Waterproofing concrete slab
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| Posted in GBA Pro Help on
I have a large V-deck which four inches of concrete has been poured. On top of the concrete we are planning of pouring four inches of color concrete to finish the deck. Our concrete contractor wants us to put a waterproof barrier between the two concrete slabs and it has been recommended to use 60 mil epdm membrane. This seems like overkill and I was wondering if a membrane is really needed or if there is are any other waterproofing applications which will work. Your recommendations are appreciated.
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Replies
Dennis,
We need more details. Is this deck indoors or out? Suspended or a slab on grade? Is it a floor or a roof?
Sorry, it is a suspended outdoor deck with a cover. It will in the winter may have a little some snow on it but it is western facing so it should melt quickly. The deck is twelve feet in depth with a 1/4" per foot drainage pitch.
One of the products I was wondering if it would work is Hydro Guard SP-1 or a similar type product.
Let me know if you need additional information.
Dennis,
OK, your slab will have occasional snow and rain on top of it. You describe it as "suspended," so I'm assuming that something is underneath it -- perhaps finished indoor space?
It sounds like a roof. You certainly want it to be waterproof. You don't want it to be almost waterproof.
I'm not familiar with Hydro Guard SP-1, so I don't know if that's a good choice. But if you are building the type of suspended slab that you describe, I don't think that 60-mil EPDM is overkill.
If you are building this type of slab, you should be able to afford a layer of EPDM. Otherwise, your design is a stretch, or your budget is too tight.
If your slab has finished space below it, or may do in the future (assuming there's headroom for appropriate levels of insulation) then EPDM is the answer. If not, it's overkill. In either case a good flashing at the house abutment is important. Uneven snow melt can result in ponding at a pitch as low as that, and the flashing is needed to protect the house wall.
most of the deck has open space below it with a garage under about 20% of the deck. thanks for your response
If the rubber is not being glued down, the labor is almost zero. See if you only are paying for material. The coating may be enough for the non garage 80%. Still, Martin posted thoughts that cross my mind often as to costs on this site. Lastly, support your contractor.
my contractor wanted to ask if the membrane used in showers would be acceptable or if EPDM is more appropriate. Also, AJ in the response above stated the EPDM doesn't necessarily have to be glued down. If it is laid and tape sealed does anything additional need to be done prior to pouring the new concrete slab?
I'm still not sure of the reason for the waterproofing. Is sounds like this is a roofing application, in which case EPDM with the correct details at the house--as James says--is a good call.
This doesn't sound like a low-budget project, and it seems like someone with expertise should have designed the details prior to construction. Having the contractors pull it together is not necessarily the best approach.
Simple is moving to complex. Epdm drylaid and flashed is the best. Nothing is the worst. My in between idea may be ok, no internet warranty though. Hiring a professional for a design is worth taking the decisions away and the liability. All projects should have complete details of the construction (but most do not). Put the rubber down glued properly to any flashing. Get a commercial roofer to help if you know one. Detailing rubber is easy (after you do it once with a pro).
Why is an 8 inch slab needed? you could land a 747 on it. I am also wondering if having 2 slabs with a membrane between them is a good idea. I would want to pin them together so they cannot move. Two rocks on top of each other with rubber between them could slide(think of the old slip and slide we used as kids). Dont you want the waterproffing at the top layer? Keep in mind the un protected top layer witll retain some mostiure, its concrete.
Just had anothe thought! You mentioned that part of it is exposed under the deck, if that is the case the snow melt could be uneven because that part of the deck will be the same temprature or colder than the rest of it. (bridges freeze before roadways because of the air movement under them)
I recently used TPO by Firestone with very good results.
http://www.firestonebpco.com/roofing/tpo/