Is a variable speed grinder essential?

[RichC]

Hi guys, I'm having a hard time finding a variable speed grinder for reasonable money. I'm wondering, is it possible to polish concrete with a normal grinder? What's the downside of this and would it just require some additional care?

Thanks

R

[Gulf]

Re: Is a variable speed grinder essential?

Rich,
I've seen where some have added "variable speed rheostat controls" to their's.
My grinder is not variable speed, but it worked fine for me on my small project.

EDIT: I might better add that I have only used the upsided down method for pouring counters. Since this method already has, most of what is wanted to be seen at the surface, it is mostly polishing with the more finer grits. But, in my case at least, the cheap grinder worked just fine.

[deejayoh]

Re: Is a variable speed grinder essential?

you can get a router speed controller from Amazon for $18. I used this and it worked fine to control the speed of an electric motor. No reason to step up to a VS grinder. Actually, you are better off with cheapy since you're going to expose it to a lot of water. The speed controller also has a GFCI fuse in it, which is helpful when you're standing in a pool of water...

Amazon.com: SE Electronic Stepless Speed Controller: Health & Personal Care

[RichC]

Re: Is a variable speed grinder essential?

Thanks guys!thsts a much better solution for me. How precise does speed control need to be for concrete polishing? Do you just turn it down and judge by the sound if it if it's at 50% of max? Or do you need to be within specific speed ranges depending on pad grit?

Thanks

R

[stonecutter]

Re: Is a variable speed grinder essential?

You could get diamond hand pads instead of cobbling something together. I've used non- insulated tools for polishing stone and concrete, it works well enough, but I wont recommend it. It's dangerous, and an unnecessary risk...especially since this is a personal project where you don't have a deadline or a client to please, consider a safer route.

Diamond hand pads come in grits from 50- 3000, and they work great. I do have a vs wet polisher, but I use the pads just as much, if not more, because they can finish areas that the polisher can't.

[RichC]

Re: Is a variable speed grinder essential?

@Stonecutter, I didn't know it was possible to do this by hand! I'm casting in situ and intend floating some broken glass into the surface. My total surface area is about 3m^2. Is it really feasible to get a glassy sheen by hand? Is it going to take a ridiculous amount of time? Some areas will be difficult to access with the grinder. I'd prefer to do this be hand if it's a realistic approach? If doing it by hand what grits should I be buying ?

[deejayoh]

Re: Is a variable speed grinder essential?

My experience was that you run the speed up to where it feels like it is working, it's pretty easy to gauge.

FWIW, I didn't feel unsafe using the grinder. Rubber gloves +rubber boots + GFCI. Only popped the fuse once and I knew why.

[stonecutter]

Re: Is a variable speed grinder essential?

@Stonecutter, I didn't know it was possible to do this by hand! I'm casting in situ and intend floating some broken glass into the surface. My total surface area is about 3m^2. Is it really feasible to get a glassy sheen by hand? Is it going to take a ridiculous amount of time? Some areas will be difficult to access with the grinder. I'd prefer to do this be hand if it's a realistic approach? If doing it by hand what grits should I be buying ?

If you are seeding your pour with glass or aggregate, then I would recommend power tools. But to answer your question, yes, you can get a glass like surface with hand pads.

What grits you would need depend on how your concrete is troweled off, type of aggregate used, and what you want to see as a finished surface.

You can buy a variable speed grinder and dry polishing pads ( metal bond vitrified are good) for a reasonable amount of money (google). Use respiratory protection when you dry grind. Metal bond pads are aggressive and usually only go to 200 grit. From there you can get resin bond and higher grit. Keep in mind, you want to use resin bond at lower rmp, otherwise the pads can burn.

[stonecutter]

Re: Is a variable speed grinder essential?

My experience was that you run the speed up to where it feels like it is working, it's pretty easy to gauge.

FWIW, I didn't feel unsafe using the grinder. Rubber gloves +rubber boots + GFCI. Only popped the fuse once and I knew why.

I'm not trying to be a safety cop with grinder use, that would make me a hypocrite in this dept.

