white residue after wet sanding

[timbertom]

Hi everyone</SPAN> </SPAN>

I have a quick question in regards white residue showing up on a tabletop that ive just finished by wet sanding Scandinavian oil (using a method outlined on other posts on this site</SPAN>)</SPAN></SPAN>

The finish is fantastic - bringing up the grain of the brush box as well as giving it a nice sheen. The issue is that the white residue seems to be showing up in places where I have spent more time with my small belt sander particularly along the joins where ive to tried sand out/level out the timbers. Any ideas of what could be happening? </SPAN></SPAN>

This has happened to me once before and I ended up putting a wipe on poly over the top which seemed to ‘wipe’ away the residue.. but I was hoping for some more ideas around what it actually is? What have I been doing that precipitated this? (im assuming its using the belt sander to heavily and burnishing the timber?) how else should I level out joins..?</SPAN></SPAN>

Cheers tom.</SPAN></SPAN>

[Skew ChiDAMN!!]

What timber? Brush Box?

Did you give it a wipe down with a tack cloth or damp rag to remove any dust traces before finishing?

I've also had similar problems with 'oily' woods, where powered sanders left the surface coated in a fine, wax-like substance that the hand-sanded areas didn't. I don't see it until I start to apply a finish... and then, like you... I've always assumed it's excess heat from the sander heating & spreading the timber's natural oils. (But that's neither here nor there. )

In this case, wiping down with acetone to dissolve surface oils immediately before applying the finish usually works.

But I think you said Brush Box? That's not usually oily, is it? (I can't say that I'm familiar with the stuff. )

[timbertom]

<O</OHey, thanks for the response.

Yes the timber is brush box and doesnt seem too oily. Its recycled timber so should be quite dry in comparison to new timber.

I did give it a wipe down using metho although it was a quick wipe as opposed to a thorough focused wipe down.

I also thought it may be glue residue pushed into the grain..? could that be it? And how is it that a coat of poly can make it disappear??

Do you, or anyone else, have any suggestions as to how i can fix the issue?? I applied the Scandinavian oil last night orbital sanding from 400 to 2000 grit

Cheers
tom<o></o>

[Skew ChiDAMN!!]

That "residue" is under the finish, in the wood surface? That certainly could be the glue. What type did you use? I imagine either a PVA or epoxy?

It may be that you'll need to go back to sanding to remove it...

(I mis-read your post & was thinking the residue was appearing on the surface of your first coat. )

[timbertom]

I use titebond... its like a PVA.

im not toally convinced its the glue as the issue appears in other small areas where there really shouldnt be any glue but that have definately had some more intense belt sander action!

Another interesting thing i should mention is if i was to rub the area with my finger, it seem to worsen the situation.

puzzling.. i know!

[Skew ChiDAMN!!]

Yes... Titebond is a PVA. Good stuff.

Some sort of contaminant might've ended up 'stuck' on one of the sanding belts and was spread around. D'you still have the belts to look at or were they binned as used?

Me, I'd rub it back to fresh surface and start again. (While grumbling to myself every step of the way. )

But, yeah, it would be nice to know 'why is it so?' Sorta helps a lot when avoiding the problem next time, eh?

[timbertom]

Yeah i do have the belt laying around and ahve used it multiple time on a number of projects... 80 grit i think..</SPAN>

I might just rub it down with one light coat of wipe on poly.. hopefully that makes it disappear! </SPAN>

Dop you think i should wipe it on or buff it on with steel wool? Keeping in mind the surface has been finished by burnishing Scandinavian oil...</SPAN>

[Skew ChiDAMN!!]

Me, I won't use anything other than waxes over an oil finish.

You have more oil left? It'd probably be a good idea to apply some to a scrap piece and then see how the poly goes on that. (And no, I wouldn't use steel wool. Some people do, but I find any bits of steel that may break off leave rust-marks in the finish over time. I suspect that's a holdover to a time before modern synthetic abrasives became available. )


80 grit? On the belt-sander? And then you sanded everything down to... what? ...400ish? with a ROS or by hand?

