I have recently had my duct work put in the ceiling as my floor vents were rotting after 25 years of water in them. Although i have had sump pump for 18 years, it still happened. Someone told me to place a piece of plywood over the duct opening, dump sand into the vent and top it off with about 4" of cement. With all that said, what is going to happen to the sand and is it eventually going to settle if water is still getting in there?
Denise ~ Enid, Oklahoma
Hi Denise, One of the things I like about residential construction is that no longer how long you have been doing it there is always the opportunity to learn something new, and that's what happened when I read your question.
If I am understanding you correctly, you are saying that your old duct work is in or below your concrete slab? I have never seen that before, it may be a regional way of installing duct work, but I don't understand why they would have done it that way. You say you have a sump pump, so that would indicate that you have a basement. Usually in a basement the duct work runs off of trunk lines installed at the ceiling, and runs up into the main level through the floors and walls of that next floor up. Any duct work serving the heating needs of the basement is usually at the ceiling level or occasionally in a wall.
If you have floor registers in your basement, that mean that the duct work is either in the slab, which would be difficult to do with a typical concrete slab being 4 inches thick, or it is running in the gravel below the concrete, and just coming up through the concrete. That would mean that the other end of the duct work is also coming up from the concrete to get to a trunk line somewhere.
I feel like I am missing something here, and am hesitant to suggest pouring anything into your old duct work without knowing more about what is going on. You need to make sure your old duct work is disconnected at the other end, the last thing you want is to pour sand or concrete into your old floor registers and find out it is going into a trunk line you are still using. I think you should have an HVAC contractor local to Enid, Oklahoma come out and take a look to make sure it is okay to close off that old duct work that is going somewhere below your slab and coming up somewhere else.
If they okay closing it off, and it is indeed going below your slab, I would suggest a very wet concrete mixture, it is sometimes called slurry. There have to be some bends in that duct work, and it might be difficult to close it off with sand or gravel. If it's not closed off completely, there is a chance a small animal could crawl in there and you might never get it out. A liquid concrete can be poured from each end of the duct, and should just flow until the duct is full. It should get just as hard as normal concrete.