Troubleshooting Sand-Through Problems with Dye Finish

      Here's a detailed discussion of sanding materials and techniques, with a view to avoiding the problem of sanding through light finishes while scuff-sanding between coats. October 19, 2014

Question
I have been having a hard time scuffing my first coat of finish without taking the stain off also. I spray my dye and stain, and it happens even if I just use the dye. I make it a point to not leave any sharp corners, they are all rounded. I've been using 400 grit sanding sponges to scuff with. I don't see why the stain would come off so easily with a coat of finish on it? I allow the stain to dry plenty - is 400 grit too aggressive? It wasn't as bad when I used to wipe stain, but did happen occasionally.

Forum Responses
(Finishing Forum)
From Contributor F:
Four hundred grit should be fine. We use 240-320 in our shop. I would say you just need to lay a heavier build on your seal coat. Do you thin your sealer out at all? Not sure what you are using but maybe you should find a finish with a higher solid content.

Are you burning through the stain and hitting bare wood or is it that the sanding dust is the same color as your stain/dye? If the latter, it’s not uncommon when we use spray stains or dye that the sanding dust is the same tint as the stain.



From contributor H:
Try purple Scotch-Bright instead of a sanding sponge.


From contributor B:
Sponges should only be used for finishing raw wood or by painters/drywallers. They're too stiff that's why you’re sanding through. You should be hand sanding with 400 and always stay away from edges. Use the Scotch-Brite for edges.


From Contributor F:
The way we usually scuff is with silicon carbide sand paper over a sanding sponge. Then we will actually use just the sponge for radiuses and sometimes very lightly hit the corners with the sponge.


From contributor T:
With spray-only stains and dyes, the color doesn't really penetrate like when you wipe it on; the color is just lying on the surface. We use the very soft sponges to scuff with (I think 400 grit would be too fine IMO). When we do get those white lines I keep a few broken blend-all sticks in the spray room and I just lightly pull one of those of the appropriate color across any exposed profiles. It usually just takes a very light pass on a corner or the sharp edge of a bead, etc.


From contributor A:
I've used fine abrasive coated sponges for most intercoat finish sanding for 30 plus years. I like the line from Webb Abrasives - not that I don't also use sandpaper in certain situations. It seems like the burn-through issue in this case has to be more about technique than other factors. I have to say I remember having the same problem - but after 15 years or so of touching up burn-trough’s I guess my hands finally were trained to avoid it.


From Contributor D:
We use 320 grit sanding sponges as well for scuffing clear over sprayed stain, and no issues as long as we're being careful. We actually have fairly sharp corners as that is the design of our product, however we don't scuff the corners. Don't know if it makes a difference, but we are 100% water based - stain, sealer and top coats.


From the original questioner:
I appreciate the responses. I agree about the dyes and stains that are sprayed lying on top of the wood vs. a wiping stain. It wasn't as big of an issue when I was wiping. I will look into the purple Scotch-Brite pads.


From the original questioner:
Are you guys talking about the purple Scotch-Brite pads that is a scour pad that is used in the kitchen? Made sort of like a bow tie? Just want to make sure I'm looking at the right thing.

From Contributor W

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I teach people about sealer sanding for a living. The paper or sponge you use for sealer sanding does have a major effect on your success, but the issue may be a lot deeper than that. Can you let us in on your process for prepping the wood for stain? What woods seem to be the issue? What sponges are you using? What actual type of sponges are you using? Are they sand paper stuck to a thin sponge? Even a spray stain should penetrate the wood and bite in. The sealer coat should bind it to the wood. My guess is that the age old issue of polishing might be rearing its head. Also, the sponge you use matters. Our double sided 1/2" sponge is the absolute most flexible sponge on the market. It will only sand where your finger pressure is. It is a great help in this situation. There is nothing better for profile work, especially once I show you some really neat basic techniques. Our 220 grit double sided sponge sands like a 500 grit and is very easy to control. Use our 1" blocks for the flats because it's stiffness doesn't allow it to wrap around the corners. Start with 220 or 150. The 150 is like a 320.


From Contributor D:
Scotch-Brite is a brand name, widely known for its use in the kitchen. The generic term is non-woven abrasive, sometimes called synthetic steel wool. You can use the stuff sold for kitchen use - it's widely and easily available. We use Mirka Mirlon that we buy in 4-1/2" x 33' rolls, also available in discs and pre-cut pads.


From contributor N:
Are you using a self-seal system? If you are you might try using a sanding sealer first instead, generally they sand way easier with less hand pressure than most self-seal systems. With the lower build of a sanding sealer you could even apply two medium coats before sanding which should insure very limited burn through and still keep you in the ballpark if you have film thickness limits with your finish system. It's more work of course (and more waste if you're using a post cat system) but maybe less in the long run if you're touching-up lots of dye/stain and that inevitable touch-up miss which can result in a very long detour. Also if it's been cold in your shop maybe give your stuff some more time before sanding. An extra 30 minutes can make a world of difference, esp. for CV.


From contributor E:
It takes a lot of practice to do it successfully but I use a flat sponge block wrapped in 320 grit paper and old school 4-0 steel wool on the edges. I've just always liked steel wool better than Scotch-Brite pads. A couple of things that make life easier: Pay attention to the way corners are broken, if you leave an edge or a ridge on the break as opposed to a smooth rounded break, it will be easy to sand through the ridge line. When flat sanding with the sponge block, use a lot of care when you get close to the edges, keep slightly more pressure on the side of the sponge that's away from the edge. Keep checking your work by blowing off the sanding dust and inspecting the edges rather than waiting until you have done the whole piece.


From the original questioner:
We have the Surfprep pad sanders and like it. We have not used it to scuff, just been using it to sand the profile on our raised panels before assembly. I plan to get with my distributer and get some of those maroon pads.

From Contributor W

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Use a 5mm very fine or super fine pad. Make sure the sander is flat on the part before turning it on. It won't wrap the edges at all and do a great job on all the flats.



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