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Spot Sanding Water Based Poly (fixing imperfection).

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Forum topic by MudPuppy posted 11-02-2016 03:27 PM 839 views 0 times favorited 15 replies Add to Favorites Watch
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MudPuppy

6 posts in 406 days


11-02-2016 03:27 PM

Hello, I have been spending a month constructing a dining room table for the family and everything up until yesterday, it was looking excellent. Table is made of rough cut cedar. I used a Minwax stain. And currently in the process of applying Minwax Water Based Ultimate Floor Poly to the table (using HVLP gun and compressed air to apply) with light sanding (400 grit) between coats. But, last night as I was going to apply my 3rd coat of poly I noticed some small, dark, liquid splatter stains that were covered between the 1st and 2nd coat of poly (not on the stain stage of table). I have no idea what it is and almost looks like someone opened a can of soda next to the table and it sprayed on it or it even looks like small tiny dots of unwiped stain. My question is this: Is it possible to just sand the small 5” x 5” area down to the splatter marks, eliminate the splatter marks and then rebuild the poly up to the original mils as the rest of the table and blend it back in or am I looking at way too much work for something that will most likely not be noticed by anyone else other than myself? Just bothers me cause I know they are there and I have put so much time into the table. I’m worried that I may sand down to the stained layer or even then not be able to blend the small sanded area back to blend in with the rest of the table. Appreciate any direction or advice. I will include a pic of the table as it sits today.


15 replies so far

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Carloz

965 posts in 427 days


#1 posted 11-02-2016 04:00 PM

You could do this with lacquer or shellac but not polyurethane. The repaired are will be worse than it is now.

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MudPuppy

6 posts in 406 days


#2 posted 11-02-2016 04:58 PM

Appreciate the response. I think I’ll just leave it be….

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Carloz

965 posts in 427 days


#3 posted 11-02-2016 05:50 PM

Many expect that finishing is the easiest part of making the project and everyone can do it. Show some of your projects to your guests and everyone will ooh about the joinery but rarely anyone is impressed with the finish, simply because they think it is simple and they could do it too.

For me personally it is the most difficult part. I rarely redo the main work but it also rarely happens that I do not have to redo the finish.

So get a sander, take the finish off and reapply it. You spend a month on the table so spend few more hours to get the finish right.

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Loren

9613 posts in 3483 days


#4 posted 11-02-2016 05:59 PM

I would use razor blades with the corners dubbed
off on a grinder. Scrape through the finish to get
just the spots out, sand with 220 grit stearated
paper and apply more finish. If you go down to
the stain you’ll never get it to look right but if
you can stay in the poly layers you can build it
up again, then cut back using sanding blocks.

I’ve done this on guitars.

You might make a practice piece to make sure
you can pull off the nuanced scraping and get
a satisfactory rebuild of the poly. Fortunately
the water poly cures so fast the practice can be
completed in a few days.

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MudPuppy

6 posts in 406 days


#5 posted 11-02-2016 06:00 PM

To be honest, I’m happy so far with the finish (satin poly). It was just the splatter stains that went unnoticed that is now locked down and under the finish. They are very small splatter stains and most likely will only bother me. I’ve put 3 coats of water based poly on it (HVLP Gun). How many coats in your experience would you put on if you were spraying on a water based poly? I have heard 3-4 is the minimum. It is a satin poly.

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Loren

9613 posts in 3483 days


#6 posted 11-02-2016 06:03 PM

I brush. I’ve never had any fun spraying, never had
the space for a truly clean room to do it in.

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MudPuppy

6 posts in 406 days


#7 posted 11-02-2016 06:05 PM

Loren. I like that idea. Almost surgical. I was just more paranoid about building the poly back up after removing the stains locked within the poly layers.

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Carloz

965 posts in 427 days


#8 posted 11-02-2016 07:15 PM


I brush. I ve never had any fun spraying, never had
the space for a truly clean room to do it in.

- Loren


You need a truly clean room when you brush too. Dust does not care if you sprayed or brushed.

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Carloz

965 posts in 427 days


#9 posted 11-02-2016 07:16 PM


To be honest, I m happy so far with the finish (satin poly). It was just …
- MudPuppy

Exactly ! It is always just .

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Loren

9613 posts in 3483 days


#10 posted 11-02-2016 07:21 PM

My experience with water base gloss poly is that
it behaves a lot like shellac in terms of repairability,
which is a good thing. I haven’t used oil based
poly in awhile as it is now hard to get in my state
but I am, after initial reservations having tried
waterborne finishes a decade ago, very impressed
with water-poly. It’s about as forgiving as I could
ask for.

It can be padded on like shellac but leaves ridges
as it doesn’t dissolve itself when you go back over
a drying section. It builds reasonably fast and cuts
back pretty easily with sandpaper. I still haven’t
matched the smoothness of a french polish with
it (my french polishing isn’t that great anyway)
but it’s still pretty cool stuff, imo and I plan to
continue experimenting with padding methods
with it.

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Carloz

965 posts in 427 days


#11 posted 11-02-2016 07:51 PM


My experience with water base gloss poly is that
it behaves a lot like shellac in terms of repairability,
which is a good thing.

- Loren

You might easily get this.

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Loren

9613 posts in 3483 days


#12 posted 11-02-2016 07:57 PM

stop being a troll Carloz. You’re not a credible person
here yet. I have noticed that you think you know it
all. Here’s a newsflash: you don’t.

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MudPuppy

6 posts in 406 days


#13 posted 11-02-2016 08:55 PM

Ok. Here is where I’m at: went ahead and tried the razor blade method. It lifted all the black splatter marks just fine. However, after knocking it down with 320 sandpaper and then spraying the first (re) coat of poly there will be some obvious difference between the razored knicks and rest of the table. But, the good thing is as I continue to spray and build up the poly I imagine it will become less noticeable but never really going away. Regardless of there always being a slight blemish in that area it is much more camouflaged now vs. the severe contrast difference of dark almost black splatter marks resting on top (within) the light brown color of the table. My practice of painting cars is coming in handy with adjusting and spraying the poly. Live and learn and appreciate all the advice and warnings.

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Sunstealer73

128 posts in 1928 days


#14 posted 11-02-2016 10:32 PM

I hate to be that guy, but does your top allow for wood movement? Having a frame around boards like that is a recipe for disaster when the seasons change. The splatter marks will be the least of your worries if you have everything butted up tight like it appears. It will buckle, crack, and split if that’s the case.

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MudPuppy

6 posts in 406 days


#15 posted 11-03-2016 12:21 AM

It looks tight, I agree. But I think there is room between my awful cuts as they did not go in like puzzle pieces. The bottom is open on her to breath and I don’t live in the south so she won’t soak up too much water, I hope. I guess I’m just saying regardless of what happens, I’m excited to have gotten this far.

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