sanding shellac question

Tim Sherwood

Tim
Corporate Member
How long should sandpaper last before it loads up ? I'm sanding the first thin sealer coat of shellac on baltic birch plywood. I'm only getting about four square feet before the disk "corns" to the point of useless. I'm using Klingspor's new green stearated discs, 220 grit. I've turned down the speed on my random orbital Bosh as far as it goes. I pre sanded the plywood sheet to 180 grit then sprayed Sealcoat, diluted 50%. Any suggestions on how to get better results? At this rate I could eat up 16 discs per sheet of plywood.
 

danmart77

Dan
Corporate Member
How long did you let the shellac set? Did you use the shellac from a can or did you mix your own?
 

Oka

Casey
Corporate Member
Hand Sand it. It is better because you can feel when you are heating up the material and can fell if the sand paper is beginning to get corns
 

Graywolf

Board of Directors, Vice President
Richard
Corporate Member
Yes, sanding by hand would be better, and use a light touch
 

Tim Sherwood

Tim
Corporate Member
Dan I used Zinzers Sealcoat from can. It's dried for a couple of weeks. I have tried hand sanding, with a rubber block in the past. I still get corning. I suspect the results would be better if I were using hardwood instead of ply.
 

Rwe2156

DrBob
Senior User
I suspect its due to heat building up. Everything else you're doing sounds right.

I never go near shellac with an orbital sander - always by hand. And it doesn't take much.

I use 3M gold paper never less than 320.
 

creasman

Jim
Corporate Member
I don't have a lot of experience with shellac, but all the advice I've read indicates sanding by hand and spritzing with water as a lubricant.
 

Phil S

Board of Directors, President
Phil Soper
Staff member
Corporate Member
Tim, I suspect the "corning" is due to something in the shellac coming to the surface during curing/drying - some epoxy does the same. Before you hand sand, try washing the shellac with a light spray of ammonia - quality window cleaner should work well. Spray it on, wipe off with a clean paper towel and let it dry before hand sanding. This should also improve power sanding if you decide to go that route
 

Tim Sherwood

Tim
Corporate Member
OK, hand sanding with 320 will be my method after the second coat. I chose 220 grit and machine sanding because the first, thin coat raised the plywood grain badly. Would you guys recommend another finish for plywood? Something that doesn't raise the grain or is better for sanding? Phil I hadn't heard about using ammonia. Thanks, I'll try it.
This application is drawer boxes. I like to get the first coat sprayed and sanded before I cut the joinery. I'll spray a second coat After assembly, then hand sand, lightly with 320.
 

FredP

Fred
Corporate Member
OK, hand sanding with 320 will be my method after the second coat. I chose 220 grit and machine sanding because the first, thin coat raised the plywood grain badly. Would you guys recommend another finish for plywood? Something that doesn't raise the grain or is better for sanding? Phil I hadn't heard about using ammonia. Thanks, I'll try it.
This application is drawer boxes. I like to get the first coat sprayed and sanded before I cut the joinery. I'll spray a second coat After assembly, then hand sand, lightly with 320.
Lacquer...... seals well sands well and can accept most any top coat.
 

Tim Sherwood

Tim
Corporate Member
Thanks Fred. I may try that when the weather lets me spray outdoors . I don't have much of a paint booth in my basement shop. Just an open window and a filtered box fan. I've stayed with water based finishes or shellac .
 

Jeremy Scuteri

Jeremy
Staff member
Corporate Member
That has always been my experience sanding shellac, the paper corns up in a hurry no matter how long I let it dry. Phil held a spray finishing class and we sprayed lacquer, I was amazed how it powdered up when being sanded less than an hour after spraying.
 

Tim Sherwood

Tim
Corporate Member
That sounds good to me Jeremy. Shellac dries as fast as lacquer . It must be the friction heat that makes it a pain to sand. I tried Phil's suggestion of ammonia based window cleaner. It did help! I think I got 50% more sanding per disk. Thankfully, I'm done with the plywood. Next step is to seal the cherry drawer fronts. And then sand them, by hand.
 

Hmerkle

Hank
Corporate Member
@Tim Sherwood I would give Klingspor a call and double check on the sandpaper - they (I think it was actually Klingspor Abrasive) did a number of videos on sandpaper choice and I was amazed at the plethora of choices based on the job.

I have used scotch brite pads successfully in the past, but I am simply scuffing the surface for the next coat, but don't seem to get the build-up that way...
 

