Having completed my first attempts, or as I like to call them, experiments with concrete, I decided that I really needed to find a more versatile way of creating the molds for the rectangular pots. While doing some research, I found this video by ReoFlex which covers how to make a one piece urethane block mold. The mold that is shown in the video intrigued me and I wondered if I could make something like that work with concrete. I drew up some plans and began to build it but it would take me at least a week or two to complete it. In the interim, I carried out further experiments.
Thin walls
On my wish list was the ability to create items with thin walls – 1/8 – 1/4 inches. My first shot at this was done using two plastic containers from the deli section of our local grocery store. I made a fluid mix using the Quikrete Non Shrink Precision Grout and poured it into one of the containers. Then I pressed the other one in and placed some weights into it to keep it from floating up. I used small foam blocks between the two rims of the containers to get a ‘fairly‘ even wall spacing. Here is the result:
First round concrete pot attempt
I was amazed at how smooth the surface was and at how few air bubbles there were. I learned later that this is because of the very smooth surface of the container and the fluid mix. I was not that impressed with the top edge or the consistency of the wall thickness. I had to use a file to grind down the top edge and again realized that I needed a better way to smooth things out.
I decided to try something larger using the countertop mix and an aluminum bundt cake mold. As the countertop mix can not be made as fluid as the grout, I had to press the mix into the mold. Here is the result:
Large concrete bowl / pot – using a budnt cake mold.
If you try this, us a LOT of release agent, I basically destroyed the bundt cake mold removing the pot from it. Fortunately, it was a used one that only cost me a dollar. Note all the air bubbles. This piece is quite heavy and will get used in our garden somewhere.
A thinner mix
The budnt cake mold experiment convinced me that for what I was trying to accomplish, a more pourable (fluid) mix was needed. I did more research and found a local company called National Concrete Accessories. I gave them a call and spoke to a young man named Ryan who was extremely helpful and patient with all of my questions. He suggested I try a countertop mix made by a company in Vancouver called Starpatch Concrete Products. I contacted Starpatch via e-mail and another very helpful man, Bendix, suggested that I try a product called Kast Krete. I had a look at the data sheet … wow! Kast Krete is a specially formulated polymer-modified concrete mix. It can me mixed to a consistency like pancake batter which makes it very easy to pour. It’s white and can be removed from molds in as little as 15-30 minutes. I immediately ordered 2 bags from Ryan as well as a bag of their Counter Mix and picked it all up a few days later.
I decided to start with a small pot and I wanted it to have a drainage hole. This time, I used two Ikea food containers that nested well together. I drilled holes in the bottom center of each container and then ran a screw through the holes and placed a 1/8″ spacer made from some rubber tubing between the 2 containers. I then tightened that up with a wing nut. This gave me a more even wall thickness. Alas, I do not have a picture of that to show you but I drew up this diagram to better illustrate the pot mold.
Pouring mold diagram
I mixed my first batch of Kast Krete and then poured it between the 2 containers. I jiggled it around so that the mix was well distributed between them. Here is the result.
Now we’re getting somewhere! Note the lovely color, the very smooth surface and the drainage hole. And, this came out of the mold in one hour!
Sanding
The top edge was still pretty ragged so I tried sanding it using a 60-grit sandpaper. I just placed the sandpaper on a board, then holding the pot upside down, I made circular motions and that worked very well to remove the jagged edges.
Sanding with 60 grit sandpaper
Pleased with the results of that pour, I made another pot using larger containers and a thicker wall. I added some charcoal iron oxide to the mix – my first color experiment. Here is the result of that pour:
Concrete bowl using Kast Krete and some charcoal iron oxide to color it.
Note that the top edge is getting smoother. Again, I used the 60-grit sandpaper to knock off the jagged edges. Then, I used these!
Diamond Hand Polishing Pads
I found these on ebay from Caliber Stone Tools. They are foam-backed straight diamond hand pads for use on granite, marble, concrete, glass edges and surfaces. The set has 7 different color-coded grits, from rough grinding to final honing: 60, 120, 220, 400, 600, 1800, 3500 grit. For the pot above, I have only used the 60 and 120 thus far. These pads are great! I’ll re-visit this pot soon with the finer pads.
