Jump to content
Maestronet Forums

Crack Filling and Leveling


Brad H
 Share

Recommended Posts

Arghh!     I have had varying levels of success with this but find too much frustration to be a common ingredient in my attempts.   I am using a fill varnish of copal with lesser amounts of shellac and sandarac in everclear.    The consistency is like thin syrup.  The brush I am using to fill the crack is probably lacking in bristles because I am continually having to reload with varnish and the resultant "bead" is kind of choppy.  Below is a pic of the brush I have been using.  

After applying the fill, I wait around 2 days before leveling.   It seems like, no matter what I use - scraper, curved knife - I get chatter.   Worse yet,  sometimes it seems that voids appear where I could swear there had been varnish atop.

Questions:

1.   I know that consistency/viscosity is hard to verbalize, but your attempt  at describing your fill varnish would be appreciated.

2.   What type of brush do you use?   A pic would be great.

3.  How long do you let the fill dry before leveling? 

4.   Any tips on leveling?

IMG_2594.JPG

Link to comment
Share on other sites

I use a similar brush and sometimes use a "point" (bamboo, etc.) for application.  

If the crack is tight, try applying a thinned coat first... maybe two.

The scraper needs to have the angle shifted on pretty mush each pass, and have little or no burr (I know some restorers who use safety razors), but if you're already "going there", try altering the formula a bit (add more shellac) or add some aluminum hydroxide.

I level it as soon as it's dry enough to do so.  This depends on the size of the bead.

Hope one or two of these things work.

 

Link to comment
Share on other sites

Your fill varnish can be thicker than your regular retouching varnish because it’s going to be leveled and is only applied in small amounts.

As for viscosity, I think mine ends up similar to that of Deft. I can generally get away with scraping after a few hours of drying. The drying time varies with humidity, though. 

A knife or scraper can do a good job, but they need to be quite sharp for the best results. I keep one scraper set aside just for varnish. I’ve also found that a light touch is crucial. I can sometimes level the varnish decently even if the scraper isn’t as sharp as it ought to be.

I have some varnish I made for retouching from shellac, mastic, and sandarach. For extra body I have some aluminum hydroxide. For a while I had a little bottle of Bullseye with the aluminum hydroxide ready to go for fill, but I stopped using the Bullseye after finding the retouch I made was easier to use and dried faster. 

Link to comment
Share on other sites

Thanks for the replies.   Regarding brush size, I was hoping someone would recommend a brush with more bristles - I find that continually having to reload and then to re-find the "sweet spot" of the brush tip position to apply a bead (and not a valley) is trying.   Varying the scraper angle is something I haven't tried but makes sense.

Do you typically fill the crack in one pass?   

What is your source for aluminum hydroxide?

What is the preferred type of shellac?

How do you sand the scraped fill?

Link to comment
Share on other sites

I use a larger brush on occasion...  if it's a long cack or varies i width.

One pass depends.  If it's a tight crack I thin a coat or two and finish with a slightly raised bead.  If it's a wider void, it's sometimes easier to get even with two passes.

I believe Kremer has aluminum hydroxide.

I use what is often referred to as de-waxed flakes (but there's still some wax in it), but I don't use the blond stuff.  Short shelf life.

I sand the fill as little as possible.  If required, I use 1500 grit, carefully.

Link to comment
Share on other sites

Jeffrey,,

Thanks for the tips.  I was just reading an old thread in which you suggested using only fresh, high quality alcohol in the filler recipe.    Uhoh...the 190 proof grain alcohol I am using is probably 10 years old.   I assume that the concern for older alcohol is the propensity to absorb water.    I wonder whether this is part of my problem.   

Link to comment
Share on other sites

20 hours ago, Jeffrey Holmes said:

^ what he said too.  

I have found, though, that an advantage of a fill varnish including copal and sandarac is that it tends to swell less when applying color/touchup over the surface of the leveled fill. Not something you can't compensate for, however.

Jeffrey,

I find the swelling while adding color to be a major difficulty. Does your filler flatten again when it dries? I have used everything from the shellac, copal, sandarac mix to pure copal and always struggle with what was a smooth surface raising back up as color is applied.

Also I often have trouble with filler "climbing" back out of the crack as it is applied leaving either a ridge on either side instead of staying in the crack or beading on top of the crack so that scraping  reveals voids underneath. 

Link to comment
Share on other sites

11 minutes ago, nathan slobodkin said:

Jeffrey,

I find the swelling while adding color to be a major difficulty. Does your filler flatten again when it dries? I have used everything from the shellac, copal, sandarac mix to pure copal and always struggle with what was a smooth surface raising back up as color is applied.

Also I often have trouble with filler "climbing" back out of the crack as it is applied leaving either a ridge on either side instead of staying in the crack or beading on top of the crack so that scraping  reveals voids underneath. 

My filler seems to swell less, and flatten well.

The "climb" seems to happen for me when the filler is applied slightly too thin or there isn't enough sandarac in the mix.

 

Link to comment
Share on other sites

3 minutes ago, Jeffrey Holmes said:

My filler seems to swell less, and flatten well.

The "climb" seems to happen for me when the filler is applied slightly too thin or there isn't enough sandarac in the mix.

