Instructables

Faux concrete ultra-lightweight pot

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Maybe you've seen those pots in the stores that look very heavy but are in fact very easy to lift?  I think this is a great idea, however their prices are still unreasonably high. 

Here's one way to make a large lightweight pot that could pass for being made of concrete on casual inspection. 











 

 
 
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Step 1: Why bother?

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I wanted to plant some things and went to get my favorite large pots from the backyard, but look what happened to them!  I pondered how to fix them and decided I would just try to make something new.

Well sure, it's a lot less effort to just go buy a pot, but I always wondered if I could mold things out of spray foam insulation, and after a few tries, I found out that I could.

It remains to be seen how long it will hold up to the elements and whether plants will tolerate being in a pot made of polyurethane foam.
Ninzerbean1 year ago
One other thing I want to add is when it is really hot outside, say in the 80's, the foam drips and drips - and it gets on everything and yes I got it in my hair and had to cut it out.
foobear (author)  Ninzerbean1 year ago
yup! been there!
PS1182 years ago
I'd like to do this, but I'd want to do several matching ones for all around my deck.

The problem is I don't really want to buy a jillion cans of "great stuff". Is there a way to get this foam stuff more cheaply -- like by the gallon or something?
foobear (author)  PS1182 years ago
Not sure about that, but if you find a good deal somewhere, let us know
It comes as a two part mix, you can google it under casting with expandable foam, lots of youtube videos.
saturnengr2 years ago
I found this to be a great idea for duplicating a hard-to-find pot for my wife, but I also found myself wondering if I could use it for other tasks. It seems that, properly painted and protected, that this would make a nice method for forming other solutions also. The foam core seems to be used both to provide a smooth boundary for the foam as well as the strength to resist the expansion of the foam, forcing it evenly into the spaces between the form. But I believe you're destroying the form each time.

I was hoping you could comment on a way to reuse the forms. Perhaps a wooden form covered with wax paper or even plastic (you can get big, cheap rolls of plastic), allowing the wax paper/plastic to be destroyed when you remove the forms, but leaving the wooden forms for use again.

In my case, I was hoping to make about a half a dozen of the same mold, which would be a small trough-like planter about two feet long, but only about 6 inches or so high. I can easily make a mold out of wood from hobby store then cover the wood in wax paper/plastic and make about one or so copies every day. In this manner, each copy would be nearly identical.

In any case, thank you for the wonderful idea.
foobear (author)  saturnengr2 years ago
You're welcome. I have heard that this type of foam will not stick to plastic trash bags, so if you can devise a method to line your mold with that type of plastic, you might have a reusable mold there... Good luck and let us know how it turns out. Thanks for your comments!
jlyvers7432 years ago
This is a fantastic idea and your instructable is very clear and easy to follow. Have you filled any of these with dirt and watered the plant, to see if it can withhold the weight? Thank you for posting.
foobear (author)  jlyvers7432 years ago
See the last step. I planted them today and I will post pictures of their progress over time
foobear (author)  jlyvers7432 years ago
Thank you! I was making sure all the paint was dry first. I'll probably try that tomorrow and post a pic.
Cambenora2 years ago
Excellent 'ible, RaisedByRobots!

I think polyurethane foam is a fantastic material, but you're right, there are some precautions that should be taken, particularly the flammability. Take it from one who has found himself knee deep in a pool of flame - do this outside, with no flames anywhere nearby!

For the curing time, before inserting the inner frustrum, try spraying the foam with water, using one of those misting sprayers you use for ferns and such. Just use a little water. This will speed up the curing time. It may make it foam a little more as well. Reacting with the moisture in the air is what makes it behave the way it does.

Incidentally, for those playing at home, make sure the foam you get is polyurethane. There are water based acrylic foams on the market which, while intended as a non-toxic, water based alternative to the polyurethane, actually behave in a completely different way, and would not be suitable for this particular task. Once dried, (it doesn't "cure" as such) it has the consistency of sponge cake.
foobear (author)  Cambenora2 years ago
Interesting, I may try the water spraying next time. I'll also be looking out for that water based one.. Does it have a name? thankx!
The water based one is Selleys Space Invader. That's an Australian product, so I don't know whether it would be available in your part of the world. But there's sure to be an equivalent.
BTW I'm not criticizing Space Invader (in case any Selleys people are reading ;-). It's advantages are: non-toxic, non-flammable and easy to clean up using water. You'll probably find these things written on the can. That's how you can tell you got the non-polyurethane one.

jim_lewis12 years ago
it's a nice effect and good result, but I suspect you'll find issues with water/soil working its way through the sides.
However you could of course just put the soil in a plant pot inside this pot to avoid this issue.
If you were so inclined you could also embed LED lights, (or anything really) into the pot prior to forming
foobear (author)  jim_lewis12 years ago
Sure, it still needs to stand the test of time. I'm more concerned about sunlight and exposure wearing it down too. Solar powered led night lights is a great idea too.