Thread: 2nd floor condo, concrete subfloor. measuring for flat and repair cracks

I'm putting in a new floor (laminate wood) in my condo. We are located on the second floor of a 3 story building with a subteranian garage (4 total floors?) We live in Newport beach CA. The subfloor seems to be made of a brittle dirty white stuff like concrete, but not nearly so solid. Taking up the tacking strip created divots when the nails came up. There are cracks in the concrete subfloor, possibly when the carpet was laid last time around. The condo is 30 years old. I want to install laminate, Right now I'm trying to figure out how to

1. determine if the floor is flat - not level - FLAT.

2, what to use, or if to treat, the cracks.

thank you in advance for any advice!

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I'd break free any loose pieces with a scraper or similar and fill in the floor. The most common product is called "Fixall" - it traditionally comes as a powder that you mix with water and apply with a trowel. There are also pre-mixed versions of it (and/or similar products) but they are probably more expensive so it depends on how large of an area you are dealing with.

Basically, if it's loose or sticks above the surface, break it free and fill in the gap left behind. I'd use a strong shop-vac to get a somewhat clean surface prior to filling in the gaps (after chipping away the imperfections).

A laminate floor is pretty "forgiving" meaning it will take up some imperfections better than tile, wood or sheet vinyl.

Preparing the surface is nothing difficult at all.... just spend some time and it will come out fine.

Many condos from that era use "Gypcrete" on the floor. It is used because its lighter than concrete, has a fire rating, and provides some acoustical benefits. And its cheaper.

It can be patched with many products, including most self-leveling compounds. Cracking in these floors is quite common around here in older condos.

Since laminate flooring "floats", the sub-floor can be somewhat imperfect. Read the install guide for the flooring product you're considering for specific information on flatness, patching, etc.

Dom.

All I can say is thank you
And appreciate your time and advice!

If you have a helper, take a string line and two blocks of wood that are the same size. If the floor is close to flat, it should be the same distance from the concrete to the string all along the string line. You can get away with quite a bit of deviation with laminate flooring, as the others said. Unless the divots are pretty big, I probably wouldn't worry about filling them in, if it were me.

Originally Posted by Matt Fellman

it will take up some imperfections better than tile, wood or sheet vinyl.

[quote=Jim Robinson;173829. You can get away with quite a bit of deviation with laminate flooring.[/quote]

I just wanted to clarify that most laminates require that:

"Variations in subfloor flatness should not exceed 3/16″ in 10′ (4.76 mm in 3.05 m) or 1/8″ in 6′ (3.17 mm in 1.83 m) - ARMSTRONG
"The maximum difference between two adjacent high points and the intermediate low point is 3⁄16 of an inch in a 10-foot radius." -PERGO

If the floor is insufficiently flat, the movement of the flooring will result in breakage of the interlocking joints. Also, and particularly with really inexpensive flooring, the placement of heavy point loads (such as from furniture) can cause additional stresses if located close, but not on, high spots of the subfloor.

I argue for a "Make it the best you can" approach rather than a "That's good enough for laminate approach."