Concrete Rock Pot/Slab?

[cishepard]

I would like to try my hand at pot making but can’t seem to find the acrylic patch product in my area - can I add this to a portland cement ready mix and get the same effect?

 

[moke]

@moke - I missed the original post earlier. Nice work. The product you chose, Vinyl Concrete Patch, is exactly the type of product I would suggest for pots and slabs, as these are ''thin'' applications for concrete. Good choice. It is a Portland cement mix, with a vinyl component that adds flexibility to the set product. The addition of fibers really reduces fine cracking, and using an expanded metal mesh will add structural strength. Well done.

I believe Eric K uses Ciment Fondue, a product more readily available in EU, not really used much in North America, except for certain specific applications. The Vinyl Concrete Patch product is based on Portland Cement chemistry, which I understand to some degree. Ciment Fondue is not Portland Cement, it is a cement with a much higher aluminum content, and much lower silica content than what is found in Portland Cement. The chemistry is somewhat different, and it reacts differently to additives than portland cement. It is also more expensive than portland cement. It does make a good finished product, as Eric K has proved. Ciment Fondue is used in foundry applications, because it is stable to much higher temperatures than Portland Cement.

@BE.REAL - mixing peat moss or any water absorbent material, like paper into a concrete mix will guarantee freeze thaw damage. With the ''hypertufa'' the spalling off of the outer surface over time, the cracking and crumbling is all part of the ''charm''. Actually a design benefit. But if you want long lasting pot or slab, do not mix any organic material into the mix. In frost free Florida, hypertufa can last 100 years. In Illinois, it might last 5 winters. But it will ''look cool'' as it degrades.

Separately I also question your addition of unslaked lime or lye to the mix. I am retired from the concrete admixtures manufacturing, and I never heard of unslaked lime, calcium hydroxide or sodium hydroxide, adding any freeze thaw resistance to a concrete mix. The concrete mix already contains a significant amount of calcium oxide, which becomes the unslaked lime or lye when added to water, adding more will do nothing more than weaken the final strengths of the concrete more towards the properties of mortar. Mortars are based on the dominant binding agent being calcium oxide reacting with water to make calcium hydroxide which reacts with carbon dioxide to make calcium carbonates (limestone). The superior strength of Portland cement depends on calcium aluminosilicates hydrating to form a much stronger matrix than calcium carbonates could form. There is calcium oxide in portland cement, but the percentage is low compared to the anhydrous aluminosilicates. Adding extra calcium hydroxide merely weakens the mix more toward the properties of mortar. Not good for frost-freeze resistance.

It is possible that @BE.REAL - you might be thinking of the addition of calcium chloride to concrete mixes. Here the effect of the calcium chloride is that it accelerates the initial set up of the concrete, allowing normal set times when the concrete is poured in cold weather. So you would see calcium chloride added in cold weather, but it actually acts on speeding up the initial strengths, and actually slightly lowers the end final strengths. Set time is temperature dependent, and for most jobs, if it is below 50 F outside it is normal to add an accelerator to the concrete mix. This is probably what you were thinking of. If you use metal, especially aluminum or iron mesh or rebar in your concrete - added chlorides, like calcium chloride will have a chemical reaction that will eventually corrode the metal and cause the concrete to fail. That is why calcium chloride is not allowed to be used in bridges, tall buildings or nuclear power plants. It is okay for house foundations, the least demanding task for concrete to perform. I hope you don't feel I'm ''busting your chops'' that is not my intent. I just don't want others to accidentally screw up their own projects by following what was probably an accidental mis-statement you made. And since I worked in the business, I thought I'd set the record straight.

There are techniques and additives that would help with freeze thaw resistance.

# 1. - One is to use as little water as possible to your mix. You want to add just barely enough to make a smooth, but still stiff paste. The amount of water needed for the various hydration reactions is so little that if you only added what the chemistry required, the mix would still seem ''dry to almost dusty''. The extra water makes it easier to work with, but the water as it evaporates leaves micro-channels, that allow water to re-enter the concrete, and when the concrete freezes, the water expands and cracking begins.

