Will using a sealer on a precast concrete pillar change color with rain or time?

Answer 1

It is not clear if you want to know if the sealer itself will change color over time, the concrete without sealer change color, or the combination of the two change color.

Freshly poured concrete, without sealer, will darken over time.

Concrete sealer is used to minimize the absorbtion of water into the surface of the concrete. Some of the cheaper sealers are oil based and the better sealers are silicone based. Both need to be reapplied periodically as they tend to be washed away by rainfall. The application of an oil based sealer will immediately darken the concrete to some degree. Silicone sealers tend not to darken the concrete as much as oil based sealers after application.

An oil based sealer will cause airborne dirt particles and a whole host of organic particles like pollen to stick to the surface. As they accumulate, the concrete will darken. As the rain washes the oil off, this becomes less and less of a factor. These particles tend not to stick to silicone sealer as much as oil sealer.

In the end, no matter what you do, concrete will darken over time. The degree of darkening will depend a lot on the environment. If you live adjacent to a heavy industrial area, you can expect your concrete to darken more noticeably than if you live in a rural area. In either case, I don't think it is much to worry about.

Good luck with your concrete project.

Answer 2

depends on what the precast is made of. The more portland cement, the less the change... the more innert agregate, the greater the change.