How much should I thin spar urethane?
- Thread starter JHZR2
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Originally Posted By: JHZR2
If I want to rub a highly thinned version for the absolute final coat, is there a preferred cloth that is sure to be dust and string free?
Not really. I had a few tack cloths screw up jobs over the years. Sometimes it just luck, or the lack of it.
If I want to rub a highly thinned version for the absolute final coat, is there a preferred cloth that is sure to be dust and string free?
Not really. I had a few tack cloths screw up jobs over the years. Sometimes it just luck, or the lack of it.
Originally Posted By: JHZR2
Why did you think that was going to happen?
My plan is definitely to rub it out, that's part of the learning process too... But I just can't seem to lick the issue at hand...
Wonder if I can coat the spar with another harder finish to rub it out better?
Still I need to figure out how to do it right so this doesn't happen. So bummed when there were more nibs after cleaning and leaving then there were other times when I hung around and tried messing with it further to get bubbles and stuff to clear out...
You're still under the impression you can apply a perfect finish. You can't. No one can. Not even Flexner. He admits it's a beginners trap. THERE WILL ALWAYS BE SMALL DEFECTS IN IT. Period. Yours looks excellent to me.
Once you've built up four or five layers, you need to leave it alone to cure for at least two weeks. Then you can begin to flatten it, which will remove the defects and level the finish. You need to read about the process from a pro like Flexner or Jewett or Dredsner.
Why did you think that was going to happen?
My plan is definitely to rub it out, that's part of the learning process too... But I just can't seem to lick the issue at hand...
Wonder if I can coat the spar with another harder finish to rub it out better?
Still I need to figure out how to do it right so this doesn't happen. So bummed when there were more nibs after cleaning and leaving then there were other times when I hung around and tried messing with it further to get bubbles and stuff to clear out...
You're still under the impression you can apply a perfect finish. You can't. No one can. Not even Flexner. He admits it's a beginners trap. THERE WILL ALWAYS BE SMALL DEFECTS IN IT. Period. Yours looks excellent to me.
Once you've built up four or five layers, you need to leave it alone to cure for at least two weeks. Then you can begin to flatten it, which will remove the defects and level the finish. You need to read about the process from a pro like Flexner or Jewett or Dredsner.
JHZR2
Staff member
It sat for about two weeks. I really did a job going over it. Sanded from 160 at the raised areas) through 320, then 0000 wool. Really, really smooth. Rub a hand across and it was smooth as glass. Perfect.
Had run the fan with the ultra fine filter on it, no visible dust in the air. Washed down the area, had vacuumed 3x. Tack clothed multiple times. Heated the space. Got a new chinex soft 3" brush. Leveled the surface with a long level to perfect so that the urethane couldn't flow.
Thinned the (strained) urethane with naphtha this time around 20% so it would dry faster. Applied it.
I did see a few more, larger bubbles, but they popped fast.
But by the time I got to the one end I could see nibs on the other. Ugh. Plus it wasn't flat. I think the naphtha makes it run more than mineral spirits.
Now what?
Per the post immediately above, it will never be perfect, these nibs will always show up. Not sure if bamboo is worse in this regards?
I'm thinking of sanding with 400 as soon as I can, brushing one more layer on, uneven or not, and then when that dries for a week or two, move to 4f pumice and rotten stone.
Had run the fan with the ultra fine filter on it, no visible dust in the air. Washed down the area, had vacuumed 3x. Tack clothed multiple times. Heated the space. Got a new chinex soft 3" brush. Leveled the surface with a long level to perfect so that the urethane couldn't flow.
Thinned the (strained) urethane with naphtha this time around 20% so it would dry faster. Applied it.
I did see a few more, larger bubbles, but they popped fast.
But by the time I got to the one end I could see nibs on the other. Ugh. Plus it wasn't flat. I think the naphtha makes it run more than mineral spirits.
Now what?
Per the post immediately above, it will never be perfect, these nibs will always show up. Not sure if bamboo is worse in this regards?
I'm thinking of sanding with 400 as soon as I can, brushing one more layer on, uneven or not, and then when that dries for a week or two, move to 4f pumice and rotten stone.
Are you applying thin coats? The coat above looks heavy. I didn't ask before but i feel if you put down too heavy of a coat, it skins over on the top and the bottom is going to need to gas out hence bubbles. Even if you thin it out a bit, i like several thin coats with a light sand in between.
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You're getting better! It looks like the material was applied just a little too thick. The nubs are probably airborne.
