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View Full Version : DIY shake-on concrete hardener recipes?



Stephen Tashiro
09-02-2013, 3:15 AM
There are "shake-on" concrete hardener preparations sold in big barrels (e.g.http://www.bontool.com/product1.asp?P=HARDENER). I've never see such a product first hand, but I read that they are used to create a layer of colored concrete on a slab that is more durable than a stain that is only applied to the surface. Are there any DIY recipes for such a hardener that can be used on small projects like casting concrete pavers?

A friend showed me that swirling together differently colored batches of thin-set cement (the kind used in leveling floors) can be used to create interesting designs on the surface of concrete pavers when they are cast. But we don't know if this kind of cement is durable. Since shake-on hardeners are used on driveways, I assume they can stand traffic.

Curt Fuller
09-02-2013, 11:02 AM
Stephen, there are two companies I know of that do custom hardened concrete floors on large commercial buildings. I don't know if their products are available on a DIY level but you might email them and ask. Their product is broadcast onto the surface once the concrete is down and then floated into the surface and actually burnished. That would be hard to do on individual concrete pavers.

http://kalmanfloor.com/ (http://kalmanfloor.com/)
http://www.thefrickscompany.com/

Concrete pavers are made from a mix that is mostly rock, 3/8" to 1/2", not much sand, very low water to cement ratio, and then pressed into the mold. The mix would be almost dry enough to pack in your hands and form a ball. So if you're casting your own, keep that in mind. Water is the enemy of concrete in terms of strength and durability.

Stephen Tashiro
09-03-2013, 1:50 PM
, not much sand, very low water to cement ratio, and then pressed into the mold. The mix would be almost dry enough to pack in your hands and form a ball. So if you're casting your own, keep that in mind. Water is the enemy of concrete in terms of strength and durability.

This is a point that I "know" in the sense of having heard and obeyed it often, but I'd like to understand it. My conception is that if you put a lot of water in concrete then when you fill a form you are taking up part of the volume with water. When the concrete hardens it chemically combines with some of the water. The excess water or the space it leaves when it evaporates are the source of weakness. Is that correct? (If that's correct then I don't understand why "air entrained" concrete is good.)

When a paver is cast without much water, I understand that it would be hard to float the surface if it had a lot of aggregate in it. But as a general rule, doesn't aggregate make concrete stronger for load bearing? I've seen articles with diagrams of "ideal" concrete where the aggregate is looks like a stonewall and the cement and sand just fill the spaces in between. These articles emphasize that cement itself is a weaker material that most aggregates. (Compared to these diagrams, I don't understand the typical bags of conrete mix sold in hardware stores. They don't have much aggregate in them.)