Crafted Landscapes constructed an outdoor kitchen using concrete for the worktops, this blog post will reveal the step by step procedures, materials used, including tips and tricks for a successful finish along the way.
Introduction
Concrete worktops can be used in many circumstances, whether that be inside the home or externally in the garden for a dining table or perhaps outdoor kitchen, the principles and construction methods are similar.
Design brief
So where do we start, as with all projects, begin with your budget and design brief, create a list of everything you want from your outdoor kitchen, below are a few things you may wish to consider, these are just a few, and every project will vary depending on your specific requirements
· Integrated sink
· Plumbing requirements (taps)
· Preparation space
· Overall size
· Whether you will cast in place or in a workshop
· Foundation support
· Materials that will be used in conjunction
· Style of property
· Surrounding architectural features
· Budget
· Reinforcement
· Level of skill (DIY or Professional)
· Concrete dye / Coloring
· Polish and sealant
Site survey and plans
Once you have considered your brief and prioritised your requirements achievable within your budget, its time to create a design. This can be done with a simple hand sketch, or if you are more technical, a CAD drawing or 3d model would be helpful. The plan needs to take into account the location of the proposed outdoor kitchen, so start off with an existing survey of the space, measure this out accurately being sure to observe all of the site features, below is a list of things to consider
· Proximity to services if you are planning to connect (water / electricity)
· Site topography / levels
· Existing ground conditions / type of soil
· Will a foundation be required or is there an existing slab (bearing capacity)
· Orientation
· Circulation space
· Proximity to trees
· Proximity to fences (risk of fire)
· Proximity to other outdoor dining spaces, how will the space function once its has been built.
· Existing Lighting
Once you have plotted the existing space, you can begin planning how big your new outdoor kitchen will be, consider the kitchens overall dimensions but don’t forget you need plenty of space around the working area to make sure it is inviting and functional.
Will you have one long worktop, or perhaps an “L” shaped design, this will all depend on the space you have to work with.
Below are a few sketch designs we used for our outdoor kitchen
As there are so many design styles that could be integrated within your outdoor kitchen, we are only going to focus on the concrete worktop section of the build. Below are a few materials that could be considered for the main counters
· Concrete block with render
· Timber frame
· Pre-fabricated metal units
· Cast in place concrete
· Brick work
· Tiles
· Corten steel
The finish needs to be durable to the outdoor environment, so consider quality materials that can provide integrity during the changing weather conditions. Any screws or fixings should be stainless steel, timber used should be treated or painted, Hardwood obviously being preferable.
In this example, our kitchen design incorporated two separate concrete worktops, this was advantageous because we cast the slabs in a workshop, and transported them onto the kitchen units once they had cured under cover. This option of course is not always possible, if you are building a continuous heavy slab, it will need to be cast in place, with the weather being so unpredictable here in the UK, we decided this was the best option for us. If you do not have a workshop or barn to obtain cover, you could always set up a temporary tarpaulin or pop up rain cover (canopy) to provide protection whilst working on the slab in-situ.
Material checklist
· MDF melamine or ply formwork 18mm
· High strength concrete (premix)
· Reinforcement mesh
· Screws and fixings
· Tape
Tools and equipment checklist
· Drills
· Tape
· Pencil / marker
jigsaw
circular saw
· Sander (diamond blade polishing pads)
· Angle grinder
· Hammer
· Trestles
· Support beams (timbers)
· Trowels
· Levels
· Tamping equipment
· Clothes and cleaning equipment
· PPE - Dust masks / goggles / ear defenders / gloves etc.
The process
Site set up
Get set up in your work space, create a large area that you can easily work and move around. Using your trestles create a raised platform to undertake the process.
Depending on your size you may wish to use three or even four temporary stands with an additional sheet of ply to spread the weight of the worktop.
Temporary formwork
Using your pre planned design, cut your melamine mdf or ply sheeting to create temporary form work, be sure to allow for an overhang on your worktops. The MDF will also need to be larger than the overall countertop, as you need to fix upstands to the ends and sides, if using 18mm, this will be an extra 36mm to the length and width see below image for clarity.
The ends and sides also need to be cut, we made our worktop 50mm thick.
Once cut accurately, Place your main board onto the trestles and screw down the sides / ends.
We recommend placing masking tape over your screws, as once the concrete spills over, its sometimes hard to re locate the heads.
The edges should be sealed using a sealant
We have seen some contactors using a release agent on the formwork, we did not use this and had no problems releasing the timber once the concrete has cured.
Be sure that all of your formwork is very secure and there is no risk of the wet concrete pouring out, you can add corner brackets and additional screws if you are concerned.
TIP – we would recommend pre drilling the MDF as it can split.
Mixing the concrete
Once you a have prepared the form work, its time to mix the concrete, we used a pre mix, high strength cement bag. This ensures that the mix ratio is very consistent and you will achieve the perfect colouring throughout. Mix the concrete with an electric mixer, or by hand in a wheel barrow.
