Finally, i get to share with you how I designed and made the most challenging mold I was commissioned to make by Concrete Etc. We are talking about a massive mold - 500x500x350mm. Here is the model itself :

Credit: Model design by Concrete Etc

OK, OK… it is actually the first cast of the mold, but since I forgot to take a picture of the model this will do. Either way this is more about how I made the mold. Nevertheless you have to admit that the shape is simply stunning.

We have to begin with the design of the mold itself. A requirement was a perfect seamless finish and a long lasting mold. Which basically left me with only one chose - thin silicone seamless sleeve mold with a hard supporting shell. And since I wanted to keep the mold on the light side decided to make a fiberglass shell, which also made assembling the mold quick and easy.

Here is a good place to note that the planter/coffee table is available at the Concrete Etc online shop - www.concreteetc.co.uk and also at the upcoming

Midcentury Modern show

Dulwich, Sunday

17th November 2019 - 10am - 4pm.

Tickets are available at

www.modernshows.com/shows/

You’ll have a chance to see this gorgeous looking concrete piece and of course the chance to make it your own.

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The next step was to actually start making the mold. I decided to apply the silicone rubber by brushing it directly onto the model in layers - really unconventional technique for this material, but the complexity - number of overhangs and angled planes.

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This was a long and stressful process as the silicone rubber is not really meant to be used this way and I had to make sure to apply even coats every single time. So, over the course of a week I was able to make the silicone sleeve. The next step was to make a fiberglass shell to support the rubber. Again, this being the world’s most complicated shape - this was not as straight forward as it sounds. The shell had to be made in sections.

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So, as you can see I divided the sections with acetate sheets and it was to *fiberglass.

Fiberglass is a type of fiber-reinforced plastic. To achieve it’s strength and light weight the randomly arranged and flattened into a sheet fibers are being soaked in epoxy or as most of you know it as thermosetting polymer matrix. It is being applied on layer.

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The next step was to make holes for the bolts that will allow the shell to be assembled and held together firmly. And as we all know - You can never have enough clamps.

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Aaaand here it is! The story of the world's most complicated concrete shape and the creation of it’s mold.

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Now, don’t get me wrong I LOVE making molds and I make them good, but it’s all about what you pour in the mold…

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3D printing allows you to turn a digital model into a solid object. The model goes trough a “slicing” software which divides it into layers. The 3D printer uses the information and starts building the object layer by layer from the ground. Three-dimensional printing is an additive process. A process in which all of the material is used to create the desired shape - Additive Manufacturing.

Now, that we have the theory out of the way - here are two statements:

3D printing is an amazing piece of technology that allows you to create anything you like.

3D printing is an amazing piece of technology that allows you to create anything you like out of concrete.

Which one has more of a ring to it? Exactly!

I was recently contracted to make a model and a mold for a custom concrete sink by a UK based company - Concrete Etc. I’d like to take you on a journey and show you how I made it.

I started by 3D modelling the sink according to the specifications that I was given. The order was for a circle sink with the following dimensions - 370 mm diameter, 180 mm tall and 18 mm thick walls. Important part here was giving the sink a sloped base to ensure that the water will flow into the waste. Once I had the model created I was faced with my first challenge - actually printing this sink.

Now, 3D printing the sink wasn’t as straight forward as it sounded. There are very few 3D printers that are actually able to print this size at once and sadly I do not own one of those bad boys. My workaround was to slice the model into nine more manageable pieces. I came up with a pin alignment system and it looked like that:

After I checked, double and triple checked the dimensions I started the printers. I used 5 of my 3D printers for this project. It took a little bit over 130 hours of printing, but in the end, voila the sink model was a reality. As you can see from the images 3D printing leaves distinguishable layer lines that can be sanded and filed for a perfect finish.

Next was assembling the model and finishing it. The first part was pretty straight forward as the fit was perfect. Filling, sanding and polishing the model sink on the other hand were a bit more challenging. This is the most important part of the build. You want, no you need your model to be flawless as it will be molded and every single cast will be as perfect or imperfect as your model. This part takes a lot of patience and as a general rule - the more time you put in, the better it will look like. I stopped at a mirror-like finish.

