How To Make A Polished Concrete Worktop
It’s not rocket science and you don’t need to reinvent the wheel! However it does take a little thought and prep.
When we first started our sister company, Concrete Carrot (take a look www.concretecarrot.co.uk), we made every mistake possible. So with a little help from us you won’t have to make them and can benefit from all the setbacks we endured!
Below is our easy guide to making a basic PRECAST concrete worktop or concrete countertop with a list of the items and ingredients you will need.
PLEASE NOTE - this guide is not for “in situ” or “cast-in-place” concrete countertops. We have a separate guide for this (to be uploaded soon).
Before you start your project we recommend that you read through this entire guide and arm yourself with as many of the tools as possible. In the guide we have listed tools and materials required and where relevant they will be suffixed with “[I]” for Ideal, ‘[A]’ for Alternative, “[O]” for Optional and “[E]” for Essential
[I] is the ideal and where relevant a lesser [A] Alternative will be given. [O] is stuff that can be really useful but you can get by without!
Also dotted throughout the document we have listed handy HINTS which will be of use.
So lets begin and start with...
a. Space and a surface large enough to make your worktop
b. Access to the space that will allow you to easily move the concrete to its final location
HINT - Space all the way round your “casting” table is very useful to get to all sides of your mould so you can nail down the details
HINT - Do a walkthrough of everything from building your mould to transporting your concrete from your workshop to the final location. Visualise it in your mind, every step. Sounds daft but in the early days this simple exercise saved us lots of bother.
2 MOULD BUILDING TOOLS & MATERIALS
- Glue gun [E]
- Carpenter’s squares [E]
- Table Saw [I], Circular Saw [A]
- Silicone tools [I], rounded pencil [A]
- Glue sticks for glue gun [E]
- Melamine sheet(s) [E]
- General purpose silicone sealant [E]
- Silicone sealant gun [E]
3 TOOLS & MATERIALS FOR MAKING YOUR CONCRETE
- Forced Action Mixer [I], Paddle Mixer [E]
- Paint brushes [O]
- Clean clothes or rags [E]
- Bucket trowel [O]
- Midget [I], standard size plastering trowel [A]
- Plastic Sheets to cover the concrete [E]
- Pump sprayer [O]
- Heated blankets [O], Non-heated blankets [A]
4 TOOLS & MATERIALS FOR FINISHING THE CONCRETE
- Trestles [I]
- Hoover/dust extractor [E]
- Mirka Sander [I], Standard Orbital Sander [E]
- Sanding Pads [E], Mirka Sanding Pads [I]
- Roller frame [E]
- Foam roller [E]
- Kettle [E]
- Pump Sprayer as above [O]
- Food mixer [I], Whisk [A]
- Flexible filling knife [E]
What’s not listed above is equipment to clean down after each and every process. We’ll assume you’re going to wash your trowels and mixer paddles, bin or recycle any waste etc.
So now that you’ve been on your shopping spree you can begin! The basic method in chronological order is listed below;
- Build moulds
- Silicone moulds
- Apply mould release to moulds
- Mix & Cast concrete
- Pre-demould finesse
- Etch & Clean
- Neutralise E & C
- Polish off slurry
- Sealer 1 to 4
1 Build Moulds
Take a look at the video which shows how to build a basic mould;
2 Silicone the mould
Take a look at the video which shows how to silicone a mould;
3 Grease Moulds
Take a look at the video which shows how to apply mould release oil to a basic mould;
4 Mix & cast the concrete
Videos Coming Sooooooon! In the meantime, check out the application instructions provided with the Premix Kits.
Once you have finished casting your concrete you may be tempted to down tools and leave. Don’t. You have one or two more small tasks to do.
Those plastic sheets and blankets are in your shopping bag for a reason. You’re now going to cover your concrete over with the plastic sheets to prevent too much water escaping for the next 12-18 hours. If too much water does Escape and the concrete begins to dry, it compromises the early curing of the concrete and can weaken your it in both the long and short term.
In fact before covering with plastic, you’re going to splash or spray the concrete with plenty of water to prevent the concrete from drying at all. Don’t be mean, be liberal.
