Polished concrete tables.

[Tscarborough]

Re: Polished concrete tables.

The wetter the mix, the more prone to shrinkage cracking. I would not fix the corner, although you could simply by mixing up a little bit somewhat dry, applying a bonding agent, and then filling it. It will not match perfectly, but no one but you will ever notice it. I pulled the edge forms within 2 hours of finishing the pour and then filled the bugholes while it was still workable and I had the same material to do so.

[ggoose]

Re: Polished concrete tables.

Mike

That counter looks great! I wouldn't worry too mich about the chip - very small and on the bottom. Perhaps slurry and polish the sides and call it good...because it really looks good!

gene

[splatgirl]

Re: Polished concrete tables.

Well, IME, the only times I have had issues with losing bits was when I got impatient with pulling the forms. From what I have seen, that type of issue declines in direct proportion to time in the form. Obviously...more cure time means more strength.
I disagree with the 24 hour advice, but what do I know.

Inside corners almost always crack. Yours has the added bonus of wrapping around the whole front, right? I suspect that multiplies the inside corner cracking issue by a lot. That said, I do not have any direct experience with that situation.
Of course "wet" and "dry" are relative, but to my eye the look of what's going on in the edges of your slab say a wetter pour than not.

It looks good. What are you going to address the height difference between the hearth and the counter?

[Tscarborough]

Re: Polished concrete tables.

Splatgirl, it depends upon the design of the formwork. Always use screws, and for cantilevered pours, always make it such that the form for the bottom stays while the form for the face is removable. Then you can leave the support and still dress the face.

[splatgirl]

Re: Polished concrete tables.

I am familiar with the ins and outs of formwork. That is by no means the only or even the biggest factor in extracting a perfect slab with all bits intact, even assuming construction with a good exit plan in mind and careful removal. Sometimes all it takes to break off a corner or an edge of a very green slab is the force of the actual face board coming away from the material.

"Dressing the face" really has no bearing on a 24 hour old slab. As you know, it's not wet enough to dress and not cured enough to have any strength. If it's a DIY, pulling the form early like that makes absolutely no sense to me. Leaving it on a good few days-- and reaping the added bonus of more moisture in the slab over a longer period-- is a cheap and easy insurance policy against this and other problems IMO.

OTOH, when a guy wants to get paid and get outta there, well...

[Tscarborough]

Re: Polished concrete tables.

I am talking about dressing it within a couple of hours, not 24. You never pull the formwork away, you slide it, and always into the corners.

[Nic The Landscaper]

Re: Polished concrete tables.

Mike I think your work looks great. with more practice and experience you could have worked things like those bug holes out while pouring but some slurrying will get those patched right up.

as for the corner cracking and pulling forms at given time points etc. one thing I noticed looking back through the process leading up to the pour is that the forms were made from dimensional lumber. When I am working on counter top projects I always use melamine not lumber, this is something so natural to me that I don't even think to discuss it. Un -coated dimensional lumber will wick moisture from a fresh pour, as well as any surface imperfections and pores will fill with concrete and want to pull away pieces like the corner did.

At 24 hours Mikes counter top should have been at 50% hardness so roughly 2500psi which is more than sufficient to strip the forms on a simple counter like this. Also with all the additives and counter flow the mix should have appeared to be wet, I wouldn't be too concerned about cracks, especially with a 4" pour.

[splatgirl]

Re: Polished concrete tables.

Yes, melamine is my M.O. for anything like this, too. And in situations where the use of melamine isn't feasible, a layer of packing tape on the interior face of the form board.

As you know, Nic, 2500 psi is descriptive of compressive strength only. Not a very applicable measure of what a cast decorative piece is going to be subjected to. In this case, it looks to be more about tensile strength which even fully cured concrete has very little of.

Anyway, my point remains that leaving a piece in the form longer is the best preventative, and that if 24 hours were "more than sufficient", he probably wouldn't have lost that bit. But who knows. I am just speaking based on what I have seen in practice. Even under the most perfect of circumstances, concrete always has a little bit of a mind of it's own. Absolute predictable perfection is not it's strong suit, but it's also why it's so fun and so interesting, right?

[Mike D]

Re: Polished concrete tables.

Thanks for all the support everyone,

I think that corner broke off because my friend was vibrating the hell out of that corner (before I was able to tell him to do the whole thing not just that corner). That was my fault, I was busy mixing and moving the cement. The aggregate sunk really hard and that corner that broken piece was mostly aggregate.

- I don't know what I was thinking building the forms with lumber. My test piece was with melamine. I think I was on auto pilot from the top slab of the hearth. The side counter will be done with melamine.

-I pulled the forms after 24hs to polish the counter while it was still a little soft. I don't have a wet polisher so I was doing it by hand with the 5" diamond pads. My arms are rockin right now but I think things are working out.
-I will try to epoxy that piece on and put a slurry around it and see how it goes.
-overall, I think it is going to come out fantastic. Thanks for all the help.

Mike

[Mike D]

Re: Polished concrete tables.

Splatgirl-

The front area will get a row of brick under the cooking floor that will extend out to rest on top of them. This will connect to the outer arch/vent area. I needed to do this counter first to move on to finish the arch/vent transition. This has been a long road of education, but that first pizza is going to be dam good.

Mike

[Mike D]

Re: Polished concrete tables.

I epoxied the corner and put a slurry coat on to fill the holes. I think it came out nice (good enough). We will be the only one who know about the corner.

Here is a picture with the front arch that I just finished. Next comes the flew and the decorative brick to go around the outside.

Mike

[Neil2]

Re: Polished concrete tables.

