How do I remove scratches between layers of polyurethane?

Question

My husband and I have been building a farm table and we are oh-so-close to being done, but we are having issues in the final coats of polyurethane on the top. Here's a rundown:

We stained the wood with gel stain and put three coats of Minwax polyurethane on top. I used steel wool between coats and it looked pretty good, except we noticed brush marks in about three different spots. I think the brush didn't have a wet tip and the poly dragged or something... the rest of it looked great.

We used steel wool again and did another coat of poly, this time with a foam brush. When it dried it left these weird spots, so we put on another coat with a foam brush... even more weird spots. (they almost looked like water marks?)

This time we took 220 grit sandpaper and sanded the entire top of the table (with our hands... we didn't do enough research to learn that we should have used a sanding block... we're total newbies!) and put on a coat with the brush again. The coat itself looks great! But we can see scratches from the sandpaper under the poly :(

I've seen mixed advice online about how we should proceed.... do we need to sand down to get rid of the scratches (and probably sand out all of the stain and start over), or will using steel wool again and applying more coats of poly get rid of the scratches? I so do not want to sand down completely and start over, especially when we are this close to being done. But I also want our table to have a beautiful finish. Please help!

Answer 1

except we noticed brush marks in about three different spots. I think the brush didn't have a wet tip and the poly dragged or something

This sounds like it could be possible. It could also have happened if you didn't keep a "wet edge." What this means is that you don't want to apply wet finish over partially dry finish.

We used steel wool again and did another coat of poly, this time with a sponge. When it dried it left these weird spots, so we put on another coat with a sponge... even more weird spots. (they almost looked like water marks?)

I assume you're talking about a kitchen sponge, which I would avoid using for finishing tasks. Since they're designed to soak up water, I have a suspicion that your sponge may have been partially damp when you soaked it with finish. If the finish is oil-based, that could be the cause of your spots.

Steel wool is fine for lightly scuffing the recently-dry layer of finish to promote better adhesion of a subsequent layer, but as @Graphus states, it's not meant for flattening. If you want a truly flat surface, sandpaper on a sanding block is the way to go.

This time we took 220 grit sandpaper and sanded the entire top of the table (with our hands... we didn't do enough research to learn that we should have used a sanding block... we're total newbies!) and put on a coat with the brush again. The coat itself looks great! But we can see scratches from the sandpaper under the poly

At the risk of contradicting myself, not using a sanding block isn't necessarily a bad thing. You don't need a pristine, totally flat surface to apply finish. I don't think I've ever made a piece of furniture where the surface didn't have little dips and bumps due to uneven sanding. I can almost guarantee no one will notice.

What you do want to do, however, is sand thoroughly enough that you remove the sanding marks from the coarser sandpaper used previously. Say you start with 150 grit paper. Next you would use 180 grit and sand until you can no longer see any 150-grit size scratches. Then use 200 or 220 grit and sand until the 180 grit scratches go away. And so on, until you're satisfied. Personally, I think anything over 220 grit for normal furniture is overkill. I usually stop at 180 grit.

do we need to sand down to get rid of the scratches (and probably sand out all of the stain and start over)

If you have scratches under a layer of finish, there's unfortunately only one way to get rid of them - remove the finish and sand or scrape them out.

or will using steel wool again and applying more coats of poly get rid of the scratches? I so do not want to sand down completely and start over, especially when we are this close to being done.

As I said, steel wool won't really do anything besides scuff the top layer of finish - it's not made for gross finish removal.

If you want a consistent coat in the final product, unfortunately I think you'll have to sand to bare wood and start over. It sucks, I know. I've done it plenty of times, and it doesn't get any easier each time. But unless you think you can live with the scratches, that's the route you'll have to take.

As an aside, depending on how noticeable the scratches are, you might be making a mountain out of a molehill. Remember that most people will never notice the small mistakes that the person who crafted the piece will.

Answer 2

I've seen mixed advice online about how we should proceed....

That is unfortunately par for the course, mainly because there's no single way to do most things and people have their preferences.

Here though, in addition to this it's very difficult to get a firm read on the problems you've had without clear, unambiguous photographs to help. Even though your descriptions seem quite clear it's easy to make incorrect assumptions about what each problem was and therefore the best approaches to take. The weird spots you got after using the sponge for example, there could be three or more possible explanations there.

do we need to sand down to get rid of the scratches (and probably sand out all of the stain and start over), or will using steel wool again and applying more coats of poly get rid of the scratches?

