I would like to have a concrete slab that is white (or very light), does anyone know how to achieve this?
If you follow the practices of plastic boat/surfboard builders, you polish and wax the mold. Then you apply a "topcoat" and can proceed with casting and reinforcing. Someone suggested epoxy, but I'm unsure if it adheres to a waxed surface. What are the alternatives?
wireless2000: You can mix your own concrete with cement, water, and white marble sand.
wireless2000: You can mix your own concrete with cement, water, and white marble sand.
A thought here:
For those of you who have achieved a mirror-like surface (as pictured in Finja's brochure), how did you do it?
I have tried sanding on a small test plate down to 1200 grit, but it doesn’t become glossy.
Also, it might not hurt to tap the outside of the mold with a hammer drill and a cut-off SDS chisel during casting. It creates significant vibrations when you place it against the mold.
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By the way, I'm thinking about the TV program from a few years ago about a Japanese construction company tasked with building a concrete house. The demands were very high, and one of the responsible builders was there at night, polishing and crying over the air bubbles.
As I remember it, they compacted the concrete with long rods that they spun back and forth, while others stood outside the molds and tapped.
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For those of you who have achieved a mirror-like surface (as pictured in Finja's brochure), how did you do it?
I have tried sanding on a small test plate down to 1200 grit, but it doesn’t become glossy.
Also, it might not hurt to tap the outside of the mold with a hammer drill and a cut-off SDS chisel during casting. It creates significant vibrations when you place it against the mold.
----
By the way, I'm thinking about the TV program from a few years ago about a Japanese construction company tasked with building a concrete house. The demands were very high, and one of the responsible builders was there at night, polishing and crying over the air bubbles.
As I remember it, they compacted the concrete with long rods that they spun back and forth, while others stood outside the molds and tapped.
----
Apprentice, thank you for the answer. We shall look for such things.
One more thought, how to handle an under-mounted sink, is it possible or is flush-mounted etc. preferable in this case?
One more thought, how to handle an under-mounted sink, is it possible or is flush-mounted etc. preferable in this case?
Water stop, also known as Water glass, can be used to protect and harden concrete, but it should ideally be applied only when you are satisfied with the smoothness. Water stop/glass penetrates a few mm into the concrete, so you can polish further afterward and also apply several more thin layers. (the surface becomes like glass if you have many layers on)
Best regards, Jawen
Best regards, Jawen
make sure you don't spill anything acidic, like wine or similar, on the concrete, you'll have problems with corrosion
Just finished concrete countertops for our new kitchen, installed them last week. We did some "test stains" with great results. If you let wine sit for a long time, of course, it leaves stains, but it takes quite a while now. We treated them first with paraffin oil and really saturated them. They were more or less soaked in oil for a few days... Once they dried, we waxed them with carnauba wax, resulting in a relatively hard surface that is really good against liquids. It doesn't get completely glossy, but still a really nice surface... Before that, I sanded them with wet sandpaper. 60, 80, 120, 240. 400, 600, 800, 1000, 2000. For the finer "papers," I can highly recommend abralon if you don't have the luxury of grinding with diamond sanding, it's probably the best.
Jawen, you seem very sure that water glass is the best solution. Does a concrete slab treated with water glass resist acidic substances (wine, lemon, etc.) so that stains do not occur? As Hasse mentions, acidic substances leave unpleasant stains on concrete, at least with all the treatments I have tested (I have not tested water glass).
Out of curiosity... how is concrete negatively affected by oil?
Out of curiosity... how is concrete negatively affected by oil?
The question is what type of surface you want; as mentioned, water glass seems to be good if you want a "piano lacquer." If you want a more "natural" surface, oil combined with wax has been great. The result is concrete with a "wet-look." I happened to break two glasses of red wine over the slabs this weekend, and there were no issues, no stains at all.
Upon request, here is a small description of how the slabs were cast. I used regular fine concrete from ByggMax, and the molds were made from formplywood. For reinforcement, I used a 5 mm rebar mesh with 100 mm large grids. I mixed the concrete quite loose; it was easier to get it right that way. One thing to keep in mind is that there will be quite a bit of water spill, but the result was, as mentioned, better. I filled the mold to about 2/3 and vibrated a lot! For that, I used an orbital sander without paper, which I ran on a board placed on the form's edges. My tip is to vibrate a lot and then just as much again; it makes a big difference in getting rid of pores. Then add the reinforcement and fill with the rest of the concrete and vibrate again. Then I raked/"sawed" the form with a board to remove excess. Finally, I troweled it with a mason's trowel. It is important that the underside is even; otherwise, the slab will sit unstably on the kitchen units.
While the concrete is curing, I watered it during the first few days and let it cure under plastic. I cast indoors at 20 degrees; I don't know how it works in other temperatures. It took about a week and a half before I turned the slab over, and when doing this, be extra careful with the edges, as they are brittle.