I haven't used this stuff in 25 years or more so I don't know how the VOC laws have impacted it. You might want to read up on it, and possibly test it on a small sample board.
http://www.gnhw.org/qaarchive/japan-drier
There is always a trade off with these types of products. You get faster dry times which is good because the likelihood of dust messing it up is reduced. The downside is, too much might impact color or crack, and you'll have less open time, so you'll have to work fast! When used properly it can be helpful.
If you do decide to use it make sure the surface is totally dry!!!!!!!
Edit- As already mentioned perfection doesn't exist.
A top quality job is usually spray applied in a dust free spray booth. Finally, sometimes you can over apply a finish looking for the perfect job and end up with something worse than you have.
I haven't used this stuff in 25 years or more so I don't know how the VOC laws have impacted it. You might want to read up on it, and possibly test it on a small sample board.
http://www.gnhw.org/qaarchive/japan-drier
There is always a trade off with these types of products. You get faster dry times which is good because the likelihood of dust messing it up is reduced. The downside is, too much might impact color or crack, and you'll have less open time, so you'll have to work fast! When used properly it can be helpful.
If you do decide to use it make sure the surface is totally dry!!!!!!!
Edit- As already mentioned perfection doesn't exist.
A top quality job is usually spray applied in a dust free spray booth. Finally, sometimes you can over apply a finish looking for the perfect job and end up with something worse than you have.
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JHZR2
Staff member
I wouldn't doubt that I put it down thicker. The chimex bristles held material a bit different, and I too left that I did. Plus though I put naphtha in this time, i don't think I thinned it as much overall (eyeball thing, I never have measured volumetrically).
I read that nibs can be due to the brush, but since I used a new one, well cleaned, I know it wasn't the cause.
Maybe I'll be pleasantly surprised tomorrow morning. Doubt it though...
Question is if I should go to rubbing it out, rubbing down nibs with a paper bag or nib file, or apply again. If I apply again, it will be Sunday night probably. Not sure if I'll sand it this time, since I'm definitely nearing the end, there's no reason to add more layers, and I'm not solving the nibs or other issues on this piece...
I read that nibs can be due to the brush, but since I used a new one, well cleaned, I know it wasn't the cause.
Maybe I'll be pleasantly surprised tomorrow morning. Doubt it though...
Question is if I should go to rubbing it out, rubbing down nibs with a paper bag or nib file, or apply again. If I apply again, it will be Sunday night probably. Not sure if I'll sand it this time, since I'm definitely nearing the end, there's no reason to add more layers, and I'm not solving the nibs or other issues on this piece...
At this point I would try everything possible not to apply another coat.
FTR-Pure bristle is a better choice in brushes for that project. Chinex brushes are OK, but for varnishes and poly nothing beats pure bristle, or hogs hair. Chinex's claim to fame is having the ability to be used in any finish without having to worry about the tips "exploding." What that means is if you were to take a pure bristle brush and use it in latex paint, a 3" brush could spread out to a 5" brush. Similar things happen to nylon brushes if used in oil base products and washed. That doesn't happen with Chinex, the trade off is they tend to apply oil base products a bit on the heavy side.
What you could actually be seeing as nibs might actually be small bits of the very tip of your brushes. If you look closely at the tips what you might find is the very tip of each bristle looks like it is divided or split into more bristles.
Either way I think you've done a very nice job. Striving for perfection can drive you nuts when applying brushed on finishes!
Sorry for the long winded rant on brush types.
FTR-Pure bristle is a better choice in brushes for that project. Chinex brushes are OK, but for varnishes and poly nothing beats pure bristle, or hogs hair. Chinex's claim to fame is having the ability to be used in any finish without having to worry about the tips "exploding." What that means is if you were to take a pure bristle brush and use it in latex paint, a 3" brush could spread out to a 5" brush. Similar things happen to nylon brushes if used in oil base products and washed. That doesn't happen with Chinex, the trade off is they tend to apply oil base products a bit on the heavy side.
What you could actually be seeing as nibs might actually be small bits of the very tip of your brushes. If you look closely at the tips what you might find is the very tip of each bristle looks like it is divided or split into more bristles.
Either way I think you've done a very nice job. Striving for perfection can drive you nuts when applying brushed on finishes!
Sorry for the long winded rant on brush types.
JHZR2
Staff member
Very interesting about the brushes! I didn't know any of that, but when I saw the nice, soft and consistent chinex brush, it just felt good and the bristles all looked identical and consistent, so I thought that might be a good thing.
