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Subfloor buildup options

| Posted in Construction Techniques on August 17, 2002 03:55am

Greetings all carpenters who have way more experience than I!!

I am preparing to remodel my condo’s kitchen, and I am going to have to do a complete flooring redo in order to satisfy my anal retentive qualities.   The condo is an upstairs, one bedroom unit with an original plywood subfloor on the joists with a mortar bed of about 1.5 inches.  I have already done the bathroom, in which I put in a new layer of 3/4″ plywood over the old subfloor and then placed 1/2″ concrete backer board on top.  I intend to do the kitchen the same way for a tile floor.  The problem is that the kitchen will intercept a very significant portion of the rest of the living area, and I do not want to have a change in elevation from one room to the next.  I already know that the mortar under the carpet, especially in high traffic areas is fractured to all get up. 

I presume that the purpose for the mortar bed was to be a sound deadener for the downstairs unit, but I might as well, so it’s got to go.  Originally I thought that I would probably just put in a layer of 1/2″ and 3/4″ plywood the rest of the way throughout, but I am second guessing that idea since I don’t know if there would be anyway to keep the floor quiet enough.  So, I had a brainstorm the other day, and I thought that possibly I could use some 1/2″ furring strips over the joists and then set in 1/2″ pink rigid insulation between the furring strips, and then follow with a new quasi-subfloor of 3/4″ CDX. 

Is this idea feasible?  Are there any other ideas that I should consider?

Thanks a ton for the help!!!

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  1. User avater
    Mongo | Aug 17, 2002 07:57am | #1

    First...not to be a nag...but does the condo require any specific methods of floor construction to minimize sound transmission from one unit to another.

    Okay...nagging over.<g>

    Consider using Homasote Soundboard as part of your flooring sammich. There are many methods to create a quiet floor, Homasote is one of them, and is easy for a DIYer.

    I'd advise calling Homasote's 800 number and talking to a representative. Give them your joist sizing/spacing, the type and thickness of your finish flooring, and what the overall thickness (from top of joists to top of finish flooring) you have to play with. They'd be more than happy to help you make a quiet homasote sammich. Tell them you're a DIYer and they'll work with you.

    Tile is the worst for minimizing sound transmission. Be judicious in your construction details.

    1. Redfly | Aug 18, 2002 01:15am | #2

      mongo, you took the words right out of my keyboard. 

    2. nandress | Aug 18, 2002 09:23pm | #3

      Mongo,

      Thanks for the hint!!  Sounds like some great stuff and might be just the ticket.  Would you use the the fire retardent type, or is just the regular Homasote good enough?

      Otherwise, the tile is just going in the kitchen, carpet everywhere else.  And I once had a window salesman walk out on me without even letting me look at the windows he was selling, because he didn't even want to talk to me about windows without knowing what the condo association would allow.  Imagine, a salesman who refuses to sell!!!  That company will never be allowed in my door again!!

      Once again, thanks for the help.

      1. User avater
        Mongo | Aug 23, 2002 06:37am | #6

        I suppose I could be mistaken, but I was under the impression that pretty much all Homasote structural products are made of recycled paper, a wax or paraffin binder,  additives for pest control, and a fire retardant.

  2. archyII | Aug 19, 2002 04:05am | #4

    I don't understand "I already know that the mortar under the carpet, especially in high traffic areas is fractured to all get up." Does this mean the existing mortar bed is fractured? What is your plan for the final finish floor for the kitchen.  A reinforced mortar is recommended by TCA for tile installed over a plywood subfloor.  A properly constructed mortar bed (right amount of portland to water, correct sand and reinforcing) provides a stable and flat surface for tile (or most any finish). The mortar bed has no impact on eliminating sound transmission (other than low freq.) in fact it will increase impact sound transmission (walking on a tile or wood surface especially with high heels).

    1. nandress | Aug 19, 2002 06:28am | #5

      Yes, the existing mortar bed is fractured in many places.  It moves under foot if you step on certain pieces.  When I did the bathroom, I had to do a minor repair to an area in the entry to the bathroom where chunks had to be removed.  I am also fairly certain there is not any reinforcement in it.

      The final finish floor in the kitchen only will probably be tile, though I haven't ruled out vinyl for possible economic reasons.  I was going to screw down a new layer of 3/4" CDX and then do a layer of 1/2" cement backer board.  A new mortar bed is beyond my scope of ability.

      If the mortar bed was not intended as a means to deaden sound transmission, what would its purpose have been?  For the original floor, the perimeter of the condo was surrounded by 2X4's, including all holes for drains, and then a bed of mortar was spread throughout.  There was never original tile, just carpet and vinyl.

      Edited 8/18/2002 11:29:40 PM ET by NANDRESS

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