How To Create A Waterfall Edge

What is a Waterfall Edge?

ChatGPT describes it as;

"A design feature in concrete worktops where the surface extends vertically down the sides, creating a seamless, continuous flow from the horizontal plane to the floor or cabinetry below. Often used for aesthetic appeal and structural integration, a waterfall edge enhances modern and minimalist designs while showcasing the material’s texture and durability."

Personally I think ChatGPT did a great job there!

So how does one create the mould for a waterfall edge? Well instead of writing a TLDR article I've come up with some lovely pictures. But first lets have a chat about the general materials you'll need.

Materials

The materials you will need will of course depend on your design and where you are building it. Indoors, outdoors, kitchen etc. In our guide we assume you will be creating a frame or carcass from timber but you can of course use masonry or blockwork and indeed if you are creating your masterpiece inside for a kitchen island for example you'll likely be thinking about going over kitchen cabinets.

Outside of the substructure we recommend the following for building your mould:

Cement board (9 or 12mm thick)
18mm thick Plywood
15mm thick Melamine
4x2 timber for reinforcement
general purpose silicone sealant to be applied between all materials and edges.

In this example I will show you how to build a mould which for a concrete edge profile that is 42mm in thickness. Exact? Yes it is. If you read on you will see why.

Step 1 - Build Your Frame

As said above there is no hard and fast way to do this. It really depends on the design you are wishing to achieve or copy.

In this example we're going to assume that the structure is being built from timber.

The image above is to just show the waterfall edge so ignore the dangling bits of timber!

Step 2 - Cement Board

Once your frame is built, you have to have something for the concrete mix to sit on once you've poured it right? Otherwise you'll be plopping straight onto the floor or ground. We recommend cement board either 9 or 12mm. The reason? Its strong, inexpensive and most importantly expands and contracts at a similar rate to concrete. Thus you will be less likely to get any hairline cracks.

Affix the cement board to the frame with screws. Bond any joints with construction adhesive. Use a type with low modulus, the type thats harder and less rubbery. Try to be neat and bond the edges, board to board. Don't smear it all over the surface.

You will nead to overhang the cement board over the edge of the frame by at least 25mm. You'll see why in the next step.

Step 3 - Attach 50mm Plywood Strips to the Cement Board

Now I should have mentioned this before: the cement boards are going to stay in place in this method. If you want to remove them then I would definitely council you not to on the horizontal surface. Firstly it would be a much more complex build, secondly the cement board will provide a great level of support and reinforcement and thirdly its not going to be seen! Unless you're falling down drunk and you're on your back beneath the countertop, in which case you wouldn't care anyway!

For the waterfall edge you may want to have it all exposed, i.e. concrete visible on all edges. In which case you will have to come up with a way of removing the shuttering. That's for another discussion, which myself or the team are happy to have but not for this article.

So with the cement board staying in place, screw the 50mm plywood strips to the underside of the cement board. 25mm beneathe the cement board, 25mm jutting out.

This is going to form the base of the lip which is going to overhang the cement board and allow the cement to be hidden when the concrete is cast.

Step 4 - Attach Melamine Strips

Screw the melamine strips to the plywood attached in the previous step.

Why melamine and not plywood? Well melamine will give a MUCH better finish right off the bat as compared with plywood which could potentially suck in moisture.

The melamine strips should be the thickness of the plywood plus the cement board plus the thickness of the concrete you wish to cast (we recommend a min. concrete thickness of 30mm) so in this case the melamine should be 30+12+18=60mm wide.

30mm for the concrete, 12mm for the cement board and 18mm for the plywood strip.

Step 5 - Attach the Vertical Outer Formwork

We recommend using melamine for the end panel formwork or shuttering for the same reason as above - you will get a very smooth finish from it.

Also on the vertical edge, when the concrete is poured the fibres won’t show up because they are bound within the concrete.

Screw the board in place, but also put a bead of silicone sealant along the edges of the melamine where they meet and also along any other meeting surfaces, in this case the brick wall and the patios floor.

Step 6 - Reinforce the Melamine Shuttered Edge

Now here's a thing. I'm a bit of a nerd so I'll use this as an opportunity to teach a bit of physics!

Concrete when its poured onto a horizontal surface won't apply a lot of pressure. Imagine lining up a load of bricks side by side on the floor. The force each brick exerts on the floor is the weight of that brick on simply the area of the floor its sat on. Now imagine those bricks sat on top of each other. Same combined weight but all pushing down on the area of a single brick on the floor below!

This force increases the higher you go and the same goes for concrete. And when the concrete is still in a liquid state, the pressure on the concrete at the bottom of the waterfall edge is extremely high.

This is coincidentally called "hydrostatic pressure". Lesson over. Class dismissed.

So you will need to reinforce the vertical formwork to prevent the concrete from blowing out of the mix.

Oh and by the way, if you're asking yourself the question, "is this enough reinforcement?", you've just jinxed yourself. Add more. More is better than less!

Step 7 - Mould Prep & Casting

This is in the instructions for Cast-In-Place moulds so check out this link for further info. The same applies to the the vertical surfaces as it does the horizontals, so be mindful that when you're incasing your vertical waterfall edge mould you'll strill want to prime the cement board, apply a silicone bead and apply mould release the the parts that will be stripped away once the concrete is cast and cured.

When you come to casting, cast the waterfall edge first and fill that up. Give the mould a good tap whilst doing it to release trapped air from the mix and poke a stick down the gap to ensure there are no big voids. This is unlikely because the mix is self-compacting and self-levelling but do it anyway just to be on the safe side. Once the vertical panel is filled then you can pour the horizontal as per our instructions. Here is a useful video for just this.

So just for completeness its worth showing you dear reader, how the concrete will look once the outer mould parts are stripped away so here is a nice little animation below to help....

I hope all of the all of the above has helped you in planning your project and as ever if you have any queries please reach out to us and we will help you achieve your project success. Go on! Have a go. You can do it!