None of my grinders have guards or handles. I don't feel unsafe, and I have been doing it for years with no problem. That doesn't make it a safe practice...especially when people that aren't use to working with them that way are trying a technique for the first time.

I stand behind my previous post. It may have worked fine and dandy for you, but I won't recommend doing stuff the way I do it, if I had to modify technique and tools outside of standard safety practice...even if the results achieved are spectacular.

Let the readers/builders use discernment.....

[RichC]

Re: Is a variable speed grinder essential?

Thx guys, back to grinder with speed control then never polished concrete but well used to power tools! Do you need to start this process shortly after pour or is it best to wait longer ? Or can I leave it until I find the time to get to it?

[stonecutter]

Re: Is a variable speed grinder essential?

Wait a minimum of a week, longer with cooler temps, or you will tear out your seeded aggregate and the surface won't polish well.

[Gulf]

Re: Is a variable speed grinder essential?

Rich,
Since you are going to pour in place, you can still use one "trick" of an upside down pour. That is preseeding your counter edgings. (Down here, we call them bands).





I used colored window glass for mine. (Not a lot, since I had a lot of other stuff going on.) I went to a local glass company, who was glad to sell me a couple of broken pieces of their stained church glass drops, cheap! To pre seed the bands I just glued the glass pieces to the form with a very slight dob of latex caulking. When the form is removed, the caulking releases easily from the form.



If you can obtain some church glass that is simular in color to your broken glass for the surface, it will help the bands to match. I shaped my glass shards with a pair of "wire dikes". The hand pads that Stonecutter mentioned are crutial for polishing the bands. And preseeding the bands will save you a lot of time.

I can't stress enough the need for the GFI as Dennis mentioned. I also decked out in what I call Full PPE (full rain geer , rubber boots, face sheild, and rubber gloves). Also, wether or not is a double insulated grinder/polisher or not, do place the plug in higher than the lowest point of polishers cord!

[RichC]

Re: Is a variable speed grinder essential?

Thanks for the advice guys! That's a beautiful job Gulf, turned out great. I was wondering how to 'seed' the edges... Haven't heard of latex caulk before so I'll need to check they out. Why that particular product? I would have expected it to pull off with the formwork and leave a depression in the countertop but it obviously doesn't? Could a small dab of superglue achieve the same thing?
Also, is that just a bead of standard silicone that you used to fill the sharp corners of the form work? I was trying to think of a good way to chamfer the edges of the finished counter

[deejayoh]

Re: Is a variable speed grinder essential?

I stand behind my previous post. It may have worked fine and dandy for you, but I won't recommend doing stuff the way I do it, if I had to modify technique and tools outside of standard safety practice...even if the results achieved are spectacular.

Lol. Well said. I wasn't taking your comments any way other than as recommending standard practices.

[Gulf]

Re: Is a variable speed grinder essential?

....... I was wondering how to 'seed' the edges... Haven't heard of latex caulk before so I'll need to check they out. Why that particular product? I would have expected it to pull off with the formwork and leave a depression in the countertop but it obviously doesn't? Could a small dab of superglue achieve the same thing?
Also, is that just a bead of standard silicone that you used to fill the sharp corners of the form work? I was trying to think of a good way to chamfer the edges of the finished counter

Thanks Rich,

I had not heard of latex caulk being used for this either. It may have, but I never ran across it in my little bit of research. It doesn't take but a very thin film of the latex caulk to hold two flat surfaces together. I would not use superglue, I don't know if that would work. I did not have the first piece of glass or prefilled and polished seashells pull away from the concrete. I did use silicone to chamfer the corners, but you will notice that the hand polishing blocks will easily add a little more chamfer.

If you are are using crushed glass bottles etc., you will not end up with flat edges to apply to the bands. Again, I used broken colored glass window panes. Maybe, you can find some that is a similar colored to what you plan to seed the top. They may not be a perfect match, but maybe an accent or complimentory color. If you add any aggregate larger than sand, that will make a big difference in the look also.