Hmerkle

Hank
Corporate Member
Here sia response from @KlingsporUSA on IG:

klingsporusa

@hankmerkle Normally, silicon carbide grain would be the best for sanding between coats and finish, but when loading occurs, we recommend our GreenTec material (available in 60-2000 grit), because it has a proprietary composition and coating technology that allows the loaded materials to simply be blown off with an air hose or come clean of the disc when it is spun on a clean rag. This allows it to perform like new all over again. Does that help? You can always talk to someone in our technical or sales department in case you have further questions or need to talk n detail about your specific project :)

I replied - Thank you for the help!
 

MikeZ

New User
Mike
OK, hand sanding with 320 will be my method after the second coat. I chose 220 grit and machine sanding because the first, thin coat raised the plywood grain badly. Would you guys recommend another finish for plywood? Something that doesn't raise the grain or is better for sanding?
I have a question, what did you thin the Shellac with? Alcohol-based products are meant to not raise the grain in their application and you stating it raised the grain. This made me think that you used something other than denatured alcohol to make the 50% diluted mix. If so this could have been the cause of immediate corning. Shellac is basically a candy coating. I like to reference Skittles or M&M's as the candy shell is shellac-based. With any amount of friction, heat is caused and shellac loads an abrasive quicker. Using window cleaner, as Phil recommended, is a great way to lubricate the cutting action of the abrasive without adding any other factors to your finishing process. Silicon Carbide is the recommended abrasive grain between any coat of finish because of it's cutting action. SC cuts finish like a knife, making larger surface area scratches for the next coat to adhere to. Any other abrasive grain acts more like an ice cream scoop. While it works for most applications it rolls or "balls up" the finish causing corns to form much quicker on the abrasive surface.
 

Rwe2156

DrBob
Senior User
Shellac will definitely raise the grain.

Tim, a good choice for spraying are water based urethane or polyacrylic. Both will raise the grain, but they sand out easily and dry quickly. The polyacrylic will dry clear, some urethanes will tint a little.

Lacquer is a great finish, but its toxic. Respirator are ventilation precautions are needed.

Target Coatings has some water based conversion varnishes I've used that spray and finish extremely well. I really like them. EM8000cv is the product I believe.
 

Tim Sherwood

Tim
Corporate Member
Hank thanks for asking Klingspor about this issue. I have some feedback for their tech people. I AM using their greentech silicon carbide disks. Perhaps some other finish would clean off easily. Shellac does not. I was able to flake off most of the corns on the one disk I attempted to clean. I tried a vacuum with a brush; a fingernail; a crepe rubber cleaning stick; a brass brush; a very stiff steel brush; and finally a razor blade. Certainly not worth the effort. I less than two minutes the disk was clogged again.

Mike I always use alchol when thinning shellac. When I spray it on a hardwood the raised grain is minor . I can usually rub it smooth with a nylon pad. But even though I pre-wet and sand my plywood , shellac raises the grain again. I like to seal coat my furniture parts as early in the process as practical. It keeps the wood a lot cleaner during the build. Of course I mask off or skip any gluing surfaces. In this case the router will clean up rhe dovetails before gluing. Next project I'll try using thinned Poly as my sealer. I'll be using General Finishes water based High Performance poly for the top coats. I suspect this green coat disk will work ok with.
 

Hmerkle

Hank
Corporate Member
Hank thanks for asking Klingspor about this issue. I have some feedback for their tech people. I AM using their greentech silicon carbide disks. Perhaps some other finish would clean off easily. Shellac does not. I was able to flake off most of the corns on the one disk I attempted to clean. I tried a vacuum with a brush; a fingernail; a crepe rubber cleaning stick; a brass brush; a very stiff steel brush; and finally a razor blade. Certainly not worth the effort. I less than two minutes the disk was clogged again.

Mike I always use alchol when thinning shellac. When I spray it on a hardwood the raised grain is minor . I can usually rub it smooth with a nylon pad. But even though I pre-wet and sand my plywood , shellac raises the grain again. I like to seal coat my furniture parts as early in the process as practical. It keeps the wood a lot cleaner during the build. Of course I mask off or skip any gluing surfaces. In this case the router will clean up rhe dovetails before gluing. Next project I'll try using thinned Poly as my sealer. I'll be using General Finishes water based High Performance poly for the top coats. I suspect this green coat disk will work ok with.
I am now suspect of the shellac, that it is not drying or curing properly, but my suggestion is to get in touch with Colman @woodworkingshop.com and he or one of his guys should be able to help.

I am going to "jump-in" on the "poly as a sealer" idea, I have NEVER had success with that, it seems like it is "pasticy" and loads a disc faster than anything! YMMV but it would NOT be my "go-to"
 

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