 

When you say "flattens well" are you saying the swelling shrinks back to flat as it dries? Also do you open up or smooth the varnish at the edges of the crack to allow you to apply filler better?

Link to comment
Share on other sites

On 6/24/2018 at 10:16 AM, nathan slobodkin said:

...I often have trouble with filler "climbing" back out of the crack as it is applied leaving either a ridge on either side instead of staying in the crack...

This always happens to me.  Until now I assumed it was normal and unavoidable.

I also have all the other problems that have been mentioned here, and one that hasn't been mentioned and for which I may have just discovered a solution:  When scraping off excess filler, I find it difficult to tell exactly where the scraper will cut until after I have scraped a pass.  Then after I have scraped a pass I see that I missed the filler and scraped off a bit of the original varnish next to the filler.

Solution:  Yesterday I remembered that I have an eraser shield and I wondered if I could use it to mask the filled crack and prevent the scraper from touching the varnish outside the filler.  It worked.  I found that the widest slot in the shield will guide a scraper with the right curve to scrape the filler down exactly flush with the varnish without removing any varnish.

For those who don't know what they are, eraser shields are thin pieces of sheet metal with various shapes and sizes of holes cut in them.  They are used by artists and draftsmen to erase some pencil lines in drawings without erasing any you want to keep.  Eraser shields are available in art supply stores.

74791520_erasershield.jpg.8bcbfefd92d2a99f50851bab11cb64cb.jpg

Yes, I have tried covering all but a bit of the scraper edge with tape to restrict where it cuts, and that never worked for me as well as I had hoped.

Link to comment
Share on other sites

Yesterday I had more consistent success in laying down a bead.    Holding the brush tip motionless for 1 second after initial "contact" with the crack seemed to help the varnish grab onto the crack.   Then, it felt like I will pulling the varnish along the crack, like an engine pulling a train.

There seems to be a fine line between fill varnish that is too thick or too thin.   Too thick and it won't leave the brush easily enough.  Too thin and it wants to form a valley and not a bead.   One trick that someone showed me was to periodically refreshen the bristles in alcohol in order to keep thicker varnish flowing from brush to crack.

Link to comment
Share on other sites

11 hours ago, Brad Dorsey said:

This always happens to me.  Until now I assumed it was normal and unavoidable.

I also have all the other problems that have been mentioned here, and one that hasn't been mentioned and for which I may have just discovered a solution:  When scraping off excess filler, I find it difficult to tell exactly where the scraper will cut until after I have scraped a pass.  Then after I have scraped a pass I see that I missed the filler and scraped off a bit of the varnish surrounding the filler.

Solution:  Yesterday I remembered that I have an eraser shield and I wondered if I could use it to mask the filled crack and prevent the scraper from touching the varnish outside the filler.  It worked.  I found that the widest slot in the shield will guide a scraper with the right curve to scrape the filler down exactly flush with the varnish without removing any varnish.

For those who don't know what they are, eraser shields are thin pieces of sheet metal with various shapes and sizes of holes cut in them.  They are used by artists and draftsmen to erase some pencil lines in drawings without erasing any you want to keep.  Eraser shields are available in art supply stores.

74791520_erasershield.jpg.8bcbfefd92d2a99f50851bab11cb64cb.jpg

Yes, I have tried covering all but a bit of the scraper edge with tape to restrict where it cuts, and that never worked for me as well as I had hoped.

Some guitar repair techs use a safety razor with scotch tape applied to only reveal a small portion of the blade to avoid hitting the surrounding varnish.  This was pointed out to me by Joe Grubaugh.

Link to comment
Share on other sites

26 minutes ago, Jeffrey Holmes said:

Some guitar repair techs use a safety razor with scotch tape applied to only reveal a small portion of the blade to avoid hitting the surrounding varnish.  This was pointed out to me by Joe Grubaugh.

Joe is a freakin' smart and resourceful guy, isn't he.

Link to comment
Share on other sites

23 hours ago, Brad Dorsey said:

Yes, I have tried covering all but a bit of the scraper edge with tape to restrict where it cuts, and that never worked for me as well as I had hoped.

The scotch tape under the single edged razor blade was a Frank Ford idea for leveling high spots that I passed on to Craig a few years ago along with a lampblack making technique - he never complained about either - must of worked.

Single edge blade taped except where you want the blade to run across for leveling - so easy even I could do it..  

Link to comment
Share on other sites

On 6/23/2018 at 9:10 PM, The Violin Beautiful said:

Jeffrey,

I didn’t use copal in my last batch of touchup varnish because the shop was out of it, but I have some now for my next batch. What is the advantage of adding copal vs. sandarach? Is there any benefit to making retouch varnish with shellac, copal, mastic, and sandarach?

I find Manilla Copal and Sandarac, with Shellac, works well for me (for the reasons I mentioned), but modification with mastic should be fine if you want things a little softer.  I have mastic dissolved separately so I can add it to various things if I want, but rarely reach for it. I think too much will cause the fill to take on solvent a little faster when applying touchup over the top (and swell a bit), but I bet you can control that with ratios to make it workable.

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.
Note: Your post will require moderator approval before it will be visible.

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.

Loading...
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.


×
×
  • Create New...