- Lay the straight edge onto the floor with one end starting at the wall. Straight edges can be purchased or rented from a home improvement store or an equipment rental shop.
- Turn on a flashlight and place the light parallel to the straight edge onto the floor. Point the beam of light to the straight edge and examine the floor beneath the straight edge.
- Look for points where one unlit section is surrounded by two lighted sections beneath the straight edge. The lighted sections are dips, while the unlighted section between indicates a high point. Using a marker, make a mark on the high points under the straight edge. Most ceramic floor tile installations can handle slight dips with a bit more thinset mortar or a leveling compound filling the lower areas, but high points need to be leveled off to prevent tile damage.
- Move the straight edge across the surface of the floor, marking each high point as you encounter one. Perform two passes with the straightedge, with the second pass perpendicular to the first in order to center each high point for later leveling.
How to Find a High Spot in a Concrete Floor for Ceramic Tile
Proper preparation of the subfloor beneath your installed tiles is crucial to any good ceramic tile installation. The subfloor needs to be smooth and level in order for the ceramic tiles to lie properly. Any high spots or dips in the floor can lead to stress points in the installed tiles, causing cracks or breaks in the tiles with use. Finding a high spot or a depression can be done with the use of a precision aluminum or magnesium straight edge, a long metal bar with an absolutely level surface. Along with the aid of a light, spotting the irregularities can be done quickly.