View Full Version : Advice needed for 450 gallon water tank foundation

04-15-2011, 03:29 PM
We have ordered two 450 gallon, rain water catchement tanks to collect water at the back of our house to water our raised beds. The weight of each tank when full of water should be just under 3900 pounds. The company representative recommends a 4"slab with rebar to support the tank, no further installation instructions are provided. In order to get sufficient gravity feed we need to raise the tank 2 feet off the ground with sufficient support for the bottom of the tank. I wanted to use keystone wall blocks stacked up in a circle to raise the tank to the proper height, because one fellow on another forum did that but with a 300 gallon tank and it looked really nice.
He used some type of gravel to fill the inside of the ring, don't know what kind? The tanks are at:
http://www.plastic-mart.com/class.php?item=3698 (http://www.plastic-mart.com/class.php?item=3698). The tanks are due to arrive next week and I'm concerned about proper installation. I do not know what type of gravel to use, and I think sand would/could too easily be washed out from under the tank, plus I'm not sure if I could use it with a cement base or even need to?
Any suggestions as to what to fill the rings with or any ideas on a different way to support the tanks would be greatly appreciated. I'm concerned about doing it correctly to avoid the bottom of the tank breaking and it looking nice.

04-15-2011, 04:06 PM
Just to get the discussion started --

I don't know where you live, but here, the key concerns would be earth settling over time and frost heaving. You'd need to make sure the supporting pillars are well below the frost line and big enough to support the weight. Granted, only two tons to support, but you need to make sure the compaction under the piers distributes the weight adequately.

Seems like plain old river gravel or even pea gravel would work fine for filler. I wouldn't spend much money on it, it's only filler.

I wouldn't worry too much about the tank, similar tanks I've seen and used can handle 4"-6" gaps in the base they sit on. Obviously, 100% bearing surface is better, but not really needed unless the plastic gets warm and soft.

Edit: Oh yeah -- after you get the base built and the gravel in, with the base plate ready to go on, get a can of that expanding foam to spray between the gravel and the plate. It's amazingly tough stuff that resists compression, and will fill any gaps between the gravel and the plate, allowing a very uniform load on the plate.

04-15-2011, 04:39 PM
I'm in south Ar. and the tanks will be on the north side of the house so they will only get morning sun. DH wants to go with gravel but me being a worry weeny think we should use cement. If we use cement we would have to mix it ourselves bc of the minimal amount required for delivery. He has bad shoulders and does not want to use cement. I just don't want to screw up the base and waste the $$ we spent on the tanks. Basically he says that you confirmed what he told me about the base. I thought that every small space not filled in would result in a cracked or broken tank.
I'm going today to try to get the stuff to set them up with and I'll pick up some foam too. I hope we can get these set up correctly the first time with no major problems. Thanks for the tips and recommendations.

04-15-2011, 05:38 PM
Just to put a fine point on things--

The tank is 45" in diameter. Pi x r^2 means that you have about 1600 sq in to support ~4000 lbs or water, or 2 1/2 pounds per sq in. That is a pretty light load -- you can support more than that with a toilet paper tube standing on end.

Bottom line is, so long as your support is solid and passes the weight to good footings, you shouldn't have much to worry about.

05-19-2011, 05:57 PM
I wanted to update ya'll on the water tank adventure. The tanks were delivered on May 5 by Saia :(Trucking. (BTW, if you ever have anything delivered to you from them and it is damaged so that you have to reject it, be sure you file a claim report with them or else you get stuck with it. Does not seem fair but that is how it was explained to me. They will then have 30 days to review your claim.):confused:

One tank was punctured clear through on the bottom by a forklift at Saia Trucking (plastic-mart did not have them in or on a crate) so we refused it and notified both parties. The good tank we have now set up and are waiting for the rain that is due to arrive by Friday. For the base we decided on using concrete to fill in the center of the rings so it took 18- 80 pound bags. We mixed it up 2 bags at a time because our wheelbarrow is kinda small. Meanwhile we are still waiting on tank 2 or at least word of it's delivery.

Yesterday we finished up the base for our second tank that we are still waiting for. We decided to go an extra 2 rings high for it so we used 27- 80 pound bags of concrete. We had to make the outer dimensions larger on the first ring of the base to assure enough width for the top ring to accomodate the tanks large bottom. The base for both tanks looks nice and that is important to us, but if I had it to do over again I would have done it different. I would not have ordered through plastic-mart.com!!
They are terrible to do business with!!!

After numerous phone calls today to plastic-mart.com sales rep, (Scott Silvey) trying to find out when we will be shipped our second tank, it seems they dropped the ball again by forgetting to send us our second tank! They recieved $744.90 from us on April 15 for the 2 tanks and shipping charges and after that we seemed to have been lost in the shuffle somewhere. Our first delivery was delayed due to their poor processing of orders which we suspect is why the tanks were shipped without a crate? When I talked with the sales rep today,(Scott Silvey)he was at a loss for an explanation. His story then morfed into I had to wait for my second tank because Saia had not paid for the tank they damaged, even though plastic mart had not even bothered to file a claim with Saia , I checked with Saia myself on the phone! Bear in mind it has been over 2 weeks since the damaged tank was rejected and we still have not heard anything from them, we would still be waiting till the cows come home had we not called numerous times today! I called Saia to see what I could do to hasten the process and they said either us or plastic-mart had to file a claim and none has yet to be filed! I guess that is what Scott meant when he said it was not his fault or our fault it was the trucking Co's fault the tank was damaged and we just had to wait.

The bottom line is plastic-mart has lousy service! I only hope after spending $744.90 that the tank is of good quality. I also hope we don't get screwed out of the second tank we paid for. I'm still waiting for word from plastic-mart.com!:mad::mad:

05-19-2011, 06:34 PM
I'm sure sorry to hear about your problems with Plastic-Mart. I hope their tanks are better than their sales and service departments.

But, on the bright side, your foundation will last a long, long time! Even if the tank falls apart. <G>

05-19-2011, 07:27 PM
I know thats right for sure!! When we finished pouring the second one yesterday, I was exhausted! We considered using gravel for the filler but as high as we had to go with the rings for the tanks we both felt better using concrete, even after pouring it all, just real tired and worn out. We sat out and had one of DH homemade brews last night to celebrate even though it was not Friday, we had to admire the base we made. We both had a potato beer and came to the same conclusion you did. LOL
Those bases will be there for a very long time, and pretty too!

I just got an e-mail from plastic-mart saying my second tank will ship out today! I checked with the freight co they are using this time, (Yellow) and she confirmed it. I told her my story and she said some freights have that policy but said yellow files its own claim and makes good for the product to the consumer. She said, had it been shipped through Yellow originally, I would have recieved my second tank within 7 days from the first one.

I will steer everyone I know away from plastic-mart! I pray the tanks will last a few years anyway, but guess we'll have to wait and see.

05-23-2011, 12:14 PM
Squeaky, I am so sorry about the experience you have had at Plastic-mart.com. While I am sure nothing I say can make up for the lack of service you have received, I am hoping you will contact me directly with any additional problems or request for quotes. My Name is Travis Calvert I am the Sales Manager with Plastic-mart.com. I will be having a talk with Mr. Silvey and in the future if you choose to use us again I will take this experience into account when quoting you the best price available.