Thursday, July 30, 2009

White Concrete Desk Reveal

One of the characteristics that helps lighten white cement is fine grinding, even finer than Type III high early strength cement. I will vouch for that. This countertop was hot to the touch 6 hours after placing. Good news is that it can be finished much sooner.
The desk proved difficult to strip the forms since the aggregate was glued in place. The glass stayed in placed and was well distributed across the surface. In this picture I started slurry coating the surface to fill the holes left from the curved part of the glass. In a day or so it will get a grind with 50 grit and then another slurry coat.

Monday, July 27, 2009

Placing the White Desk

To get the colored glass, blue and green wine and beer bottles were soaked in water to remove the labels then crushed and rewashed. The mold was sprayed with glue to hold the glass in place.
All the ingredients, all white. Sand, cement, metakaolin, and latex.

I stripped a couple sides. It will cure under a wet towel for four days before grinding and another week before polishing.

Saturday, July 25, 2009

White Desk Project

Everything has been prepared for the white desk. The mold is a pretty standard construction. I had some leftover MDF so I used that and spray painted to seal the wood. The desk has a thickened front edge to cover the in-place frame.
The desk will be white concrete with crushed glass in the surface. I saved some good blue and green bottles. First they were soaked in water to remove the labels, then crushed with a hammer to the appropriate size. Beer bottles can be problematic if not cleaned properly. The sugars in the beer tend to retard the concrete set. These were washed again after crushing.
How do you make white concrete, mmm use white cement. This is a little harder to track down for the average person since Home Depot doesn't carry it. Masons and stucco guys use white cement or call your local decorative supplier. This cement and sand was donated by Mike Murry at Decorative Concrete Supply. The only real difference between white and regular Portland cement is they leave out the tetracalcium aluminoferrite. It is a small part of regular cement that doesn't really contribute to strength.
Another concern for making white concrete is the aggregate. Regular sand tends to make the white cement concrete a tanish color. You can buy pure silica sand (ash tray sand) at local suppliers. Since this is a small desk, shrinkage isn't really a concern so a mortar mix is appropriate.
The mix will be a standard mortar mix; 2.5:1 sand to cement, water-to-cement 0.40, 10% metakaolin clay, high range water reducer, viscosity modifier, latex, polypropylene fibers, cellulose fibers, and de-air entraining agent. The total batch will be 1.0 cf.

Wednesday, July 8, 2009

White Concrete Desk Project

Since the last project was black, time to do something white. We built a closet in our guest bedroom and left room between the window and the closet for a built-in desk. The room is green with orange accents and blond birch trim. The plan is to build a white concrete countertop for the desk with exposed blue and green recycled glass.
Below is the black fireplace with the slate tile and new carpet.
Wood strips were secured to the studs to support the plywood top and eventually the concrete. There is a hole in the back right for cords. The countertop will be 1 1/2" thick and cap the front to end up flush with the wall. Truly white ground concrete is a difficult animal. First, you have to use white cement. Second, traditional aggregates have color and tend to make the concrete grey or tan, so you have to use something else. This mixture will be a mortar (no coarse aggregate) and have white cement with pure silica sand. Silica sand is often used as ashtray sand. Some metakaolin clay (a bone white SCM) will add strength. Blue and green bottles will be crushed and laid into the surface. It should produce an interesting effect.