Q: A concrete walk I made last year has started to develop a crazed surface, almost like dried mud, with fine lines running in all directions. What's wrong? I mixed the concrete myself, and used extra cement in the mix to make it extra strong. A: Your problem is caused by the extra cement you used in your mix. An overly rich mix tends to shrink more than one made to the proper specifications, and the shrinkage causes the crazing. Next time, mix your concrete by the book.
Meanwhile, you can repair the crazed surface fairly easily by brush-coating it with a resurfacing product (such as Top'n'Bond). To do this you mix the resurfacer to a thick, paintlike consistency.
Spray your sidewalk to dampen it, but remove any standing water. Pour the resurfacing mixture onto the walk and spread it with a soft pushbroom. After the mix is spread out in a thin coat, use parallel strokes of the broom to create an even, attractive surface texture. Q: The concrete floor in our basement rec room always seems to be dusty. We sweep it, but the dust reappears. In fact, it looks like the floor is wearing away in spots. This is most noticeable in heavy traffic areas, especially at the ends of the Ping-Pong table. Would painting the floor solve this problem? We don't want to spend the money it would take to put down tile or carpeting. A: The best way to solve your problem is to apply an acrylic-polymer concrete sealer (sold at paint stores), which will soak into the dusting concrete and set, binging the surface together. If you like, you can then put on an acrylic latex floor paint. This will brighten the room and give the floor additional protection. Don't use an epoxy floor paint: Though tougher than the latex paint, it won't adhere well to the sealed surface. Q: What's the difference between prepackaged concrete mix, sand mix and mortar mix? I want to cast some steppingstones about three inches thick and 18 inches across, and I'm not sure which prepackaged mix to use. A: Concrete mix is a blend of Portland cement, sand and gravel; sand mix is the same thing but without the gravel; mortar mix is a blend of masonry cement (not the same as Portland cement) and sand. For your steppingstones, use concrete mix, if you can; the gravel adds strength and cuts costs. As long as the diameter of the gravel is not too large -- no more than about one-fifth the thickness of your work -- it will be an asset; but if it's too large, it will be hard to pack it down and make a smooth surface. Some brands of concrete mix use fairly small gravel (around 1/2"), which would be fine for your job; other brands, with larger gravel, might cause problems. If you can't find concrete mix with small gravel, use sand mix. Don't use mortar mix: It's intended for bonding bricks and blocks together.