Dirty smears from fine grit sandpaper

[GrahamRounce]

Hi - As the subject line says, sanding a light wood with fine eg 1000 grit paper, after 600, in preparation for painting with gloss (and yes it does seem to make a difference, for a super shine leaves smears on the wood the colour of the paper. Should I use light paper (aluminium oxide) for light wood, and dark paper (?) for dark wood??
Seems a hassle, and u know the smears are still there, you just can't see them very well!
Thank-you,
Graham

 

[Phil Pascoe]

Gloss paint? 1000 grit wouldn't improve the finish any with (primer and) undercoat on top. If anything it would encourage the paint to lift.

 

[paulrockliffe]

Same question from me, hade the same issue with 160 grit paper when sanding some ash over the weekend?

Along similar lines, how do I remove pencil marks without smudging the graphite into the grain? Use something instead of the pencil?

 

[GrahamRounce]

Hi - it was only for 3rd & fourth coats with very thinned paimt anyway, but forget the painting!

The same happens when sanding bare wood (for any reason!). "Should I use light paper (aluminium oxide) for light wood, and dark paper (?) for dark wood?? Seems a hassle, and u know the smears are still there, you just can't see them very well!"
Thank-you,
Graham

 

[Shrubby]

If you`re using silicon carbide (wet&dry) paper the grit is friable and can break down leaving dark remnants in the grain
Matt

 

[rafezetter]

It's always a good idea to wipe off any work you have sanded before adding any film type finish (paint / varnish / shellac etc), with a tack cloth at the very least, but to make sure that there is no residue of wood or sandpaper dust I wipe the item over with white spirit (so it doesn't lift the grain) which has the added advantage of also removing finger grease which can cause an oil based finish to fish eye. I then put on latex gloves to handle the item after that during applying the finish - even if I'm spraying - to avoid finger oils getting back onto the workpeice.

You could try using stearated abrasive papers which have a sort of light coloured powdered coat on top of the grit to reduce clogging, but to be honest - my method of just wiping it down with spirit after has never left any discernable reside liek you describe.

As far as the 1000 grit before painting - pointless. 240grit / possibly 320 but no more - for softwood damp the wood with water on a rag and let dry - this will raise the grain, so cut that back with 320 grit then wipe with spirit. 1 GOOD coat of primer (or 2 thinner ones), lightly cut back with 600 wet n dry to remove any brush marks then 2 coats of top coat - each one also lightly cut back, and a 3rd thin coat on top which you then hit with 1200 grit wet and dry on a block LIGHTLY literally just moving the block with your fingertips. Obviously wipe each time after with spirit before applying the next coat.

You'll end up with a very good flat finish.

For hardwood the same, but no need to damp to raise the grain as there won't be any to speak of.

 

[Alexam]

Same question from me, hade the same issue with 160 grit paper when sanding some ash over the weekend?

Along similar lines, how do I remove pencil marks without smudging the graphite into the grain? Use something instead of the pencil?

HI Paul,

pencil markings ned to be removed with a pencil rubber before sanding. The lead in the pencil will take a great deal of sanding otherwise, as I found out earlier.

 

[AndyT]

What sort of abrasive paper are you actually using?

There is some utter rubbish about. If your paper came from China via a poundshop, the answer is to buy better quality paper. Mirka and English Abrasives are two well known, trustable brands.

 

[Sheffield Tony]

Agreed. The Titan stuff from Screwfix sheds dark grit all over. Mirka has been my favourite. I remember being taught at school never to go back to using a plane or scraper after sanding, because the grit left behind in the grain takes the edge off the tools.

For pencil marks I use the pencil rubber too, and then a card scraper. Abrasive paper seems to just rub the graphite further into the grain. In fact, the scraper seems a better answer than abrasive paper in general; it leaves a nicer finish.

 

[GrahamRounce]

Thanks. Yes, it must be the abrasive dust coming off. I've looked on EBay for Mirka paper, and the varieties include:

Hiomant
Mirox
Avomax Plus
Yellow Oxide Reusable
Aluminium Oxide
Professional Water Wet Latex
Water Abrasive Paper Latex

Help!
It's for wood, prior to finishing/polishing. Grades from 120 to 1200.
Ta again,

 

[mrpercysnodgrass]

I have been using Mirka Carat flex for many years, it is excellent quality and if you buy it in the rolls it is fairly economical too. You don't say what sort of finishing you are doing, but for oil, shellac, varnish or paint you should not really need to go finer than 240 grit, your finish needs something to grip on to otherwise as Phill.P says, you are in danger of the finish lifting off. Most of my finishing is with shellac but I sometimes use oil, varnish and on occasion paint. I have four grits, 100, 150, 240 and 400, I do keep some papers both coarser and finer than these but hardly ever need to use them.

 

[AndyT]

The decent Mirka stuff that I have is marked Mirox. It's yellow.

 

[Eric The Viking]

Pencil eraser: ask for a "putty rubber" at an art shop. I think the last one I bought was Windsor & Newton. They do go hard and crumbly after a while, but you can cut them in half and put the unused bit in a plastic bag. I reckon they'll keep for a year or so after which they lose their usefulness and do smear.

Also, always use a soft pencil - 3B probably. You can quickly sharpen it to a point or a chisel edge, but you want it to mark the surface with the graphite, not make a groove. That way it's easily removed as it isn't forced between the fibres. A hard pencil doesn't make a finer line, it just wears more slowly.

I do use hard pencils for rough work, but for anything that needs to be <0.5mm accurate, either a sharp, soft pencil or a knife (edge of pencil mark on the dimension needed).

My preference is 4B for fine work, 2B at the hardest. Trad carpenters' pencils are OK if you have the patience to sharpen them, but I find they don't sit well behind the ear, and if I put them on the bench they get lost, and it's a PITA getting that chisel edge just so and keeping it that way.

I have found the sanding belt cleaning crepe also works as an eraser (cut off a clean corner with a knife), but not as well. You can also lift graphite off a wood surface with cotton wool dampened with meths or xylene - best as the final clean up after you've used a putty rubber.