What I learned and what I want to learn
- I can now smoothly sand edges. I need to learn more here but I am well on my way.
- Still – I would LOVE to have a very smooth edge without sanding. In the next post, I will show you what I discovered about upside-down vs right-side-up!
- Kast Krete is an amazing product. I just ordered two more bags. Another white, and a tan. Looking forward to trying the tan.
- Vibrating/tapping/jiggling the mix in the mold is very important if you want a smooth surface and no air bubbles. Here is a pot I made with the Starpatch counter mix that I did not spend enough time getting the air out. It was made using the same mold I used in part 1 – the grey pot. This one has 1/2″ thick walls though. I just made my foam insert 1″ large in all dimensions.
White concrete rectangular bonsai pot – rough finish
In closing this post, I just want to again thank Ryan at National Concrete Accessories and Bendix and his brother Peter at Starpatch Concrete Products. All three of them have been very helpful and happy to share their knowledge with me even though I am a very small customer in the grand scheme.
See you in part 3 where I will show you the evolution of my adjustable mold!
Read more in this series:
Part 1 – Concrete Creations: The Journey Begins
Part 3 – Concrete Creations: upside-down or right-side-up?
Photo Credits
Diamond Hand Polishing Pads – Caliber Stone Tools
All other photos by Gil Namur – All Rights Reserved
Hi, thank you for your blog! Regarding kast krete, I know the instructions say you can de-mold in 15-30 minutes however I waited a couple hours and mine kind of crumbled in the middle of de-molding.
Could this be due to just the heat in the summer or do you think my mix was too runny? I just made a mini bowl so I’m not sure why it hasn’t set after a couple hours. thank you!
Hi Jamie,
Did you use actual Kast Krete? I never had that problem. How runny was your mix?
The folks at Star Patch are very helpful. Perhaps reach out to them:
https://starpatchconcrete.com/contact_us.php
Good luck!
Cheers,
Gil
Hello I am wanting to try to make my own concrete mold! The type I am wanting is just like your 4th photo. Do you know what you used to make that shape?
Hi Samantha,
I used a few plastic salad / fruit bowls that fit into each other. I got mine from a thrift store. Something like this.
Then I just poured to about 1/2 full.
Hope this helps!
Cheers,
Gil
I just made my first concrete bowl using plastic containers. I bought the wrong Quickcrete – had large lumps of aggregate but decided to go ahead. The pot came out with a high gloss inside and out and I can’t find anything online that tackles avoiding the shine. Delighted to have found your articles and I plan on ordering the mixes you recommend.
Hi Jill,
Thanks for your comment 🙂
Indeed, they do come out of plastic containers that way, with a gloss. What I have done is to use a wet / dry sandpaper, 150 – 200 grit, with water, to remove the shine. The faster setting concrete mixes like the ones I mention from Starpatch, as soon as I remove them from the mold, IF I do not want a shine, I use a nylon scrub pad with the item in water to remove the shine.
Hope this helps!
Cheers,
Gil
hi gil,
i love your work. Especialy on the Part 3 the type of mold. I recently tried myself working with conrete planter. But the mold i used made out of silicone which i bought on the market. My Question is
Can i used grout cement instead of concrete cement?
Hi Ridhuan,
Thank you!
I have tried grout on a few projects and was happy with the result. Experiment! And let me know how it goes 🙂
Cheers,
Gil
Those are very nicely finished! It takes work to sand and grind, so I sometimes just ‘accept’ the media’s characteristics and ‘go’ with it. I especially like to dunk fabric/yarn and then form it… Amazing effects can be achieved.
http://www.madebybarb.com/2016/11/03/concrete-lighted-step-spook/
or
http://www.madebybarb.com/2015/10/04/concrete-garden-orbs/
This could make a nice lamp as well. I’ll be watching your projects
Hi Barb,
WOW! NICE work! Very nice. Thank you so much for sharing them with us 🙂
Actually, the mix I use comes smooth out of the mold with very little sanding or grinding. Just the edges, IF I choose too. You might appreciate these 2 posts:
http://lifeasahuman.com/2014/arts-culture/creativity/concrete-creations-a-configurable-mold/
http://lifeasahuman.com/2016/arts-culture/creativity/concrete-creations-concrete-planters/
Let me know what you think!
