Sanding after pore filling

[watergunn]

Hi all.

Had a quick question regarding sanding after doing a pore filling. I have always sanding to 220 before I stain and pore fill.
After pore filling the surface is super smooth, almost like glass. Do I need to sane this again with 220? It puts major scratches in the finish when I do. Also it is very easy to hit the stain as well. I am finishing a set of EIR now and have a couple of coats of nitro on over the sealer. When I do the tape test it will come off the back and sides. But the top remains intact when doing the tape test. It has only been 24 hours or so drying time. Maybe it needs more cure time. Just not sure about how aggressive to be with sanding after pore filling.
Thanks for any advice

RG

[B. Howard]

The finish must have an anchor. I assume from your post you are using an epoxy and leaving a thin wash over the entire surface. When I do an epoxy fill I sand out at 320 to prep for nitro. I also will omit the sealer over the epoxy as there is not really a need for it. When prep sanding the epoxy it is not necessary to do any more than make the surface "white".

[btberlin]

I won't address the sanding question, but, if the Nitro is pulling away from the sealer with tape, then the bond between the Nitro and sealer isn't good. I do question why you are doing this on the actual instrument though. Can't you experiment on cutoff pieces before shooting the finish? At any rate, though, if the nitro is pulling off, perhaps it does need more cure time. Never worked with it though, so am guessing.

I'm starting on a cocobolo back/sides, and sitka top J45. I bought a separate piece of coco to resaw, and try finishes on. It's usually a good idea to try stuff out on scrap.

bert

[watergunn]

Thanks for the replies.

I was masking off the bindings to spray a sunburst and the tape caught the side of the body.

That was when I noticed it had pulled off the finish.

Never had it happen before. But the top's lacquer will not pull off.

So, not really sure why the sides pulled but the top does'nt.

[B. Howard]

Did you use epoxy on the top? Most likely not as it did not need a grain filler so the nitro bonded to the wood. You will most likely have adhesion problems down the road on the back and sides.

[watergunn]

No filler on the top.

I am using pore o pac as the filler

I stripped the back and sides down again and stained them again.

My procedures usually are:

Sand to 220
Stain
Sealer
Pore fill
Seal again
Then lacquer.

I noticed in the pore filling that the surface was really smooth.

Should I have come back and sanded again after the pore fill?
Whenever I do that the sandpaper leaves major scrathes.

I am wondering if I should just stain, pore fill, sand, stain it all again and then do the sealer. Leaving out the first seal coat after the stain.

How does that sound?

[Darryl Young]

Maybe try this:

Sand to 220
Stain
Sealer
Pore fill
Seal again
Light sand with 320g-400g to create a mechanical bond for the lacquer.
Clean well to remove all dust before proceeding.
Then lacquer.

[btberlin]

Leaving out the sealer after the stain coat won't affect the bond between the sealer and the lacquer. If I were you, i would call the manufacturer of the lacquer's technical support line. Explain what you are doing, and get their recommendation. They will be able to tell you if their lacquer will bond to the sealer -- i.e., if that is the problem. Of course, if you have any kind of scrap wood, you can try the exact same steps you wish to use on the guitar, and then when the nitro is good and dry, THEN do the tape test. As per Fine Woodworking, make perpendicular scores in the finish with a razor knife. The scores should be about 1/4 inch apart, leaving 1/4 inch squares outlined by the scores. Then, use some packing tape - the clear kind that really sticks, and press a piece firmly over the scored area. Then rip. YOu can then judge by whether there are no, some, or all squares pulled off, how good the bond is between the sealer and the nitro.

bert

[watergunn]

Thanks for the replies. I talked to John Hall earlier today and I think the issue may be the stain I am using.

It is Cabot brand but I do not think it is mineral oil based and I think that it is just pulling off the wood itself.

I am going to verify and will report back.

The top itself is fine. The only difference being that the back and sides have stain in them.

RG

[B. Howard]

My basic lacquer schedule is;
Prep sand to 180
sealer
paste pore filler, perhaps 3-4 coats
sealer
prep sand at 320
apply first coat of lacquer.

Alternately you can do the paste filler right over the bare wood and it will act as a stain and filler, This is what I believe Gibson has traditionally done on Mahogany. Then shoot one coat of sealer and take it from there.