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Had a sub put down a K-15 equal all across the floor, they left small ridges in the floor where I guess there screed pulled across the floor. Our installer says it all has to be either feather skim coated or they need to take a large grinder to the floor and lightly knock the edges down. Ever happen to you? How to fix?

Aslo are small holes in the underlayment, they look like bugs bore through or micro bubbles or something normal?

This is not uncommon even with an experienced installer. Light grinding is fastest and you don't need to "blend" the ridges into surrounding areas in order to achieve a nice flat surface for the floor covering.

As far as pinholes, that is typically a result of the K15 being installed over a highly absorbant slab, resulting in the mix water being sucked out of the K15 too fast. Did they prime the concrete with P-51 Primer as required? Highly absorbant concrete needs to be "double primed" with P-51. Prime with P-51 mixed with 3 parts water, dry for an hour or so, then prime 1:1 with water (normal mix ratio), before installing the K-15.
JK Nixon
Concrete Restoration Services, LLC
Pittsburgh, PA

CCR is spot-on.

The ridges can be sanded down if you catch them early enough. K15 dries hard though so you have to catch it early. There are pads for grinders made of a material that looks like a Brillo pad, my distributor calls them TAZ pads. They will eat through K15 rather quickly and not clog. You probably know that using diamond grinders doesn't work well on patch material.

The ridges were probably formed because they got on the leveler too late with their smoother. This can also be a factor of a porous substrate sucking the water from the mix.
JD Grafton
Concrete Answers for Flooring Problems

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