Karl Fields
Well-known member
- Joined
- May 29, 2012
- Messages
- 75
Anyone know how much concrete you can take off by grinding BEFORE you hit aggregate?
grinding a floor
- Thread starter Karl Fields
- Start date
Edger
Well-known member
A guess would be 1/16th in., but it will vary a little in highs and lows.
HoustonGarageFloors
Member
Every slab is different. The answer is: As much as necessary to get to rock.
What you are removing is called laitance. It is a negative result of too much water being added to the concrete pour. To get an idea of how much laitance your slab has, you can take a heavy duty flat head screw driver and try to dig the head of it into the slab by putting ALL OF YOUR WEIGHT on it while twisting the screwdriver into the surface of the slab. The deeper you can go into the slab, the more grinding you will be doing and more dust you will be creating. If your slab is hard and it is difficult to create powder or go deeper than a millimeter, then you have a solid and sound concrete slab which will result in less dust upon grinding and a better bond to the epoxy.
It is critical to remove ALL of the laitance on the surface of the slab. Coating over laitance is like coating over brittle chalk, when you apply weight on it, the chalk below will crumble and the epoxy will pop up in sections with brittle concrete stuck to the bottom of it.
Over grinding is better than under grinding.
Best Luck!
What you are removing is called laitance. It is a negative result of too much water being added to the concrete pour. To get an idea of how much laitance your slab has, you can take a heavy duty flat head screw driver and try to dig the head of it into the slab by putting ALL OF YOUR WEIGHT on it while twisting the screwdriver into the surface of the slab. The deeper you can go into the slab, the more grinding you will be doing and more dust you will be creating. If your slab is hard and it is difficult to create powder or go deeper than a millimeter, then you have a solid and sound concrete slab which will result in less dust upon grinding and a better bond to the epoxy.
It is critical to remove ALL of the laitance on the surface of the slab. Coating over laitance is like coating over brittle chalk, when you apply weight on it, the chalk below will crumble and the epoxy will pop up in sections with brittle concrete stuck to the bottom of it.
Over grinding is better than under grinding.
Best Luck!
LegacyIndustrial
ALLIANCE MEMBER
Karl, the goal is not to hit aggregate.
The goal is to open up the surface.
If your concrete is as Don mentioned, soft or easily gouged, then you want to grind until you reach good hard concrete. You should be able to tell once you get there.
The goal is to open up the surface.
If your concrete is as Don mentioned, soft or easily gouged, then you want to grind until you reach good hard concrete. You should be able to tell once you get there.
OP
Karl Fields
Well-known member
- Joined
- May 29, 2012
- Messages
- 75
I am NOT wanting to hit aggregate.
Problem is a crack in my new concrete. Not just a crack, but the crack itself is maybe 1/8" higher than surrounding concrete. Seems to be a pressure issue. We did encounter a natural spring when excavating but thought that was fixed with the French Drains. Guess not
Anyway, contractor suggested grinding it down flat with the surrounf area, doing the floor and then re looking at the issue in 6-12 months. If needed he will remove and re-pour quadrant in question at that time.
So my question is I don't want aggregate exposed as I'm using stain and clear only. Just wondering the chances of hitting it.
Problem is a crack in my new concrete. Not just a crack, but the crack itself is maybe 1/8" higher than surrounding concrete. Seems to be a pressure issue. We did encounter a natural spring when excavating but thought that was fixed with the French Drains. Guess not
Anyway, contractor suggested grinding it down flat with the surrounf area, doing the floor and then re looking at the issue in 6-12 months. If needed he will remove and re-pour quadrant in question at that time.
So my question is I don't want aggregate exposed as I'm using stain and clear only. Just wondering the chances of hitting it.
Edger
Well-known member
Every chance. You will hit aggregate.
Shea
Well-known member
If you grind too much your stain will not take. Stains are reactive and need the laitance or free lime that is on the surface of the concrete in order to color it. You may have to use a color dye to blend with the stain in the areas that you grind.