3 story house (built 1979) in Flagstaff, AZ with a walk out basement. I have two bids to install 3/4 oak hardwood, 5 inches wide, with a glossy finish on the second floor. Both contractors prefer to use portland cement leveling compound.

Flatness is much more important than levelness. Maximum out of flat is 5/8ths inch over a 10 foot span. Other places are out of flat by 1/2 and 3/8ths inches. Joists are 2/10 spaced 12 inches in some places, 16 inches in the rest, with one layer of 3/4 inch plywood over the joists. One of the contractors states, "90 percent of the floors in Flagstaff are like yours. We always use SLC."

Maximum out of level is 1 11/16 inches over a distance of 25 feet. If one applies the minimum amount of SLC to achieve 3/16ths flatness in 10 feet, the finished floor will have a 1.25 inch low spot near the center of the room. The room is 35 feet long and the oak planks will be oriented north-south. If I stand at the north picture window and look towards the south picture window, will I see a dip in the floor as reflected by the glossy finish?

Why do both contractors insist nailing thru SLC is ok to use when so many posts on this forum recommend against it?

Ceiling drywall in basement appears to have been repaired and no cracks are showing now. Perhaps I should remove a piece of plywood and look for a structural problem?

Thanks, Doug

SLC wants to level itself so in come cases when your just lookg for flat you need to build a stopping point and try and screed it flat, not level.

Next question is why SLC over a wood substrate, are they planning on gluing? I would not try and nail though any sort of cemeticious leveling compound. Did you try asking Charlie at Delta?

Hi Stephen,

Both contractors want to nail through the cementous compound. They say they don't have problems nailing thru cement. I insisted they get confirmation from Armstrong. One of the contractors called in and now he tells me Armstrong does not recommend nailing through SLC. He's willing to use felt and plywood to flatten the floor.

The remaining issue is a 1.25 inch dip will be in the finished floor after the installation. Will this be visible? The 5 x 5 foot entry area at the front door is flat and it will have tile. At 5 feet from the door, exactly on the transition from tile to wood, one can easily see and measure where the floor is sloping downwards at a rate of 1 inch in 10 feet. It dips down to 1.25 inches and then starts rising the remaining 25 feet to the opposite wall. One can make the floor flat to 3/16 inch in 10 feet, but will the 1.25 inch dip be visible in the finished floor?

How do I contact Dave at Delta?

Thanks, Doug

1 & 11/16 is a huge dip id say you will be able to see that in reflective light. and agreed that on a wood subfloor use wood to bring it up flat.

Charlie Binghauser@ delta floors in Prescott. www.deltaplusfloors.com