I have a friend who built an acoustic guitar with a cedar top and he applied a coat of Bulls-eye shellac sanding sealer to the cedar top and it is now blotchy.

The back and sides are figured sycamore and they look great.

Any thoughts?

HI Scott, I don't know much about finishing cedar but I'll help you research your question. I belong to a couple forums that have some pretty knowledgeable  finishers and I'll ask them. Stay tuned, might take a couple days.

 

Do you know what kind of cedar it is.

 

Rich

not sure I can be of much help on this. I sprayed shellac on two cedar chest last night. I guess the first thing would be to make sure it is sanded good and clean and smooth. Do you know if any oily finish may have gotten on it while it was sitting around in the shop?

 

I am guess you are talking about the dark places on the right side, near the bottom and the small spot on the left. At least those are the ones that stick out in the picture.

 

It almost looks like something was on the wood when the shellac was put on there. But that is just my guess at this point. I am sure Rich will get some good information from some of the top finishers.

 

 

Cedar is a very OILY wood and depending on what type you used it can be a little troublesome to finish.

 

First off is what type of cedar is it?

 

There are spanish cedars that are easy to finish to aromatic cedar that smells great but is very oily.

 

I'm betting that isn't cedar but it does look like spruce, which is used in a lot of musical instruments.

 

Is that a copy of a blond guild Madiera guitar?

 

As far as finishing goes, sand it back out with 220 and then go to a lumberyard/ wwod supply and get a few pieces of spruce to try out your finish on.

 

By the way, use a pair of latex gloves when sanding cause the wood when bare of finish will actually ABSORB oil from your fingers into the wood.

 

Did you wipe down the face with anything BEFORE you sand/sealed it?

 

You'll need to wipe it down with denatured alcohol to lower the level of contaminents (oil/dirt/ etc.) before you finish it.

 

And you really don't need a sanding sealer on it as the grain isn't that porous, just more layers of finish because the wood soaks up more than say, Maple.

 

And old sanding sealer is not good to use either.

 

Let me know when you have your test pieces in hand.

This is what I got so far.

…what your friend has applied is simply a pre-mixed 2-pound cut of more or less blonde shellac.  Zinsser’s corporate decision to call the stuff “sanding sealer†is no doubt the result of extensive consumer research on terms that sell.  Looking at the photo (always difficult to interpret) I suspect the “blotching†issue is directly related to surface preparation.  There is no pigment in shellac and virtually all of the naturally occurring dye has been removed by the time we reach the blonde grade.  Further, since shellac is optically clear the only thing that is likely to have produced the streaked look we see in the photo is uneven or inconsistent surface preparation.  Note that the “blotching†is quite linear in appearance suggesting that it has little to do with any random grain anomalies in the cedar.  The problem appears to be in the reflective qualities of the wood beneath the finish, not in the finish itself.  A less likely cause would be uneven application of the shellac.

 

How did your friend prepare the surface for finishing?  How was the finish applied?  As an additional curiosity, why the choice of the Zinsser SealCoat®?

 

Steve

Finishing & Refinishing Forum Host

Richard McComas said:

This is what I got so far.

…what your friend has applied is simply a pre-mixed 2-pound cut of more or less blonde shellac.  Zinsser’s corporate decision to call the stuff “sanding sealer†is no doubt the result of extensive consumer research on terms that sell.  Looking at the photo (always difficult to interpret) I suspect the “blotching†issue is directly related to surface preparation.  There is no pigment in shellac and virtually all of the naturally occurring dye has been removed by the time we reach the blonde grade.  Further, since shellac is optically clear the only thing that is likely to have produced the streaked look we see in the photo is uneven or inconsistent surface preparation.  Note that the “blotching†is quite linear in appearance suggesting that it has little to do with any random grain anomalies in the cedar.  The problem appears to be in the reflective qualities of the wood beneath the finish, not in the finish itself.  A less likely cause would be uneven application of the shellac.

 

How did your friend prepare the surface for finishing?  How was the finish applied?  As an additional curiosity, why the choice of the Zinsser SealCoat®?

 

Steve

Finishing & Refinishing Forum Host

I have had great success using Charles Neils Blotch control on woods that blotch like pine,maple,cherry.

Thanks for the video link Jim, I may give that product a try.

