I am making some practice forms and experimenting with pigment before making my own concrete countertops. I have the book by Du-Teng Cheng and he says to sand using water, diamond sand paper and an electrical sander. I am not finding these at any of the home improvement stores. Can you use regular sandpaper? Anyone have any experience with this?
You'll find it at lapidary suppliers -- people who cut gems and other stones. It's about $1.00 per square inch. Dr. Cheng probably makes enough profit from his countertops to afford lots of it.
-chib
I should clarify that by "these" I mean the diamond sanding pads is what I can't find easily. I understand they are also very expensive.
Yes, but you won't get much mileage out of it. The portland cement itself is very soft but any quartz or granite aggregates will be very hard.
Consider a rubberized diamond polishing pad in a rotary polisher:
I used regular belted sand paper to remove some glass from some doors I was making. Yep screw up by that much. I should have used the ones for glass but they were way expensive. You might try harbor freight for what your looking for. The stuff is for sure not contractor quality but for me it works just fine.
I'm in the midst of pouring my countertops and heres what I'm using and what advice I can give.
I bought this polisher from Harbor Frieght:
As far as sanding media goes get the diamond pads anything else will not hold up. I have access to an autobody shop and tried the best wet/dry paper I could get and it didn't hold up for more than 5 minutes of hand sanding. I ordered from Cheng Design:
As far as sanding the 200 takes the top down fast and easy, but its much to aggressive for the sides of my 2 inch thick counters. It brought up the aggregate very very quickly. Since then I've only used the 800 and higher pads on the sides. (I don't want much aggregate to show, on the top the 200 brings up specks, on the side it brings up pebbles! )
Grinding is messy and wet! GET A WATERPROOF APRON! Concrete can and will give you a chemical burn if your skin is exposed to it for a prolonged time! This is not a suggestion, It happened to me doing this job. Get an Apron!!!
For the concrete we started using one 60 lb bag of Quikrete fiber reinforced and one 80 lb back of Quikrete 5000 mixed, which gives you a hair over one cubic foot of concrete. We've since located a local supply of concrete fibers and are now using just the quikrete 5000 with these fibers added.
For vibration we've been using two sanders on either side of the mold and leaning in to each other while working back and forth round the mold. We've also covered the sander with a plastic bag and gently plunged it into the concrete. We've also given the mold a good beating with a rubber mallet. I've also heard that you can use a saws-all to vibrate, but I've not tried this one, but see no reason why it would not work.
The only other major advice I'd give is to allow the counters to stay in the mold for a minimum of 7 days and 10 would be better. RESIST THE URGE TO LOOK!!!! Its tough I know! But the corners and edges need the time to really firm up and set so that when you do remove the counter they don't crumble.
How much use can you expect to get out of these diamond grinding pads? Are we talking 1 countertop or dozens?
Let me put it this way I am pouring 52 square feet of counter and from what I've seen so far the pads would do this job and have several more jobs left in them. How many is hard to say cause I'm not done yet...but if I had to guess I'd say at the pads would last through at least 300 square feet of counter and maybe more. All this is going to depend on how much agg you plan on exposing and how long you wait to grind the concrete as it gets harder everyday.
In the 2 samples I have made, I kind of like the look unsanded. Any comments on choosing not to sand?
Not sure what to tell you on this one... but I'll say that if you like what you see I'd wait between 2 and 3 weeks then start with 400 grit. You should be able to maintain that unsanded look but still smooth the concrete to the touch. Not sure what this will end up lookin like for sure, but its the best recommendation I can give you based on my limited experience :-)
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