#2. - use a Portland cement mix with an additional polymer in the matrix, such as vinyl, there are also acrylic - cement mixes. These are high tech mixes, designed for patching, and have complex chemistries that should not be ''messed around with'' in the mixing process. Just follow the directions.

#3. - adding a plastic fiber, who's shape was cut to maximize strengthening the concrete (like little bow ties). This is what Moke did. Good move. Sometimes after the concrete is set you can feel the fibers sticking out from the cement paste. Just hit the finished piece with sand paper to sand the surface smooth. They will smooth right out.

For small batches of concrete, the above is all I would do. Until you get a batch size closer to one ton or more of concrete any chemicals you could add would have to be added in very small amounts. Not easy to get right without laboratory scales or volumetric equipment. Some are also not exactly safe to handle in a home setting. For large scale construction, to make extremely freeze thaw resistant concrete the redi-mix plants will add various soap like compounds to entrain air voids for the ice to back up into, naphthalene condensates and or lignin liquors to reduce total amount of water added, silica fume to create a more dense concrete, and a host of other chemicals.

Wow, thank you @Leo in N E Illinois for the great info you always provide!!! I wish I could write as smart as you, I try my damdest.
I usually run a small torch over the cement when hardened the burn the fuzzies off they pretty much just vaporize.

 

[moke]

I would like to try my hand at pot making but can’t seem to find the acrylic patch product in my area - can I add this to a portland cement ready mix and get the same effect?

View attachment 218977

I would imagine this is all that is put into the product I am using?

 

[Generic User]

Wow, thank you @Leo in N E Illinois for the great info you always provide!!! I wish I could write as smart as you, I try my damdest.
I usually run a small torch over the cement when hardened the burn the fuzzies off they pretty much just vaporize.

On the spec sheet it says it cures to 5000psi after 28 days.

 

[Lorax7]

On the spec sheet it says it cures to 5000psi after 28 days.

That’s compressive strength, which is never really going to be relevant in the context of a bonsai pot/slab application. The weight of the tree, roots, and soil is negligible compared to the compressive strength of any concrete mix. However, concrete has a fairly low tensile strength, which is why reinforcement with a wire armature and/or including some kind of fibers in the mix is important.

 

[Leo in N E Illinois]

I would not add or mix the acrylic patch product with the vinyl patch product. Simply because the polymer chemistry between the two is different. I don't know if they will interact, or interfere with each other. Read the spec sheets for each and see if they recommend mixing the acrylic with the vinyl. If not recommended, don't do it.

Both polymers, vinyl or acrylic function similarly in concrete. You only need one of the two. Both is probably "too much"

 

[Leo in N E Illinois]

I would like to try my hand at pot making but can’t seem to find the acrylic patch product in my area - can I add this to a portland cement ready mix and get the same effect?

View attachment 218977

Yes, that is exactly how this type of product is designed to be used. Read the directions, be sure to get the dose right . Remember, if it talks about dose per weight of cement, that bagged ready to use concrete is only about 20% to 25 % cement. The rest is sand, & stone. The Quickcrete product probably does specifically tell you how much to use for each bag of Quickcrete ready to use concrete. So if you won't have to ''do the math''. Just read the directions.

 

[Leo in N E Illinois]

On the spec sheet it says it cures to 5000psi after 28 days.

The 28 day strength for ''common'' Portland cement based mix designs (recipes) is about 75% the final compressive strength. It takes a year to come up to 95% to 99% final strength. The final strength is a theoretical, it never really gets there. Concrete will set under water, the hardening process is a hydration process that also requires carbon dioxide, from either the water or the air. Drying out has nothing to do with the ''set up'' of concrete.

