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Flooring on concrete : slope to drain

Discussion in 'Room Acoustics / Studio Design' started by Raffael Cavaliere, Sep 6, 2014.

  1. Raffael Cavaliere

    Raffael Cavaliere Active Member

    My project is just starting. I bought a house and I have a 20' by 17', 16' ceilings garage (which was previously used as a painter studio). The garage is not attached to the house.


    First things first, I need to make a decision about the flooring. As many people, I thought first building a wood deck, two plywoods on top of it, then regular maple or oak wood. But... I read some of the threads here and I figured that this would possibly cause problems and will be expensive just for nothing after all...

    My main problem is that there is a drain in the middle of the room, and a slight slope that leads to it.

    I found something interesting, a company that does concrete painting and epoxy finish for half the price of engineered wood, and it looks amazing :

    Once the concrete is flat and smooth it costs about 6$ fs.

    So... I wanted to have your thoughts about this. What do you think of this solution ?
  2. paulears

    paulears Well-Known Member

    It the floor is fitted with a drain, the first question I'd ask is why? Properties with flood risks or real damp problems have them. You can always batten the floor horizontal, and then timber floor it. The drain would worry me a bit - can it back up and flood your new space if local conditions change? There are also other uses with the battened floor - cabling can be hidden easier and timber is warm. Concrete floors, especially the new shiny polished types can suffer badly from condensation and become slippery. acoustically they're not helpful and if you are going to use carpet to help the sounds, then timber would be much simpler and cheaper.
  3. Raffael Cavaliere

    Raffael Cavaliere Active Member

    Thanks paulears for your comment !

    The room is actually very dry. There is a drain because the guy who build the garage is a painter, and he needed water to clean his brushes (there is actually a hot tank too).
    I don't think water and humidity will not be an issue here. It is actually much dryer than the basement in the house. And there is a check valve (water can't return inside) in the drain. The only way I could get water on the floor would be if the entire garage was flooded.

    As you said wood is a premium choice in terms of timber. So, here is my plan, everybody can feel free to argue :

    Just note that sound isolation is not an issue, at least from the floor. If a second room is added (control room) it will be built on a separate slab at the back.

    So, from bottom to top :

    - concrete
    - wood deck structure (joists) (screwed into concrete ?)
    - plywood nailed to deck
    - another plywood (opposite direction) glued and nailed to plywood
    - regular hardwood (not engineered) nailed to the deck

    Now, do you see a problem with this plan ? Should I fill the deck with sand or any other material ? Should I add some kind of barrier for humidity ?

    If you wonder why I need 2 plywoods that is because the hardwood manufacturer told me that this is a prerequisite for any hardwood (not engineered) placed on a concrete slab that stands directly on the earth.

    That's it, please forgive my accent, but I am French speaking.
  4. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Hey welcome to RO! This is a great site with a lot of smart people. I invite you to this link http://recording.org/index.php?threads/read-this-before-you-post.26684/ Rod Gervais doesn't respond to posts that don't.

    Anyway, in general it's just unclear what your trying to accomplish as an end result.

    As far as wooden decks go your overall plan and building codes would determine what is best overall as a floor solution as whole, not just the finish.

    Relax think about the project as whole, and just start from square one, not somewhere in the the middle. Studio projects get big and expensive Fast, and it's nothing that just gets slapped together, every detail is important.

  5. DonnyThompson

    DonnyThompson Distinguished Member

    Before you do anything, and I mean anything, I strongly suggest that you pick up this book:

    Rod Gervais, Home Recording Studio, Build It Like The Pros
    kmetal likes this.
  6. Space

    Space Well-Known Member

    "Concrete floors, especially the new shiny polished types can suffer badly from condensation and become slippery. acoustically they're not helpful and if you are going to use carpet to help the sounds, then timber would be much simpler and cheaper."

    This is not a fact but merely an observation from Mr. Paul. The Fact is, concrete does not suffer from condensation. But a concrete slab that was never intended to be part of an enclosed environment, like a drive way or sidewalks, rarely have a vapor retarder e.g. 4 mil plastic sheeting, installed before the concrete is poured. So moisture will diffuse into the concrete and create the observation Mr. Paul refers to as fact.

    So how do you tell if your slab has a vapor retarder or not? You place a 3' X 3' piece of plastic on top of the concrete and let it stay there overnight and for at least 24 hours. If you have condensation after this period then you do NOT want to build a wood floor on top of the concrete since you will only encapsulate the area and build a soon to rot floor.

    The drain is already an open area where moisture can migrate up into the structure. If you did anything to the floor you would have to plug that drain. By plug I mean remove what is there, install a vapor barrier that goes underneath the existing slab, and then place concrete into the open void.

    I would never suggest that anyone, you included, install an elevated wooden floor on concrete with out taking the necessary precautions to stop potential moisture issues.

