Need help sanding mahogany endgrain

[Novatuc]

HELLLPPP: I am having a world of trouble sanding the edge of mahogany bodies for clear finishes. I am always getting what I can best describe as sanding residue on the end grain of the bodies. The "residue" leads to discoloration when the finish is applied. (All water based finishes) I have tried sanding the edges parallel to the body across the endgrain and I have tried sanding in the direction of the endgrain. I have tried sanding to 220 and spraying the sealer and I have tried sanding to 600 and spraying the sealer. I even tried Scotch-Brite. There seems to be no rhyme or reason to the residue. Almost all bodies show it to some degree. Sometimes it is obvious while sanding, sometimes it doesn't show up until after spraying. HELLLPPP please. Anybody?

[Shepherd]

Did that body have a finish on it previously? Looks like it's not absorbing the finish evenly.

[MojoMonster]

Did you use a grain filler first?

[Tom Pettingill]

A cabinet scraper can be very handy when dealing with end grain.

[piece of ash]

Try some compressed air...

[Novatuc]

Thanks for the replies fellas.

Sheppard: yes, that body was previously finished and scraped / sanded back to what I thought was bare wood. I took a picture of that body in particular because I knew the discoloration would show up. The residue I get looks similiar just not that bad.

Mojo: I am trying to grain fill with multiple coats of water based sanding sealer. Water based products for grain filling are a whole other nightmare and I won't get into that here.

Tom: I have tried using the mini cabinet scrapers in various directions around the endgrain and have had some positive results but I am definitely not a scraper master. For my limited ability, I was getting rid of a lot of the residue but the scrapers were leaving patterns in the endgrain that reflected light differently and caused color mismatches for lack of better words. As above, water based products may be causing some of the problems.

Ash: I have used compressed air to blow of the surfaces but have not tried cranking up the pressure to see what would happen to the sanding residue. I have a 200PSI compressor, I'll give it a try.

[PinewoodRo]

Is it possible that the water-based filler is not compatible with the previous finish?

[Novatuc]

Hello Pinewood: All the finish products I use are water based and almost all from the same company so hopefully they are compatible with each other. Most time I can see the sanding residue, before a finish goes on. When I sand the visible residue spot it usually just moves over a bit.

Sometimes I almost think it is a light reflection problem, because as you roll the body around, the discoloration can change from really visible to nearly invisible. Then the finish goes on and it becomes really visible again.

[lx79]

Exactly...Can't figure this one out either. I know exactly what you are talking about, it's driving me crazy.

[flatfive]

Originally Posted by piece of ash

Try some compressed air...

You could also try a stiff brush, or a shop vac, or both
in combination.

[motor_city_tele]

I remember reading about a similar problem a while back and it was traced to sharing the shop with a can of silicone. Somehow, the sandpaper, rags and tools got contaminated.

[flyingbanana]

What about using some Zinsser Seal Coat around the body over the end grain. Sand to 320 lightly, and apply a very thin coat of the Zinsser with a foam applicator. Let dry for a few hours and lightly sand. You should be good at that point. If not, apply one more light coat. (if you can get that stuff in Canada.) It's not water based, but made to be an effective barrier for various situations and does that well. Also, it shouldn't change the color too much. Try it on a piece of scrap first if you can.

Wood loves to absorb Zinsser Seal Coat and that should end your issue. It's also wax free, so don't think you'll have any compatibility issues with your other products.

[Axis29]

Have you tried wiping it down with a rag generously soaked in mineral spirits or some other solvent?

Might help show up some of the old finish left in the pores?

[Vizcaster]

It looks more like uneven absorption rather than residue. Maybe a spit-coat of thinned sealer, sanded back, before you proceed with sealing/grain filling/building?

[old_picker]

i seen this when i was using em6000 and the wb sand / sealer from stewmac
you need to take off some wood as that sealer does penetrate and is hard to get rid of
when i was using that stuff you could not have a sandthrough as it would show up until it was sanded right out
you gotta man up and hit that sucker hard with 120 all over
use a block [square] with the body supported above the [very flat] deck by around a mdf of thickness - scrub unit you have taken off a little and check the surface with some metho to see if the ghost is still showing - might be good to rub it down with acetone as well as thinners - btw if you have a good bench press and sanding drum it is easy to sand off -

if you cant get it right look at solid colours

[Vizcaster]

So, old picker, you're guess is that this is a shadow of some of the original finish that's not allowing the new finish to soak in evenly?

Novatuk, have you posted this over at targetcoatings to see if Jeff Weiss has some insight? He can usually sniff out these issues.

[flyingbanana]

From my own research, this seems to be sanding residue pushed into the porous end grain during sanding. The question is....how to pull out what's in there already and prevent it from happening again.

Some people have used a bronze bristle brush along with mineral spirits to remove the particles. After doing that, and when it's finally looking better, use the Seal Coat I mentioned. It will lock the pores and keep this from happening again. Hopefully.

[lx79]

We both have a maple top and mohogany body and I was seeing these unatural color variations that would disapear at different angles, exactly as you described it. After hours of scrubbing with acetone to see if I could remove what I thought was a residue/or sealer I discovered that sanding in one direction with the grain got rid of those dark spots. So once I picked a direction I pulled the sandpaper consitently in the same direction like petting a cat. It got rid of all those minor variations that I could see only at certain angles. So don't go back and forth, find the direction that clears the spot and keep the paper moving in that direction. Also, I highly recomend Eagle abbrasives Super Assilex sandpaper. It is an amazing sandpaper, state of the art. I hope this helps. Keep me updated.