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Raised concrete deck

47K views 10 replies 6 participants last post by  Gary Garrison 
#1 ·
So a house I'm doing had originally called for a wood deck off the rear. About 1200 square feet. Owner liked the woodgrain stamped pattern concrete sidewalks on the front so well he decided he'd rather have the same on the rear deck. So, having never done a raised concrete deck, I started sniffing around and came up with a plan. Here's what I have:
Deck is just below slab level. Brick ledge is three feet down. So we bolted a 2x12 ledger at the proper height to the slab. Poured a footing 8' off the house. Double 2x12 beam sits on 6x6 posts every 4' on said footing. Joists come off the house and cantilever over the beam by 2', for a 10' deck. At this point I had the rock guy lay 8" block from the brick ledge up around the joists and stop level with the top of the joists. Then we decked with 3/4" plywood but just overlapped the block by 1/2" or so. Deck was built to engineered specs to hold 2 1/2" of concrete. Not lightweight concrete. Normal stuff, I think 6000 psi with fibers. Also going to put wire grid panels in the concrete. All the lumber is treated.
That's where it now stands, and I can take pictures if I need to.
Does this all sound right?
What is the best way to waterproof? I planned on the concrete filling the block when we pour. So any membrane on the plywood will have to stop before it hits the wall. After it's poured, rock will lay on the concrete and go on up the wall. Thus the need for block down to the brick ledge.
Any thoughts will be appreciated.
If it sounds crazy, tell me. I want to do it right the first time, so if I need to alter my plan, now's the time.
Thanks.
 
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#2 ·
It sounds o.k, can you post your design? If you haven't waterproofed a deck before, I would sub that out to a waterproofer. Are you sure fiber reinforced concrete can be stamped? Are you subbing out the stamping to someone experienced in it? You don't really need it fiber reinforced if you only want a 6000 psi mix. Fiber reinforcement is needed to bring it up to around 20,000 psi. You can add more sacks to the mix, maybe some plasticisers to get 6000 psi. The concrete plant can design the mix for you.
 
#3 ·
Curious here, why not use lightweight concrete? Seems like it would be a better match for a raised deck, but then again I've never been around a project like what you're describing.

Anyway, the concrete will be easy to get to 6000 psi without any fiber reinforcement. Around a 0.32 W/C ratio with a high-range water reducer will do the trick.
 
#4 ·
Don't have a drawing. The lumberyard I use has an in house engineer and he specked out the package. 2x12's on 16" centers. 3/4 inch plywood. It's all actually been subbed out. I've gotten input from my framer, rock guy and stamped concrete guy. All very experienced and quality subs, not fly by night hacks. They've all been a little different in their recommendations, and what I'm doing is kind of a hybrid of all the info I've gotten. My stamp guy has done similar, but the waterproofing is what's a little different. Do I need to run it over the block all the way to the wall, and then flash up the wall. Once it's poured, it will have rock laid. The concrete guy was of the opinion that I just need to seal the decking, and don't worry about flashing to the wall. I'll post a pic in the morning. That might help. Thanks.

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#5 ·
The only reason to not use lightweight concrete is price. It's more difficult to supply apparently, and the consensus of everyone I've talked to is that 2 1/2" of regular concrete works as well. My main concrete guy has done several like that with good success. He's not doing it, cause he doesn't stamp.

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#9 ·
I'm thinkin' maybe you could pour a small curb, fill in the block prior to the slab pour. Then handle it like through wall flashing. You most definitely want to flash up the wall approx 8". Also, maybe a rubber roof system for the main deck. Tough call there.
 
#10 ·
Waterproof, waterproof, waterproof, waterproof did I say waterproof yet? Although this is low to the ground and a failure would likely not kill someone I have seen a failure on a 10' high deck with a patio below. They water proofed the surface, however the stucco crew messed up just slightly when they detailed the beams and it caused a leak. This in turn rotted the beam horribly. It had not fallen yet, but I was quite nervous to be under it while checking it out.

The major problem with a concrete deck (besides the fact that they are fugly, even when stamped) is the perception by owners "It's concrete, it will last forever and I never need to think or worry about it." That is exactly what happened with the 1 I looked at, they told us that the stucco kept falling off the beam and they had a stucco guy fix it like 3 times. I knew I had to see it so I came and took a look... Like I said it was scary.

Did I say it needs to be waterproofed properly?
 
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