Once the model was ready it was time to mold it. Now, I wont be going into detail with the molding process as it is really specific and deserves a separate post. If you’re curious now though, you can check the follow post - What is a sleeve mold and how it's made. And without further ado here it is the first cast of this unique sink. What started as a 3D model or even a sketch on a piece paper is now a real concrete sink!

Sleeve silicone molds are in my opinion the best option when casting objects out of concrete and plaster. Clear benefits are the ease of use, consistent results and perfect finish. A downside is the difficulty of creating the sleeve mold itself. Let’s get right into it. When designing a mold or figuring out how to mold an object there are a few things to consider:

1. Lifetime of the mold ( Usually measured in number of pours )

2. Ease of use ( Or how easy it is to demold and reset it )

3. The finish of the poured piece ( Will it have seam lines or not )

4. Materials you’ll be using ( Silicone rubber, Latex, Fiber glass, Plaster etc )

The method of molding an object depends on the complexity of the object. A simple object for example is a sink. The best way to mold a sink is to use a sleeve mold. The function of a sleeve mold is to give the piece an entire finish without any seem lines or imperfections. Those molds usually require an additional support shell, as they are thin to allow easy demolding. The diagram describes the molding process. You start by building a support outer shell and inner plug that will contain the rubber as it is being poured and will act as support when casting pieces.

The sleeve molds are a great way to start producing concrete object.

That is a question I was asking 4 years ago when I was first introduced to the decorative concrete industry. I don’t like to blow my own trumpet, but who else will? I’ve made more than 1200 concrete countertop forms, worked on countless bespoke concrete projects and studied the science of concrete so that I’m able to formulate strong and light weight concrete mixtures. After this introduction, today I can say with confidence that… I’m still learning.

Before we go any deeper we should answer a question that a lot of people ask me - What is concrete? Concrete is NOT just water and cement. Water and cement is a simple mix that is weak and prone to cracking.

To make concrete you need cement, aggregate (sand with or without gravel) and water. Sounds simple right? Well, it’s not. Trust me on this one. Making concrete requires a basic chemical reaction to take place - hydration, the hydration of cement. The water is as important as the cement and the aggregate. You could even say that it is the most important ingredient because if you put too much water you will have an easy to work with mix, but it won’t be strong. And if you don’t put enough water you’ll end up with a mix that is impossible to work with. So, water amount is the most important part in making strong concrete, right? Wrong! There’s more.

The next part is your cement to aggregate ratio. This will only depend on the application of the concrete. It just makes sense - you won’t use the same mix you made a planter with to make a concrete countertop. An industry spread standard ratio is a “50/50” or equal parts of sand and (white) cement. Having said that, this should not be your go to mix as the high amount of cement creates the danger of high temperature and rapid setting, and eventual cracking of your cast. A “50/50” is best used with additional additives that we’re really not gonna go into now. But only FYI there are products on the market that are available - known as GFRC or Concrete admix, that will help you easily produce strong concrete. Or you can also choose to source and formulate the additives yourself - for Set-Retarding, Air-Entrainment, Water-Reducing, Accelerating, Shrinkage Reducing, Corrosion-Inhibiting, Superplasticizers etc. Great way to start in the industry is using ready made admixtures, but eventually you want to start making your own mix deigns. Why? Well, when you go to a restaurant and order Italian pasta do you expect the cook to make the pasta from scratch for you or to use a store bought one? That’s what I thought. Bespoke concrete doesn’t just mean bespoke size and shape, it also means bespoke mix for the unique application.

Next on the list is the type of cement and aggregate you’re using. Choosing those will depend on your budget, the application and your willingness to steal sand from the closest children’s sand pit - just joking about the last one, but sand there usually is of great quality. Every brand of cement is slightly different, every type of cement has different qualities (grey and white cement have different setting and curing times for example), sand varies on size of the grain and water content. Actually the water content in the sand is the main reason I can’t just give you a simple formula to follow. If I tell you to use 3 liters of water for a 10 kg (5 kg sand and 5 kg cement) mix and your sand is soaking wet your attempt of making strong concrete will fail.

The only way to learn to make strong concrete is to start mixing. The right amount of water, sand and cement will produce the strongest concrete on the planet. Ask the Romans, they never bought any admixes…