Polishing your concrete worktop or tabletop.
So you’ve been on YouTube and poured your concrete worktop into a mould with lots of nice shiny bits of aggregate and glass and all the correct reinforcement rods in place. It’s time to tip it out of the mould and see what you have. It’s finishing time.
Firstly before you even start polishing you need to understand the setting and curing process of your concrete. This differs from mix to mix and from manufacturer to manufacturer, so the following advice is generic.
Your concrete will be set within 3-4 days, enough for it to be removed from the mould carefully. If you’ve produced your worktop upside down on a nice flat mould of melamine or similar, you’ve taken it out of its mould and you’re happy with the look of the surface, then you’re ready to polish.
However first your top needs to cure, the concrete is set at 3-4 days but it takes up to another 28 days to harden completely. If you try to polish too soon it won’t be hard enough to get that high glass like sheen you’re after. What you can do though is smooth anything out at this stage, any rough marks or areas that you’re not happy with, polish wet with your diamond polishing pads from 50 grit up to 200. At this stage it’s not worth going any higher in number than that, you’ll need to wait a few weeks until the concrete cures hard to get the polish.
A set of wet polishing pads is ideal for this process. The number and quality of pads you need is determined by the area that you’re polishing. If this is a single table top, then our economy 7 pad polishing set will be ideal. If you’re producing a full set of kitchen tops or intend to do a number of projects we’ve put together a set of pads made up with a mixture of copper bonded and premium wet that would be more suitable. Links to each of these items are at the bottom of this article.
What if I want to expose more aggregate in the top?
You’ve taken your top out of the mould, (or removed the shuttering if it’s a cast in place worktop) and all the nice shiny pieces of glass/marble/stone have sunk a little bit and you’re faced with a plain boring grey concrete slab. What you need to do now is grind the top back to expose the interesting bits. This isn’t polishing it’s something different. Don’t think you can just use polishing pads to remove the surface, you’ll burn through lots of pads and time and just get frustrated.
What you need for this job is a metal bonded diamond turbo cup wheel. These are available in three grits, coarse (36), medium (80) and fine (150).
If all you’re looking to do is remove 2mm to 3mm absolutely maximum then the fine (150) grit cup wheel is ideal, it removes a small amount of material at a time and gives you more control over the surface finish. Alternatively, if you’re not comfortable using a metal cup wheel and you want a bit more control, then the #30 Copper pads are pretty much half way between grinding and polishing, they will remove the surface of the concrete but it will be slower than the metal cup wheels.
If you’re looking to remove more than 3mm of material, you should consider the medium (80) grit wheel. If you feel the 80 grit isn’t going to be enough, then I’d seriously consider pouring your tops again as that’s a serious amount of stock removal!
If you’re not comfortable using the turbo cup wheels or you feel they might be a bit too aggressive, then we suggest our Vacuum Brazed grinding discs. These will be more aggressive than copper pads but less aggressive than turbo cup wheels. Ideal if you want to remove between 1-2mm from your concrete.
You can start grinding a top as early as 1 to 2 weeks, then allow it cure further and create the final polish. It wouldn’t matter if you allowed the mix to cure for the full 30 days, it will just take a little longer to grind.
Once you’ve ground your top with a turbo cup wheel, you’ll have a few marks and gouges that may need to be tidied up. This is where you need a copper bonded polishing pad.
The copper bond pad is a transition between the cup wheel and polishing pads, it’s more aggressive and longer lasting than resin polishing pads, but not as aggressive as the metal bonded turbo cup wheels. Usual one or two of these at 30# are enough to tidy up any marks you’ll have in your concrete top.
Once you’ve ground back the top, smoothed it out with a copper pad you can then start the polishing process.
If you find at this stage that you have some small pits or voids in the surface then now is the time to fill these with a slurry mix of concrete that matched your existing mix (recipes are available on the web for the slurry mixes). Allow this to set for a suitable time (according to the mix) – then start your polishing process.
What machine do I need for all these polishing pads?
Ideally, you need a wet polisher that operates in the speed range of 1500 to 4000 rpm. A regular angle grinder is not suitable for any of the above processes, it simply revolves to fast (usually at around 11,000rpm). A 110v dry variable speed grinder will do if you’re able to run a hose across your work.
We do offer suitable machines manufactured in Germany by FLEX Powertools which are professional quality as we tend to deal with a lot of professional stone masons.
Wet or Dry polishing, which is better?
This is basically two ways to end up at the same result. A professional company doing this day in, day out will polish concrete wet. The consumables are cheaper but the machinery is more expensive and it’s messy.
The advantage of dry polishing shows particularly with cast in place tops where you can’t have puddles of water sloshing around a fitted kitchen. The machines are less expensive (and more versatile) but the consumables (pads) are more expensive and don’t last as long as the wet pads.
Want to put a nice even pencil round on the edge of the finished top?
We produce a profiling tool for this purpose, an r5mm half bull nose tool that fits straight onto a variable grinder or polisher.
If you have any questions, we’ll answer what we can. Feel free to call us for advice on 0203 130 1720.