Concrete Rock Pot/Slab?

[Katie0317]

Very cool! Am looking forward to trying it. We have one my husband made but out of concrete only and I love it. Think the old basket ball cut in half is a great idea. Really like the round one with rocks and tiny green moss?

You have to then put something smaller into each shape after you pour the cement to make the mold though? What did you use or how did you go about that part?

 

[moke]

You have to then put something smaller into each shape after you pour the cement to make the mold though? What did you use or how did you go about that part?

Yes exactly, we put either another box or container or whatever we have laying around. but you do have to try and keep it submerged in the concrete because it has a tendency to want to float out, we will either fill the container with rocks or by some means of keeping it from floating. you can also insert a piece of dowel or branch in the bottom to create a drain hole, the wood can usually be tapped out or drilled if needed once the cement cures. I have even drilled drain holes with a masonry bit after the cement has cured. I will also wire brush them to give it an aged and more weathered rough look before it fully cures.

 

[john blanch]

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?

Does using slightly corroded steel, I mean steel with powdery rust colour effect the cement? Am I right that once its locked into the cement there will be no problems?

 

[Leo in N E Illinois]

Does using slightly corroded steel, I mean steel with powdery rust colour effect the cement? Am I right that once its locked into the cement there will be no problems?

Corroded steel, rust, is not a problem if no further rusting (corrosion) is occurring. COR TEN steel, A242 and or A606 steel are self protecting grades of steel, where they form a protective layer of rust, oxides, that seal off the interior of the steel from further corrosion. Using these types of steel as reinforcement inside a concrete pot would be no problem at all, because no further oxidation will occur. Iron oxide takes up about ten times the volume of an equal molar amount of iron. So when iron rusts, the resulting oxide expands, and if this expansion is inside a concrete pot, or inside a concrete column holding up a bridge deck, the concrete will crack and flake off. We all have seen concrete columns under bridges with rusting reinforcing bars exposed, and concrete cracked and falling away. For hobby size concrete pots this is unlikely to be a problem, but it is best to use stainless steel mesh as support, or coated mesh as support. Avoid iron armatures, as the iron will rust, the rust will become the source of expansion and cracking.

Iron oxides can be used to color concrete, because once formed, iron oxide is stable.

Plain iron, low grade steel, should not be used inside a concrete construction because as the iron or steel rusts, the rust will expand, to take up 10 times the room the iron is was took. It is the transition from metal to oxide that causes problems, in the process of turning to rust, the iron expands and breaks your concrete.

It is okay to use steel, A242 and A606, which are CORTEN steel, and or higher grades of stainless steel. Not good to use are plain iron re-bar, and lower grade of iron is not good. I honestly can not tell you how to read the mill marks or stamps and or mill specifications. I am not a structural engineer.

 

[john blanch]

Thankyou,

 

[queenofsheba52]

Love this thread, love the forest, the pots and @Leo in N E Illinois great knowledge.

 

[moke]

Took this pic this morning while sipping some coffee with the trees.

 

[Weta]

Awesome creative vision Moke.

 

[queenofsheba52]

Agree! I felt as though I was in the forest myself!