Cement Pots For Beginners?

ShadyStump

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I'm hoping to get around to experimenting with making cement pots over the summer. Anyone with experience have some good resources to study before I over extend myself once again?

I'd like to do more than the simple DIY, two bowls as a mould thing, but that's about all I'm finding on YouTube. The sand moulds might do, but I'd like to be able to make a few if I can get a good design.

One thing I'd really like to work on if I can get that far is textures. For example, I have a large round terracotta pot that's old and spawling on the sides, and I actually rather like the look. How could an effect like that be achieved?

Thanks for any help!
 

Wires_Guy_wires

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For example, I have a large round terracotta pot that's old and spawling on the sides, and I actually rather like the look. How could an effect like that be achieved?
Thin layers of pure cement without the sand could do that trick. Force dry it and it should start chipping, if that's what you mean.
 

Beanwagon

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I made a few last year


There are loads of tutorials on YouTube.

I really enjoy the creative side of concrete pots and was planning to make some more soon.
 

Leo in N E Illinois

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I never made a pot, but I worked in the concrete industry. Some advice:

Do not retemper your.mix, add 75 % or more of your water, then add just enough water to make the mix plastic, easy to work into place. That's your 100%. Add no additional water. If the mix gets stiff after an hour or so, throw it out, additional water after set process has begun will result in weak zones, and spalling when exposed to freeze -thaw cycles.
 

Kullas

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I keep seeing these posts about concrete pots. I guess I'm going to have to make some. I have been trying to stay out of pot making but looks like I'm being sucked back in. :)
 

sorce

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Don't make the pot.

Make the tools that make the pot.

I poured flats for my netting in food storage boxes.

Any nesting containers, like them Russian dolls cuz I'm a Putin apologist would work well.

Sorce
 

Leo in N E Illinois

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I keep seeing these posts about concrete pots. I guess I'm going to have to make some. I have been trying to stay out of pot making but looks like I'm being sucked back in. :)

Concrete pots get heavy quickly as size increases. Look at Viet Nam and Indonesia bonsai, they use very large scale concrete pots, pots big enough they require fork lifts to move them around. Many are poured in place, never to be moved. More like "cement swimming ponds" to quote Beverly Hillbillies.

To keep concrete pots strong and light weight, use of fibers, plastic and or fiberglass, and internal supports and or armatures are crucial. Concrete has great compressive strength, but not much flexural strength, so the reinforcement is crucial.

Home Depot, Lowe's and other big box sell concrete patching compound for vertical patching of concrete. Seek these types of products out, they are hybrid materials consisting of a cement and vinyl or acrylic polymer blend. They'll be strong and resist cracking as pots. Some are cement as powder, adding the acrylic or vinyl as a milky white liquid. Some are totally dry, preblended, just add water. BASF pays my pension, so buy their brand if you see it.
 

Kullas

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Concrete pots get heavy quickly as size increases. Look at Viet Nam and Indonesia bonsai, they use very large scale concrete pots, pots big enough they require fork lifts to move them around. Many are poured in place, never to be moved. More like "cement swimming ponds" to quote Beverly Hillbillies.

To keep concrete pots strong and light weight, use of fibers, plastic and or fiberglass, and internal supports and or armatures are crucial. Concrete has great compressive strength, but not much flexural strength, so the reinforcement is crucial.

Home Depot, Lowe's and other big box sell concrete patching compound for vertical patching of concrete. Seek these types of products out, they are hybrid materials consisting of a cement and vinyl or acrylic polymer blend. They'll be strong and resist cracking as pots. Some are cement as powder, adding the acrylic or vinyl as a milky white liquid. Some are totally dry, preblended, just add water. BASF pays my pension, so buy their brand if you see it.
Thanks I will check it out. Does adding pigments for color hurt the strength? Would adding calcium dust instead of sand hurt it?
 

ShadyStump

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I never made a pot, but I worked in the concrete industry. Some advice:

Do not retemper your.mix, add 75 % or more of your water, then add just enough water to make the mix plastic, easy to work into place. That's your 100%. Add no additional water. If the mix gets stiff after an hour or so, throw it out, additional water after set process has begun will result in weak zones, and spalling when exposed to freeze -thaw cycles.
I was actually thinking on a way to produce the spalling effect without significantly reducing the overall integrity of the structure.
Would intentionally re-tempering the mix and using it as an outer layer on an otherwise finished pot do this, or would you risk the entire layer peeling away over time, losing the effect?
It might just be easier to re-wet the outside of a finished pot part way through the cure, but I don't have enough experience with concrete to say for sure.
Concrete pots get heavy quickly as size increases.
This is the point of hypertuffa, but it's not as durable, lasting maybe a decade the way I hear it. Is there any reason not to use perlite to make it lighter?


