We decided to attempt a concrete bench top for the kitchen. We priced laminate which was going to be $900, so because we were on a budget and wanted to give it a go we went for the concrete. There would have been much, much less work involved in a laminate top, but it wasn't the look we were after.
Note : This is not the way professional concrete polishers do the job I am sure, but we wanted to DIY it and are happy with what we achieved.
After making up some samples we decided on a fairly light coloured concrete with white stones.
We sifted through all the stones and still some dark grey ones slipped through into the mix, but we did learn that the stones sometimes grind up a different colour to what is on the surface (ie some white stones polished up pink!).
Lesson - be very careful with the stones you choose.
The two right pictures above show the stones and the finished coloured concrete.
We also used a white oxide in the mix to get it as white as possible, but it is still not white because of the grey specks in the sand.
The bench top was poured in place. This was because we didn't want joins and didn't have the man power to lift such large pieces of concrete.
Preparation-
We boxed up the top of the cupboards with timber and covered with black tape (to help with removal and smoothness of edges).
The concrete was mixed in batches in a mixer and we barrowed it in.
The mix consisted of -
- 4 parts washed white sand
- 1 part white quartz aggregate
- 2 parts off white cement
- water (enough to target a 150 slump or approx 6 litres?)
- polyfibres
- water reducers and retarders
It was then levelled and trowelled with a steel trowel.
Grinding -
What we found out next was very important. Because we used such high sand content, we didn't need to use a diamond grinding pad, however, it also meant that the concrete took longer to dry. Add this factor to very high humidity in the air and we found ourselves waiting at least two weeks before we could start grinding with any success.
*Note - we did have hairline cracks in areas around sink and stove, however they are not major and we just sealed them with some dust when grinding and then the top coat sealer fills them again.
All the kitchen was sealed up with plastic, but it was still extremely messy, the fine dust escapes through any hole and this made for lots of cleaning!
Using a 5 inch hand grinder we started with a 50 resin pad then added a densifyer - moisture fix (not sure if this made any difference or not) after that 100,200,400,800 and 1500 resin pads were used in that order until we reached the desired smoothness we were after.
I was not wanting a high polish finish, I never wanted a granite look, after all it is only concrete. It was smooth finish we achieved in the end, after quite a bit of work.
Sealers-
This was a difficult thing to find, as most sealers don't have a food grade/safe label. We thought about waxes, but they are not stain proof, which is a worry with such light coloured concrete and they need to be applied constantly.
Eventually I found a product called Fortis 519 matt finish sealer, which acts as a water and stain barrier. We rolled it on in three layers with sanding in between just as you would a timber bench. Happy with the finish.
Final product -
Cost was minimal for the core products, under $200. The grinding pads, densifier and sealer were most expensive and including the purchase of the grinder we were still under the laminate cost, however this does not include labour costs.
It was a good experiment and we learned quite a lot, which we will need for the next major concrete project.
Some finished photos...
PHOTOS OF FINISHED BENCHTOP IN MORE DETAIL WHEN KITCHEN HOPEFULLY FINISHED IN THE NEXT 4 WEEKS...if you are interested of course.
See here for the finished kitchen.
