We get asked a lot of times by customers whether they should shotblast or grind their floor. In this post we will discuss the Pros and Cons of each. First lets start with the fact that shotblasting a floor is cheaper than grinding at the outset. The problem with shotblasting is that unless using an aggregate such as sand or doing a heavy flake job you will see what we call lawn mower lines in the finished epoxy. The reason being is that where you overlap with the shotblaster as you go up and down the floor it leaves a line of deeper indents from the shotblasting beads. Then as you apply epoxy those deeper indents hold more pigment and thus show up as lines as you can see in this photo below.
The benefits of shotblasting other than the lower cost is that it gets down into the small nooks and crannies of very dirty floors that are in poor condition. We would recommend grinding after shotblasting to remove as much of the shotblasting lines as possible but when you do this it obviously increases the cost dramatically.
So grinding 95% of the time is the way to go and most times on smaller floors you can rent the floor prep machine from Home Depot which will do the job just fine. For larger floors or extremely dirty floors you will need a larger machine from a tool rental place. When renting a grinder get the biggest grinder you can handle it will make the job easier and faster also whenever possible get the Vac attachment, that goes for the Home Depot machine too. Grinding generates a lot of dust. After grinding make sure to remove all the dust. If time is not an issue you can hose or power wash the floor and while the floor is wet you might as wet scrub some etch in. This will accomplish two things, one it will open up the concrete pores more and second it will clean any low spots the grinding wheel could not reach.
Once the floor is prepped we like to hit it with a good leaf blower just before apply the coating to get the last bits of dust off the floor, you’ll be surprised at how much dust is left. So in conclusion figure to grind rather than shotblast in all but extreme floor situations. Use the floor prep machine from Home Depot on small to medium floors and for larger floors use an industrial size grinder preferably one with at least 3 heads and new diamonds in about the 25-30 grit range. Always try to use a Vac attachment with your grinder, shop vacs won’t work, they clog up in two minutes. Grinding Vacs have pulsating filters to keep them clean as you vac up all the dust. And as always if you have any questions on the condition or preparation of your floor just give us a call or shoot us an email.