Oh, by the way - the hydration reaction, is a time sensitive process, there is a progression, and to get the concrete, or mortar to set up as a single, amphoteric crystal unit, which is the state of maximum strength, you can not add water to the mix after the first 5 or 10 minutes. Once water is added, the slurry begins to change to a gel, then the gel will continue to stiffen until it is hard as rock, about 4 hours. Any water added after this gel begins forming, will never quite mix in. The results will be weak spots where the water remains. So once you make your mix, don't ''re-temper'' it by adding extra water if it gets stiff. Just use it up as is. Retempering will leave weak spots. All of you with patios that have spalling off of the surface less than 2 years after it was placed is because some ''damn yellow hammer'' on the ready mix truck used the garden hose to add extra water into the redi-mix truck, or washed the concrete out of the shute, leaving puddles of weak concrete on the surface of your expensive new concrete patio. Tell your concrete contractor that if you see the water hose get used while the redi-mix truck is on your property, you won't pay them. Water added after concrete has begun curing in the gel phase is the number one cause of concrete failure. Water added is a very common cause of spalling and water added can accelerate cracking if the water is added after the initial curing begins. Water is to only be used for clean up after the pour is complete and none of the water-concrete wash waste is to come in contact with the newly placed concrete. Put it in writing on your next patio or driveway contract before you sign the contract.

Yes, @Lorax7 is right, concrete is great at holding things up, resisting weight, but not so much in a bend, fold or pull situation. At work, in the R & D lab, we had business cards made from specially modified concrete. They felt like hardened cement paste, like mortar, yet you could bend and twist them without them cracking or breaking. They were about the size & thickness of a credit card. Neat what can be done. If scaled up to a useful project it would have been horribly expensive. Proof of concept doesn't have to be practical.

I was asked about what is considered a thin application for concrete.

In concrete world, anything less than 4 inches (10cm ) is considered thin. I would use ''thin patch'' products up to 5 inches (12.5 cm) for the shallowest thickness. So if any part of the pot is less than 5 inches thick, use a thin patch product. Most concrete uses are massive, think roads, bridges, buildings. That is why when patching cracks on a road, the jackhammers take out a whole segment of the road. Anything less, and the patch doesn't hold.

 

[Generic User]

The 28 day strength for ''common'' Portland cement based mix designs (recipes) is about 75% the final compressive strength. It takes a year to come up to 95% to 99% final strength. The final strength is a theoretical, it never really gets there. Concrete will set under water, the hardening process is a hydration process that also requires carbon dioxide, from either the water or the air. Drying out has nothing to do with the ''set up'' of concrete.

Oh, by the way - the hydration reaction, is a time sensitive process, there is a progression, and to get the concrete, or mortar to set up as a single, amphoteric crystal unit, which is the state of maximum strength, you can not add water to the mix after the first 5 or 10 minutes. Once water is added, the slurry begins to change to a gel, then the gel will continue to stiffen until it is hard as rock, about 4 hours. Any water added after this gel begins forming, will never quite mix in. The results will be weak spots where the water remains. So once you make your mix, don't ''re-temper'' it by adding extra water if it gets stiff. Just use it up as is. Retempering will leave weak spots. All of you with patios that have spalling off of the surface less than 2 years after it was placed is because some ''damn yellow hammer'' on the ready mix truck used the garden hose to add extra water into the redi-mix truck, or washed the concrete out of the shute, leaving puddles of weak concrete on the surface of your expensive new concrete patio. Tell your concrete contractor that if you see the water hose get used while the redi-mix truck is on your property, you won't pay them. Water added after concrete has begun curing in the gel phase is the number one cause of concrete failure. Water added is a very common cause of spalling and water added can accelerate cracking if the water is added after the initial curing begins. Water is to only be used for clean up after the pour is complete and none of the water-concrete wash waste is to come in contact with the newly placed concrete. Put it in writing on your next patio or driveway contract before you sign the contract.

Yes, @Lorax7 is right, concrete is great at holding things up, resisting weight, but not so much in a bend, fold or pull situation. At work, in the R & D lab, we had business cards made from specially modified concrete. They felt like hardened cement paste, like mortar, yet you could bend and twist them without them cracking or breaking. They were about the size & thickness of a credit card. Neat what can be done. If scaled up to a useful project it would have been horribly expensive. Proof of concept doesn't have to be practical.

