Well I thought it was time I have a crack at writing this latest blog update on our newest project.
As you are well aware, Bec and I love to undertake jobs that are challenging, and this one is definitely up there!
Behold the beginnings of our Concrete Benchtop...
Finally we have made it to this point, designing and building our own kitchen benchtops. This has been something we have wanted to do for a while, after getting quotes for caeser stone, corian and polished concrete seemed outrageously expensive with some quotes exceeding $8000.
So where to start with this process? A lot of research, and a lot more research. Plenty of people around the world have done them, and a small handful have written great blogs explaining processes, what to do, and what not to do. This was helpful, but like all things it makes more sense if you just jump into the deep end.
We started by creating templates using corflute. We already had a tap and sink picked out. It was helpful to create the cutouts for the sink and drain sizes which would be integrated into the mould.
It seemed Melamine was a very popular choice for moulds, possibly cos it was cheaper and easy to work with? But I liked the idea of using formply because it's surface is super shinny and smooth and the material is structural. We created the moulds at 50mm thick because wet casting requires steel reinforcement and the steel needs sufficient concrete coverage below and on top.
We decided to incorporate a 'waterfall' end to our kitchen, so four moulds were created in total. The largest would be for the breakfast bar which was just over 3 meters long. We purchased a sheet of Yellow Tounge for this one which was long enough at 3200x900. This proved to be the hardest mould to get correct due to its size. All the moulds were created so that the base of the moulds would actually be the top face once flipped, so they were all built upside down.
After levelling out under the house (Septembers blog) we set up stands for each benchtop using a bunch of old computer bases that were salvaged from a job I was working on, and saw horses. Sub frames were made up to sit on these stands which were levelled out ready for the moulds to sit on.
After a lot of experience with making moulds from my uni days, I decided it was easier to pay someone to make my foam 'cut outs' which would be used to create the voids in the benchtop ie sink cutout and drain and hotplate. Polystyrene was used and cut using a CNC hot wired machine to create exact cutout sizes. 50mm Alloy angle was used where long straight edges were important to get right, these were also salvaged off a job.
The sink and drain wedge were sikaflexed to the formply in the correct position. I also had to make up the cutout hole for the tap which our friends Rach and Luke purchased on our behalf from Harvey Norman commercial. This was simply a bit of PVC pipe and a spray can lid.
Once the moulds were created they need to be sealed. This is super important because sealing serves two purposes:
1. Forms a nice rounded edge on your finished surface once the benchtop is flipped over
2. Stops water from the concrete escaping the mould and leaving dags
A mould release was then sourced from Know How concrete in Brissy which funnily enough had never been sold for the use in concrete benchtops??? Although this was not necessary and others didn't mention it in their process, I thought it couldn't hurt especially on the yellow tounge. This was simply wiped into the moulds on all the surfaces.
Pour Day!!!
We were lucky enough to score the help from one of my managers for the day, who's had a lot of concreting experience in his time.
All the steel mesh (3mm 100mm square grid which I managed to score from my crossfit coach) was cut in the morning for the moulds and stored ready for use.
This particular batch was made using Sunstate GP Cement, the whitest washed river sand available and a small 5mm drainage aggregate.
We spent about 4 hours that Sunday and were super stoked with the efforts for the day! Then it was playing the waiting game....
Instagram Saves the Day
A few pics were posted on Instagram that day and a few days later I received a comment on one of them with a few helpful tips. It was from Mitchel from Mitchel Bink Concrete benchtops....funnily enough a Canberran with his workshop in Hume....what are the odds.
He mentioned it was important to get the moulds flipped ASAP onto foam blocks and that having them cure in the state they were (in the plywood) could cause 'curling' which is where one side of the mould (the face down side) cures slower than the other and can make the concrete curl.
I was straight onto this, and the following weekend I stripped the edges of the moulds and started flipping the small moulds by myself onto foam blocks as directed. These were pretty heavy on my own and I wasnt looking forward to flipping the larger ones alone, so I brought in some muscle! The neighbour gave me a hand with his mate and we flipped the sink mould and then the big mumma was next!
3 guys, 1 stupid mistake and 1 little hairline crack later...
The small ones were looking so awesome and the sink one turned out almost perfectly! The foam cutouts worked great and they would all just require a good sand and polish to complete.
Big mumma had received a stress crack from dragging along and flipping against a small screw which was still embedded in the formwork.
I was pretty bummed at this stage, but deep down I already had a bad feeling something was going to happen given the size of this thing...approx 220kg (from the calcs).
A few days passed and the crack kept getting bigger and bigger and I realised this was no longer a small hairline crack and was actually structural.
More Research
Mitch had put me in contact with the boys from
Pop Concrete here in Brissy. I spent some time with Sami checking out there workshop and processes and shared my experience of which he inputted that alot of his clients don't like the 'green' look and some tips to eliminate other issues.
The Remake
The decision was made to cut the damaged 'hotplate' side out and just remake that part of the benchtop! I remade another mould but before we proceeded to pour, we tested a small part of the concrete with the sealer we would use once polished. We coated it twice and bought the piece into the kitchen only to realise that we weren't the biggest fans of the colour. Using the GP cement gave the concrete a green tinge, hence the name 'green concrete'. This was not apparent out of the mould and only once the clear sealer was brushed on.
We ummed and arghed and we decided to just remake them all! We learned that we should have done some test pads in the beginning using different coloured cements.
A few small moulds were made and a lot of 'stepping stones' created because we tried all sorts.
- Offwhite Cements with various percentages of black oxides 0.01% - 1% (1% turned almost completely black)
- White Cement with percentages of oxide ranging from 0.01% to 0.1% which was actually more dramtic than you could imagine.
Finally we found the colour! The moulds were put back together last weekend, new foam pieces were made and this time we got the hotplate cutout made as well.
Mach II
Today we re-poured all the benchtops, this time with Bec as the main batcher and I was the mould filler and leveller.
The Mix (multiplied by 3 to get 1 barrow load)
3lt bucket = 1 Part
3 Parts - Cement Australia White Cement
5 Parts - White River Washed Sand
8 Parts - 5mm grey drainage gravel
2.25 Parts - Water with Davco Plasticiser (250ml in 150lts fresh water)
0.05% - Cement Australia Black Oxide
2% - Trinic Admix
1.5 Cups - Micro Polyfibres
At 30 weeks pregnant, Bec was a pro on the mixer which was so helpful. We killed it together and spent about 4.5hours form go-to-whoa.
Another hot tip given was to cover the tops with 200um black plastic once they had been troweled off and set.
We will now wait a week and a bit to 'strip and flip'. Then we will wait 28days for a full cure before attempting any grinding and polishing! This will be a whole other blog in itself so stay tuned.
Until then,
I hope I haven't bored you, this was also for my personnel records just in case we decide to do this in the future.
Azza