"Anyway, my point remains that leaving a piece in the form longer is the best preventative,"

I agree completely splatgirl.

Once it is poured and in the form, "the die is cast". Keep it moist and allow it to reach full strength - 7 days plus. Then remove the form and evaluate any touch ups required.

[Chainsaw13]

Re: Polished concrete tables.

I wet polish all of my concrete with 5" and 7" wet polishers. You will do the majority of your "cut" with the 80 grit, get the exposure to within 75% to 80% of what you want to expose with the the 80 grit, the first 1/8" will come off very fast, after that it slows down as you cut into the aggregate. Then I follow up with increasingly finer grits, typically with diamond pads the grits go 80, 100, 200, 400, 800, 1200, 1600, 3000. I will only polish to 200 grit on day 1. After 200 grit you will have minimal removal of material, mostly just increasing degrees of shine. The reason i stop at 200 is that i like my surface to dry at this point so i can see if there are any pinholes in the concrete that have been exposed or if there are any swirl marks from the 80 grit that did not get polished out in successive polishes.

If there are pinholes, I fill them with a slurry coat (Portland cement, Tammsweld acrylic admix and color) screeded in with a putty knife. Let cure 24 hours and polish out with 200 grit, 80 and 100 grit are too aggressive.

If there are swirl marks I go back to the 100 grit and 200 grit to polish out the swirl marks.

When I am happy with the surface at 200 I proceed to finish to a minimum of 800 grit but prefer 1600, personal preference at this point.

One of the hardest things to remember for people starting with polishing is to keep the head of the polisher flat to the surface. If you tip it up on edge it will cut faster but your surface will be very wavy, it is almost impossible to get the swirl marks out and it will wear your polisher bearings and pads out very fast.

You will spend most of your time on the 80 grit pad getting close to your desired exposure. Assuming your surface is exposed evenly and flat, you will only need to spend about 2 to 3 minutes per square foot with 100 through finish grit.

When Polishing concrete and stone water is your friend! I operate the polishers at their full water capacity, it keeps the dust down, washes the surface as I go and lubricates the disks so they last longer.

I hope this helps.

Hi! I'm looking to create either a smooth concrete worktop, or table and wanted some advice on the concrete mix.... There is a stack of advice in the USA about products, but most of them aren't available here. So, I need a nice strong concrete mix that's going to give me a really smooth finish without any gravel showing through, but i'm unsure as to the quantities of everything I need. I'm thinking of: - Standard Cement - Builders Sand (not sharp sand) - 10mm Gravel aggregate - Plasticiser - Wire mesh ....If anyone has better ideas, let me know!! Has anyone on here made any nice concrete tables before? If so could you give me some advice on mixes/products? Thanks in Advance!

[Gulf]

Hi Chainsaw13,

Welcome to the forum.

.......There is a stack of advice in the USA about products, but most of them aren't available here..........

Where is "here"? You've listed the United States as your location? There are folks on this forum from all round the world. I bet someone here in the US can help. But, someone on this forum who is from your area may have already solved your material sourcing question.

[Chainsaw13]

Re: Polished concrete tables.

I wet polish all of my concrete with 5" and 7" wet polishers. You will do the majority of your "cut" with the 80 grit, get the exposure to within 75% to 80% of what you want to expose with the the 80 grit, the first 1/8" will come off very fast, after that it slows down as you cut into the aggregate. Then I follow up with increasingly finer grits, typically with diamond pads the grits go 80, 100, 200, 400, 800, 1200, 1600, 3000. I will only polish to 200 grit on day 1 polished concrete floor cleaner. After 200 grit you will have minimal removal of material, mostly just increasing degrees of shine. The reason i stop at 200 is that i like my surface to dry at this point so i can see if there are any pinholes in the concrete that have been exposed or if there are any swirl marks from the 80 grit that did not get polished out in successive polishes.

If there are pinholes, I fill them with a slurry coat (Portland cement, Tammsweld acrylic admix and color) screeded in with a putty knife. Let cure 24 hours and polish out with 200 grit, 80 and 100 grit are too aggressive.

If there are swirl marks I go back to the 100 grit and 200 grit to polish out the swirl marks.

When I am happy with the surface at 200 I proceed to finish to a minimum of 800 grit but prefer 1600, personal preference at this point.

One of the hardest things to remember for people starting with polishing is to keep the head of the polisher flat to the surface. If you tip it up on edge it will cut faster but your surface will be very wavypolished concrete floor cleaner, it is almost impossible to get the swirl marks out and it will wear your polisher bearings and pads out very fast.

You will spend most of your time on the 80 grit pad getting close to your desired exposure. Assuming your surface is exposed evenly and flat, you will only need to spend about 2 to 3 minutes per square foot with 100 through finish grit.

When Polishing concrete and stone water is your friend! I operate the polishers at their full water capacity, it keeps the dust down, washes the surface as I go and lubricates the disks so they last longer.

I hope this helps.

So looking to see if this is a dumb idea, or would work. I’ve been looking at pics and videos of people doing polished concrete tables, and am looking to do one eventually. I have to build a small work bench for very light weight work (not automotive and doesn’t have to hold much weight/not even in the garage) I figured I’d could use this as a test to see how it would come out, before undertaking a more aesthetic project. In the planning stages right now, but thinking of a work bench on 4x4s (due to weight of the concrete), roughly 2’Dx4’L, with a 2” concrete top. But it would give me practice for down the road, and if it doesn’t come out perfectly it’s okay. Was also thinking of sinking bolts in it for a small vice, but would be used more to hold while i work, than any real twisting force. Am i barking up the wrong tree, or does this seem like a sound idea?