install a subfloor in the first place? Since it's a workshop, though, I can understand if you want to do things like run a dust collection system under the floor? Do you want just an insulation type value under the floor?

I guess, ultimately, what you want to achieve with the floor would determine the best way to proceed.

 
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03-30-06, 09:06 AM   #3  
darinstarr
I should have been a little more clear. The room was originally designed/built as a workshop, I will be using it as a music recording room. The slab is also very old, and while generally in very good shape, has a little cracking and some slightly uneven spots. Overall from edge to edge, it is very level. It is not perfect enough though that installing tile directly on it would look or work all that great, I don't think.

 
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03-30-06, 09:31 AM   #4  
Posted By: darinstarr I should have been a little more clear. The room was originally designed/built as a workshop, I will be using it as a music recording room. The slab is also very old, and while generally in very good shape, has a little cracking and some slightly uneven spots. Overall from edge to edge, it is very level. It is not perfect enough though that installing tile directly on it would look or work all that great, I don't think.
would it be possible to flash patch the uneven spots? Like the man said no better surface then a concrete slab to lay tile.

 
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03-30-06, 01:26 PM   #5  
darinstarr
What is involved in flash patching? I was resigned to building a wooden subfloor, but in thinking about it, if concrete is ideal and I can save some money in the process, I am more than willing to at least take a closer look.

I have a couple points of concern that are too difficult to describe without pictures. I'll take some tonight when I get home.

Thanks!

 
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03-30-06, 04:53 PM   #6  
darinstarr
Upon further review, maybe it's not all that complicated, but nonetheless I am not great at descriptions, so here are some pictures:

Outside looking in

Outside the shop, looking in. This pic isn't very useful.

Inside looking out

Looking from the inside out to where the first pic was taken. Note that the slab of the shop is on top of the foundation for the rest of the house, but the shop is not elevated above, as the rest of the house is. Crawlspace access visible under the door. The 'pit' around the door will be framed over and covered with a landing area, with 2 steps leading down to the right.

Cracks

A closer look at one of the cracks in the slab. The crack running top to bottom on the right edge covers about 75% of the width of the room. It is not huge, but something that would need patching nonetheless. They grey primer around the 'pit' area marks roughly the area that would be covered by the landing, mentioned above.

Crumbly stuff

The concrete has broken up a bit in this location, and one other spot in a corner looks similar. Can this type of damage be filled in/repaired effectively?

Feedback is appreciated, thanks guys!

 
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04-01-06, 05:59 AM   #7  
Ok, I see the pictures and there is no way you could tile over it. The cracks are way to wide and you see elevation differences between the sides of the crack. That makes them structural. I'm not a framer, but from what I see, I'd probably do "sill plates" for the joists to rest on to elevate the floor from the movement of the slab sections.

Post the size of the room. That will determine the minimum size of the joists. You won't be able to use a sleeper system, which would be 2x4's laid on there side and plywood adhered to that.

 
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04-01-06, 12:49 PM   #8  
darinstarr
Room is 13.5'x13.5'. The landing area that will cover the pit at the entrance will take up about 1/4 of the room, about 6'x6'.

 
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04-08-06, 12:06 AM   #9  
darinstarr
If I followed that suggestion of placing sill plates on the edges, and another in the center, would 2x4 be sufficient at 16" oc? That would give me an unsupported span of 6 1/2'

 
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