PSA: Stop using metal trowels on exposed aggregate concrete, you're wrecking the finish

I've seen three different crews on sites around Phoenix this year using standard steel finishing trowels on freshly poured aggregate walkways. Every single time, it pulls the top layer of cement paste right off, leaving the stones loose and the surface looking patchy and weak. A super experienced concrete guy I worked with on a museum plaza job last fall showed me the trick: you have to use a magnesium float for the initial pass. It's softer and doesn't dig in and displace the aggregate. Once it's set up a bit, then you can hit it with a steel trowel for the final sheen. Has anyone else run into this, or found another method that works better?

3 comments

3 Comments

lilykelly14d ago

That trick with the magnesium float reminds me of my buddy's messed up patio.

barbara_campbell14d ago

Honestly, magnesium floats done right can make a patio look amazing though.

eric7231d ago

Remember my neighbor's patio? He tried that and ended up with weird waves in the concrete, lol.