Concrete pot

[maroun.c]

Looking great.
Can u share the cement/sand ratio you use ?

 

[Woocash]

Pretty well. The only bummer is the amount of cracks I had along the outside edges.
View attachment 327066

I plan to repair these sections ... or maybe I just leave them in disrepair, especially since I plan to put a weathered old (looking) oak in there.

Yea it will certainly suit a gnarly tree. I like it though, but I know what you mean if it’s not exactly what you were going for. I guess you can’t really give it any real pressure or vibrations when trying to settle the mortar down. Maybe try an electric toothbrush to massage the lolly sticks? Or glue them to some MDF or plywood so you can make a more rigid mould, perhaps.
I don’t know your skill level, but I imagine trying to repair each section without looking like it was repaired or without losing the definition would be pretty tough. Kudos though, very creative.

 

[John P.]

Yea it will certainly suit a gnarly tree. I like it though, but I know what you mean if it’s not exactly what you were going for. I guess you can’t really give it any real pressure or vibrations when trying to settle the mortar down. Maybe try an electric toothbrush to massage the lolly sticks? Or glue them to some MDF or plywood so you can make a more rigid mould, perhaps.
I don’t know your skill level, but I imagine trying to repair each section without looking like it was repaired or without losing the definition would be pretty tough. Kudos though, very creative.

I actually used a massager on the exterior after the “pour,” LOL:

 

[Krone]

I am planning to use the sam guide as you did. The thing i am still researching is the sealer or some protective coat between the concrete and the soil. And, I am also interested about the ratio of the cement/water/sand an also, what kind of sand did you use?

 

[sorce]

This

sealer

Quickcrete Cure and seal No. 8730-02

Is the one I used. Roots are always happiest on the Crete!

Sorce

 

[Hack Yeah!]

I haven't sealed mine yet, thanks for the suggestion @sorce . I had used a premixed quikcrete product called shapecrete, so no extra sand. I'm not sure if they still sell it, I've had the bucket for a year or longer. I also think I may sand and stain mine before sealing.

 

[Leo in N E Illinois]

Shapecrete is a good product. Excellent for making pots. It is actually a brand name owned by Sakrete. I'm retired from a BASF subsidiary that made chemicals for the concrete industry. The group I was in our customers were the Ready Mix plants, but we had a section that handled mortars and products for different finishes. We did not really get into retail consumer use products. I did not actually work with placing concrete, but learned quite a bit about the chemistry of concrete. Plants, orchids and bonsai were how I kept my sanity after a very industrial day.

Shapecrete should still be available, and in stock at Home Depot.

 

[Krone]

Can't get this product in our country, so i am still not sure whit kind of sand should i use to achieve smooth surface.

 

[Leo in N E Illinois]

Trowelling, and vibration bring the "creme" to the surface of your concrete, even concrete with a fairly coarse aggregate will have a smooth surface after being "floated" and then "trowelled". The tools used for flat concrete work are the "bull float" and the "hand trowel". For columns they have various tools used to vibrate the concrete as it is being placed.

In making concrete pots - you need aggregate of various sizes, to get the interlocking needed for strength. If you can find a silica sand that is very fine, like flour. Also find a sand that is somewhat more coarse maybe 0.05 to 0.2 cm, and a sand that is even more coarse maybe 1.0 to 2.0 cm in diameter. A blend of equal parts of these 3 size ranges of sand to make 3 parts, and one part Portland cement or Alumina cement (brand name Ciment Fondue by Lafarge) will make a very smooth mortar mix that you can use for concrete pots. Art supply houses will sell marble powder, for use to be added to a concrete mortar mix for art projects. The cast product then resembles marble to some degree.

 

[Hack Yeah!]

Leo, how do you feel about fiberglass concrete additives? I think that is one of the ingredients in the shapecrete, and I cannot find it for sale currently.

 

[Leo in N E Illinois]

Fiberglass, especially in small, less massive applications, the fibers give flexural strength to the concrete. Bonsai pots, even the big ones that are made in Vietnam, Malaysia and Indonesia, are considered small, less massive uses of concrete. Woven fiber mesh, imbedded into the concrete, and or loose fiberglass fibers mixed throughout the paste both add flexural strength. Similar are the cross linked polyethylene "bow ties" or "little tiny I beams" that are added as fibers to concrete. These are excellent at adding flexural strength. Concrete has great compressive strength, but when a pot is picked up with one hand, or set on an uneven surface, it does not have much ability to flex. These fibers, either fiberglass, polyethylene and other fibers from other vendors all add strength. When you use a mold to make a pot with high fiber content concrete, sometimes you can feel the nubs of the fibers poking out of the otherwise smooth surface of the concrete. Usually a few passes with extra fine steel wool, or medium or fine grit sandpaper will smooth the surface right out. I know of one person who used a torch to flame off the tiny bits of plastic. That won't work with fiberglass. But fine sandpaper will work.

