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Discussion Starter #1 (Edited)
So I edited this post because this a more thorough explanation of what is going on - I need help with this finishing problem. Understanding what went wrong - and how to do it correctly in the future now that I have to go back and sand back down to bare wood.

I am finishing a stained bench top. I applied 4 coats of Helmsman Spar Urethane and waited 4 hours in between coats. I lightly sanded in between coats with 400 grit. After the 4th coat - I sanded with 400 grit. then wet sanded with 600 using a soap and water spray. and then wet sanded with 1000 with the same spray. I wanted to get a nice smooth surface before I applied a last coat of Helmsman and final sanded.

Anyway, after I removed the soapy slurry - I noticed that in numerous places that I sanded to the wood - a tiny spot here and there. And the highest points of the grain are lighter in color than the rest as the stain was sanded as well. I tried to add a touch of stain - but it just glides right off. I don't know how I could of sanded through 4 coats of spar urethane with such light sanding - and now I have to sand the whole thing back down and start over.

Can someone see what I did wrong? What would be a better process/product so that I don't have to work on finishing something for 3 days, and then have to start over. I appreciate all help.
Thanks
J

J
 

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It's hard to say without a picture. If the spot is small you might be able to touch it up with a touch up marker. If it is a little bigger you might use a dye stain. It would be better sprayed, kind of like you were air brushing it on. The biggest if is how much of a color difference are you trying to suppliment? If you plan to lay a lot of pigment on one spot to color it in then it will always look like a patch and you might as well use some paint and varnish remover and start over.
 

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Not sure I understand the problem but to answer you question, Minwax sell stain markers in a number of wood colors. They are like "Magic Markers".

Go to a paint store that sells Minwax problems.
 

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We have all had issues with stain and sand through. Its typical when so much sanding is done. You end up with several areas that do not have thick enough top coast to protect the base coats.

You have enough post now to be able to post a picture. That would help us to "see" the problem.
 

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It's pretty clear what you did wrong. You didn't let the spar dry long enough between coats and when you did sand you sanded too agressively. The spar varnish should have dried 24 hours between coats. All you are really want to do sanding between coats is smooth the finish where the finish raised the grain. After the first coat you must sand very sparingly because one coat isn't enough to really sand. It's only after the second coat you can sand.

It's a bad practice to sand a finish off to refinish something. Sanding takes off what finish is on the surface and leaves what is penetrated in the wood. Then when you apply the stain there are spots here and there that don't stain. It's always best to use a paint and varnish remover to take a finish off.
From where you are if you still want to touch up the finish I would let the finish dry a week before doing anything. The wood is sealed with the spar and you can't use stain on the spots. The colorant a paint store has in their machines to color paint is a universal tinting color. Without knowing the color of what you are doing I couldn't say which color but you could mix a small amount of the color with some of the spar varnish and use that to touch up the spots. Just don't expect the spots to look like you never sanded through but it will look better. The only way to really fix it is to strip the finish off and start over. A better touch up would be to use a dye stain with an air brush. A dye mixed with alcohol would be more transparent. You would then have to spray a coat of spar on because wiping or brushing it would wipe the dye off.

If you want a finish that dries fast get the means of spraying and use lacquer. You could finish a piece of furniture completely done in the morning and use it that afternoon. It's not a exterior finish like the spar though.
 

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It's pretty clear what you did wrong. You didn't let the spar dry long enough between coats and when you did sand you sanded too agressively. The spar varnish should have dried 24 hours between coats.
That spar varnish could take weeks to cure, and possibly never get very hard.




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Discussion Starter #9
weeks to cure?? is there another option for outdoor furniture htat won't require a recoat every year?
 

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Sorry but it's time to start over. It's not sand through. It's either a chemical reaction with the stain or you left sanding dust in the low part of the grain and finished over it. How long did you let the stain dry before you applied the first coat of spar? It really needs 3-4 hours in warm weather. Longer in cool or damp weather.
 

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Discussion Starter #12
I waited 2.5 hours. as the can stated to wait at least 2 hours. but now I will wait at least 24.

so I have to sand it down.. that's what I thought... damn.
So after I sand it through.. re-stain it. Please give me some detailed info on how to do it right next time...
first coat spar.. no sanding?
second coat spar (after 24) - sand with ?? i've seen 220.. 400. 600. dry or wet?

I want to put a total of about 6 coats. all info/knowledge appreciated. I don't want to screw this up a 2nd time. thanks again guys. This forum is always so helpful. Once I get this down pat - with a bad ass finish - on the regular - i'm going to post for others how I do it - hopefully will help someone out.

thanks
J
 

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I waited 2.5 hours. as the can stated to wait at least 2 hours. but now I will wait at least 24.

so I have to sand it down.. that's what I thought... damn.
So after I sand it through.. re-stain it. Please give me some detailed info on how to do it right next time...
first coat spar.. no sanding?
second coat spar (after 24) - sand with ?? i've seen 220.. 400. 600. dry or wet?

I want to put a total of about 6 coats. all info/knowledge appreciated. I don't want to screw this up a 2nd time. thanks again guys. This forum is always so helpful. Once I get this down pat - with a bad ass finish - on the regular - i'm going to post for others how I do it - hopefully will help someone out.

thanks
J
Well first a word about the Helmsman spar. The finish is intended to be used on wood that is outdoors. It is made a little softer so it can expand and contract with the temperature extreames of exterior wood. If your project is used indoors use an interior oil based polyurethane. It will make a harder more scratch resistant finish.

Your first step would be to use a paint and varnish remover and strip the finish off. On a warm day 70 degrees or above use a methylene chloride remover and strip the finish. I normally use Kleen Strip remover. It's available and the box stores and walmart. Brush a liberal coat on and let it soak for about 15 minutes and scrape as much of the finish off with a broad knife. Then as quickly as you can rinse the residue off with either lacquer thinner or I use a power washer that is less than 1500 psi. The low power won't hurt anything and will clean the wood better than any thing you could use. Let dry an hour with lacquer thinner or overnight with water.

Then thoroughly sand the wood with 180 or finer grit sandpaper.

Then stain the wood with a oil stain and quickly completely wipe the excess off. If the weather is warm and dry especially if there is good ventilation it should dry in 3 hours. If you wanted to let it dry overnight it would certainly be dry.

Then apply the spar or poly with a very soft brush or wipe it or spray it and let each coat dry 24 hours. With 220 grit sandpaper or a fine glit sanding pad lightly sand the finish without water or soap just enough to smooth it a little and apply another coat. I don't like the idea of using soap between the coats. If any was left it could cause a chemical reaction. Note: If you are wiping the finish three coats are equal to one coat so allow for that when sanding. The next sanding you could wet sand with 400 grit but keep it to minimum. After wet sanding wash the sludge off with water only and let dry. Before applying another coat wipe what light dust there may be on the surface off with a dry cloth and procede. When dry if the finish looks good and feels smooth call it the final finish and let it cure for a week. If not repeat with another coat. When done if you wanted a hand rubbed finish you could wet sand it with 1200 grit sand paper and buff the finish with rubbing compound. At present while the finish is relatively fresh you could use a clear coat safe polish to bring the sheen back. I wouldn't use any wax on it until the finish was at least a month old.
 
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