Has anybody had luck making cast-in-place concrete look like limestone? The project has cast-in-place concrete entry way/steps that we want to match the limestone lintels/sills/ornaments on the historic brick building.
Thanks!
Why does it have to be cast-in-place?
If it does, apply a veneer of cast stone.
Or, apply a coating of lime-based plaster.
Since Portland cement is named that because of the resemblance of the concrete made therefrom to Portland Stone–a dark cold gray (and IMNSHO, particularly unattractive) limestone from near Portland in the South of England–You might be able to match Portland limestone fairly well, but standard P. C. concrete doesn’t match Indiana limestone, Texas limestone, Jerusalem stone or any other variety of limestone that I know of very well. As with “cast stone,” experimenting with various blends of white and gray cement, and various colors of fine aggregate, might work. The key is probably avoiding or minimizing the use of gray cement. Matching the texture is another thing entirely…
If color is the issue, see my article in Construction Specifier. It discusses integral pigments and the impact of cements, additives, aggregates and finishing technique. http://www.daviscolors.com/Downloads/Literature/DC618.pdf
Other useful references on color and appearance is at www.daviscolors.com/Literature
I’ve done this a few times for lintels and trim pieces, and typically write a spec for “cast stone”. its concrete, but without the large aggregate and the mix is a little different and it shop done, shop cured (in a warm moist environment). Masterspec calls it out in Division 04. The units are set like stone.
The most frequently-requested finish we are asked to specify for precast concrete is a light sandblast, “simulated limestone” finish, which removes the laitance but does not expose aggregate. It also is the typical finish for cast stone. With a combination of this finish, and blend of white and gray cements and color pigments as Michael suggested, a reasonable match to the limestone trim should be achievable.
However, we have rarely specified sandblasting for cast-in-place concrete, primarily because of clean air regulations and the difficulty of limiting the dust and overspray.
I’d be more comfortable with precast concrete than with cast stone for walking surfaces. I think that cast stone would be abraded/worn in short order.
On the subject of concrete appearance - I need to update a spec for Architectural Cast-in-Place Concrete. Aside from finish and tolerances, need to align design intent with requirements of specs. Any one with examples you would be able to share or point me in the right direction.
Thanks
pbabinec@gbbn.com
We specify cast stone on about 1/3 of our projects. It is a special subset of precast concrete with tighter tolerances and better finish requirements. You can find out more from the Cast Stone Institute including a list of producer members in your area.
And yes, you can get cast stone steps as well as cast stone balustrades.
A “kissin’ cousin” would be glass-fiber-reinforced concrete. These items are thinner which results in less weight.