Leveling a Badly Sagging Floor for Laminate

Use a level to determine the areas of the floor that are too high or too low, causing the overall flooring to slope more than 1 inch across 6 feet.

Use hydraulic jacks to gently raise a badly sagging floor from beneath. From the crawl-space, basement, or lower story, set up hydraulic jacks. Center the jacks on the floor joists in the area where the floor is sagging. Determine how high the floors need to be lifted to become level with the rest of the flooring. Divide the total distance by four. On the first day, move the jacks up one-fourth of the total distance. Over the next four days, lift the jacks one-fourth of the total distance until the floor is raised.

Run the vacuum over your plywood or concrete subflooring. Pay attention to any debris left behind after removing carpet or other flooring substance. Dust often collects between the floor and subflooring.

Mix baking soda and water in a large bowl in order to create a paste-like substance. Scrub the paste onto any visible stains on the subflooring. Rinse with clean water and allow the areas to dry completely.

Apply a latex-based leveling compound to areas on the floor that are too low. With a wide-bladed tool, fill in the depressions. Use the flat blade to smooth out the leveling compound. Allow the leveling compound to dry completely.

Use a concrete grinder or electric sanding tool to sand down any areas of the floor that are too high. On plywood subflooring, sand lightly and gently. Work with the grain of the wood. Work concrete grinders in slow, even circles to grind down high areas.

Vacuum the floor after grinding. Be sure to remove the all dust and debris left behind by the sanding process.

Use your level to ensure the floor is properly level at this time. If the floor is still uneven, repeat the filling and sanding process as necessary.