Backfill settling under new concrete deck - advice needed

[Dirk]

Depends on the construction of the joint, but typically it's encased in whatever expansion joint material is used. In my case whatever they'd used was long since gone, and there was a 1/16"-1/8" gap where the expansion joint material had been originally. There were 4 pieces of rebar I encountered when I cut out a section of my deck to add a water feature wall, and they all were rusted about 1/3 of the way through at the joint. The rust didn't seem to penetrate very deeply inside the decking, and I didn't mess with the bond beam to see how far the rust had penetrated there. Best I can tell, the pool was constructed between 1979 and 1984, and the rebar did its job admirably. It kept the decking from moving laterally into or away from the pool, but allowed it to tilt without anything cracking when the soil settled over the years.

OK. I see. It does corrode, but takes a long time. I thought I heard somewhere that rust actually helps inhibit rusting. It becomes a sort of protective coating. Obviously not an impervious one, but maybe enough to slow down the process.

It makes sense that rebar would tie pool to deck, otherwise, what's to keep the two from misaligning. Like maybe the deck would eventually slide over somehow, and one side would touch the shell (or coping) while the other side had a large gap. So the rebar keeps the two aligned, but without the concrete bond the rebar gives enough to allow expansion/contraction. Something like that?

 

[blakeusa]

You turn the pool decking rebar to pool she'll rebar for electrical bonding. I would want an expansion joint between the she'll and the deck. I expect the deck to eventually crack. Did they use wore mesh in the deck. If so that would make it more secure.

Again poor compaction is the root cause and I would want some material pumped under it because it is new and should be corrected now

 

[PoolguyinCT]

Miner Jason has nailed it again. It is not a steadfast rule to separate pool & decking.
Some like to use what we call a “slip sheet” to segment & tie the steel between the two.

To say one is right or wrong, without application, engineering or site details will mislead readers.

 

[delrayser]

Thanks everyone for the feedback, much appreciated. On the expansion joint issue, there is a joint in between the gunite shell and the decking, at least at the surface (I don't know how far down it runs). It's currently filled with some sort of foam separator, the PB told me they'll pull that out at the end and put down some sort of mastic between the coping and the decking. I assume that would encase whatever rebar goes between the shell and the deck, assuming it isn't encased in the concrete itself if the joint doesn't cut all the way through.

Agree that the issue is one of poorly compacted backfill and the deck shouldn't have been poured over this area, and I'm not comforted by the "oh the shell will hold it up" explanation. PB is coming out today to look at it with me, I'm going to push hard on him to get some sort of fill injected under there. Will report back.

 

[Dirk]

Thanks everyone for the feedback, much appreciated. On the expansion joint issue, there is a joint in between the gunite shell and the decking, at least at the surface (I don't know how far down it runs). It's currently filled with some sort of foam separator, the PB told me they'll pull that out at the end and put down some sort of mastic between the coping and the decking. I assume that would encase whatever rebar goes between the shell and the deck, assuming it isn't encased in the concrete itself if the joint doesn't cut all the way through.

Unless it's now encased in dirt or sand. Perhaps that's what the "foam separator" is doing, keeping the joint from filling with dirt and debris...

Good luck with the PB today!

 

[bmoreswim]

Usually the foam separator has a tear-off perforation which allows the top portion to pull off and leaves an appropriate sized opening for the mastic while providing a backing so not so much of the mastic is needed. Not ours mind you, but often that is the case.

Hopefully you get some news to make your ears happy from the PB.

 

[delrayser]

Just to close out the thread - I spoke with our PB and he was adamant that there isn't a structural issue with the portion of the deck over the settled backfill and "you could drive a truck over the deck" and it wouldn't break or settle because of the rebar. But I wasn't satisfied with that, mostly because if there is an issue it probably won't show up for several years and by that time I won't have any recourse. So he agreed to fill the void when we get the final landscaping done.

Thanks again for the sanity check, it's nice to have folks who will let you know you're not being unreasonable in these situations.

 

[Dirk]

Ha, ha. I just tried the "You could park a car on it." defense in another thread. Didn't work there either!!

Glad to hear you got the resolution you were after.