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Should I use mineral spirits after sanding between polyurethane coats



 
 
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  #1  
Old January 17th 07, 07:42 PM posted to rec.woodworking
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Posts: 5
Default Should I use mineral spirits after sanding between polyurethane coats

The first application of polyurethane finally dried on my red oak
baseboard. I sanded the baseboard and used a tacky cloth to remove the
dust. Should I wipe down the baseboard with a rag dipped in mineral
spirits before I apply the next coat of polyurethane?

Thanks.
Sandy

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  #2  
Old January 17th 07, 08:03 PM posted to rec.woodworking
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Posts: 48
Default Should I use mineral spirits after sanding between polyurethane coats


wrote in message
ps.com...
The first application of polyurethane finally dried on my red oak
baseboard. I sanded the baseboard and used a tacky cloth to remove the
dust. Should I wipe down the baseboard with a rag dipped in mineral
spirits before I apply the next coat of polyurethane?

Why would you want to do that?
I certainly never have.


  #3  
Old January 17th 07, 08:16 PM posted to rec.woodworking
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Posts: 274
Default Should I use mineral spirits after sanding between polyurethane coats


" writes:
The first application of polyurethane finally dried on my red oak
baseboard. I sanded the baseboard and used a tacky cloth to remove the
dust. Should I wipe down the baseboard with a rag dipped in mineral
spirits before I apply the next coat of polyurethane?


No. Poly uses a mechanical bond between coats, you want as little as
possible between coats so as to get the best bond. Just make sure you
get the dust off, that's all.

And I hope by "finally dried" you mean "I waited as long as the can
said to wait". If you don't recoat in the time specified, you need to
wait at least a week or two (to fully cure) and sand before recoating.
If you recoat in the time specified, you only need a light sanding (to
remove raised grain and such) as the poly hasn't fully cured so it
will bond with the next layer whether you sand or not.
  #4  
Old January 18th 07, 08:51 AM posted to rec.woodworking
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Posts: 449
Default Should I use mineral spirits after sanding between polyurethane coats

The first application of polyurethane finally dried on my red oak
baseboard. I sanded the baseboard and used a tacky cloth to remove the
dust. Should I wipe down the baseboard with a rag dipped in mineral
spirits before I apply the next coat of polyurethane?


No. Poly uses a mechanical bond between coats, you want as little as
possible between coats so as to get the best bond. Just make sure you
get the dust off, that's all.


Once cured there is nothing wrong with wiping down with mineral spirits. I
have done this with as little as 8 hours curing time.


And I hope by "finally dried" you mean "I waited as long as the can
said to wait". If you don't recoat in the time specified, you need to
wait at least a week or two (to fully cure) and sand before recoating.


B.S. You can sand after 24hrs. I usually use 320 grit wet/dry paper and
lightly sand.


If you recoat in the time specified, you only need a light sanding (to
remove raised grain and such) as the poly hasn't fully cured so it
will bond with the next layer whether you sand or not.


So are you saying that you can only sand during the time specified on can (3
hrs usually) and after one week? This makes no sense.


  #5  
Old January 18th 07, 08:56 AM posted to rec.woodworking
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Posts: 449
Default Should I use mineral spirits after sanding between polyurethane coats

The first application of polyurethane finally dried on my red oak
baseboard. I sanded the baseboard and used a tacky cloth to remove the
dust. Should I wipe down the baseboard with a rag dipped in mineral
spirits before I apply the next coat of polyurethane?


Sure. There is nothing wrong with doing this. As long as you wait long
enough for the poly to cure sufficiently (varies by temperature/humidity).

If you were able to sand successfully, than your poly was cured
sufficiently. There is no danger in wiping sufficiently cured poly with
mineral spirits. I have done this NUMEROUS times.

After all, most people use mineral spirits as a solvent to dilute
polyurethane. How could this same solvent be counter indicated for wiping
cured poly?

Go right ahead!

Stoutman,
www.garagewoodworks.com



Thanks.
Sandy



  #6  
Old January 18th 07, 09:06 AM posted to rec.woodworking
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Posts: 449
Default Should I use mineral spirits after sanding between polyurethane coats

The first application of polyurethane finally dried on my red oak
baseboard. I sanded the baseboard and used a tacky cloth to remove the
dust. Should I wipe down the baseboard with a rag dipped in mineral
spirits before I apply the next coat of polyurethane?

