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First time using EM600 and have had some sand throughs.
I've already brushed on and leveled two of them but had a question about scuffing
Do I need to scuff coarser than 1200 before touchup with brush (I did not scuff beyond 1200)?
Is 5 thickish brush coats enough to avoid another sand through (1200 then 1500 then buffer) or buffer burn?

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Measure Twice,

Karl Borum

EM6000 burns into itself. You don’t need to scuff sand between coats. If it has been a while since the last coat, or if it’s a repair, I sometimes wipe the area with an alcohol damped rag to soften the EM6000 surface so it will burn in faster. If I go all the way to the wood, I usually rub in some shellac (which I used for the seal coat on the wood initially) so the color of the burn through will match. When I redo a burn through area with a brush, it takes me 4 to 6 thin coats to get it back to where it will disappear with leveling and polishing. When I brush EM6000, I like to do very thin coats, sometimes diluting it, so each coat isn’t any thicker than if I had sprayed it. It makes leveling a lot easier. I seldom use any machinery to polish and when I do, it’s a small automotive rotary polisher. Polishing by hand minimizes the burn through. Since folks on this forum turned me on to Assilex, I have used that to level (with a hard backer) and then worked up through the grades. A couple of grades of polish after that gives me a reasonable finish although not the glass-like shine that I’ve seen others get with the buffer.

When I had sand throughs with EM6000 I didn't do any scuffing or sanding of the finish before applying repair coats. I've found four or five brushed-on coats can be enough to avoid sand through. This probably depends on the sanding medium you use and the grits used though. I let the finish cure at least a couple days before leveling it. Never tried shorter times but it might work fine. The tricky bit for me was to sand the repair coats so that they ended up level with the surrounding finish so that the repair was invisible in reflected light. Something that helped with that was to overlap the repair coats onto the surrounding finish by slightly larger amounts with each coat. So, first one or two coats covered just the sand through, the third coat extended out a bit onto the existing finish, the fourth coat a bit further, and so on up to maybe 1/8" total overlap. This was helpful for getting an invisible repair particularly on flat surfaces, such as on the headstock face, where slight imperfections in the leveling will show in reflected light.

I'm another fan of Assilex on a hard block for this. If you are worried about the buffer burning through, you might want to let the repair finish cure longer to make it more resistant.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Will continue with the brush on.

After so many positive comments on the semi-recent threads on Super Assilex, I'm dry sanding this one with the Assilex, on a hard block. Even the 1200 cuts really fast compared to the equivalent 3M Wet or Dry- used wet. I'm loving dry sanding! On this guitar, based on a lot of comments in OLF, new and old, I'm going to 1500 on a hard block then move to buffer.

THe EM-6000 seems to have more surface tension and pulls back more than NC lacquer on the corners (well relieved, I might add) and the odd pore . I've had to do a lot more drop fills on grain lines and pores with the EM6000 (pore filled 2X with Silvertip). All the sand throughs were in places where a pore/ grain-line didn't fill and I attempted to flat sand those out without doing a drop fill. Thats a lesson learned for sure. I could usually flat sand a shiny grain line or pore with NCL.

_________________
Measure Twice,

Karl Borum

Using the cross-linker with the EM6000 reduces the surface tension and makes it less afraid of edges. It doesn’t totally help the pore-fill problem, but it improves the behavior of the wet finish around them. If you use the cross-linker, find the video on the Target Coatings website on how to mix it.

I imagine sometimes that the edgephobic quality of the EM-6000 makes unfilled pores worse. The finish pulls back from the edge of the pore leaving an edge. After a few coats, the pore is deeper than when you started finishing. It requires perfect pore filling. Someday I might achieve that.

Edgeaphobic is right! I had some very tiny pinpoint voids around the headstock inlay that I couldn't even see. They turned into tiny, deep wells, like you said.

I tried something I'd not done before under clear finish and mixed some West Systems colloidal silica with the lacquer, 50/50-ish by volume. Applied it into the holes with the pointed end of a StewMac plastic drop-fill toothpick, with a swirling action, like mixing cake batter. Used it on most of the other deep pockets too, about 3 dozen in total. Two fill sessions and done, about 3 dozen "wells". And very minimal center crater. In addition to making the lacquer into a pore filler of sorts, I think the silica helped break the surface tension.

Good to know about the cross linker. I have watched the video - I found Jeff's "now pay attention" comment hilarious, but I don't think he intended it to be......

_________________
Measure Twice,

Karl Borum