If I was making a pot or slab more than 8 inches across, I would probably always include fibers in the concrete mix for the added strength.

I had a concrete slab built by someone else, not me. It was maybe 16 inches long. It had soil in it, but was empty, the tree had expired. I lifted it up just by one end. The concrete snapped at that point, and exposed the bands of fiberglass mesh, or webbing, like that one would use in an epoxy resin & fiberglass boat. The web was not strong enough to keep the concrete from breaking even though the weight was maybe 10 pound at most. Concrete is weak when it comes to flexural strength. Always pick up pots and slabs using 2 hands, keep in mind you don't want to flex the pot.

But like I said earlier, I have personally never made a concrete pot, my experience is simply from being "in the business" for 40 years. (eh gads, that makes me sound old).

 

[Crawforde]

I’ve made a couple of slabs and pots when doing my bathroom with extra tile adhesive and I broke as many as I succeeded with.
The ones that didn’t break when unearthed had a bit of chicken wire, or drain mesh, or scraps of old twisted up bonsai wire in the mix. Sort of like tieing in rebar before pouring a form for a wall (ahhh the good old days of doing unskilled labor that at times got so brutal I joined the military to escape and get the GI Bill, (yea I know, I didn’t think that out real well) Just something to resist the flexing forces.

 

[Hack Yeah!]

The corners on this one didn't turn out too crisp so I lightly sanded all of them and applied a couple of coats of stain. It's been sitting for months, need to get a sealer on it now.

 

[leatherback]

That is turning out really nice.

Any more pots you built?

 

[Hack Yeah!]

Thanks, I had taken a rudimentary shot at a small slab before but it didn't turn out that great. I've got plenty of materials to try another one. I'll certainly try to go thinner as this one must weigh around 12lbs/5kg

 

[Arizona bonsai]

I was thinking of adding perlite to my next pot to lighten it.

 

[Leo in N E Illinois]

At large project in the Chicago area uses recycled glass foam as a lightweight aggregate. The glass foam is essentially perlite. Perlite is made by heating obsidian mined from rhyolite or other high silica volcanic deposits. Perlite pumice, expanded shale and other light weight particles have been used to create light weight concrete. Depending on amount, and particle size distribution, there can be issues with strength. But in concrete pots, flexural strength is the more important trait. Perlite would not affect flexural strength in a way that would affect a pot.

I would use one of the "vertical patching" or "thin application" cement-polymer composite products. But plain old Portland cement can work if you don't go too thin.

Your design is good. I don't think it is too "thick" because concrete is not durable when too thin. Anything less than 10 cm or 4 inches is considered a "thin application" for concrete.

I like the color of the stain. Looks good.

Did you soak your pot in a bucket of water? For concrete fish ponds, the recommended soaking is one to two months with weekly water changes. For plants, the soak to leach out excess hydroxides does not need to be as lengthy. 2 to 4 weeks with a water change once a week should be sufficient. It it was outdoors in the rain for several months, it is probably ready to use already.

 

[Hack Yeah!]

@Leo in N E Illinois , thank you for the input. I didn't soak it, it sat under plastic for a couple of weeks then outside for a couple of months before I stained it. It's been outside another 3 to 4 months since. I like the look of it when I see it wet now, so I'm trying to decide if I should put one more coat of stain before sealing it. I'm also curious if standard sealing will preserve the "wet" look or if I'd need to do anything special to help preserve it.

 

[Leo in N E Illinois]

@Leo in N E Illinois , thank you for the input. I didn't soak it, it sat under plastic for a couple of weeks then outside for a couple of months before I stained it. It's been outside another 3 to 4 months since. I like the look of it when I see it wet now, so I'm trying to decide if I should put one more coat of stain before sealing it. I'm also curious if standard sealing will preserve the "wet" look or if I'd need to do anything special to help preserve it.

Keeping the concrete moist, wrapped in plastic does cure the concrete. It is the favorable condition to come up to full strength. Technically concrete never achieves "full strength", as it is an asymptotic curve. After 30 days you should be in the 90% to 97% or better range.

I worked in the concrete chemistry business, but actually have very little hands on a trowel experience. Lots of theory, thin on handling cement paste. So I don't know if your stain or sealer will keep the wet look or not. A lot is brand dependant. Even if you listed brands, I never used any "consumer quantity" products. I was happy a bridge deck didn't collapse, or that the 33rd floor of a 75 story building didn't pancake onto the 32nd floor. Also was most concerned with surviving audits by nuclear power contractors. As our products went into concrete of confinement vessels.

Usually a second coat will look wet. That look may last a while. I would get the stain to the intensity you want. Then coat with the sealer. The sealer is more likely to have a "wet look" than the stain. Most sealers are based on an oil like linseed oil used for paint. You can simply re-coat once in a while to keep the "wet look".