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Help! Waterbased polyurethane tiny spot attack

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Forum topic by ENwooding posted 06-28-2017 07:38 PM 752 views 0 times favorited 8 replies Add to Favorites Watch
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ENwooding

2 posts in 530 days


06-28-2017 07:38 PM

Topic tags/keywords: cherry finishing

Hi woodworking community of the ethers. This is my first post, as I combed through all sorts of forums and could not diagnose my problem…

I’m finishing a cherry foyer table, and going through some serious issues. I put boiled linseed oil waited like 3 days, put on Zinnser’s wax-free shellac on, and then water-based polyurethane. I put on 4 or 5 layers on, sanding with 400 in between, and it was coming out good, but for some reason the last coat resulted in these tiny dimples. I’m pretty sure these dimples didn’t exist before the last coat. I ended up sanding it down a good amount to get rid of the spots, and then reapplied, but same result. The polyurethane just seems to pull away from certain aways, leaving dimples, or nubs or whatever they may be called. Pretty much after a minute or so of applying these pockets show up…

I’m not sure what to do now, whether applying more coats would eventually cover it up, sand it down and just go with lindseed oil… Not sure. Would love any advice on ways of remedying this. There’s a bunch of brush marks left becasue I tried to see if brushing over these spots once the poly was setting would cover up the spots, but they pulled aways nonetheless… Thanks for your time.


8 replies so far

View rwyoung's profile

rwyoung

409 posts in 3670 days


#1 posted 06-28-2017 09:09 PM

Did you use a tack rag? If so, is the tack rag “rated” for waterborne finishes?

-- Don't sweat the petty things and don't pet the sweaty things.

View EricTwice's profile

EricTwice

246 posts in 731 days


#2 posted 06-28-2017 09:30 PM

You have a non compatibility issue. In this case it is probably water not sticking to oil.

basically, Your oil was not completely dry and it got through the barrier coat of shellac.

How do you fix it? If you are not in a hurry let the whole thing set for 3 or 4 weeks. you can tell it is dry when finish dropped on with an artist’s brush will stick in the dimples (fish eyes)

Beyond that, see if lacquer will stick to your water base finish,(It worked with the early minwax water base poly, but I don’t know what you are using) if it does, try a dropping a bit of lacquer on those spots and sand it flat and have another go.

Me, I would not try to mix oil and water.

-- nice recovery, They should pay extra for that mistake, Eric E.

View pintodeluxe's profile

pintodeluxe

5798 posts in 3011 days


#3 posted 06-28-2017 09:56 PM

Fish eyes are usually a sign of contamination on the surface. Dust, silicone, dirt, fingerprints etc. will all cause them. I clean the surface with a cheesecloth (not tack cloth) and bristle attachment on a vacuum.

It also can be a compatibility issue between the different finishes. Everyone says shellac is universally compatible with other finishes, but the only times I have had issues was when I used shellac first, then another finish like lacquer. If the finish gets too warm it will crinkle. If the finish is applied too heavily it will fish eye (even without contaminants).

Since you were getting good results up until the last coat, my guess is it went on a little too heavy. Sand it back and apply another light coat.

Best of luck with it.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View ChefHDAN's profile

ChefHDAN

1171 posts in 3047 days


#4 posted 06-29-2017 12:30 PM

I finish my cherry pieces with 5 to 7 applications of boiled linseed oil BLO and allow to fully cure which is at least a week in summer 80*f+ & 60% to 70% humidity and sometimes two weeks in the winter if I’m not allowed to bring the piece into the house, (SWMBO)... Once cured, I’ll do a wipe with a clean rag dampened with mineral spirits to wipe off any dust. By the time I can get ready with the water based poly the surfaces are dry and I apply the poly. Preference is to shoot it with my HVLP gun but i do still use a brush. I’ve sometimes had to go back and clean up some dust nibs or dammed little bugs, but never have had an issue with the fish eyes.. knock wood.

I think you’ve got no choice but to sand out the poly to the oil and start over…I’ve got a fair bit of practice but am not an expert, but, Charles Neil is and if he chimes in I’d go with his advice.

-- I've decided 1 mistake is really 2 opportunities to learn.. learn how to fix it... and learn how to not repeat it

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CharlesNeil

2457 posts in 4068 days


#5 posted 06-29-2017 12:45 PM

If this is appearing after 4 or 5 coats of water base with no issue then your issue lies with whatever could have contaminated the last coat .BTW you dont need 4 or 5 coats thats a bit excessive , usually 3 is a good number .
I would sand it down well ,then clean it good with naphtha, wiping it on wet then off , repeat a couple of times,always new cloths in between .then do a very thin coat of dewaxed shellac just to be sure the contamination is sealed off, give that a light scuff sand and then do a final topcoat

View Carloz's profile

Carloz

1147 posts in 789 days


#6 posted 06-29-2017 01:02 PM

View ENwooding's profile

ENwooding

2 posts in 530 days


#7 posted 06-29-2017 01:43 PM

I appreciate all the perspectives and quick responses. What an incredible resource!!

First of all, learning that it is fisheyes is very helpful. I couldn’t quite figure out what exactly was going on and in my limited search attempts, was not able to properly diagnose the problem.

I’m still not quite sure why it appeared after so many coats, but it feels as if the poly might be reacting to the BLO?? Anyways, I’m going to go ahead and give it a good sand, clean with naptha, apply a thin layer of de-waxed shellac and try a few thin layers of poly after that. Meanwhile I’ll go pay obeisance to the lords of finishes that they may contenance sofly on my plight. I appreciate all the expertise and generosity in this room. Will report back!

View ChefHDAN's profile

ChefHDAN

1171 posts in 3047 days


#8 posted 06-29-2017 03:00 PM

Whoops, forgot my manners, Welcome to LJ’s

Make sure to check out Charles Neil on YOUtube too, lots of good help there too, Thanks for all the content Charles, I’m going to make a point of doing more with the dewaxed shellac, with all I hear read I have it in a category of not knowing what I don’t know and should learn the next level for my finish game…

-- I've decided 1 mistake is really 2 opportunities to learn.. learn how to fix it... and learn how to not repeat it

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