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Waterproof porch floor

2Paul | Posted in Construction Techniques on August 20, 2008 06:28am

I have two covered porches in a new house I’m building in <!—-><!—-> <!—->Massachusetts<!—-> <!—->, and I’m looking for ideas for permanent waterproofing the floors because there is living space below each one.  Currently, I have a layer of  Ã‚¾Ã¢â‚¬ Advantech subfloor on each porch floor, and it is 2 ¼â€ below the adjoining interior floor to allow for building a slope above for drainage.   

 

One porch is in a circular tower, it’s 14 ft inside diameter and I plan to put a single drain in the center.  The second porch is about 7 ft x 13 ft, and I plan to put the drain at the center as well.  

 

My idea is to put a layer fiberglass mat and resin on the subfloor and 6†up the sidewalls to create a robust “shower panâ€, integrate a 3†pvc drain pipe into the fiberglass, then screed thin set (I’ll use high strength non-shrink mortar 14,000 PSI with Nycon fiber reinforcement) on top from about 2†at the edges down to a minimum of ¾â€ to create a drainage slope to the center.  

 

I’ll polish, stain, and seal the mortar to get a great looking water-shedding surface, and place a 2†brass drain and pipe nested inside the main 3†fiberglass drain below.  The fiberglass pan will act as a secondary seal if water gets under the concrete. 

 

My concern is that water will get under the concrete and freeze, causing potential cracking.  The concrete will be in intimate contact with the fiberglass, so there won’t be much room for water to be, but it could happen.  

 

I figured fiberglass, which works for boats, would be more durable and better sealing than PVC or EPDM, because there are no joints.  

 

Should I slope the fiberglass pan as well?  I thought I could step a few layers of plywood and flare it with some bondo to make a sloped base for the fiberglass if needed.  That would also make the thin set a uniform thickness of ¾â€ all around and take off a little weight from the floor.  What do you think?


Edited 8/28/2008 2:29 pm ET by 2Paul

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  1. User avater
    McDesign | Aug 20, 2008 07:14pm | #1

    Seal-O-Flex over Advantech.  No more complicated than that -

    http://forums.taunton.com/tp-breaktime/messages?msg=73188.31

    Forrest

    1. 2Paul | Aug 20, 2008 08:35pm | #2

      Thanks for the info.  I had also found a product called Sani-tred that is similar. I want a durable concrete floor, since this is a porch floor not just a roof.  My concern is that a thin rubberized Sealoflex layer could fail under the concrete someday and leave me with no water seal.  Do you have any experience using sealoflex under concrete?  Would you make a shower pan from it?

      Thanks, Paul

      1. User avater
        McDesign | Aug 20, 2008 09:39pm | #3

        Does it have to have concrete on the top?  How about this SealoFflex top coat

        http://www.sealoflex.com/node/177 ?  It's listed for pool decks and similar.

        Forrest

  2. rnsykes | Aug 20, 2008 11:29pm | #4

    Fiberglass them like they do at the shore. Roof Decks are very common and almost always have living space below them.

    1. 2Paul | Aug 20, 2008 11:57pm | #5

      What do you recommend below the fiberglass lay-up to create a drainage slope?

      1. rnsykes | Aug 21, 2008 12:11am | #6

        Tapered sleepers and a plywood deck. Do you need to drain them to a drain? Or could they just shed water off?

        1. 2Paul | Aug 21, 2008 12:14am | #7

          That's what I was going to do.  I need to drain to the center, so I'll bond the fiberglass to the drain.

    2. 2Paul | Sep 02, 2008 10:35pm | #16

      What weight of fiberglass do you recommend for this application?  I'm inclined to go heavy for extra strength.  I've seen 3oz. up to 50oz. per sq yd.

      1. rnsykes | Sep 02, 2008 10:45pm | #17

        I'm no expert, but when I build surfboards, I use 4-6 oz cloth, so I'd go with a considerably heavier weight cloth than that.

  3. peteshlagor | Aug 21, 2008 12:20am | #8

    Here's the approach I took:

    http://forums.taunton.com/tp-breaktime/messages?msg=91581.1

     

  4. toolbear | Aug 23, 2008 08:34pm | #9

    My idea is to put a layer fiberglass mat and resin on the subfloor and 6” up the sidewalls to create a robust “shower pan”,

    @@@

    If you want to attach fiberglass to a wood substrate, use expoy. It costs more but it bonds. Polyester likes to bond to polyester.

    The polyester resin does not really like to stick to wood, leading to lifting and deck rot in a few years (my previous boat had this over marine ply and it was a common repair issue).

    I recommend the WEST system. They have metering pumps that insure that you get the correct mix ratios each time, without fuss.

    <http://www.westsystem.com/>

    The ToolBear

    "I am still learning." Goya

  5. User avater
    Dinosaur | Aug 23, 2008 10:21pm | #10

    Kerdi.