    But if I did, I would warn the owner (you) that you have to take care in order to reduce the real fact that you are creating a drum head with this floor and it will make noise all on its own at whatever the natural frequency is. You could install sleepers and place sand in the empty bays to reduce the air cavity effect.

    "If you wonder why I need 2 plywoods that is because the hardwood manufacturer told me that this is a prerequisite for any hardwood (not engineered) placed on a concrete slab that stands directly on the earth."

    Actually, it is a requirement that the substrate be 3/4 of an inch. But we install 5/8 inch OSB and then 1/2 inch 4 ply plywood as a general guideline and the requirement is met. So that is what that is all about :)

    You can also, once all condensation concerns have been satisfied, place concrete over the existing concrete and get it back to being level and flat. Then you would install indoor/outdoor carpet or use rugs under your mics, etc.
    bigtree likes this.
  7. Raffael Cavaliere

    Raffael Cavaliere Active Member

    Ok let's start this again.

    I want to do a tracking room in my garage. I bought the book and already read half of it.

    I am not new to sound recording, I actually studied in this field, but I am lacking experience when it comes to flooring, ceilings and walls. I recorded lots of people in great halls and nice studios without thinking too much about what was behind the walls or under the floor.

    So, my goal is to build a professional sounding room, in which I could record 1-4 musicians, mainly classical and jazz. There will be a 7' grand piano in this room (I am a pianist).

    I am not very loud, but even if I was, this is not very much an issue since I will be recording rock very rarely. And the building is not attached to the house anyway, the neighbors will tolerate the low frequencies if this happens occasionally.

    Existing floor : 10' reinforced concrete, with vapor retarder, over 12' of 0-3/4 rock.

    But as you know the man who build that garage was thinking about reselling the house, and thought it will be nice to have a drain there in case somebody would want to wash his car... That is the only reason. There is a sink in the garage (which I will replace) that flows into the drain, and the drain is connected to the house drain. Water flows from this drain to the house drain only when it overflows. There is stagnant water in the drain all the time.

    Now reading Space's post I know that I have to get rid of the drain. Maybe I could simply connect the existing pipe to the house drain, and then fill the hole with concrete ? If I let the water flow for about 2 minutes at maximum pressure, the water will go to the house drain anyway. There is a brand new pump in the house drain that does a great job.

    Or should I just do without water in the studio ?
  8. audiokid

    audiokid Staff

    Was the painter a spray painter?

    I am a professional painter and as soon as I looked at the shop, my heart got all warm and fuzzy! I'm betting that drain is really open, working fine for flushing out the dust.

    back to the Op.
  9. Space

    Space Well-Known Member

    " Maybe I could simply connect the existing pipe to the house drain, and then fill the hole with concrete ?:"

    No sir you cannot do that and stop the migration of condensation into the wooden floor you are thinking of building. You cannot even do that and pour concrete over it. Granted we are talking about a small thing, but the small things are what create large problems down the road after time passes by.

    You have to have a contiguous vapor retarder and you do not have that as of this writing. It would be just as easy to remove the drain and fill the void properly as it would to connect it to the house drain...I am certain of that.

    The issue is not the drain...it is the penetration thru the slab that creates an open void from earth to upper levels that exists that the drain is in...that is the concern.
  10. Raffael Cavaliere

    Raffael Cavaliere Active Member

    "You have to have a contiguous vapor retarder and you do not have that as of this writing. It would be just as easy to remove the drain and fill the void properly as it would to connect it to the house drain...I am certain of that."

    I don't understand of what you are proposing... In order to create a contiguous vapor retarder will I need to brake the concrete around the drain to create a bigger hole and make sure the vapor retarders overlap properly ? And then pour concrete in the hole ?
  11. Space

    Space Well-Known Member

    You will need to take the drain out...this will give you access to the earth below. Then you dig it out, find the existing vapor retarder, clean up all the edges and cut a piece of thick mill plastic oversized then the hole is and glue it into place.

    Sounds simply right:)
  12. paulears

    paulears Well-Known Member

    While I agree on the basic concept that the vapour barrier solves the problem of condensation, it fails when you increase the heat in the space quickly, especially when there is no overnight heating. I spent quite a while in a studio space in a TV studio that was a converted scenery store. The floor was semi-polished concrete that never had the proper studio flooring laid due to a budget cut, when it was downgraded to storage. When it was put back into use for a series of programmes needing an industrial feel, the floor at the overnight temperature god very slippery as soon as twenty or so people and the lights were suddenly present, first thing in the morning. I assumed that the temperature difference between air and slab was to blame? If a concrete floor is laid on the barrier preventing moisture rising from below how does this prevent condensation forming on the surface when the air above is at a different temperature and humidity level? Quite a few dance studios have severe condensation problems with mirrors, first thing in the morning when they've been empty over night. What is different in a recording studio?
  13. Space

    Space Well-Known Member


    As an alternative to the vapor retarder method I described above, you can cut the pipe below grade and cap it off, spray for termites and install asphalt into the void and achieve the same results
    paulears likes this.
  14. Space

    Space Well-Known Member

    The difference is that you control an environment that has electronic gear in it, simple as that. A vapor retarder does not fail to stop the migration of condensation from Earth to the cooler side. What you are seeing is that the heat is placed into a cold environment at a rapid pace and the condensation you witness does not come from below the ground...it is in the air.

