More on cement pots

paul11390

Hi all

I received a PM complementing me on my cement pot shown in another post, and asking for info about how it was cast.

As to the manufacturing process, the first thing that is needed is a mold. To date I have always used only a mold. No core, or plug, or inner mold or whatever term you care to use. The mold is actually a plastic container. I have used kitty liter pans in the past. This particular one is a regular plastic container from Kmart that I cut down. Once the container is cut down to the height that you want the outside of the pot to be (plus ¼ inch) it becomes somewhat weak. Making a frame to support it is required. This frame can constructed of whatever material is at hand (in this case, I used ¾” Medium Density Fiberboard (MDF)). The next operation is to drill holes in the bottom of the mold and through the MDF support structure where you want the drainage holes to be in the finished pot. The holes should be sized to fit the outside diameter of a P.V.C. pipe losely, and of adequate size and quantity for the pot, this completes the mold. See first and second pictures. Then, cut the pipe sections to length (the distance through the mold plus the desired thickness of the bottom of the pot.) in my case this was ¾” for the M.D.F. plus 1/16” for the thickness of the container and 5/8” for the thickness of the pot bottom, a total length of 1 7/17”in this case. I will add a note here; take care to cut all pipes equal in length, as they will ultimately control the thickness of your pot bottom.

We also need a way to control the thickness of the sidewall; this can be done with a simple form tool, as shown in picture three. Picture four, shows it in position. (the arrow shows where it hit’s the mold, thereby controlling the sidewall thickness.)

At this point, you have all the tools that you will need except for a “screed” to flatten the bottom surface with. This can be a regular concrete “trowel” or a simple board. It is just scraped over the bottom until it scrapes the top of the pipe sections

As soon as you prepare a piece of ¼” hardware cloth for reinforcing the bottom with holes in it to clear the PVC pipes you are ready to begin pouring.

Hints:

A) The cement will want to fall down from the walls, this can be helped by slanting the mold at a corner. Working two sides at a time.

B) On big molds, pour the bottom first, but only out to the outer most holes. Finish the bottom as you poor the side wall. This will prevent shrink in the bottom from pulling it away from the walls

C) As you use the sidewall form tool, I have found that a outward stroke rather than scraping motion to work best.

D) I have always used; Sakrete Fast Setting Cement Patcher.

In a week or two, you can pull your pot out of the mold. First put a hacksaw blade in the center of the pipe sections and saw through the wall of the pipe, this will release the pressure caused by shrinkage of the concrete. Then take the pipe sections out and turn the mold over onto corrugated cardboard (this will cushion the pot as it comes out of the mold.)

It is now time to put some feet on your pot I have always done this with a simple mold as a secondary process. Picture 5 shows the foot mold for this project, it will cast on one side of the pot at a time. Place it directly on the bottom of the pot and pour concrete into it. The duct tape is just a quick and dirty way to get a good finish on the mold in a hurry. Note how the cuts will allow the mold to be removed easily.

I hope this will answer your questions, if not let me know and I will be glad to help.
Good growing
Paul

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paul11390

Hi
Here are the two other pix.
Good growing
Paul

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MacInOakRidge

Paul,
Do you have a couple of photos of the pot that comes out of your system? And the dimensions? Perhaps a general view and some details of sides, in and out, and the feet.

Also what thickness are you shooting for in the bottom and thickness in the sides? If I missed that in the description, sorry.
Mac

paul11390

Hi Mack

This pot is 20"x15"x 4" outside, the bottom is aprox 5/8" thick and the sides are about 1/2" thick. Can't take any detail pix of the feet, as the pot is now full. The only other pix that I have of the tree are posted here. The cast in holes in the bottom do not show very well, but they are there if you look close. The color on this pot was applied after molding using Minwax wood stain, and a "dry brush” technique with a stabbing action like you would use stenciling. I have been told by a friend that the Minwax lasts ok outside on concrete pots but this is my first with this product. I have also used regular concrete stain with good results. Hope this helps you.

Good growing

Paul

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MacInOakRidge

Paul,
I was born and raised in St.Pete area, actually lived out 66th St. North about 128th Ave. That was woods, wilderness, snakes and ticks back then.

Thank you for all the information. This I something I can put to good use.

You don't have to face freezing of the soil there. I wonder how well cement pots will hold up where the soil turns to a block of ice in the winter time. Cement being porous it may just break and spall into pieces when it gets really cold. Perhaps a way to make the cement impervious to water is out there. You have any input about that? Anyone?