A-1 Jim said:

I have had great success using Charles Neils Blotch control on woods that blotch like pine,maple,cherry.

Hi Everyone,

Thanks for all the quick replies.

The top is red cedar and am leaning toward the advise/suggestion from Richard McComas that indicates a surface prep issue. Wiping down the cedar with some denatured alcohol is another good piece of advice...thanks dragon1 (Mike). I need to get back with my friend and determine if he may have used a tack cloth. Using this may have introduced some oil and created the darker areas. Let me get back with you all with some further info as to the prep. The worst case scenario is sanding the top only (fortunately it's a solid top) and try again with a focus on prep and being sure that no contaminates are introduces (tack cloth).

Thanks again for all the advice posts.

Scott D

Scott contaminates don't cause blotching ,it's wood that have a variation in their hardness the soft parts hold more stain or finish the the harder parts of the wood. if you have any type of contaminates naphtha works very well to remove them.

Scott Dixon said:

Hi Everyone,

Thanks for all the quick replies.

The top is red cedar and am leaning toward the advise/suggestion from Richard McComas that indicates a surface prep issue. Wiping down the cedar with some denatured alcohol is another good piece of advice...thanks dragon1 (Mike). I need to get back with my friend and determine if he may have used a tack cloth. Using this may have introduced some oil and created the darker areas. Let me get back with you all with some further info as to the prep. The worst case scenario is sanding the top only (fortunately it's a solid top) and try again with a focus on prep and being sure that no contaminates are introduces (tack cloth).

Thanks again for all the advice posts.

Scott D

Scott, I did a Google "Finishing Red Cedar" and got a few hits. Here's some reading for you.

 

http://www.google.com/search?q=finishing+red+cedar&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

To all,

Thanks again for everyone that provided some input.

I talked with my friend and learned that he had sanded all the way up to 600 grit. Yikes!

The recommendation I have for my students is to sand no higher than 150 or max 180.

Higher than that and you're polishing the wood which will prevent an even finish.

I should have asked that at the beginning and caught that sooner.

 

I went back to my friend and suggested he sand everything off the top, back to bare wood and final sand to 150.

The pic below shows the result....a success story.

 

Lesson learned.....surface prep is critical.

While sanding wood to super high grits seems like a good idea....it's not and witnessed here is a perfect example.

That silky feel will ultimately come from rubbing out the finish so no need to sand to super high grits.

 

I am happy to report the turnaround of this project and he's now well on his way to a complete success story.

I've asked that he send me a final pic when it's all done and I'll be happy to share that when that happens.

 

Thanks.

Scott D

Awesome Scott!!! Great job and hopefully our guys here sparked a thought in you that made this all work out. Can't wait to see the guys final product.

 

Glad to see it's working out. That top is looking much better.

Rich

 

Scott Dixon said:

To all,

Thanks again for everyone that provided some input.

I talked with my friend and learned that he had sanded all the way up to 600 grit. Yikes!

The recommendation I have for my students is to sand no higher than 150 or max 180.

Higher than that and you're polishing the wood which will prevent an even finish.

I should have asked that at the beginning and caught that sooner.

 

I went back to my friend and suggested he sand everything off the top, back to bare wood and final sand to 150.

The pic below shows the result....a success story.

 

Lesson learned.....surface prep is critical.

While sanding wood to super high grits seems like a good idea....it's not and witnessed here is a perfect example.

That silky feel will ultimately come from rubbing out the finish so no need to sand to super high grits.

 

I am happy to report the turnaround of this project and he's now well on his way to a complete success story.

I've asked that he send me a final pic when it's all done and I'll be happy to share that when that happens.

 

Thanks.

Scott D

Just curious, was the shellac sprayed or brushed. Sanding up to 600 is ok, just not necessary. Spraying shellac in very thin light coats is key here.150 to 180 is a good place to stop if you are applying a stain, because the pigment in the stain need something to hold on to. So sanding wood at 600 and wiping a stain, would be like staining a piece of glass, just wipes off. So sanding to 600 would help seal the woods pores for a clear finish only.

 

I'm just guessing, It appears the shellac was applied to wet and was pulled in. This guitars wood is thin, and is like trying to apply finish to a paper towel and pulls it straight in to saturation??????

 

Its tough finishing with different woods on a project. They don't respond alike. Glad you got it worked out...rock on!