Tried a magnesium float finish on a garage floor and it backfired

I used a magnesium float on a 400 sq ft garage slab last Tuesday thinking it would close the surface tighter, but it ended up sealing too fast and trapping air bubbles underneath. The finish came out patchy with little craters that I had to grind down and patch the next day. Has anyone else had trouble with mag floats on certain mix designs?

3 comments

3 Comments

stella_scott963d ago

Oh wow, that's rough... I actually wonder if your mix had a higher water-cement ratio than the mag float was designed for. Those tools work best on stiff mixes, and a wetter batch can trap bleed water under that smooth surface faster than you'd expect. Might be worth checking your batch ticket for the slump next time.

sean_barnes243d agoMost Upvoted

A buddy of mine runs a small crew and swore by mag floats on everything until he had a 4-inch slab delaminate on a garage floor last spring. He sent me pictures of the peeling skin and I changed my tune real quick after seeing that. Stella_scott96, your point about bleed water makes total sense now, I used to think you could just muscle through any mix with that tool but clearly you gotta match it to the slump.

theas283d ago

A buddy of mine had the exact same thing happen on a patio job last summer. He was so annoyed he just covered the whole thing with a stamped overlay and called it a "design choice.