Now cover the concrete with the plastic sheets and rub the plastic sheets to “wet” them against the concrete.
The final stage of this process depends on the temperature in your workshop. If you’re lucky enough to have a heated workshop or it is the middle of summer then you will hopefully have an ambient temperature of +18degC. No blankets required. You can demould in 12-15 hours.
If you have a temperature between 15-18degC the curing process will slow but will nonetheless take place.
If you have heated blankets then they will be useful in speeding up the initial concrete curing ready for demould. Without you’ll be looking at approx 18 hours before you can demould. With heated blankets you can demould at 15 hours.
If your workspace is at 15degC or below the concrete curing process will grind to a halt. So you will need to provide assistance. The easiest way to do this is with heated blankets. Modern heated blankets are low-cost and low energy. Leave them in place and on for 15-18 hours.
If you are using heated blankets, make sure ALL of the concrete is covered.
HINT - Confucious (probably) said “A patient person will not snap concrete”. He was extremely wise. Don’t demould too soon.
HINT - after the above prescribed durations, uncover a corner of the concrete, stick your nail in. If you can’t dig into the concrete, grab a proper nail. Dig that in. If you can’t dig any concrete away, you’re ready to demould.
6 Pre-demould finesse
Ok. So you’ve been very patient. You’ve watched the clock and.... IT’S DEMOULD TIME!
But wait. Sorry. Not yet. If you’ve cast your concrete as per the instructions so far, you have a little finessing to do. The good news is you can uncover the concrete. Pack those blankets away for the next project and fold up that still wet plastic neatly.
Where you’ve cast your lips, downstands etc. you will want to sand off the tops within the mould to neaten them off. Plug in your orbital sander, attach it to your hoover and put on your PPE. Now start sanding off the lips. Have a look at the video below for guidance.
Again a warning. If you’ve reached this section too early, thinking you can somehow cheat the system and try to demould too early be warned. Be afraid! The author (hello!) in the early stages of his concrete career did just that.
The you'll have to be even more creative...
So be patient. Stick to the curing times listed in the previous section and you’ll be good.
So time to demould.
Before you do anything have another walkthrough. Think about where your hands are going to be holding the concrete where you’re moving it to etc. Most likely you’ll be flipping the concrete to a location nearby. You’ll be putting the concrete onto trestles the right way up. Your first view of your new baby!
You don’t want to be moving it too far because it WILL be heavy. This will be a minimum 2-person job if not more.
You may be wondering why the trestles are important. Up until now, the concrete has been enclosed on all sides. Moisture loss has been even from all surfaces. If you now flip your concrete and place it right way up on a solid surface moisture will leave the upper air-exposed surface faster than the enclosed lower surface. During this secondary stage of the curing process the concrete can still move and will curl if the moisture loss is not even. The trestles will ensure that a pretty much equal surface area on the underside will be exposed in comparison to the upper surface.
Time to get started. Knock off the melamine formers encapsulating your concrete. Clear the excess snots of concrete, glue and remaining bits of melamine stuck to the casting table around the concrete. Why? Because you’re most likely going to be sliding the concrete off the casting table and any excess bits stuck the the table will scratch the surface of your concrete.
Gently lift the concrete away from the tabletop. DO NOT use scrapers or chisels etc to try and lever up the concrete, you’ll just damage it. Grab a corner and pull horizontally. This is where the release oil will do it’s magic. It’s still there and it’s providing a thin film of “anti-friction” between the table and your concrete. Be patient. The concrete will move eventually.
When it does, slide it to the edge of the casting table, raise it up... actually. Forget the verbal description. Watch the process in action. In the video below, the team are remoulding a small section but the same applies to larger pieces as well.
8 Etch & Clean
Firstly, well done. You’re now at the top of the downhill stretch with the finish line in sight! There are still a few hurdles but these can easily be avoided if you follow the plan.
You’re fresh and freshly demoulded concrete is now resting (still curing) on trestles in your workspace. Right now the surface of your concrete is looking cloudy, a bit scratched from the demould process and can look a bit, well, poop. Don’t worry. Things are going according to plan!