Cheers,
Gil
I am not sure I can get that mix in my province. Maybe I’ll have to look into another brand of countertop mix. I have embraced the roughness since I like rocks and stones. This will make you laugh:
http://www.madebybarb.com/2016/08/04/live-edge-concrete-bowls/
Better yet would be a way of mixing the colours and having distinct layers! And I dream of some transparent resin layers… (the crazy mind of an artist)
Hi Barb,
Very nice work! I too like the rough edge.
You should check out Shapecrete which you can order from Home Hardware. It is VERY cool.
http://www.shapecrete.com/project-gallery
Some nice videos on YouTube on things that can be done with it 🙂
You can use it like clay or pour it – but it’s a concrete. I have a bucket but have yet to try it out.
Here are some vids: http://www.shapecrete.com/videos
Yes! The shapecrete has been on my radar. Now if I could only get the weather to cooperate here. You’ve got me thinking of some new creative ideas. Thanks for your quick responses.
I hear ya on the weather!
Let us know what you come up with!
Cheers,
Gil
Hi Gil,
I’ve made few things from white cement and the result looks pretty nice. No bubbles 🙂
The only problem is that dust keeps coming off the concrete. Is there something to do to make it stop without painting it?
Thank you
Hi Einat,
Have you tried using a soft stiff brush and washing the piece? I do that with mine and have no dust issues. What kind of concrete did you use?
There are some waxes out there you could try. Look for concrete counter top waxes. That would work 🙂
Cheers,
Gil
Hi
I’m looking to make a mold for a concrete yarn bowl / I can send a picture to you but if you look up ceramic or wood yarn bowl, it should give you an idea. It has a cut out on one side of the bowl for the yarn to pull through.
Do you gave any suggestion on how to make a mold for this or can you be contracted for this?
Hi Biz,
I do not do work on contract. However, if you want to try and make something like this:
http://www.wildernesscreek.ca/uploads/2/6/7/3/2673884/1758279_orig.jpg
Suggest you read this post (Concrete Creations: Concrete Planters) and look at the molds.
http://lifeasahuman.com/2016/arts-culture/creativity/concrete-creations-concrete-planters/
For the slot in the yarn bowl, I would cut a piece of rubber or flexible foam to the shape of the slot and sandwich it between the 2 mold halves.
You could look at this product for the concrete: http://www.shapecrete.com/
It can be poured which is what you will need to do this.
Hope this helps!
Cheers,
Gil
Your post gives some very useful DIY tips on using concrete for creating a pot. Thanks for sharing this post. By reading this post, anyone can create concrete pot by themselves.
I was wondering whether you know of any flowable, fiber reinforced brands in the US. I’m NYC based and trying to find something similar to what you are using
Hi Dina!
When I was searching for this kind of mix, I did find a company called Blue Concrete in Covington, GA. They suggested this:
http://www.blueconcrete.com/gfrc-zfrc-mix-design/
The fellow I spoke (e-mailed) with there is Jeremy French and he had some good info he sent me. The other thought is to contact some custom concrete counter-top companies and ask if they know of any good mixes.
Hope this helps!
Cheers,
Gil
Thank you Gil!
My pleasure 🙂
Gil,
I am loving your experimentation. Having worked in the dental field I am loving your discovery of vibration. When pouring dental models – the model is placed on a vibrating plate (at low speed otherwise everything flies) and the pour is done and allowed to flow through the teeth as the bubbles disperse. The mix is done on the vibrator as well to help disperse the bubbles before the pour.
I wonder if there isn’t some kind of pliable smooth plastic that can be placed between the walls once the pour is done to smooth that surface as well?
Keep it up – fun to watch the progress!
Madelaine
Hi Madelaine,
Thanks! Glad you like it. As for your idea of pliable smooth plastic, wait for part 3 and 4 😉
Cheers,
Gileeeeeeeee