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Proper Sub-Floor Preparation

 Prevent Flooring Problems Prior to Installation 

February 24, 2019

BY Laura Anzures

Our professional installers are experienced in preparing the substrate for installation.  For those who would like to install flooring on your own, here are some tips to avoid problems with your flooring down the road.


SUB-FLOOR MUST BE FLAT:  That means no humps or dips in the sub-floor or slab.  If you have a plywood sub-floor, and one of the plywood sheets is higher than the one next to it, you need to sand the higher one down, so that they are even on top. If you have low spots in a concrete slab, you need to use leveling compound to even out the level of the slab. (NOTE: LEVELING COMPOUND IS ONLY FOR LEVELING CONCRETE. Do not use it over plywood) If you have a hump in the concrete slab, you need to grind that down to the level of the rest of the slab.  The entire area DOES NOT need to be "Level".   Most homes settle, and many slabs are not level. A gradual slope is normal. 


SUBSTRATE MUST BE CLEAN AND DRY: This is so basic, but you would be surprised at how many people simply bring home a floor and lay it out for installation without even sweeping or vacuuming the surface where it will be installed.  The result can be a crunching sound, like walking on gravel. 


USE THE CORRECT FLOORING/SUBSTRATE COMBINATION: For example, if you are installing ceramic tile, be sure to install on top of cement board and not directly on top of the plywood sub-floor. When tile is installed on plywood, it cracks. When installing solid hardwood flooring, you need a surface that will hold staples or cleats.  Never nail wood flooring to particle board. Only nail wood flooring down on wood, plywood or flooring grade OSB (looks like chunks of wood pressed together)


UNDERLAYMENT: For solid wood flooring, you want to have a rosin paper, like 15 lb. roofing paper. It is a vapor barrier that will keep humidity from rising up from a crawlspace or basement, but doesn't trap moisture under the wood, like a plastic would.  For floating floor like, engineered flooring, luxury vinyl and laminate, you want to get an underlayment that absorbs impact and has sound deadening qualities. There are loads of options for this, including cork, foam, neoprene, and many more. Many laminates and luxury vinyl floors now come with the underlayment attached to the bottom of the flooring.


SEALER OR ADHESIVE WITH VAPOR BARRIER:  For engineered flooring that is being glued to a concrete slab, you will need to either roll on a sealer or install the flooring using an adhesive with a vapor barrier to prevent moisture from the slab from reaching the wood. 


ELIMINATE/REDUCE SQUEAKS:  When we install a plywood sub-floor, we use glue and screws.  Some sub-floors were installed by builders who just use nails to fasten the plywood to the joists. When homes settle, the plywood and joists shift slightly.  You can hear creaking and squeaking when you walk on the floor. This is caused by the plywood moving up and down on nails.  Before we install flooring, we screw the sub-floor down to stabilize the sub-floor and reduce or eliminate the noise. 


Some sub-floor issues require professional repairs. Please give us a call to assess your sub-floor and provide a quote for repairs.