If you want to change the colour of the concrete, add dyes to your preference. We left ours to have a natural look. You can also add coloured stones / aggregates and tiles to add further detail, this is something we may try in the future should we get the chance.
Add water to create a semi solid consistency, you do not want this to be super wet, but equally not too hard as you have to ensure it is moveable within the formwork. The pictures below may help you determine what we found to be just right.
Spreading the concrete
Once you are happy with the mix consistency, begin adding the concrete to the formwork. Once you have spread 25mm over the whole area, smooth and tamp the concrete ensuring it is well compacted.
Inserting the reinforcement
Once this first layer has been filled, place your reinforcement in, this wants to sit in the center of the slab, cut the sheet with at least 50mm less on the outside edges, you do not want to see the mesh on the polished finish.
We used a rendering steel mesh, seeing as the slab was not super thick, a typical concrete mesh seemed to large for the circumstances. You can also add fiber reinforcement to the mix, but we decided this was not something we wanted to include.
Once the mesh has been placed neatly into the first layer, you can add the second layer of concrete, this should again be pushed into all the corners and crevices, fill to what you think is the top of the formwork, and then begin spreading and compacting.
Tamping / leveling / screeding
Tamping and screeding the concrete is next, this is helpful with a second person. Using a level or straight piece of timber, tap / tamp the concrete from the top, this is another form of vibrating.
Once you have gone along the entire surface, screed the top by pushing and pulling the level across the formwork, this will show if the concrete is too high or too low. Simply add concrete if it looks low, and remove any excess if the bar pulls it away.
Keep doing the tamping and screeding until you are satisfied the finish is level and consistent, you do not want any imperfection in your final slab.
Vibrating
Using a hammer or vibrating rod, go around the slab, tapping over the whole area, this is a very important stage and will help remove any air bubbles from the finished cast. You cant do this too much, so keep vibrating the formwork until the bubbles are no longer emerging.
Let the concrete dry slightly, and use your trowel to iron any issues.
Curing / drying
Once you are happy with the levels and finish, cover the slab up with a tarpaulin sheet, this helps the concrete stay hydrated and not dry out too quickly.
Inspect the slab the next day, check to see how it has set.
We left our slab 48 hours before removing any formwork, of course there are so many external factors that can change this time such as temperature, humidity, etc.
Removal of formwork
Peel off the tape and find the screws, remove all fixings.
Being careful, remove the upstands and reveal the concrete slab, be careful not to chip any of the edges, just go slow and gently detach the MDF sides.
If you do happen to find some areas have crumbled or chipped slightly, you can likely repair this on the sanding and polishing stage.
Sanding and polishing
To obtain a smooth and clean look, you will need to use diamond polishing pads. Starting with the lowest grit, sand your worktop, don’t press down to hard, let the pad do the work, you can add water or do this dry, the wetter the surface the harder the pad will cut into the concrete. Determine how much aggregate you want to expose by sanding more in certain areas. Each time you finish a complete polish of the surface, clear the dust and debris. Work through all of your pads, using a finer grit as you pass over each time. The last pad will be a buffing pad this should leave you with a shiny, glass like finish. Remember to do all the sides and edges taking out any imperfections as you go.
Sealing and finishing
Once the sanding and polishing has been completed and your are satisfied with the overall finish, its time to seal the worktop. There are lots of different sealants available, they help make the worktop waterproof, improve the longevity, and make it easier to clean off stains and marks. Make sure you use a sealant that is safe for handling food and drinks on.
Move your worktop into place.
Transporting
Assuming your kitchen worktops or table has been pre-assembled, it is now time to lift your slab into place and secure.
Of course the more people you have for this the better, one person on each end or corner would be great. Be extra careful not to injure yourselves or damage the worktop in the process.
Fixing
Check everything fits nicely by “dry” installing the slab, providing everything is ok. Spread an adhesive sealant on the underside of the slab or units and place the worktop down, the weight should easily be sufficient to keep itself in place whilst the adhesive dries.
Summary of the process
1. Design brief
2. Site survey
3. Plan your design
4. Material checklist
5. Tools and equipment checklist
6. Site set up
7. Temporary formwork
8. Mixing the concrete
9. Spreading the concrete
10. Inserting the reinforcement
11. Tamping / leveling / screeding
12. Vibrating
13. Curing / drying
14. Removal of formwork
15. Sanding and polishing
16. Sealing
17. Transporting
18. Fixing
Conclusion
That’s the crafted landscapes blog on how to build a concrete worktop,
Thank you for reading my HOW TO BUILD a Concrete work top blog! I hope you have found it useful, and perhaps inspired you to build your own! For similar HOW TO projects, feel free to come and visit my website - www.craftedlandscapes.co.uk
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I hope you have found this HOW TO guide easy to follow and informative. If any of the steps are unclear and require further clarification please feel free to contact us.
References
All of the photographs used within the blog are work of Crafted Landscapes, The clients have given permission to use the Images for this article. The drawings are copyright of CL & have been sketched by Jamie Dobinson. Please contact or credit us with a reference and link back to this source if you would like to reuse any content. Any drawings should be used for Illustrative purposes only.
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