The cloudy-looking surface you are looking at is called the “latence”. The latence is a very weak layer of cement paste. This has settled at the bottom of the mould and forms a kind of temporary protective layer between you and your soon to be beautiful new concrete! It’s time for the ugly duckling to become the swan.
Firstly put on your PPE, making sure any exposed parts are covered. Read the MSDS sheet provided with the Etch and Clean and EC Neutraliser and take them seriously.
Specific instructions are provided with both products which are useful, but there’s nothing like seeing the process done live through the medium of a dodgy smartphone video (see below). The trick with this process is to watch for a slight foaming or “fizz” of the concrete surface. At this point the cloth you are using to move the solution around will begin to drag a bit more than at the start. You’re roughing up the surface ever so slightly and the process can take up to 5 minutes. Once the surface feels uniformly “rougher” then thats the time to stop. Check out the video below to see the process in action.
9 Neutralise the Etch & Clean
For this stage you will need the aptly named Etch & Clean Neutralising Solution. The purpose is to obviously negate the effects of the etch and clean process, i.e. stop the chemical reaction which is removing the top layer of cured concrete. In a similar fashion to the Etch & Clean Solution use, apply the Neutraliser and make sure all areas have been doused, including any vertical surfaces. After a minute or so, wash the Neutraliser off with clean water again giving the concrete a good dousing.
10 Sanding The Concrete
You can now sand the concrete using an orbital sander and either dry sand with 80, 120, 180 grit papers or better still using wet/dry sanding pads (80,120,180).
If you are wet sanding, keep your sander on a low speed and use a water sprayer to continually keep the concrete wetted down.
Work up through the grits ensuring that you are sanding evenly so that you get a nice continuous finish.
Don't be afraid to go back a step if you think that you haven't quite got things right.
11 Apply Smoothing Paste
You’re now at the last part of the processing stage. Unless you are extremely lucky you will undoubtedly have a few pinholes and larger “bug” holes which will now need filling if you want your surface to be in anyway hygienic.
For this you will need our Smoothing Paste Kit, the pump sprayer, a filler knife or spatula and gloves.
Firstly mix the Smoothing Paste according to a thick creamy consistency or thick custard depending on your preference. Once thoroughly mixed and blended, lightly spray your concrete surface with water from the pump sprayer. It only requires a very fine mist which will prevent the now drying concrete worktop from sucking the moisture straight out of the Smoothing Paste mix.
Next pour a small amount of paste onto the concrete and work into the pin and bug holes. Use either your hands or the spatula, either way the aim is to fill the holes level with the concrete surface whilst leaving as little paste residue on top of the concrete surface. The flat edge of a spatula or filling knife makes light work of this.
Watch this short video of paste being applied.
12 Polish Off Smoothing Paste
So 4 hours have passed. You’re now ready to sand any paste residue. The easiest way to do this is to use an orbital sander (such as a Mirka) with a 120 to 180 grit sanding pad. Just like any cement-based material the smoothing paste will take a few hours to harden and go through the various curing stages.
You're aim here is to ensure ALL of the residue is removed from the surface and the now hardened paste remains ONLY in the bug and pin holes.
(If you aren't happy with the holes and you think they may need another pass, then do so. Get it right before you move on.)
Before you can move on to the next stage (sealing) the slurry needs to have cured/hardened enough so that its not simply washed away. We’ve learnt the hard way!
We suggest again approx 4 hours as a minimum.
13 Sealer Coats 1-4
Before we dive straight into the sealing its worth just having a little chat about what you’re actually doing when you use our sealing methodology. Sounds daft I know but if you get the concept you’ll understand why we advocate 4 coats, the time intervals they should be applied in, the mixing combinations and the ambient conditions we recommend.
So to begin...
When you think of sealing your concrete, think not just of the surface but of the top 5-10mm of the concrete. You’re effectively trying to fill up that 5 to 10mm with sealer consecutively over the four coats, with the final coat, which is the least dilute, sat pretty much at the surface.