On that note, anyone know if you can permanently dye perlite different colors? Then you can polish down the outside of the pot when finished to reveal colored specks. Saw a video where they did this with colored glass.
 

Leo in N E Illinois

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I was actually thinking on a way to produce the spalling effect without significantly reducing the overall integrity of the structure.
Would intentionally re-tempering the mix and using it as an outer layer on an otherwise finished pot do this, or would you risk the entire layer peeling away over time, losing the effect?
It might just be easier to re-wet the outside of a finished pot part way through the cure, but I don't have enough experience with concrete to say for sure.

This is the point of hypertuffa, but it's not as durable, lasting maybe a decade the way I hear it. Is there any reason not to use perlite to make it lighter?


On that note, anyone know if you can permanently dye perlite different colors? Then you can polish down the outside of the pot when finished to reveal colored specks. Saw a video where they did this with colored glass.

Pouring the "structural" main part of the pot, allow it to begin setting up, then adding a layer that has been retempered separately would probably work, if you could make the logistics work. Concrete "sets" by chemical hydration, crystal lattice structures develop as the cement powder hydrates. Water is consumed in this process. Concrete will set under water. The hardening process is a crystal formation process, has nothing to do with drying out. Drying out will arrest, or stop the hydration, but the humidity in the air is often enough to keep the hydration process going, so drying concrete to stop it from setting is not a practical method.

The amount of water needed to complete the hydration reaction to change cement to concrete is so little that if you only added water the chemistry demanded the mix would still look like a dry powder, or at best a crumbly cookie dough. Excess water is added to make the mix plastic enough to place. The concrete then hydrates or "sets", usually in 24 hours you are at about 40% to 50 % strength, at 48 hours typically 75% strength, give or take and then compressive strength continues to climb for years. Slowly approaching, but never quite reaching 100% theoretical strength. (asymptotic curve).

Excess water not consumed in the hydration reactions becomes "bleed water" and will slowly weep out of the concrete through micro-channels. These micro-channels do become the weak points where water can re-enter the concrete and break it during freeze thaw cycling. This is the reason it is important to add no more water than necessary to make a mix with enough plasticity to work into the forms, molds and reinforcing constructions you have created for your project. It is better for the mix to be a bit stiff, than to be soft and runny.

One way to get the surface to "spall off", is the technique used to create exposed aggregate concrete. Create your mold or form to shape your piece. Coat the areas of the form where you want "spalling" or the aggregate to be exposed, coat these areas of the form with corn syrup or honey or a paste of powdered sugar. Sugar will retard the set of the cement paste it comes in contact with. Pour your pot. Allow to set until firm, at least 8 to 12 hours, long enough that it will be self supporting when turned out of the mold. Then use a stream of water directed at the areas where you had the sugar coating. The cement paste should be retarded to a depth of a 1/8th inch or so, wash away the paste at that location, the aggregate should be held in place by the cement paste behind it that was not retarded by the sugar. This trick works better in thicker walled pots. If your walls are very thin, the whole thing is likely to collapse and wash away on you. The original application was a patio would be laid, a colorful aggregate would be troweled into the surface, at the stage where the first bull float and smoothing trowel surface strike is done. Then a sugar solution is sprayed on the surface of the patio. Then a few hours later the cement paste is hosed off revealing the fancy stone aggregate (rose quartz, garnets, etc) that was troweled into the surface layer.

Sand blasting fully mature (90 day old or older) concrete is another way to expose aggregate and with hobby size or machine shop parts cleaning size sand blasting set ups, you can get very precise control of where aggregate is exposed and to what depth the aggregate is exposed.

As I think about it, sand blasting is probably the artistic tool that is far more useful, and easier to control than chemical retarders for modifying the surface traits of concrete. And many machine shops and even hobby shops have sand blasting set ups. Auto mechanics will have the air compressors. Sand blasting is not that hard to get a hold of. Auto restoration and machine shops are the two groups most likely to have sand blasting booths set up waiting for projects.
 

