Using cinder blocks to grind metal?

Hi guys!

I tried to use a cinder block to manually grind a fat nail into a small chisel.

While the result seems good, I was under the impression that after a while the block's surface was less abrasive than at the beginning. It is definitely smoother.

I thus had two questions :
1) Did its grinding capacity really vanish that fast? Or is it just because I should have cleaned it with water, and maybe a brush, more often?
2) Am I damaging this cinder block by doing this? Is it still usable for construction? I wouldn't want to ruin a cinder block just to make a chisel, that wouldn't sound worth it. Does it need a coarse surface to be usable in typical construction uses?

Has anybody had experience using cinder blocks as grinding stones?

Thanks in advance for the feedback!

Vic,

As the nail and the block touch, they each grind the other. The nail is shaped and sharpened by the abrasive removal of the metal and the block's surface along the sharpening channel is smoothed by the near microscopic ablation of the rough surface.

The coarseness of the block's surface, which is basically the amount of roughness on the block's surface, determines the amount of metal removed with each pass.  Because of the aggregate used in cinder blocks, that roughness doesn't last long.

I wouldn't want to use a cinder block for important construction that had much of a grove ground into it, but it wouldn't worry me for most purposes.

I think you might get better results using a much harder smooth  stone, like a common river rock,  with damp course sand spread on top, or using a cast off purpose made grinding wheel from a disc grinder. Those can probably be gathered from the trash of at construction sights.  

Note that nails or railroad spikes are not made of the same sort of steel as chisels. Without differential  heat treating of the chisel edge and striking end the chisel will not hold it's edge or be safe to strike with a hammer. Use a mallet, not a hammer to avoid the striking end from splintering and throwing bits of metal towards your face.

Primitive heat treating can be done, and would be worth the time if you are going to be using the chisel seriously and cannot get a "store built" chisel otherwise.  There's plenty of youtube videos on that.

Abrasive stone sharpening of materials has a long history in preindustrial societies, but in my experience,  is best at producing points not edges. Arrows, not chisels.

Hi guys,
Just had to add something to this thread since grinding is one of my daily operations.
While trying to use stationary stones whatever they may be, cinder block,  river rock, or an old grindstone, moving the object across the stone is almost never the way to initially shape material other than very fine honing.
Your best bet for any type of grinding or sharpening is a powered grindstone, if you have electricity then one of the bench mounted types with double stones which can be of different coarseness is a good choice.
If you don't have electricity (like us) or actually like to become intimately involved with the process such as grinding, the best option, in my opinion and from years of experience is a hand cranked grinder, with a medium to course grindstone.
You can find hand turned grind stones at auctions flea markets or just look one up on eBay.
I have at least one in each of my workshops some of them are outfitted with grind stones others are outfitted with wire wheels for brushing and fine surface removal.
With a hand turned grindstone you can easily sharpen chisels or even make one as you were trying to with the nail, although as was mentioned in the earlier post nails would not make a good chisel because of their softness, although pole barn spikes are of a quite hard steel and probably would make a reasonable small chisel.
I use hand turned grindstone's daily to sharpen wood plane  blades, sharpen cold chisels, and to reshape and fabricate small metal parts.
A hand turned grinder would be probably fairly inexpensive (I usually pick them up for around 10 to $25)  and would serve you in your shop for many years to come, and most hand turned grindstones will accept most of the currently manufactured stones.

Vic Dupont wrote:2) Am I damaging this cinder block by doing this? Is it still usable for construction? I wouldn't want to ruin a cinder block just to make a chisel, that wouldn't sound worth it.

... Has anybody had experience using cinder blocks as grinding stones?!

Modern cinder blocks seem relatively soft and quite porous. They make lousy grinding stones. And yes, IMO it is possible to weaken them to the point where they are not suitable for load-bearing construction.

i use the underside of paving bricks, generally, for crude sharpening work. As in, the 10-second edge on a shovel or hoe that's engaged in abusive work. A finer edge won't last anyway, and in another 10 seconds I have a new crude edge. Paving bricks are very, very dense. They show no evidence of wear. One long brick should last almost forever for rough work. But i do not use them on any kind of steel I care about -- they are far to coarse and irregular.

I should note that I have a couple of "antique" cinder blocks, pink-reddish in colour, left by the former owner. They are much more dense and fine grained, and they do a passable job on shovels and hoes with no indication of wear. I assume these were made in the day when things were built to last.

Thanks a lot for the replies guys!

I'll tackle each topic one by one.

1. Wear of the cinder block

Regarding wear of the cinder block, I am attaching a picture of how it looks now. There's no grove. The ups and downs of the block are still there, it's only at the sub-millimeter scale that the surface is smooth.

I'm pretty sure it's still solid, I'm just wondering whether the smooth surface would make it less adhesive to mortar or something.

I take it from your answers that I couldn't do that eternally, but in the present situation, is this block still useable for construction?

2. Efficiency of this technique

Regarding efficiency of this technique, yes I dream of having a hand operated grinding wheel. It's just that I don't have one right now, and I mistakenly thought that grinding into a chisel would be pretty quick. Turned out it took a lot longer than I expected, but it's also because I had to learn a few things to be more efficient.

The result is still pretty good. I am happy with it.

After making my chisel I also used the cinder block to flatten our whetstone, which I had damaged when I used it to make my first chisel.

3. Using a nail as chisel

Regarding bendability of this new chisel, I feel like it will be ok. It's a very fat nail, and it seems pretty rigid. I don't think it's a standard one. At no point did it show the slightest bending.

I would think it's probably true for most nails that they would be too soft to use as chisels, but I think the one I used was special. I am not even sure it was a nail actually.

Regarding its brittleness, I have to say that I plan to use it on wood only, not on metal. Thus I was thinking that if it's good enough to be used as a nail between a hammer and wood without breaking, it would be fine to use as a chisel between a hammer and wood too.

What do you think?

Working with scrounged steel and abrasives is a lot of fun, and a good way to gain new knowledge and develop new skills. You will never look at a recycling bin full of metal the same way again.

It looks like your recycled cinder block has a long history. I don't think a little grinding will change its pre-existing strength (or pre-existing weakness). Personally I wouldn't use recycled cinder blocks for a major structure like a house, but for small structures they would work fine.

Thanks a lot for the reply and for all the help!

Why don't more people recycle cinder blocks for gardens, instead of paying to dispose of? We had a part of perimeter wall (160 feet) come down in Florida during hurricane and got a bid of $12,000 for removal of debris, then $100,000 to rebuild the wall. We have space for a garden 200 feet away, but community is resistant to reusing anything.