The first coat is the most dilute and as such penetrates further into the concrete. When this begins to set or cure, it “locks” the depth to which the next 3 coats of sealer can penetrate. This is more than demonstrated during application - the first coat is sucked into the concrete and loads of liquid has to be applied to ensure the concrete is saturated during the process. In the subsequent coats the absorption reduces and by coat 4 the sealer goes a very long way compared to coat 1.
We recommend that a 10-12 hours as an absolute minimum is left between the coats of sealer. This allows the chemical reaction that takes place with each coat to be well on its way, locking out any penetration below the level already reached by the previous coats. Also if the coats are done too soon and the previous coat has yet to cure properly, you will be diluting the previous coat and at a minimum interrupting the cure and at worst preventing it from curing at all.
If you’re on a strict deadline and you’re up against it, you could seal at the beginning of the day and then at the end, but make sure that the ambient temperatures are high enough (18 degrees)
Through our own experience we know that at or below 15 degrees that curing of the sealer (and concrete for that matter) grinds to a halt.
If your workshop temperature is below this, your sealer will most likely fail. There are various things you can do to head this off. We opted for heating our entire workshop. In the depths of our Welsh winter our workshop can sometimes drop down to 15 degrees even with the heating. It’s at this point we have to break out portable heaters. This is another option if you don’t have central heating.
A further option is heated blankets, the kind used to heat the bed. These are readily available and if you plan on making polished concrete for a living these are a worthwhile investment.
Your concrete is cold. Even in a centrally-heated workshop your concrete is only going to reach about 16-18 degrees once the initial cure has taken place. It has a thermal mass but will need fairly direct heat before the temperature will raise. Why is this important? Because the sealer comes in two parts and will cure as part of a chemical reaction and that reaction will be more efficient if it doesn’t have to produce much of its own energy (heat).
You’ll need a kettle. Instead of warming the concrete up to the right temperature to receive the sealer its easier to warm the sealer. This can be done by ensuring that the temperature of the water used to mix up the sealer is at 50 degrees. Half boiled, half cold tap. Simple.
Hopefully all of that will have given you a better understanding of how the sealer works and what you are trying to achieve, when you seal your concrete.
Calculating The Amount Of Sealer Required
As mentioned our sealer is applied in 4 coats. Each coat has a different dilution with coat 1 being thinnest to penetrate deeply into the concrete. So to calculate the amounts required follow the handy guide below;
1. Measure the area of concrete you are sealing in square metres.
2. Use our Sealer Calculator to work out the amount of Part A, Part B and Water is required for each coat.
Mixing The Sealer
We provide comprehensive instructions for mixing the sealer in the form of a PDF. It differs from the manufacturers own instructions and with good reason. Our way is better!
To help demystify the process please take a look at the video below.
A few tips about the application of the sealer.
- Always use a high density foam roller. Don’t be tempted to use a cheap alternative or do something like squeegee the sealer or use a microfibre cloth. We’ve done that and many more silly ideas. They just don’t work.
- You are trying to saturate with each coat. If you work on the blanket rule that each coat takes approx 15 minutes to saturate the concrete you can’t go wrong. Once the 15 minutes is up its time to start taking the excess sealer off.
- Thin to win! The thinner the final coat the better. Or in other words, remove as much of the sealer from the surface as possible to allow subsequent coats to penetrate and with the final coat to leave the sealer just at the surface of the concrete and not on top of it.
- Use kitchen towel to remove excess from the roller when removing the sealer. Make sure you wear gloves when doing this.
- Finally, don’t rush.
Below is a video of a coat of sealer being applied.
YAY! The final stage. Once your concrete has been fully sealed and the sealer has been allowed enough time to cure and dry, you can optionally add an extra layer of protection and sheen to your concrete with our food-safe concrete wax. In fact you can use it on your hair, your shoes, your lips and any other part of your body (don’t send us photos). It’s completely safe and is a very enjoyable finessing process. We recommend this is done after installation but that’s up to you.
Oh! Installation? That’s a whole other story :)