I was asked about what is considered a thin application for concrete.

In concrete world, anything less than 4 inches (10cm ) is considered thin. I would use ''thin patch'' products up to 5 inches (12.5 cm) for the shallowest thickness. So if any part of the pot is less than 5 inches thick, use a thin patch product. Most concrete uses are massive, think roads, bridges, buildings. That is why when patching cracks on a road, the jackhammers take out a whole segment of the road. Anything less, and the patch doesn't hold.

What fiber would be best recommended? I a little hesitant if I should order Nylon, fiberglass or another type. I will likely have to do a little sanding after curing and am becoming hesitant if I want fiberglass particles around me. Thanks

 

[Leo in N E Illinois]

I would only use fiber glass as the mesh to help support a larger slab. Any mesh that is inert when in contact with concrete is okay. Plastic mesh, dry wall taper's mesh, expanded steel mesh, fiber glass mesh, all are good each better for for a different size project. Metal mesh, if not stainless steel should be coated to be corrosion resistant. Though for pots, this is probably over kill. In a bridge deck built for 75 year minimum life span, coated is necessary. So the support mesh is the only place I would use fiber glass if I used fiber glass at all, it is completely optional.

The fibers that are added to the concrete mix are usually little pieces of plastic, shaped like bow ties, or little I beams, a straight piece with a short cross bar at each end. They can be polyethylene, or cross linked polyethylene, or polypropylene or any other plastic. They could be other materials, but the plastic fibers are the cheapest. They usually come in a one pounds, 5 pound, or larger bag. They are light, the smallest bag of fibers will be almost the same volume as a 50 pound bag of cement. One bag will be good for hundreds of pots.

Does this clear it up?

 

[Generic User]

I would only use fiber glass as the mesh to help support a larger slab. Any mesh that is inert when in contact with concrete is okay. Plastic mesh, dry wall taper's mesh, expanded steel mesh, fiber glass mesh, all are good each better for for a different size project. Metal mesh, if not stainless steel should be coated to be corrosion resistant. Though for pots, this is probably over kill. In a bridge deck built for 75 year minimum life span, coated is necessary. So the support mesh is the only place I would use fiber glass if I used fiber glass at all, it is completely optional.

The fibers that are added to the concrete mix are usually little pieces of plastic, shaped like bow ties, or little I beams, a straight piece with a short cross bar at each end. They can be polyethylene, or cross linked polyethylene, or polypropylene or any other plastic. They could be other materials, but the plastic fibers are the cheapest. They usually come in a one pounds, 5 pound, or larger bag. They are light, the smallest bag of fibers will be almost the same volume as a 50 pound bag of cement. One bag will be good for hundreds of pots.

Does this clear it up?

Yes it does Leo, Many thanks. Your knowledge really aids in the creation process and sets the tone for sound fabrication. It is really nice to just ask someone with experience. I was watching videos of the Pantheon in Rome and learned they used to use horse hair as fiber within concrete for strength. Im glad I live in the age where I will not need to trim a horses mane for fiber. Have a good day. E

 

[crust]

I have had good success making custom ultra strong concrete mixes utilizing a superplasticizer (small amounts on ebay) to keep the water amounts down yes be very workable. touchy stuff but it works amazingly.

 

[crust]

@moke - I missed the original post earlier. Nice work. The product you chose, Vinyl Concrete Patch, is exactly the type of product I would suggest for pots and slabs, as these are ''thin'' applications for concrete. Good choice. It is a Portland cement mix, with a vinyl component that adds flexibility to the set product. The addition of fibers really reduces fine cracking, and using an expanded metal mesh will add structural strength. Well done.

