Finishing the finish


houstonwoodworker

Recommended Posts

26 minutes ago, Isaac said:

That is about the same for all oil based urethane/polyurethane finishes isn't it? are there some that fully cure in less than 30 days, per manufacturer instructions?

Don't know what the manufacturers say, but in my experience, It takes about a month for any poly I've used.

Link to comment
Share on other sites

8 hours ago, AceHoleInOne said:

Between coats, a finish needs a sand scratch with sand paper for the next coat of finish to hang on to while it levels and smooths.   

 

Only a modest quibble: my understanding is that no sanding is required unless the previous coat has cured.  If you are re-coating after a year, then yes you need to sand for the reason you stated.  If you are simply applying a second or third coat before the previous coat cures, then no sanding is required.

Link to comment
Share on other sites

4 minutes ago, AceHoleInOne said:

You should always  scuff sand a finish you’re building up. If you pile on finish over a rough coat of finish, what you’re doing is making the high spots grow even higher. The mid coat sandings cut down the high spots leveling the finish alowing the low spots to catch up on re-coats. 

 

-Ace -

I may have misunderstood (and still might.)

"Scuff" sanding is usually (I think) done to provide something for the next coat to adhere to, which is important if the previous coat has already cured.  If the previous coat has NOT cured, then the next coat can "crosslink" to the previous coat.

Knocking off high spots would be a different issue.  I'm interested to know more about that.

Link to comment
Share on other sites

10 hours ago, Pondhockey said:

I may have misunderstood (and still might.)

"Scuff" sanding is usually (I think) done to provide something for the next coat to adhere to, which is important if the previous coat has already cured.  If the previous coat has NOT cured, then the next coat can "crosslink" to the previous coat.

Knocking off high spots would be a different issue.  I'm interested to know more about that.

All build finishes should be sanded between coats. Since this conversation is about Arm-R-Seal which is an oil based poly which sticks itself or glues itself down to the previous coat. I don't know what the definition of crosslink is (finish makers mumbo-jumbo) and is usually spoken in terms of water-based finishes due to water evaporation and all the goodies sticking together "crosslinking" to make a layer of finish. Solvent finishes use solvent to melt the goodies together flashing off to make a layer of finish.

Each coat of finish, sticks to itself in one way shape or form, sanding provides tooth for the next coat to hold onto while smoothing and eliminating high spots typically caused from grain pockets. Finish builds up and around grain pockets. Low spots are caused by the wood pulling the finish down into the fibers. Sanding makes the surface smooth for the next coat.

Finishes (read the can) has a re-coat time. The finish is dry to the touch and can be sanded (scuff) to ready it for the next coat.

Cured, means when all layers and the wood should be fully gassed off and perfectly dry and hard ready for full service. You should only rub a surface when it's cured! Think of fully cured being when a scab on your skin falls off.

 

CAUTION, DONT SAND YOUR FIRST FEW COATS OF OIL, YOU NEED A BUILD OR SOMETHING TO SAND OR YOU'LL HAVE SAND THROUGHS.

If I do have to scuff a 1 coat, I'll go real easy with a wipe of 600 paper. Mid coat sanding, I use a 320 sponge back paper.

 

-Ace- 

 

Link to comment
Share on other sites

Any tiny speck of dust can draw finish to it and create a bump with a circular depression around it. Cutting off the peak and removing any rim around the depression is the minimum needed between coats. Flattening the surface to remove any depression is better if there are enough coats to sand that much. Sanding through to bare wood is a nightmare. 

  • Like 1
Link to comment
Share on other sites

1 hour ago, wdwerker said:

Any tiny speck of dust can draw finish to it and create a bump with a circular depression around it. Cutting off the peak and removing any rim around the depression is the minimum needed between coats. Flattening the surface to remove any depression is better if there are enough coats to sand that much. Sanding through to bare wood is a nightmare. 

Werker, have you also tried scraping the peaks?  Do  you have an opinion on whether sanding is easier/more effective?

Link to comment
Share on other sites

On super flat surfaces like a meticulously prepared counter or tabletop with several coats of finish already in place a card scraper is definitely a superior tool to use between coats. But without careful use it is so easy to scrape down to bare wood. Very sharp scraper with a small hook wielded by an experienced hand is far faster than sanding.

  • Thanks 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Who's Online   3 Members, 0 Anonymous, 57 Guests (See full list)

  • Forum Statistics

    31.2k
    Total Topics
    421.8k
    Total Posts
  • Member Statistics

    23,757
    Total Members
    3,644
    Most Online
    R Parekh
    Newest Member
    R Parekh
    Joined