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Old 04-25-2012, 04:45 PM   #1
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flat cement roof


In general, if you have a structure with a flat cement roof, what kind of treatment and/or extra roofing materials are recommended?

I have a 600 sq foot garage in my backyard that is partially sunk into the ground. The roof of the garage is cement and has a wood deck currently resting on it. It's a pretty sturdy structure--when you are in the garage and look up, there are cement ridges in the ceiling similar to what you'd see in a parking garage.

Other than the deck, there is nothing else on top--no roofing material, just bare cement. When it rains, I have some water seeping through the edges and coming down the inside walls (not ideal, but not so much of a concern) as well as some water coming through tiny cracks near the middle of the cement roof (much more concerning as recently a tiny chunk of cement fell from the ceiling).

I know that there are a couple of different types of membrane roofs that I believe would prevent any water from leaking through the cement roof.

However, I'm reading that cement roofs are fine on their own and just require a little bit of maintenance in the form of 1) patching cracks, 2) cleaning off the fungus, and 3) maybe applying some sort of treatment.

So, do cement roofs require a extra TPO or EPDM membrane roof, or are they fine on their own and just require a little bit of maintenance?

thank you very much

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Old 05-10-2012, 12:43 PM   #2
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Great, thanks for the response. I have now ripped off the wood deck so I can see better what's going on. It's a concrete roof with some topical treatment in some areas. Also it has some tar patches running along the two seams between the concrete panels.

I would like to apply a topical treatment to the whole roof to help waterproof and seal it. Has anyone used Ames Elasto or BASF Kure & Seal? Any other recommendations for sealing a concrete roof?

Thank you very much!
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Old 05-10-2012, 07:35 PM   #3
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I have been dealing with my sisters leaky roof. It also is cement with a coating on it that has never worked. She bought the place as is and this problem along with it. This has been a pita for me to try and fix. The coating route was a total waste of time for me, it failed very fast. Scraping the the loose material off and power washing it and vaccuming it clean as a clean room and recoating it with La Polla Restoration coating was to complete was of time and $. This is the product that was up there when she bought the home.

After dealing with this BS for 3 years we just ended up just doing a base sheet followed by smooth mod bit then a granulated white mod bit.

The existing flat was 15 sq's, sloped poured concrete ( up to 2.50" at the thickest point) over Mod bit. This leaked bad, i was surprised to see the Mod bit under the concrete. I think it was ment to be a deck but it was more a collender .

Sorry for the wall of text, i guess i have little confidence in coatings, put a proper roof on it and be done with it.
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Old 05-11-2012, 07:56 AM   #4
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I'd use a membrane (epdm, tpo, pvc - all three have their fanboys and detractors)) and be done with it for a while. I do some membrane work, but have never installed to a concrete deck. Hopefully someone will come along that has experience in this type installation. I'm sure there are probably some coatings that would work, but I can't recommend any. This post will move this thread back to the top.
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Old 05-11-2012, 08:53 AM   #5
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Originally Posted by seeyou View Post
I'd use a membrane (epdm, tpo, pvc - all three have their fanboys and detractors)) and be done with it for a while.

So I actually had a roofing guy come out to take a look, but he recommended NOT using EPDM or TPO because he was worried that since the garage only lips up on two sides, water could soak under the liner (note how in the far corner of the pic the garage is flush with the gravel.

He recommended looking into a blasted hot rubber roof. This sounds expensive.

So that's why I was looking into a topical sealer.

In general, the cement roof looks to be in pretty good shape. I only have water coming through the seams (three running across the middle, and then on the edges). So maybe I'll just focus on patching up the seams.
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Old 05-11-2012, 09:07 AM   #6
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Originally Posted by naturallight View Post
So I actually had a roofing guy come out to take a look, but he recommended NOT using EPDM or TPO because he was worried that since the garage only lips up on two sides, water could soak under the liner (note how in the far corner of the pic the garage is flush with the gravel.

He recommended looking into a blasted hot rubber roof. This sounds expensive.

So that's why I was looking into a topical sealer.

In general, the cement roof looks to be in pretty good shape. I only have water coming through the seams (three running across the middle, and then on the edges). So maybe I'll just focus on patching up the seams.
Yeah, some proper flashing would be required. I don't see an issue, but I'm mainly in the flashing business.

I don't do BUR (hot tar, not rubber), but that might be a viable solution. No long term solutions for this are gonna be cheap.

You could try sealing the seams. Probably won't hurt anything and it might work. If it's not too much $$, give it a try, but have plan B in the back of your mind.
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Old 05-11-2012, 12:02 PM   #7
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Good stuff, thanks. Any tips for sealing the seams? Any products you recommend? Like a silicone sealant or maybe seam tape?

Thanks again.
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Old 05-11-2012, 10:25 PM   #8
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Your in the same boat i was.

I ended up contimplating covering some of the costs of a full repitch, plywood and 3 layer modbit ect. I spent hours in sketchup doing a 3d render and came up with a good plan, problem was $. My plan would have cost 15 to 25k due to the complex shape of the roof and the HOA BS. I hit her with the numbers and she freaked, the modbit over the concrete was $4,500 for 15sq and she all of a sudden found the $.

Needless to say shes 100 miles north of me, i spent numerous weekends working on it only to have it completely fail both times. I wish you luck, but i fear your spinning your wheels with a patch. Then again, maybe i just suck.

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