We'll see how the current coat ends up when cured...
We'll see how the current coat ends up when cured...
There are some very good Chinex brushes, but as I mentioned above there are differences, and brushes better suited for certain jobs.
I find Chinex good to have when there's a new guy on the crew and you tell him to grab a brush and cut in a ceiling. If he grabs a bristle brush and cuts in a ceiling with latex paint, the brush is trash, or becomes a good duster brush!!!!!!!!!! With a Chinex he can use it in anything!
I find Chinex good to have when there's a new guy on the crew and you tell him to grab a brush and cut in a ceiling. If he grabs a bristle brush and cuts in a ceiling with latex paint, the brush is trash, or becomes a good duster brush!!!!!!!!!! With a Chinex he can use it in anything!
JHZR2
Staff member
So one other interesting issue.
I sanded really smooth, though there were a few "trenches" from the 160 grit that I was using for smoothing the high sections, which I didn't want to go after due to how much material it would remove.
I did the 220, 320, 0000 wool, with lots of cleaning in between. Really felt smooth as glass.
But this time when I put down the urethane with naphtha, not it isn't glossy. It has been every other time, now it's almost matte. Some of it is I think from the sanding, but I've sanded with 320 between each other coat and it's always been glossy and perfect.
So why this is much more matte is beyond me. Naphtha?
I'm also surprised, given our discussion of it being laid down thick, that it's actually a lot thinner and has shrunk during cure much more than usual. its also cured much faster.
So naphtha is way different in application, it seems, than mineral spirits....
I sanded really smooth, though there were a few "trenches" from the 160 grit that I was using for smoothing the high sections, which I didn't want to go after due to how much material it would remove.
I did the 220, 320, 0000 wool, with lots of cleaning in between. Really felt smooth as glass.
But this time when I put down the urethane with naphtha, not it isn't glossy. It has been every other time, now it's almost matte. Some of it is I think from the sanding, but I've sanded with 320 between each other coat and it's always been glossy and perfect.
So why this is much more matte is beyond me. Naphtha?
I'm also surprised, given our discussion of it being laid down thick, that it's actually a lot thinner and has shrunk during cure much more than usual. its also cured much faster.
So naphtha is way different in application, it seems, than mineral spirits....
JHZR2
Staff member
What do you mean retarding last coat?
If I replace x% volume with naphtha or the same x% volume with spirits, other than how fast the solvents flash what's the difference? Neither should effect the poly cross linking rate, as that's a matter of absorption of oxygen from the air.
If I replace x% volume with naphtha or the same x% volume with spirits, other than how fast the solvents flash what's the difference? Neither should effect the poly cross linking rate, as that's a matter of absorption of oxygen from the air.
Quote:
Less film naphtha is thinning it should not be using in a brush application should be retarding last coat
It's difficult trying to comprehend what you are saying here, Dave.
JHZR tried the naptha to reduce dry time in the hopes less dust would settle.
What Dave is saying is that mineral spirits will "retard" the dry time, allowing more working time for leveling, bubble dispersion, etc., which is more appropriate for the final coat. I have brushed naptha thinned poly before. It's not like it is lacquer. It has never changed the gloss level and in my experience, only slightly changes the flash off time.
The final coat still looks very thick, unless the photo is misleading. I like to put on many water thin coats. 2 per day is possible. Lay it on. Cross brush at 90 degrees for uniform level, then one or two "feather" brushing in the long direction. Walk away. Don't over brush...you can tell when it is starting to set.
Temperature and humidity can make every application different and I adjust my methods accordingly. It's so hard to convey technique via words.
This is still a confusing project. I don't understand all the nibs, bubbles, etc..
Less film naphtha is thinning it should not be using in a brush application should be retarding last coat
It's difficult trying to comprehend what you are saying here, Dave.
JHZR tried the naptha to reduce dry time in the hopes less dust would settle.
What Dave is saying is that mineral spirits will "retard" the dry time, allowing more working time for leveling, bubble dispersion, etc., which is more appropriate for the final coat. I have brushed naptha thinned poly before. It's not like it is lacquer. It has never changed the gloss level and in my experience, only slightly changes the flash off time.
The final coat still looks very thick, unless the photo is misleading. I like to put on many water thin coats. 2 per day is possible. Lay it on. Cross brush at 90 degrees for uniform level, then one or two "feather" brushing in the long direction. Walk away. Don't over brush...you can tell when it is starting to set.
Temperature and humidity can make every application different and I adjust my methods accordingly. It's so hard to convey technique via words.
