Finally started laying the solid 3/4", 3 5/8" wide prefinished Kempas floor in our 20 X 20 living room.

Looks great so far. I was very careful to get the initial row very straight, and checked again after laying a few feet, but after getting about half-way across the room, I noticed that if I snap a chalk line along the latest row, the middle of the row bows out about 3/8th inch "wider" than the ends of the row. Not enough to notice visually, but I am worried that the trend will continue and will become noticeable.

Only thing I can think of is to start putting in small gaps between rows on the ends of each row (using a couple spackle blades) while continuing to keep the middle of the row flush against the prior row.

It's kind of a pain in the behind doing this - the Bostitch stapler is excellent at drawing the boards together, grabbing the blades.

Any other suggestions?

That is a common problem. I think what happens is the end boards are usually shorts, and also you tend to whack those last few staples with more force than the field.

After several rows that gives you slight bow just like you describe. You just need to catch up somehow, then it won't be that much of a problem because you are watching out for it.

You can use dimes or washers for spacers too.

playing cards slide out easy if you want to spread it out over a little more distance so its less noticeable.

3/8" is quite abit to get out of paralell in 10'. It is common to have the ends toe in just a little. The reason is your always nailing at the exact same spot. In the field the nailing is random. I suggest you start now using thin, metal putty knifes to start spacing out the ends of the rows. The handles make removing the blades easier. Don't think playing cards are gonna make up 3/8" very fast unless you use 5 or so together. As you nail, go easy at the ends where the spacers are. Don't bang the s**t out of the nailer. Just a light tap; enough to fire the staple and have it set properly. As you nail toward the center of the rows, hit the stapler a little harder, driving the boards tight. Keep measuring your progress to see if your efforts are paying off. After you're done, allow the floor to acclimate for a few weeks further before puttying any gaps from your spacing the ends.

Gary, you're right that 3/8" is a lot in 10 feet. I think a bunch of the discrepancy came into play when I laid flooring "around" a 5X6 section of ceramic tile in one corner of the room - went from laying 15 foot rows to 20 foot rows. Up until that point, I was only out of alignment about 1/8th". Wish I would have checked the straightness at that point.

We've been pretty good about laying the floor in as random manner as possible. The wood comes in 72", 36", 30", 24", & 18" sections.

I usually don't whack the s**t out of the nailer, but even with a relatively light hit, the Bostitch has a way of pulling the boards close together. If I give it too light of a whack, the staple sticks out.

Basically, I think you're telling us to do what we had planned on doing. It just slows down installation a bit, and of course gives us a gap (although small) whereas most of the planks are snug.

Seeing as this is a pre-finished floor, we won't be using floor filler.

With prefinished flooring, you can find color matching wood filler to closely match your flooring.

Last year I had to make up a 3" difference of a framing mistake, when the home was built. One end of the room was 3" narrower then the other. I slightly gapped one end of the big room and made up the difference perfectly. Filled the tiny gaps I left with color matching wood filler. They loved it and I kept them up to date on the concerns I encountered during the entire installation, to let them make the final decisions.

well sooner or later i will start reading a little closer, 3/8 in ten feet is a diffrent story.

Theoretically, it shouldn't be too hard to make up that difference.

10 ft of 3-5/8" wide boards = about 33 rows. And 3/8" divided by 33 = about 0.011" each. Isn't a plastic coated playing card about 5 thou thick? That means that 2 cards per row should do the trick. Theoretically, of course.

While that may be true ( I haven't measured playing cards) the idea is to get back straight asap. IMO, it is better to have less gaps that are a little larger and able to be filled, and get back to straight quickly, than lay the rest of the floor with a curve and making up for it so slowly that it takes till the last board before you're straight again. Another thing that happens when a floor gets a bow (curve) in the rows is that sometimes, the ends butts get out of square. This is more common on wider planks than strip floors. But it points to the reason to get the rows straight again as quickly as possible without creating huge gaps.