OK first thing I need to say is you should stop using steel wool at this stage. It's no good for flattening. Abrasive paper, usually but not exclusively backed with a suitable sanding block, should probably be the only thing used to work out scratches and brush marks, until you get to the rubbing-out and polishing stages at the end.

I so do not want to sand down completely and start over

If you did decide that you need to remove the finish, go back to bare wood, and start again I would highly recommend you not consider doing this by sanding. It would be far preferable to scrape (using a card scraper) rather than sand: it's safer as it produces almost no airborne dust, it's less likely to damage the wood, and can actually be faster and more efficient. More on scraping v. sanding in this previous Answer.

As you've probably picked up from your reading already, the normal fix for scratches is sanding (more on this in the next paragraph) until they're gone. In addition, in finishing, adding a fresh coat of finish can hide or make invisible scratches in the surface of the previous coat. As you say you can see scratches underneath the last coat of poly you applied that could be a significant hurdle to fixing the finish you've already applied, but I think you'll have to try the normal routine and hope for the best.

The usual way to perfect a blemished varnish coat is to wet-sand (using suitable wet-or-dry paper which is usually grey or black in colour) until the visible scratches are gone — full description of the process reproduced here, from an article that originally appeared in Popular Woodworking. Also see this guide, Rubbing Out A Finish on AntiqueRestorers.com and this one, on the Rockler website.

If this results in sanding back to bare wood in spots you may have no choice but to cut your losses and start again. It's not impossible to do spot repairs but it's difficult to make them seamless and truly invisible.

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Not directly related to your query so I'll just add this on the bottom.

We stained the wood with gel stain and put three coats of Minwax polyurethane on top.

For your future reference and for other readers, it's advisable not to think about using gel stain as staining.

True staining is colouring the wood itself, using a penetrating liquid, usually coloured (i.e. wood dye or wood stain) that directly colours the surface wood fibres. Something like gel stain on the other hand is merely a coloured surface coating, which is nearly entirely on top of the wood. Hence why "gel stain" is actually a very stupid name for the product; in reality it is merely thickened, coloured varnish so calling it a stain is just bound to cause confusion.

Answer 3

I have gone through this myself. What I ended up doing is sanding and starting over. I had heard of a few different tricks but none have worked. The worst thing I did as well was to keep trying to "fix" it. Just start over and if you can borrow an orbital sander start with 120 grit then move up to 200. With the farm table that should be plenty unless the marks are not gone. One trick that works is after sanding wipe the wood with thinner to see scratches and this also gets rid of any dust left on the piece. Apply stain and then steel wool if need be and wipe it down. Now poly again and when you do have a really good light that you can shine at an angle to see those high or dry spots. I usually apply with small roller sponge ( everyone says don't but I do) key here is to go over that with a wet brush to get any bubbles out. I do it this way to make sure I have applied enough and it's even. Always when I brush paint or anything on I tend to not apply enough so this process helps with that which I think was your initial issue. Good luck I'm sure it will be fine 99% won't notice unless it's really bad.

Answer 4

I had the identical problem as stated here with
Tmiller85. I am working on my dining room dark walnut colored table. I used gel stain, and one General Finishes top coat. After that the 1st top coat completely dried, I scuffed sanded with 0000 steel wool, and after I cleaned it with a tack cloth, there were surface scratches from the steel wool, and blushing, just as was shown in the picture. I used HOMAX WHITE RING REMOVER which removed most of the blushing. After that was completed, I used MOHAWK NO BLUSH PLUS RETARDER to remove most of the remaining blushing.
I am now deciding on what to do about the surface scratches. It has been suggested that OLD ENGLISH SCRATCH REMOVER will remove surface scratches. Another option is to use a "spray on" (do not brush on or hand apply) light coat of a compatible top coat to cover the scratches. Yet another option is to use HOWARD RESTOR-A-FINISH in a color that matches your wood, but if this is used, I cannot use a polyurethene top coat. I would have to use HOWARD FEED-N-WAX. I could, also, use 220 sand paper and scuff sand, but am afraid to do that, due to what happened when I used the steel wool. I hope this helps