Should I buff Polyurethane?

[Johnhamdun]

Hey guys, first time I have used Poly. I have done a number of coats already and have some runs.

My plan is to wait a day or more and then sand with 1200 or something to smooth it out.

Questions:

1) Should I wet sand? The poly is water-based so I was thinking I should dry sand. What grit should I use?

2) Should I buff with PU? If so (and I know this is a noob question) how do I buff?

Thanks in advance!

 

[Alfang]

I'd go 400 till the runs are flat, then 600, all wet.  Carefull not to get any bare wood wet.

then if you have the stew mac buffer like I do, I'd start buffing.

If CB, jack, or Tonar chime in forget what I say and do what they say

 

[Johnhamdun]

I'd go 400 till the runs are flat, then 600, all wet.  Carefull not to get any bare wood wet.

then if you have the stew mac buffer like I do, I'd start buffing.

If CB, jack, or Tonar chime in forget what I say and do what they say

hahaha great, thanks alfang.

BTW, this one? http://www.stewmac.com/shop/Finishing_supplies/Abrasives,_polishes,_buffers/Finesse_Polishing_Pad.html

 

[jackthehack]

I don't finish with poly so I have no clue really, Google it.

 

[-CB-]

Hey guys, first time I have used Poly. I have done a number of coats already and have some runs.

My plan is to wait a day or more and then sand with 1200 or something to smooth it out.

Questions:

1) Should I wet sand? The poly is water-based so I was thinking I should dry sand. What grit should I use?

2) Should I buff with PU? If so (and I know this is a noob question) how do I buff?

Thanks in advance!

Wait more than a day more.... wait like a week more, and get the piece warmed up too.  You want that poly hard and tough and cured before you sand it.  I'd try 600 paper wet to level it, resorting to 400 if that isn't working well.  Then back to 600 and 1000.  Normally I buff from 600 on nitro, but on poly you need a finer finish before buffing.

To buff... get your compound on a rag and have at it.  Autobody compound works well.  I use Turtlewax (really!) white compound liquid.

 

[Johnhamdun]

I don't finish with poly so I have no clue really, Google it.

I would've used Nitro but the Chemist at Lawrence McFadden was worried that the acrylic was so hard that the Nitro would delaminate.

Wait more than a day more.... wait like a week more, and get the piece warmed up too.  You want that poly hard and tough and cured before you sand it.   I'd try 600 paper wet to level it, resorting to 400 if that isn't working well.  Then back to 600 and 1000.  Normally I buff from 600 on nitro, but on poly you need a finer finish before buffing.

To buff... get your compound on a rag and have at it.  Autobody compound works well.  I use Turtlewax (really!) white compound liquid.

When you said "warmed up" what do you mean? Blow dryer hot?

How many coats would you do? I have already done 6 or so but they've been really thin.

 

[stubhead]

The jugs say it reaches full hardness in a week, but I had to wait more like two weeks for my last one to harden. I wouldn't use a hair dryer or anything radical, just keep it on a top shelf or outside in a garage or something - 85 degrees is better that 60, but in the summer there's not much problem (unless you're in Antarctica? ).  A really good way to tell if it's still hardening is to smell it - if there's still gasses coming out of the finish, it's NOT HARD... At 10 days mine still stank, at 12 days not so much and at 14 not at all, so there's a definite end to the process. I put on a whole bunch of thin, watered coats in a row, like 45 minutes apart so they all bind. If you've added a dye to the poly it may affect curing time but again, the nose knows.

 

[Wana_make_a_guitar]

The jugs say it reaches full hardness in a week, but I had to wait more like two weeks for my last one to harden. I wouldn't use a hair dryer or anything radical, just keep it on a top shelf or outside in a garage or something - 85 degrees is better that 60, but in the summer there's not much problem (unless you're in Antarctica? ).  A really good way to tell if it's still hardening is to smell it - if there's still gasses coming out of the finish, it's NOT HARD... At 10 days mine still stank, at 12 days not so much and at 14 not at all, so there's a definite end to the process. I put on a whole bunch of thin, watered coats in a row, like 45 minutes apart so they all bind. If you've added a dye to the poly it may affect curing time but again, the nose knows.

If you lived in Antarctica, wouldn't it dry quicker. Unless there's a blizzard or frost, then you're finish is ruined.

 

[Johnhamdun]

If you lived in Antarctica, wouldn't it dry quicker?

That's sort of what I was thinking. Colder Air = Dryer Air so shouldn't cold air dry it faster?

 

[GoDrex]

cold air can't absorb moisture as well as warm air

 

[Johnhamdun]

cold air can't absorb moisture as well as warm air

Oh, interesting..


What if I live in humid Georgia? the hot air is already full of moisture... right? sort of right?

 

[stubhead]

I live in a swamp (Maryland's Eastern Shore... ahem, wetlands...) but I really don't think the external humidity is a big factor unless your raw wood has actually absorbed a lot of moisture. I have a hygrometer and even when it goes above 90% humidity at night it dries up into the 50-60% range during the day. My experience is that the drying process is largely unaffected by anything other than the passage of time - certainly, it sneers at mere human impatience.
Just wait... :rock-on:

 

[woj74]

I finished my Tele with 2 component poly. After applying 3 coats i wet sanded it with 1200 and than buffed with Farecla G3 compound using a buffing sponge (orange color sponge - medium hard). I think i will use 1800 or sth like that in my future jobs as 1200 leaves quite deep scratches on the surface which are hard to buff.

 

[Patrick from Davis]

Although cold air is dryer than warm air, the solvents used to dissolve the urethane monomers are not water.  So the dryness of the air is not so much of a problem in that respect.  It is a polymerization reaction to make the "poly" part of the urethane so the temperature is important.  The solvents will gas off and the the monomers will get closer in proximity to each other.  The higher temperature will give the reaction enough energy to go to completion.  Once the reaction is over, the solvents have to be removed.  The solvent cause "swelling" of the polymers, once they float away it sets in place.  This is why the temperature and the nose are important tools in the process.
Patrick