Leo in N E Illinois

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This is the point of hypertuffa, but it's not as durable, lasting maybe a decade the way I hear it. Is there any reason not to use perlite to make it lighter?

On that note, anyone know if you can permanently dye perlite different colors? Then you can polish down the outside of the pot when finished to reveal colored specks. Saw a video where they did this with colored glass.

Hypertufa - point of hypertufa is NOT that it is light weight, the point of hypertufa is that an organic - like shredded paper or peat moss or cow manure has been used to replace a significant portion of the sand and or aggregate. This results in a MUCH WEAKER product, with much lower compressive strengths. Hypertufa absorbs large amounts of water (relative to the amount of peat or shredded paper or straw or manure or other organic material used). This water then makes the surface of the hypertufa a place where mosses and lichens are likely to grow. The water also will freeze if exposed to cold in winter, expand and begin the deterioration process. Hypertufa is used BECAUSE it deteriorates. The deterioration is viewed as beautiful by the cognoscenti that deem it a perfect media for garden décor. The charm is the way hypertufa deteriorates. Depending on the water held by the organics, it can be as heavy as conventional concrete. Mosses, sometimes lichens, and sometimes ferns will grow on the surface of hypertufa. This can be very attractive, and used to good effect in garden schemes.

Perlite is a volcanic glass product, in its raw state it is a type of obsidian with a high water content. It is quarried, then run through a kiln to "pop" it to get the expanded particles. Its heated to about 1500 F or 900 C to get the internal water in the crystal structure of the perlite type obsidian to flash to steam. There are quarries where it is mined in New Mexico. It has been used as a light weight aggregate in concrete mix design but because it floats so easily, it is difficult to keep it evenly dispersed through the concrete mix when dealing with placing truckload size loads of concrete. Using perlite in small batch concrete pots should be less a problem. Keeping the perlite mixed into the mix, is key, it will want to float to the surface.

I have seen dyes for dying the color of the cement paste of the concrete. Your local concrete supply house should stock them, they might be advertised as dyes for mortar, make sure they are approved for use in cementitious mortars. When I speak of concrete I mean type II Portland cement, the most common cement sold to make concrete. Most of what I have said will apply to Ciment Fondue, which is a different material, has a slower setting rate, and is often recommended by Europeans for art projects. Ciment Fondue is more temperature resistant, it is used in foundry applications. I would just stick to Portland cement, but either product will work for most "concrete pot" projects.
 

BonjourBonsai

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@Leo in N E Illinois , once again you restore my faith in humanity! Thank you for so selflessly sharing your knowledge and experience.

I've worked with concrete and made a few concrete pots. For the pots, I used a commercially available mixture called shapecrete. It's got micro fibers that do the job of rebar in larger projects:
https://www.amazon.com/Sakrete-North-America-TV206471-Shapecret/dp/B0128CL62I#

I used plastic containers as forms with vegetable oil as a release agent. The salad bowls from pot belly sandwich shop worked nicely. Unfortunately, I made the walls too thin and the larger ones all succumbed to cracks. The smaller ones have lasted but don't look great. I never added a tint but I generally am not too happy with the look of concrete. I guess if I were more motivated, I could find a design that worked artistically.

I like concrete because, as opposed to plastic or enameled pots, it transpires and allows the water to evaporate thus cooling the roots in summer. Ultimately though, I find the Terra Cotta bulb pans or wooden grow boxes made from left over pieces of lumber just as effective and sturdier.

One thing to remember though is to make sure you've soaked the newly cured pot for a month or so to leech out the caustic stuff.
 

Kullas

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I made one that came out decent the only problem was the sand form slid sideways and I didn't know it. Other than that Its good enough to put a plant in.
View attachment 441250

This is one of the pots that survived. The tree did not make it through last winter unfortunately.
Thats a good looking pot.
 

Joe Dupre'

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One thing about the Asian pot makers on Youtube. They make it look easy. It ain't easy! You don't appreciate the subtle angle adjustments of the smoothing tools until you have one in your hand trying to get a smooth, even finish on wet concrete. The easiest rustic pot technique is the draping method. Soak a towel in a slurry of cement and sand and lay it over ( or inside) a suitable vessel. You can make 10 a day. The most detailed and custom shaped pots use damp sand as the inside form. Concrete is applied to the outside and shaped with different tools. It's by far the hardest technique, requiring skill achieved after quite a few fails. Ask me how I know. :rolleyes:
 
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