Uneven concrete density and polishing: soft spots explained
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Uneven concrete density and polishing do not mix well. A slab is not equally hard all the way across. Some areas came out hard and tight, and some came out soft and open. When we polish the whole floor the same way, the soft areas come out duller or rougher than the rest.
Your Slab Boss Polish quote has 1 group for this, with 2 choices. Our standard process costs nothing extra. Extra densifier and grout costs $67 per hour, counted by the crew hour as worked, plus materials.
Why is one slab harder in some spots than others?
Concrete is mixed in batches, and batches vary. The last truck of the day can bring a slightly different mix than the first. A crew may add water at the truck to make the concrete easier to work, and that costs strength and density that no one can add back later. A hot, windy day can also dry the top too fast in 1 corner while the rest of the slab cures slowly.
You can often find the soft spots yourself. Scratch the floor with a key. If it powders in 1 area and not in another, the slab is uneven. A soft top layer is common on indoor slabs, and most of the time it does not touch the slab’s strength.
Why soft spots polish duller
Concrete comes in batches, and batches vary. Extra water or a fast drying day can leave some areas soft and open. Soft areas soak up more and polish duller or rougher.
Standard process
Our normal densifier pass. Densifier is a liquid that hardens the slab from the inside.
Pro: It is already in your price, and it is enough for most slabs.
Con: Soft areas may still polish duller or rougher.
Extra densifier and grout
We add densifier and grout passes to harden and fill soft areas.
Pro: It gives a much better, more even result.
Con: It takes more crew time, plus materials.
Our standard process: 1 densifier pass
Every Slab Boss Polish includes 1 densifier pass after the first cut. Densifier is a liquid that soaks into the open floor and hardens it from the inside. Ours is lithium silicate, which reacts with the cement to fill the tiny pores the diamonds opened.
- Pros: It is in your price, and on most slabs it is all the floor needs. A soft, dusty top turns into a dense skin that stands up to wear.
- Cons: On a slab with soft or uneven areas, 1 pass may not be enough. Those areas can still polish up duller or rougher than the rest of the floor.
What does extra densifier and grout add?
We add more densifier passes and grout passes to harden and fill the soft areas. Grout here means a fine paste we work into the open pores, so the polish has a tight surface to shine. It costs $67 per hour, counted by the crew hour, plus materials.
- Pros: It gives a much better result on a soft or uneven slab. The soft areas get harder, the open pores fill, and the shine comes out more even across the floor.
- Cons: It adds crew hours and materials, and we cannot say how many until we see how the slab takes the first pass. A slab that is soft several millimeters down will not become a hard slab, even with extra passes.
We find most soft spots on the first cut
The first diamond pass shows how hard each area is. If we see soft areas and you picked the standard process, we will tell you before we go on. These hours are not in your quote total.
Is this worth it on my floor?
It depends on how the floor will be used. In a store, an office, or a home, where people see the shine, uneven density shows as dull patches, and the extra passes are usually worth it. In a shop or a barn, a floor that is hard and easy to sweep may matter more than an even shine, and the standard process often does the job.
Soft areas are 1 of 4 defect groups on your quote. See all 4 on the polished concrete slab defects guide, or go back to your quote to make your pick.