I believe Eric K uses Ciment Fondue, a product more readily available in EU, not really used much in North America, except for certain specific applications. The Vinyl Concrete Patch product is based on Portland Cement chemistry, which I understand to some degree. Ciment Fondue is not Portland Cement, it is a cement with a much higher aluminum content, and much lower silica content than what is found in Portland Cement. The chemistry is somewhat different, and it reacts differently to additives than portland cement. It is also more expensive than portland cement. It does make a good finished product, as Eric K has proved. Ciment Fondue is used in foundry applications, because it is stable to much higher temperatures than Portland Cement.

@BE.REAL - mixing peat moss or any water absorbent material, like paper into a concrete mix will guarantee freeze thaw damage. With the ''hypertufa'' the spalling off of the outer surface over time, the cracking and crumbling is all part of the ''charm''. Actually a design benefit. But if you want long lasting pot or slab, do not mix any organic material into the mix. In frost free Florida, hypertufa can last 100 years. In Illinois, it might last 5 winters. But it will ''look cool'' as it degrades.

Separately I also question your addition of unslaked lime or lye to the mix. I am retired from the concrete admixtures manufacturing, and I never heard of unslaked lime, calcium hydroxide or sodium hydroxide, adding any freeze thaw resistance to a concrete mix. The concrete mix already contains a significant amount of calcium oxide, which becomes the unslaked lime or lye when added to water, adding more will do nothing more than weaken the final strengths of the concrete more towards the properties of mortar. Mortars are based on the dominant binding agent being calcium oxide reacting with water to make calcium hydroxide which reacts with carbon dioxide to make calcium carbonates (limestone). The superior strength of Portland cement depends on calcium aluminosilicates hydrating to form a much stronger matrix than calcium carbonates could form. There is calcium oxide in portland cement, but the percentage is low compared to the anhydrous aluminosilicates. Adding extra calcium hydroxide merely weakens the mix more toward the properties of mortar. Not good for frost-freeze resistance.

It is possible that @BE.REAL - you might be thinking of the addition of calcium chloride to concrete mixes. Here the effect of the calcium chloride is that it accelerates the initial set up of the concrete, allowing normal set times when the concrete is poured in cold weather. So you would see calcium chloride added in cold weather, but it actually acts on speeding up the initial strengths, and actually slightly lowers the end final strengths. Set time is temperature dependent, and for most jobs, if it is below 50 F outside it is normal to add an accelerator to the concrete mix. This is probably what you were thinking of. If you use metal, especially aluminum or iron mesh or rebar in your concrete - added chlorides, like calcium chloride will have a chemical reaction that will eventually corrode the metal and cause the concrete to fail. That is why calcium chloride is not allowed to be used in bridges, tall buildings or nuclear power plants. It is okay for house foundations, the least demanding task for concrete to perform. I hope you don't feel I'm ''busting your chops'' that is not my intent. I just don't want others to accidentally screw up their own projects by following what was probably an accidental mis-statement you made. And since I worked in the business, I thought I'd set the record straight.

There are techniques and additives that would help with freeze thaw resistance.

# 1. - One is to use as little water as possible to your mix. You want to add just barely enough to make a smooth, but still stiff paste. The amount of water needed for the various hydration reactions is so little that if you only added what the chemistry required, the mix would still seem ''dry to almost dusty''. The extra water makes it easier to work with, but the water as it evaporates leaves micro-channels, that allow water to re-enter the concrete, and when the concrete freezes, the water expands and cracking begins.

#2. - use a Portland cement mix with an additional polymer in the matrix, such as vinyl, there are also acrylic - cement mixes. These are high tech mixes, designed for patching, and have complex chemistries that should not be ''messed around with'' in the mixing process. Just follow the directions.

#3. - adding a plastic fiber, who's shape was cut to maximize strengthening the concrete (like little bow ties). This is what Moke did. Good move. Sometimes after the concrete is set you can feel the fibers sticking out from the cement paste. Just hit the finished piece with sand paper to sand the surface smooth. They will smooth right out.

