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I recently bought a house with a deck that has what appears to be a thin layer of concrete over wire mesh over wooden (2x6 or similar) beams.

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A friend mentioned that he figures the concrete was not poured on thick enough, which is the reason there are tiny cracks forming all down it. The cracks are letting in rainwater and there is a spot where the wood underneath rot a little.

The dark spot you see here is an impression left when I stood on it where rainwater pooled, where there is the rot. (That's the only rot I'm aware of).

enter image description here

I've seen suggestions all over to use Quickcrete or epoxy for cracks in concrete, but the context is always a thick slab of concrete with cracks a half inch wide or more. That's not what I have.

I have an estimate to replace the deck for $4k, but I'd rather not spend it if I don't have to.

What do I do about cracks so tiny on concrete this thin?

(I'm not really concerned about it looking pretty.)

Updates

It's a dry warm climate except for the winter rainy season which was very significant this year. The temperature rarely dips below 32f. The deck is almost a story up over dirt and the A/C and entry to crawl space.

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  • What is your climate zone? How much rain, how much freezing? What is under the deck, interior living space, exposed dirt crawl? If the whole thing collapses how far do you fall - I can see a staircase leading down. – Fresh Codemonger Jun 11 '19 at 6:37
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    I believe you're going to find that the real problem is that the supporting structure allows too much movement under load and the concrete will crack as it flexes. So the only thing that ends up supporting the weight is the wire mesh. Not a good plan, so I recommend you tear this out and do it properly. – jwh20 Jun 11 '19 at 12:27
  • @FreshCodemonger details added. – Kevin Beal Jun 11 '19 at 14:02
  • @jwh20 I'll keep that in mind. I'd like to make this last until we have sufficient resources to replace it if possible. – Kevin Beal Jun 11 '19 at 14:04
  • Can you take pictures of the structure below? The picture makes it look like the surface has deflected 1/2"-1" in the area you walked. If the concrete was poured on plywood and the plywood in this area has rotted underneath I'd worry about the rest of the structural component and the whole thing collapsing. Obviously this was done wrong which leads me to worry about what else is wrong. – Fresh Codemonger Jun 11 '19 at 18:27
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You need a flexible seal Quickcrete will only crack again. A urethane calking would be your best bet to seal the cracks, urethane will flex and maintain a seal (you have 2 forms of flexing one from weight and walking on the deck and the 2nd from expansion heating and cooling) urethane sealant or caulking is the best product to use in this case to seal the cracks and there are colored types that may be a better match for your surface.

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