    I have to go back to my soft drink can analogy to perform this next magic trick.

    The simple principle of moisture migration is "from the warm side to the cold side". It's more dew point and equilibrium but you get the jist I assume.

    Kid gets an aluminum can soft drink out of the refrigerator. BTW, Aluminum is a Class 1 Vapor Retarder. Within seconds of being outside of the cold environment, the can starts to sweat.

    Now you think this sweat is part of the can don't you?

    It isn't, it is condensation in the air. It is the warm side to the cold side I out lined above. The can is cold the room is not as cold and the condensation seeks the coldest side it can find.

    My glasses fog when I get out of my cold truck into the warm Summer air in Grand Bay, Alabama. Same thing, my glasses(plastic lens) are cooler than the air around them and the warm are that is taking the path of warm side to the cold side, hits an hard obstacle, sticks to it and creates the condensation that obscures our vision.

    Now take that analogy and place it on the inside of the structure what happens?

    The gas that creates condensation when moving from the warm side to the cold side will "hit" the solid surface and stick to it. Your Floor and your mirrors are simply my aluminum can.
    kmetal likes this.
  15. Raffael Cavaliere

    Raffael Cavaliere Active Member

    Ok, let's say it is done (will be next week).
    Now I have a room instead of a garage. Some concrete has been poured on top of the existing one in order to make the slab perfectly flat.

    I have two options ( I think) :

    a) paint the floor + epoxy
    b) glue engineering hardwood (probably hickory)

    As you know, the goal is mainly to track in this room, and I will practice a lot in there. I will almost live there.
    I tend to favor the wood in this context, since it feels like I am in a studio, not in a barber shop (as I suspect painted concrete will feel like).
    I am also not very sure of what multiple layers of epoxy on concrete will do in terms of sound wave reflectivity. The girl from the company I told you about came to my place today, and she told me that it will damp the sound. But I doubt very much of this, I think she is saying that because people normally want that.

    Any thoughts ?
  16. paulears

    paulears Well-Known Member

    Er, I understand condensation ok, my point was that plain concrete floors can be slippery and dangerous when condensation happens, which it does quite often when you have a few people in a room early in the day. I was told this was opinion and not fact, so thanks for confirming the fact as valid. Concrete is a pain, especially concrete that has the surface polished.
  17. DogsoverLava

    DogsoverLava Active Member

    As I follow this thread I'm puzzled if the OP heeded the advice about the slab -- confirming first that there was/is an existing vapor barrier under the slab. Second - remove floor drain and repair vapor barrier around drain to ensure slab vapor barrier integrity. Am I right in finding that if the slab is not confirmed to have a proper vapor barrier he cannot (or should not) install wooden flooring over top the slab? So basically vapor barrier or nothing?
  18. Space

    Space Well-Known Member

    "which it does quite often when you have a few people in a room early in the day."

    This has nothing to do with anything. Please remove yourself from this conversation if your goal is to be "right". Human bodies do not create the condensation that you have seen. You see poorly constructed slabs that were not designed to do what I am talking about doing. The heat from the HVAC and the existing cold hard boundaries are all that is needed. People do not even have to be there Paul, for this to happen.

    "Concrete is a pain, especially concrete that has the surface polished."

    You are a pain...and I wish you would get more polished so you could be helpful instead of always wanting to be right.
  19. Space

    Space Well-Known Member

    If the goal were to install a wooden floor system over a concrete slab that does in fact have an condensation issue, then yes you have to have a vapor diffuser retarder under the slab to control the wetting of the slab that will lead to mold and rot of the newly installed wood/sand/insulation, etc.

    No small issue.
  20. Raffael Cavaliere

    Raffael Cavaliere Active Member

    I am not sure if I was clear, but there IS a vapor retarder under the slab.
    There was a big plastic sheet that was covering the whole floor (the guy was painting in there) and even at this time of the year when it is very humid outside, the plastic sheet was dry as a skeleton in the desert.
    And I WILL remove the drain next week, and I will do as prescribed (create a continuous vapor retarder, fill up the hole with concrete.
    I will also add another 3'' of cement on top of the slab, in order to make the whole thing perfectly flat.

    My question now is what I do next !

    I am completely ambiguous : epoxy on painted concrete OR wood ?
    This is a tracking room. It has to sound good... It has to FEEL good too.

    And if I choose wood, should I go with engineered ? Glued ?
    Should I put a sheet of plywood first ? Two sheets, so I can use regular nailed hardwood ???
    Or should I go with floating floor (when I say floating floor, I mean clipping engineered or laminate - no glue, no nails)

    Those questions are not covered in Rob Gervais book...

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