For small batches of concrete, the above is all I would do. Until you get a batch size closer to one ton or more of concrete any chemicals you could add would have to be added in very small amounts. Not easy to get right without laboratory scales or volumetric equipment. Some are also not exactly safe to handle in a home setting. For large scale construction, to make extremely freeze thaw resistant concrete the redi-mix plants will add various soap like compounds to entrain air voids for the ice to back up into, naphthalene condensates and or lignin liquors to reduce total amount of water added, silica fume to create a more dense concrete, and a host of other chemicals.

I thought Eric K used a modified thinset product such as you would use to lay tile.

 

[moke]

What fiber would be best recommended? I a little hesitant if I should order Nylon, fiberglass or another type. I will likely have to do a little sanding after curing and am becoming hesitant if I want fiberglass particles around me. Thanks

I used the nylon fiber and just ran a torch over the surface to remove/burn the visible fibers.

 

[Leo in N E Illinois]

I thought Eric K used a modified thinset product such as you would use to lay tile.

Could be, I was following his thread on IBC. I bailed out and quit reading about page 5, last time I looked it was several years later and at least 18 more pages. He might have switched, and he could have switched years ago and I would not know. I thought comment fondue, but I could be wrong. I know in some other forums, especially in EU, comment fondue is a common recommend cement type for art projects. I would reach for Vinyl or Acrylic patch cement, labeled for vertical patches.

 

[SU2]

Thanks, I also plan on working on several through this winter. You’ll have to share your work. I plan on keeping this wrapped and moist for about a month then I’m going to place it outside in the elements before planting in the spring.

Nice work!! Would definitely leach it though

And no the lime wont leach into the plant, for the tiny amount that might, wouldn't, plus with how we water our trees it will be flushed out, if it did leach a little. But I have planted a tree a month after making a pot and it is fine. After 28 days it is 98% cured and the last like 2% will take 100's of years, all cement is like that. learned that in my experimenting/education. HAHA
Side note, if any of you heard of Hypertufa, its all the rage with houseplant people, haha. but you mix peat moss with the cement, which makes it lighter and stuff.

I don't think it causes any serious problems but the trees certainly want as minimal disturbances as possible so I always cure DIY pots for a while (at least a couple weeks) but just for experiments' sakes I've used both fresh pots & slabs (ie made that very day) on bougies, an "acid loving" specie, and noticed zero consequences (noticed being the operative word there, am sure there'd be some minimal boost by not having had their fresh, extending roots hitting alkaline/basic walls

Re Hypertufa have you ever tried it yourself? Sounds like a gardener's version of the "papercrete" 'fad'(idea? have seen actual textile-blocks made with the stuff but couldn't tell if it was legit or a gimmick) With portland being so strong & cheap I just can't imagine the need to lighten it....I've got some large 'crete projects in mind and I'll be 'shedding weight' by incorporating styrofoam inside the thing, not 'watering down' my mix w/ a weak aggregate like paper or moss (both are degradable as well, wonder what their life-spans are)

 

[moke]

Re Hypertufa have you ever tried it yourself?

I have made Lots-O-Tufa, my wife and I have made it for years we make planters for around the yard many of them are 20 years old they do develop cracks after some time, but It adds to the character. I also don't think we ever added the pumice, perlite and sphagnum to make it lighter we have always added it for a more natural aged stone look. the planters that we add the sphagnum develops and harbors a lot of lichens and moss making it even better looking with age.
I want to try a Tufa type blend for a bonsai slab with a metal mesh and reinforcing fiber this is something we have never done with our garden planters and may rid of fatal cracks.
I think the naturalistic appearance would look very nice paired with a tree.

 

[Lionheart]

...wicked nice pot!

 

[Lionheart]

I have mixed everything with P. cement to see the affects. But as @moke said, the pre-mixed bags shown, are good for hobbyist and small projects.

keep on creating!

Have you posted your results anywhere?

 

[Lionheart]

I've been using Sakrete Stone Veneer Mortar. The grain is fairly fine, and the pots seem strong. But when it runs out, I think I'm gonna switch over to Vinyl Concrete Patcher.