Sanding. I used a geared orbital sander. Worked fantastically well. I rinsed the concrete slab and sanded it. I got a lot of help from a rental service in Helsingborg who helped me arrange paper etc. I started with 60 grit paper and sanded down to 500 paper. You use quite a bit of paper, but if you change it more often, it goes faster and with better results. Also, remember to have low speeds with coarse paper, etc. After the 500 grit paper, I made a paste from sifted fine concrete and water, which I "massaged" into the fibers that had emerged during sanding. Let it sit and cure overnight and then start sanding with the same grit again. If you have a lot of pores, redo the pore filling. Then continue up in fineness until you achieve the desired surface. Note! This doesn't give a glossy piano lacquer surface, but it becomes extremely smooth and nice. Several people who've seen them don't believe that I sanded them by hand. Then the treatment remains. I soaked the slabs in paraffin oil two to three times and let them sit and absorb for days. When they no longer absorbed, I wiped off the excess and then let them dry completely. After that, I polished them with carnauba wax found at a paint shop.
Material: Festool Geared Orbital Sander RO 150 FEQ-Plus
Paper: 60, 80, 120, 240 - noname stone paper, 500-4000 Abralon intended for automotive paint sanding.
Oil: Paraffin oil
Wax: Furniture wax based on carnauba wax
Cost: Material and machine rental with paper etc., around 3000 for a whole kitchen - a total of 4 m countertop
While the concrete is curing, I watered it during the first few days and let it cure under plastic. I cast indoors at 20 degrees; I don't know how it works in other temperatures. It took about a week and a half before I turned the slab over, and when doing this, be extra careful with the edges, as they are brittle.
Sanding. I used a geared orbital sander. Worked fantastically well. I rinsed the concrete slab and sanded it. I got a lot of help from a rental service in Helsingborg who helped me arrange paper etc. I started with 60 grit paper and sanded down to 500 paper. You use quite a bit of paper, but if you change it more often, it goes faster and with better results. Also, remember to have low speeds with coarse paper, etc. After the 500 grit paper, I made a paste from sifted fine concrete and water, which I "massaged" into the fibers that had emerged during sanding. Let it sit and cure overnight and then start sanding with the same grit again. If you have a lot of pores, redo the pore filling. Then continue up in fineness until you achieve the desired surface. Note! This doesn't give a glossy piano lacquer surface, but it becomes extremely smooth and nice. Several people who've seen them don't believe that I sanded them by hand. Then the treatment remains. I soaked the slabs in paraffin oil two to three times and let them sit and absorb for days. When they no longer absorbed, I wiped off the excess and then let them dry completely. After that, I polished them with carnauba wax found at a paint shop.
Material: Festool Geared Orbital Sander RO 150 FEQ-Plus
Paper: 60, 80, 120, 240 - noname stone paper, 500-4000 Abralon intended for automotive paint sanding.
Oil: Paraffin oil
Wax: Furniture wax based on carnauba wax
Cost: Material and machine rental with paper etc., around 3000 for a whole kitchen - a total of 4 m countertop
Bygga_bo:
Water glass can be used to "bind" the concrete, that is, create a denser layer just below the surface. Then you can sand lightly and treat with wax or similar, this slows down the evaporation through the slab so you don't have to maintain it as much.
But saturating the slab with oil does not give a long-term result, oils evaporate relatively quickly, and why first saturate the slab with oil to then have wax on it?? I don't find the logic here.
Regarding concrete and oil, concrete hardens over a very long time—around 50 years is normal—even though the strength specified on the bag is achieved after 28 days at 20 degrees and normal air exchange.
If concrete is treated with oils before 28 days, the strength will not be achieved, and you want a strong slab, right?
Depending on the mix and number of layers, you can control the saturation of the slab with water glass; it absolutely doesn't have to be "piano glossy."
Best regards, jawen
Water glass can be used to "bind" the concrete, that is, create a denser layer just below the surface. Then you can sand lightly and treat with wax or similar, this slows down the evaporation through the slab so you don't have to maintain it as much.
But saturating the slab with oil does not give a long-term result, oils evaporate relatively quickly, and why first saturate the slab with oil to then have wax on it?? I don't find the logic here.
Regarding concrete and oil, concrete hardens over a very long time—around 50 years is normal—even though the strength specified on the bag is achieved after 28 days at 20 degrees and normal air exchange.
If concrete is treated with oils before 28 days, the strength will not be achieved, and you want a strong slab, right?
Depending on the mix and number of layers, you can control the saturation of the slab with water glass; it absolutely doesn't have to be "piano glossy."
Best regards, jawen
I made the discs 40 mm thick.
I got tips to use both oil and wax and it has worked well... I actually had no idea that something like water glass existed, it sounds excellent! I guess you have to experiment to find what works well for you, all methods are good except the bad ones
After all, I believe that the absolute best is to polish with a diamond grinder to get a shiny surface through grinding that requires no maintenance. But, no matter how I searched, I couldn't find any except for large floor sanders, and that becomes both expensive and cumbersome.
LiMa
I got tips to use both oil and wax and it has worked well... I actually had no idea that something like water glass existed, it sounds excellent! I guess you have to experiment to find what works well for you, all methods are good except the bad ones
After all, I believe that the absolute best is to polish with a diamond grinder to get a shiny surface through grinding that requires no maintenance. But, no matter how I searched, I couldn't find any except for large floor sanders, and that becomes both expensive and cumbersome.
LiMa