# Flat Concrete Roof Cracks



## o2284200 (Apr 28, 2013)

This is a solid 6 inch concrete roof deck over an enclosed patio.  Started in the Roofing and Siding Forum but it was recommended that I might want to stop by here and get your opinions on how to best approach repair from this point forward.  Thanks in advance, your time is greatly appreciated! 

*BEFORE* 






*AFTER* 
This is as far as a 4000 psi pressure washer got me.


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## nealtw (Apr 29, 2013)

Have you figured out what the different layers are?


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## o2284200 (Apr 29, 2013)

I'm only guessing on most of  this but from top to bottom...

1) Some kind of water-proofing paint and/or membrane.
2) The big crack looks like it's been patched with a concrete or patching material.
3) The black stuff...I have no idea...some kind of sealer, primer or adhesive?
4) Then the six inch poured concrete block.


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## nealtw (Apr 29, 2013)

I still think would be to cover it with a vinyl deck membrane. The trick would be to make it smooth and take the adesive to stick it down. You may have to sandblast it before you patch the cracks. What ever you do, you want the new product to go up behind the siding for 6 inches.


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## o2284200 (Apr 30, 2013)

I'm hopeful to get to the point where all I have left to do is cover/coat it & flash it.  Right now, I'm concerned with how to get from this point to that point.  The 4000 psi pressure washer would not take up anything else so I'm unsure what would be the next step with old patch & black stuff?


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## nealtw (Apr 30, 2013)

Unless someone has a better idea I think sandblasting is the way to go.


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## o2284200 (May 1, 2013)

Thanks!  All helpful opinions on how to best approach this repair from this point forward are greatly appreciated.


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## BridgeMan (May 2, 2013)

I don't know what climate zone you're in, but I'd be tempted to install some composite deck planks, directly onto the existing surface and oriented "downhill", using a compatible adhesive.  Only doing so if the  existing surface is sound and not likely to further deteriorate, of course.


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## nealtw (May 2, 2013)

Bridgeman, This deck also has exposed rebar on the edge. Suggestions?
http://www.houserepairtalk.com/f34/concrete-flat-roof-leaks-15089/


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## nealtw (May 2, 2013)

http://dragonfly-construction.blogspot.ca/2012/07/resurfacing-old-concrete-pool-deck.html


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## o2284200 (May 2, 2013)

BridgeMan said:


> I don't know what climate zone you're in, but I'd be tempted to install some composite deck planks, directly onto the existing surface and oriented &quot;downhill&quot;, using a compatible adhesive.  Only doing so if the  existing surface is sound and not likely to further deteriorate, of course.



Tropical climate entering rainy & hurricane season.    If the existing surface is sound and not likely to further deteriorate, what would you do with the cracks before installing composite deck planks directly onto it?


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## BridgeMan (May 2, 2013)

Cracks should be sealed (after thoroughly cleaning, of course) with either polyurethane or possibly a low-modulus epoxy.  Vee-ing them out with an angle grinder will provide more purchase area for the sealant.  You could lay down some bitumen mastic sheets after the sealant has cured, to provide some extra protection.

Depending on the extent of rebar corrosion, a major repair or even complete replacement may be in order.  Being close to an ocean is often hard on reinforced concrete structures, because of all of the salt in the air permeating into the concrete.  If there are just a few isolated areas of exposed/corroded rebar, such could be repaired by sandblasting to near-white conditions (and adding some supplemental bars if significant section loss is evident) before applying dense concrete patching material.


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## o2284200 (May 6, 2013)

BridgeMan said:


> Cracks should be sealed (after thoroughly cleaning, of course) with either polyurethane or possibly a low-modulus epoxy.  Vee-ing them out with an angle grinder will provide more purchase area for the sealant.  You could lay down some bitumen mastic sheets after the sealant has cured, to provide some extra protection.


Thanks!  How much of the old black stuff & concrete patch do I need to take out?



BridgeMan said:


> Depending on the extent of rebar corrosion, a major repair or even complete replacement may be in order.  Being close to an ocean is often hard on reinforced concrete structures, because of all of the salt in the air permeating into the concrete.  If there are just a few isolated areas of exposed/corroded rebar, such could be repaired by sandblasting to near-white conditions (and adding some supplemental bars if significant section loss is evident) before applying dense concrete patching material.



The only outwardly visible rebar corrosion is under the soffits (drip edge would've been nice) almost directly in between the 2 cracks on the roof deck.  It's obviously been patched before and similar patch appears to take up most of the soffit area.  The close up pics show the worst 3 areas on the soffit, as far as I can tell.


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## nealtw (May 6, 2013)

What happens if the steel is exposed to moisture and air it will rust and expand  and break the concrete. So the idea is to remove all the loose concrete and rust, you won't know what you have until you get there.


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## BridgeMan (May 7, 2013)

When making any crack or concrete repairs, a good rule of thumb is to always remove every bit of unsound, loose or dirty material.  Otherwise, your new repair product has nothing decent to adhere to.  "Make it clean enough to eat off of", I always told my inspection techs and concrete rehab contractors.


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## o2284200 (May 8, 2013)

Thanks! So, as for Vee-ing them out with an angle grinder...  Going back to the roof deck and the large oval shaped crack; the 4000 psi pressure washer removed as much of unsound, loose or dirty material as it could.  How much more of the old concrete patch & black stuff do I need to force out OR am I just trying to now clean up the edges to provide more purchase area for the sealant?


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## nealtw (Jun 13, 2013)

Have gone any further on this mess?


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