This is still a confusing project. I don't understand all the nibs, bubbles, etc..
JHZR2
Staff member
Originally Posted By: dave123
more confusing because of the amount of bad advive.
Bad advice? I think what I've taken away first and foremost is that dust nibs happen. I had a nice coating the first time, other than some nibs...
I've fixed issues with leveling the coating, etc. the coating I put on last night actually cured to strike me as very thin. I tend to try to lay on fairly thick so I can brush on and leave it without much working, since brushing creates its own set of issues in poly.
This is a learning project without any criticality other than that I'd like to work it to the final (if not that great) product and start using the tool chest. I'm doing this in a pretty cold environment which also doesn't help.
more confusing because of the amount of bad advive.
Bad advice? I think what I've taken away first and foremost is that dust nibs happen. I had a nice coating the first time, other than some nibs...
I've fixed issues with leveling the coating, etc. the coating I put on last night actually cured to strike me as very thin. I tend to try to lay on fairly thick so I can brush on and leave it without much working, since brushing creates its own set of issues in poly.
This is a learning project without any criticality other than that I'd like to work it to the final (if not that great) product and start using the tool chest. I'm doing this in a pretty cold environment which also doesn't help.
Originally Posted By: JHZR2
I'm doing this in a pretty cold environment which also doesn't help.
How cold?
I'm doing this in a pretty cold environment which also doesn't help.
How cold?
Originally Posted By: JHZR2
Originally Posted By: dave123
more confusing because of the amount of bad advive.
Bad advice? I think what I've taken away first and foremost is that dust nibs happen. I had a nice coating the first time, other than some nibs...
I've fixed issues with leveling the coating, etc. the coating I put on last night actually cured to strike me as very thin. I tend to try to lay on fairly thick so I can brush on and leave it without much working, since brushing creates its own set of issues in poly.
This is a learning project without any criticality other than that I'd like to work it to the final (if not that great) product and start using the tool chest. I'm doing this in a pretty cold environment which also doesn't help.
A note here re: leveling/flattening a finish. What it means is using a med. to large sanding block, such as 5x7 or 8x10 to hold either a half or full sheet of sandpaper, attach the sandpaper to it using 3M spray adhesive, and sand only in the direction of the grain. This will remove the high spots and "level" the finish.
I used the center cutout from my router table. I stuck the sandpaper down on the formica side. You can use 320X safely like this because of the large block area. I think there is a picture of my sanding block in the photo section of the loudspeaker I was refinishing. Since you're doing a large tabletop, your sanding block should be the size of a full sheet of paper. Once it's level additional coats can be lightly sanded with 400x or so. You don't need to go through 0000 between coats.
Originally Posted By: dave123
more confusing because of the amount of bad advive.
Bad advice? I think what I've taken away first and foremost is that dust nibs happen. I had a nice coating the first time, other than some nibs...
I've fixed issues with leveling the coating, etc. the coating I put on last night actually cured to strike me as very thin. I tend to try to lay on fairly thick so I can brush on and leave it without much working, since brushing creates its own set of issues in poly.
This is a learning project without any criticality other than that I'd like to work it to the final (if not that great) product and start using the tool chest. I'm doing this in a pretty cold environment which also doesn't help.
A note here re: leveling/flattening a finish. What it means is using a med. to large sanding block, such as 5x7 or 8x10 to hold either a half or full sheet of sandpaper, attach the sandpaper to it using 3M spray adhesive, and sand only in the direction of the grain. This will remove the high spots and "level" the finish.
I used the center cutout from my router table. I stuck the sandpaper down on the formica side. You can use 320X safely like this because of the large block area. I think there is a picture of my sanding block in the photo section of the loudspeaker I was refinishing. Since you're doing a large tabletop, your sanding block should be the size of a full sheet of paper. Once it's level additional coats can be lightly sanded with 400x or so. You don't need to go through 0000 between coats.
JHZR2
Staff member
Originally Posted By: demarpaint
Originally Posted By: JHZR2
I'm doing this in a pretty cold environment which also doesn't help.
How cold?
Around 60F.
The nibs are visible essentially as soon as I lay down the coating, so the extra cross link/cure time isn't the big issue, but it could have some effect.
Originally Posted By: JHZR2
I'm doing this in a pretty cold environment which also doesn't help.
How cold?
Around 60F.
The nibs are visible essentially as soon as I lay down the coating, so the extra cross link/cure time isn't the big issue, but it could have some effect.
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