    Dinosaur

    How now, Mighty Sauron, that thou art not brought
    low by this? For thine evil pales before that which
    foolish men call Justice....

    1. 2Paul | Aug 27, 2008 05:47pm | #11

      I've investigated several options, and here's what I've come up with.  I've discovered it's important to uncouple the concrete finish floor from the wood sub floor, so each floor can expand and contract independently. 

      I've also discovered that admixtures can be put into concrete to make it waterproof throughout the entire concrete, not just the surface.  (I wish I had known that when I was waterproofing my foundation.)  These admixtures are typically used in commertial buildings in plaza floors. 

      I'm going to put down a layer of 6 mil polyethylene plastic on the flat floor and up the sidewall a few inches to act as an uncoupling surface, as well as prevent water in the concrete mix from bleeding out into the wood during concrete placement and curing.

        On top of the plastic I'll place expanded metal lath to help stop crack separation in the concrete. 

      I'll mix Hycrete, Everdure Caltite, or KIM Krystol (haven't decided which yet) waterproofing admixture in to the concrete mix, along with Nycon RSC15 PVA fiber reinforcement (prevents cracks, strengthens, and adds flexibility) into a cement rich concrete mix with .4 water ratio, superplacticizer, and 1/4" max aggregate. 

      I'll trowel the concrete about 1 1/4" thick at the edges and 3/4" thick at the center, giving a slope of 1/2" over 7 feet.  I found that a slope of only 1/16" per foot is typically used in food processing plant floors, and I'm not expecting much water to get on the floor anyway, since there is a roof above, so this shoud do. 

      I'll put 1/4" expansion joints every 45° (room is 14 ft diameter), and fill them with polyurethane caulk.  I'll also leave a 1/4" space to put polyurethane caulk at the outside diameter, and line the outside plywood diameter with Vinyl or Grace Vicor Plus to bond to the caulk and send any water that gets against the wall back onto the floor.

      The advantage of this system is that the concrete is the waterproof barrier.  I can inspect, test, and repair the surface if I find a crack.  All other membrane type waterproofing materials cannot be inspected or repaired after I place my concrete floor on top of them.

      Any comments?

      Edited 8/28/2008 2:31 pm ET by 2Paul

      1. User avater
        Dinosaur | Aug 28, 2008 05:53pm | #12

        It sounds like you are trying to build an interstellar space cruiser to go to the corner store for a litre of milk....

         

         

        Kerdi is not only waterproof, it is an uncoupling membrane as well. That is why I recommended it. It is marketed for waterproofing shower pans and has virtually replaced the lead-pan-and-mud-bed technique. It is quite a bit more robust than the 6-mil 'polyurethane' plastic sheeting you propose to use. (I suspect you really meant to say 'polyethylene'....)

        Attempting to make your concrete floor its own waterproof membrane is an interesting idea, but then you talk about expansion gaps that you'll have to fill with polyurethane caulk so how much further ahead are you? You'll be creating a waterproof concrete 'membrane' that is sliced into pie-shaped wedges and thus its permeable integrity will be at the mercy of the caulking.

        Finally, caulking as a substitute for proper flashing (at your perimeter) is usually a bad idea in the long run.

         

        Take a few moments and call the Schlüter tech advice line before you go any further. In the US the phone no. is: 1-800-472-4588.

         

         

        Dinosaur

        How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....

        1. 2Paul | Aug 28, 2008 07:40pm | #13

          I spoke to a Schluter rep about the options, and they sent me sample of Troba and Troba Plus.  That's where I learned about uncoupling.  Both products are designed to go over a sloped surface. 

          I'm trying to save the labor of creating a circular sloped sub-floor by going with the waterproof concrete, since I plan to slope the concrete anyway.  Also, I only have 2 1/4" to work with, and adding a 3/4" plywood sloped subfloor doesn't leave much left for concrete.

          The 6-mil polyethylene is not going to provide any significant waterproofing, just uncoupling and helping the concrete cure.  I'm relying on the concrete and the caulk for waterproofing. 

          I've seen polyurethane caulk bend and flex incredible amounts and not fail, and since the surface is visible, I can maintain it.  The curved flashing detail at the edge where it meets the concrete is the only part I'm actually worried about. 

          I'm now thinking I'll just use a roll of aluminum flashing, put a layer of foam foundation sill insulation in front of it, pour the concrete, remove the foam and fill with caulk.  On top of that I can run a piece of vinyl base molding, whick has the little lip at the bottom, and caulk it to the aluminum and concrete.

          Edited 8/28/2008 2:27 pm ET by 2Paul

  6. Hudson Valley Carpenter | Aug 28, 2008 07:55pm | #14

    Hi Paul,

    It's a lot easier to read posts which are broken down into small paragraphs.  That'll get you more responses too.

    1. 2Paul | Aug 28, 2008 09:32pm | #15

      You're right!

      I edited my posts for readability.

      Thanks,

      Paul

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