The finish is not the problem, the "ripples" you see are sanding errors. Commonly referred to as chatter.

the ripples can be caused by a number of things, most of the time from the sander's drum sander. Im willing to bet this isnt the first time it happened to them, there are ways to avoid getting this by doing the necessary steps while sanding.

This is correctable but would require resanding.

Its up to you whether or not you can live with it. Its definitely not to NWFA standard. If you plan on having a large rug over this area, then you wont notice it, but once again, its something you have to decide if you want to have it fixed.

So, it is common to run the sander perpendicular to the boards? I had assumed not.

Should the guys have known about this prior to applying the first coat?

I'm inclined to ask the contractor to agree not to take the last third payment, rather than ask that they redo it. (I'm reluctant to take more wood, and more inconvenience.) Would you think that fair? (I assume you are a contractor.)

Its Not common to run a sander perpendicular to the wood. And i dont believe your guys did that to your floor.

Theres techniques to sanding a floor that involves sanding a few degrees off parallel to the wood, but thats a different story.

Its possible that your guys didnt know it would happen, doubtful, but possible. After the first coat was applied they would have known if they didnt know already.

for whatever reason, they feel like it was acceptable and hence didnt do anything about it.

As far as getting the contractor to agree to your payment solution, i have no idea. If i was in his shoes i would want to remedy to solution by resanding, but its possible he may agree to your terms as well. But you need to contact him before you decide anything.

Its also possible that he may claim your floor has no flaws and refuses to your terms. In which case it would be advisable to hire an independent NWFA certified flooring inspector.

My contractor immediately offered to redo the two rooms most affected, and I accepted. But I'm concerned that the contractor doesn't seem sure of what caused the problem. (He says the guy supervising the job was one of his best guys, and that his equipment is well maintained.) I'm concerned it might be an issue with the sub-floor, and we'll just take more wood and end up in the same place. I think this because the "ripples" are perpendicular to the planks (parallel to the joists), and they are longer than the sander is wide. So for some reason the imperfection is occurring along the same line each time the sander passes at a different point along the line. And what adds to the puzzle is that the lines are closely spaced (not every 16" as might be the case with irregular joist height). Any additional thoughts these facts bring to mind would be much appreciated.

I should add that the the joists beneath these floors were sisterred and leveled several years ago, and I'm not sure the leveling was well done-- its possible it made things worse. There is sub-flooring. I was not correcting a problem with the sistering--I was making a lot of other improvements, and thought I may as well reinforce the 2x8 joists (again, a 1927 bungalow).

The issues you are seeing in the floor are not from your subfloor, at least not in my opinion.

Your sanders should be cutting the floor at an angle the next time, this will cut out the stuff thats already there. If they were to go parallel with the wood, their drum sander would just follow whatever dips are already there and then you WILL be back in the same position.

Its good your contractor is willing to fix, thats the biggest hurdle. If they really are professional, they'll know how to fix it.

This is my dilemma. Based on the advice I've received here, I must conclude that my contractor is either incompetent, in which case I don't want him touching my floors again, or he knows his guys knowingly finished floors that weren't properly sanded but isn't willing to say so. I think the latter is more likely, as he is very highly rated on Angie's list and has more Angie's list comments than any other contractor in my immediate area, which is a very large urban area.

They need to get an orbital 3 disc sander. Lagler calls it a trio.

http://www.homedepot.com/p/American-Sanders-Orbital-3-Disc-Wood-Floor-Sander-07164A/206514090

http://www.chicagohardwoodflooring.com/lagler-floor-sanders

The type they used is prone to causing chatter. It is either a drum or a belt sander, great for removing a lot of product but bad for finish sanding. You pretty much need a perfectly running machine and to go at the perfect pace which will never happen in real life. Lagler calls it a Hummel or an Elf.

" ... as he is very highly rated on Angie's list ..."

Not the first time we've heard this. Is he willing to redo the job using the proper equipment recommended (Trio or like machine)? I'd be leery of having him redo with the same equipment/employee. IMO, the time to talk to the customer about "unavoidable imperfections" is when those become apparent, not after you've picked up your payment plus a bonus.

Or a USand sander, available at HD and other rentals. This is what I used on our new solid hard maple floors.USand

Keep in mind that nobody's infallible. If he offered to do it over and make it right, you have no other reasonable choice than to let him proceed.

It would be wise to inquire how they intend to get the waves out though.

The owner says he is going to redo the two rooms as if it was the first time. Doesn't sound right to me, and it concerns me that they will take so much more wood. I'm hoping the guy doing it has a better plan. Also, the owner claims the initial problem was because my floor was so bad to begin with, which again doesn't sound right to me. (Bad floors means he has to go deeper, but that shouldn't result in waves.) If it weren't for the fact that this company does lots of business, gets good reviews, and is trying to accommodate me, I would run. I am nervous.

Owner has no experience with Trio machines. He uses belt and single circular sanders only. No drum sanders.

"I am nervous."

I don't blame you. If he is going to do the same job with the same equipment, why is he expecting a different result?

"Bad floors means he has to go deeper."

How much deeper can he go before he runs out of wood? If I had to deal with more sanding (and losing more wood layer), I would want to be certain that the proper equipment was being used for the desired result.

" ... is trying to accommodate me."