Huh. Maybe it wasn't something on the belty, as working down thru the grits should've gotten rid of anything left at that high a grit. 'Tis a puzzler.

[timbertom]

I’ve applied poly over oil before and its come up pretty good.. </SPAN>

To me it just seems like wherever ive dug into the timber with the belt sander that’s where the residue is… </SPAN>

Hopefully there might be some others than could provide some insights..?</SPAN>

[Hermit]

I’ve applied poly over oil before and its come up pretty good.. </SPAN>

To me it just seems like wherever ive dug into the timber with the belt sander that’s where the residue is… </SPAN>

Hopefully there might be some others than could provide some insights..?</SPAN>

Tom, any chance of a photo?

[timbertom]

ill put one up tonight.. give me a few hours..

[ubeaut]

Did you use a cheap aluminium oxide (white) abrasive?

Was the timber dry or part dry?

Was a final sanding done after the oil had dried?

First thing to do is try wiping the oil over the surface then wiping it off again. If the white disappears then the residue is most likely from the slurry of the timber and oil (that you get when wet sanding) being laid down into the pores of the wood and a wipe on wipe off coat of the oil should fix it.

If not then applying a coat of wipe on polly may actually add to the problem by locking it into the surface and making it much harder to remove later.

There may be a number of other reasons why the white is there, eg: moisture, salt residue, chemical reaction.

Hope this is of some help.

Cheers - Neil

PS I'm presuming you did use a finer abrasive than the 80 grit on the belt sander. If not then this could be a major part of the problem.

[timbertom]

Hey neil –</SPAN>

Ok, this is what I did. After gluing up the brushbox (using sash clamps) I got out the belt sander and sanded the whole table top – 80g. I paid particular attention to the ridges in order to get them as flush and smooth as possible. After this, i used an ROS starting at 100g and dry sanded up until 400g…. and yes the pads I used festool sanding discs and they were white. From 400g onwards – towards 2000g – I wet sanded the rest of the table. These discs where black. </SPAN>

Like I said earlier, the white residue only comes up in the parts that I concentrated the belt sander use… under very close inspection, its seems to sit in the grooves that the belt sander has created. </SPAN>

I applied a light coat of wipe on poly last night and it sort of improved it.. not completely. But it is better.. I should also mjention that its not absolutely obvious with it being only noticeable from certain angles in the ‘right’ or wrong light. </SPAN>

Sorry about the no pics last night.. ill try get some up tonight.. thanks for the responses!! Really appreciate it!</SPAN>

On a side note: how do you all go about smoothing out a table top?? Particularly the ridges between joins?? (don’t say a 60inch thicknesser!) J</SPAN></SPAN></SPAN>

Cheers,</SPAN>
Tom.</SPAN>

[LGS]

Hi TimberTom,

Sorry to be so late answering. I agree with Neil in that it is probably left over abrasive from the belt sander. If you still have marks from the belt sander that you can see, then you haven't succeeded in sanding the table smooth with the ROS.
It is important to rid the work piece of sanding marks from the previous grit before progressing on with the burnishing.
Personally, I'd have used the ROS with an 80 grit pad rather than the belt sander. I do this procedure almost daily and do not have problems with white marks or sanding swirlies. I've even done Brush Box with no problem. It's a shame you had to put WOP on the table, but if it fixes your problem then goodo. One more thing, did you wipe the table top down with turps or a tack cloth before assing the oil? This is essential for any oil finish.
Again. personally I'd go back and redo it. I know the system works.

Regards,

Rob

[Hermit]

under very close inspection, its seems to sit in the grooves that the belt sander has created.

If you still have grooves left by the belt sander, then you're not sanding well enough as you work progressively through the grits afterwards.
It sounds like you need to work a bit longer with the 100G and 240G with the ROS or by hand until the belt sander marks are completely gone before progressing to 400G etc.
I hand-sand that type of thing, with a block.

Edit: Sorry, Rob, I was typing while you were posting. Same conclusion though.