When we bought the house our propane tank in the back yard was sitting on four rocks instead of a more traditional concrete slab. The rocks had settled over the years so weren’t level anymore (assuming they were ever level), so we decided to remedy the situation by pouring a small concrete slab for the tank to sit on and retiring the rocks with honors.
We timed this project with the amount of propane we had left in the tank. Moving a full tank is not advised for the many reasons you can easily imagine, so we waited until we were down to about 10% full. At that point a friend of mine here in town (thanks, Dennis!) brought over his backhoe and helped me lift and move the tank out of the way. The propane tank was previously perpendicular to the fence, and I wanted the concrete slab to be parallel to the fence just to tuck it back out of the way a little bit. We lifted and rotated the tank out of the way and temporarily reconnected it to the gas pipe going to the house:
We then prepared the slab location by digging out all the rocks and weeds, and then dug the dirt out down to about 4 inches deep. I measured the tank and built a rectangular concrete frame out of 2×6’s (the frame was about 2″ bigger than the propane tank in both dimensions.) We put the frame down and leveled it, securing it with steel stakes:
After leveling the frame we added some dirt and tamped it down solidly. In wetter locations gravel is recommended, but it’s dry enough here in southern New Mexico that drainage underneath the slab usually isn’t a problem. The final thickness of the slab will be about 5″ thick…probably overkill for the weight of this propane tank, but that seems to be the way we roll.
Next came the concrete mixing. We used standard Quikrete 5000 psi concrete in 80 pound bags we bought from Home Depot, and it took almost 16 bags of concrete to fill the frame. One mistake we made was not renting or borrowing a concrete mixer: I decided to mix it by hand in a wheelbarrow, 3 bags at a time. This was not only extremely tiring, but also the bottom layers of concrete were starting to cure by the time I got all the concrete mixed and added to the frame. It worked out ok (barely), but I would definitely recommend using a concrete mixer for a project this size. If the day had been any hotter or I had mixed the concrete with any less water I think we would have had a problem. As it was, though, it turned out alright:
To level the concrete I first used a wood 2×4, then used a steel finishing trowel. I had never poured a slab or used a trowel before, but thought it would be easy. It turns out it was pretty difficult for me to get a smooth, level surface (it probably didn’t help that the concrete was drier than it should have been.) Eventually I got it reasonably smooth, but I’m sure a professional concrete person would have done a much better job. Good enough, I suppose.
I also tried to get fancy by rounding the edges of the concrete using an edger (rounded edges help prevent chipping), which didn’t work out well at all. Again, I thought it would be easy: just run the edger around the edges and you are finished, but again I was sorely mistaken: the edger kept pulling out small rocks and chunks of concrete, and the finish wasn’t anywhere near smooth. I suspect the concrete was way too dry, and my total lack of experience didn’t help. Here are how the edges turned out…good enough, but not great:
After my sad attempts at finishing the concrete surface, I decided it was probably best to stop messing with it. I covered the slab with a tarp to slow the loss of moisture, and misted the slab with water over the next 5 days as the slab cured. After removing the tarp:
A couple of notes on the wood frame: I didn’t use any kind of release agent on the inside of the frame (various people on the Internet recommended everything from mineral oil to varnish to keep the concrete from sticking to the forms.) My forms released without any sticking.
Also, I waited 5 days to remove the forms. The typical recommended time is 24 hours or so, but I never could figure out if people pouring slabs removed the forms so quickly because they needed them for other jobs or because there was some technical reason, such as the concrete sticking, etc. By luck or something else, my forms came off easily after 5 days:
I waited another week or so for the curing to continue before moving the tank onto the slab. My friend with the backhoe tolerated my almost compulsive need to have things centered, so after using a tape measure to figure out where the tank should go on the slab he skillfully put it down right where it needed to be. The propane tank in its final resting place:
Other than a few glitches with the concrete this turned out ok. I suspect nobody other than me will ever notice the slightly crappy concrete job, and the propane tank looks better and is definitely more stable than it was before, so this project is