Why would you want to do that?


The mineral spirits will remove any residue left behind by the tack cloth.
Nothing wrong with doing this if the poly has cured sufficiently.

I certainly never have.


Therefore it's not rational?





  #7  
Old January 18th 07, 04:27 PM posted to rec.woodworking
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Posts: 232
Default Should I use mineral spirits after sanding between polyurethane coats


After all, most people use mineral spirits as a solvent to dilute
polyurethane. How could this same solvent be counter indicated for wiping
cured poly?

Go right ahead!

Stoutman,
www.garagewoodworks.com


Then wipe it down with alcohol to get rid of the solvent reside.

Pete
  #8  
Old January 18th 07, 05:19 PM posted to rec.woodworking
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Posts: 274
Default Should I use mineral spirits after sanding between polyurethane coats


"Stoutman" .@. writes:
Once cured there is nothing wrong with wiping down with mineral
spirits. I have done this with as little as 8 hours curing time.


Cure time depends on the poly. The stuff I use isn't cured until at
least a week passes. After 8 hours it's only dry, but not cured.

And I hope by "finally dried" you mean "I waited as long as the can
said to wait". If you don't recoat in the time specified, you need to
wait at least a week or two (to fully cure) and sand before recoating.


B.S. You can sand after 24hrs. I usually use 320 grit wet/dry
paper and lightly sand.


Well, nobody is going to stop you if you want to sand whenever you
feel like it. I'm assuming the OP wants as good a finish as is
practical.

I've noticed that before the recoat time, I can sand lightly, and only
to remove raised grain. The poly is still soft enough that if I try
to sand into it, it just rolls up into lumps (like a pencil eraser).
Only after it's fully cured is it hard enough to actually sand into
the poly.

When fully cured, sanding poly should result in a fine, light, dusty
powder. Like what you usually see with sanding sealer.

So are you saying that you can only sand during the time specified
on can (3 hrs usually) and after one week? This makes no sense.


I'm saying that if you recoat outside of the recommended times, the
coat won't hold as well. Why? Because of how the poly layers join.
During the cure time, the poly molecules go from loose to tight, so if
you recoat during that time you can still hook into the uncured
molecules for a mechanical join at the molecular level. Once they're
cured too much, this is no longer an option for a reliable join, so
you wait until it's cured enough (i.e. hard) to sand it to make a
mechanical joint at the macro level.
  #9  
Old January 18th 07, 05:46 PM posted to rec.woodworking
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Posts: 449
Default Should I use mineral spirits after sanding between polyurethane coats

Cure time depends on the poly. The stuff I use isn't cured until at
least a week passes. After 8 hours it's only dry, but not cured.


The curing process starts after it is applied. There are degrees of
'cured'.

B.S. You can sand after 24hrs. I usually use 320 grit wet/dry
paper and lightly sand.


Well, nobody is going to stop you if you want to sand whenever you
feel like it. I'm assuming the OP wants as good a finish as is
practical.


24 hrs is plenty of time to lightly sand with 320 wet dry.

I've noticed that before the recoat time, I can sand lightly, and only
to remove raised grain.


What do you think I am talking about here? Re-read what I wrote above.

The poly is still soft enough that if I try
to sand into it, it just rolls up into lumps (like a pencil eraser).


When it behaves like this during sanding your poly has not 'sufficiently'
cured. Granted curing time is governed by humidity and temperature.

Only after it's fully cured is it hard enough to actually sand into
the poly.


Wrong. It does NOT need to be "fully cured", only sufficiently cured.

When fully cured, sanding poly should result in a fine, light, dusty
powder. Like what you usually see with sanding sealer.


I get the same results when 'sufficiently' cured. Doesn't have to be "fully
cured".


So are you saying that you can only sand during the time specified
on can (3 hrs usually) and after one week? This makes no sense.


I'm saying that if you recoat outside of the recommended times, the
coat won't hold as well. Why? Because of how the poly layers join.
During the cure time, the poly molecules go from loose to tight, so if
you recoat during that time you can still hook into the uncured
molecules for a mechanical join at the molecular level. Once they're
cured too much, this is no longer an option for a reliable join, so
you wait until it's cured enough (i.e. hard) to sand it to make a
mechanical joint at the macro level.


Sanding is usually required after 24 hrs.


 




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