Casting kitchen worktops
With some experience in creating molds and casting using mainly concrete and our love of terrazzo we decided to go large and cast our own kitchen worktops in the new extension… No pressure!
A tiny bit of background before I get into the nitty gritty…
Mr EH spent last summer experimenting with concrete and he cast some pretty gorgeous pieces using handmade molds, aggregates and dyes. The feeling was strong about using concrete for our kitchen worktops but as much as I like concrete as a material it felt just too bulky and industrial for the space we were looking to create with the new extension.
This feeling about concrete combined with unearthing these two photos I took years ago during a contract working at an old art school led us firmly into the terrazzo corner and we developed a total love for it.
There was no going back - terrazzo it was, but what base material to use?
Finding our material
We had a lot of criteria for this base material. It ideally needed to be as environmentally friendly as possible (while being friendly to the humans working with it). It had to provide a strong end product that would resist stains, repel water, be cleanable and of course non-toxic. It also needed to be pliable enough to be poured into a mold, lend itself to holding a terrazzo design and be workable from start to finish in a domestic environment without the need for specialist equipment. A pretty tall order!
Enter, the answer to all these points - Jesmonite! (At the bottom of this post I'll add a full description of Jesmonite and a link to the official website.)
But in basic terms Jesmonite comprises a gypsum based powder and a water-based acrylic that when combined creates a resin and a range of colours can be created using specialist pigments.
We experimented for months - making small items, mixing pigments and refining our terrazzo technique. (Our friends and family all got Jesmonite products for Christmas last year!) Then at the start of this year we started casting larger pieces in anticipation of the kitchen worktops!
Creating the mold
We used sheets of marine ply (expertly cut and fitted to the tops of our cabinets by one of our builders) to create a stable base. When researching our challenge had been to find a suitable product or material to create a consistent edge along the run of the worktop and island and around the cut-outs for sink and hob that we could seal to prevent leaks during casting and would give enough clearance for the cabinet doors.
Quite a tall order! We rolled through options like melamine faced chip board and polycarbonate sheeting before finding a specialist product - only available from America but totally within budget and totally ingenious! It's called Z Counterform and I'll link to it at the bottom of the post.
Basically the Z Counterform product screws in along the front of your base and provides a neat edge form in which to cast. Once your material is set the front of the form snaps off revealing your cast material for finishing. Hopefully this picture helps to explain that!
Amazing stuff! It seems to be widely used for concrete casting but we couldn't find information about using it with Jesmonite, so we tested using a short section and all good!
As with most DIY projects - small or large scale - it's all about having the right tools for the job and having a fully thought-through plan to execute. My Dad was a skilled home improver and major DIY-er and I learnt so much from him about success being in the planning and the preparation, the right tools and the right attitude! (Thank you Dad x)
We bought this amazing 'cuts everything' saw from Evolution Tools (totally not sponsored) and it was amazing for creating the very precise mitre joints we needed to make in the edging form.
Ahead of the big day - AKA the mix and pour day - I'd pre-cast lots of batches of coloured Jesmonite using specialist pigments. The terrazzo palette is based around the colours of our existing dining room chairs. To make the chips we poured thin sheets of these coloured batches, left them to cure and then broke up into chips which I then sorted into larger and smaller sizes. So, with our coloured chips and our edging form in place we were ready to get mixing and pouring!
Large-scale casting - the process
Jesmonite is available in a number of variations and we went for AC730 as it most closely replicates the strength of concrete and the powder element comes pre-mixed with an aggregate that once sanded gives a delicate shimmer finish.
It's all about the proportions when it comes to working with Jesmonite, the powder and liquid need to be mixed in particular ratios. The Jesmonite data sheets have all the information you need and their customer service is spot on for checking the detail.
And we had our reinforcements in place in the shape of rebar sections for the island overhang and fibreglass sheeting to place across the whole surface area in between pours.
So, with calculations in hand and our chips all proportioned out we measured out the first batch of materials - and we were off!
With our island area at roughly 2m2 and the other run of cabinets section at around 3m2 we needed a lot of Jesmonite to create the depth of worktop we were aiming for. With a bigger team (rather than just me and Mr EH) we could have probably mixed enough to cover each of these areas with far fewer batches of Jesmonite mix. But we decided to split things down into more manageable pour sizes, even with this approach we were mixing roughly 30-35kg of Jesmonite at a time!
The curing process for Jesmonite ranges from 5 to 15 minutes - not a lot of leeway for mixing adequately so all the powder is absorbed, adding chips and then getting the mix up high enough over the area to do an effective pour. I have to say that our first pour was totally nerve-wracking and it didn't go perfectly either! Had we made the most terrible mistake attempting to make our own worktops...?
It was pretty much tension mansions but a tea break, a rethink and some adjustments to our technique and the second pour onto the island went like a dream. Here's that second pour in place...
We repeated the process to cover the other run of cabinets section and then the really tough bit - we needed to leave the Jesmonite to cure fully and ideally that meant overnight. We had to go out to resist temptation!
Day Two - the big reveal
The whole renovation has been dusty (#therewillbedust) but this is where the levels of dust went up to the max. Like the dust-amateurs we are we thought our crime scene set-up below would help...
The dust had other ideas!
In full dust protection - goggles and masks - we started the epic process of sanding down all the Jesmonite. It's hard work but the most rewarding! The first bit of sanding takes off the very top layer of Jesmonite and this is when the terrazzo begins to reveal itself - the biggest treat!
It took us over a day to fine finish the sanding, partly because Mr EH took the skin off the end of his finger (don't worry reader he's in full recovery) and then about five hours to fully clear up all the dust! And then the Jesmonite needed sealing to protect it from staining and fading and to give it a water repellent finish.
But damaged fingers and exhaustion aside we are utterly and totally delighted with the results!
That turned into an epic post! If you are still reading I really appreciate you taking the time, and I hope that this has be useful, interesting, or at the very least has helped put you to sleep!
Now we're recovered there are plans for some outdoor Jesmonite - watch this space!
Info, Shopping List & Suppliers
Jesmonite was invented in the UK in 1984. The original compound was an acrylic-modified gypsum composite and is still sold today. Jesmonite was conceived as a safe alternative to fibreglass and as a lightweight alternative to cast concrete.
Official Jesmonite website and product info
Evolution Power Tools
Material of the Year - Jesmonite at the London Design Fair 2017