Does he believe he can fix it?

"The owner claims the initial problem was because my floor was so bad to begin with ... "

Did he tell you this at the beginning, or after he delivered the poor result?

If he wont use a trio at least use the orbital circular sander instead of the belt. Only if the pad is cupped should there be another sanding issue. They can put a straight edge on the pad and check it multiple ways to make sure it isnt cupped before they start. The trio is a step up from the single orbital sander because it helps to stop cupping from appearing if a pad gets cupped. As such, it is more expensive to buy and may be why he has not used it.

Thanks to everyone for their input. I think your expertise saved me more headache. The crew arrived this morning to do the redo of the two rooms most affected. The senior guy was the same guy who did it the first time. I wished I had been able to talk to him rather than the owner earlier. He told me the waves were already in the floor and he did his best to remove them, but his sanding machine just followed the same pattern that was already there. (I had never noticed waves before, but the floor has never had a sheen finish in the 20 years I've been in the home.) His plan was to just do the same thing again as his boss had directed him. He did not disagree that we should expect the same result. I told him about the technique gregmills_gw mentions above of sanding at a slight angle. He had never done that before and thought it would give bad results. I concluded that this floor company wants to do well, but simply lacks the necessary expertise to deal with problem floors. I canceled the redo. Without the info I got on this forum, I would not have known to do that. Thanks!

Check out #6.

http://www.hardwoodfloorsmag.com/sanding-finishing/sanding-101-wood-floor-sanding-basics.html

I concluded that this floor company wants to do well, but simply lacks the necessary expertise to deal with problem floors.

That is unfortunate for their customers, and a sorry excuse. I hope that you will give an honest review on Angies List and if allowed, post a picture of your flooring. It sounds like they knew the kind of result you were going to get and went ahead and did it anyway.

rm54, I suggest you go to home depot or a place that sells a wide variety of flooring and look at the options. Look at laminate, engineered hardwood, prefinished hardwood. You'll see a variety of textures. It may help you appreciate the nuances in your unique floor. Sometimes you have to look at things with different eyes and appreciate the character.

I am two coats of water based poly away from refinishing my solid red oak floors and I made every mistake in the book. But they don't look that bad. My floors are randomly uneven, dented, scratched and splotchy, but when the first two coats of poly went on, they actually looked nice and on trend. Today I went to Home Depot and touched the wide variety of flooring they had and compared it to mine. I like mine better! I actually think I prefer the random waves and imperfections to a perfectly smooth finished floor. Google "hand scraped wood floors" and look at pictures to see what people are doing and buying. You may learn to like your floors as is.

I Did not read all the comments but I did see someone say that this is chatter. This is not caused by chatter. Most residential drum sanders are 8" wide and when you sand you have an overlap of 2-3 in. Assuming that floor is 2 1/4 wide those lines are well over 10in. That is more then likely a sub floor issue. The sander is very heavy and when hits a soft spot in the sub floor it will sand harder creating a line. Sanding it again is probably a waste of time. It may look a little better using some different sanding techniques but I don't think it will ever be perfect with out crawling under the sub floor and fixing it.

For what it's worth, I have to disagree somewhat with Executive Hardwood. If you look closely at the picture, you'll see that this floor likely has chatter marks AND waves. I've seen chatter specified as being as close as 1/4" apart but no more that 1 1/2". If you look closely, you'll see that in addition to the waves at the top of the illuminated area, there are chatter marks that appear to be about 1/3 the width of the floorboards (right hand side of the illuminated area about halfway up the picture).

In any case, the floor could be made much better by making sure the voltage supplied to the machine is sufficient, ensuring the machine had no issues, cross cutting the floor at a shallow angle, and of course hard-plating the floor before screening, or using a Trio. That said, the subfloor/floor could be loose, making it less likely to achieve perfection (if that's even possible).

@jfcwood either way the solution you give is the best coarse of action to get the floor looking as close to perfect as possible.

I recently experienced this same issue. I am at a loss as what to do. The floors were beautifully refinished 2 years ago. We added a small addition and installed the same flooring to match the existing floors. We were told the entire room old and new needed to both be redone even though the old and new flooring only over lapped by a few feet. The floors were smooth and beautiful prior. We had to hire someone else to do this job and the floors now look as described above. Just as above we paid them in full as the floors were wet and we couldn't see any of the ripples. As they dried the problems quickly surfaced. They will return to fix them ( a month later) but I am also afraid the problem is with the equipment and the handler . It is not a flooring issue. thoughts on how to ask them to correct this issue before the start again? It is mainly on the older section not the newer area.

I just had my floors refinished and am wanting to know if this is acceptable work…? I personally am bothered by the finish work around the baseboards. Any advice on how to approach the contractor about this? The chatter he said is something that you see when you sand the floors from the machine and that was normal. The edging was done with a hand scrapper and you can see where they had scrapped and the machine started, also at the baseboard it has some rough spots. Acceptable?

Chatter, rough edges, uneven… help!

Not acceptable, sanding is not to standards. Have them fix it, otherwise contact a NWFA inspector.

What exactly would a NWFA inspector do for me in this case?

It will prove that your flooring contractor is all smokes and mirror, does not know what s/he is doing. You would get your money back to hire a new contractor if, they cannot make it right.

Start a new thread for additional advice.