Why is it important to sand between layers of varnish?

Question

Isn't that just removing the varnish? Or dulling it?

Answer 1

Basically "sanding" knocks down any fine hairs & gives a good surface for the next coat.
Having said that........
A good varnish finish ( or anything else) is "built up" w/ multiple thin coats.
Have been doing "old school" finishes for a long time & never use sandpaper unless it is very fine , wet dry tupe & just for cleaning up minor "snots".
Yes it does remove finish , but it is mainly to even out imperfections.between well dried coats.
Always used fine bronze wool for an "in between "rub as it will not dull edges & any detail.
keeping it clean w/ a tack cloth keeps any new junk from getting into the next coat.
I used spray gear , but consider that the old masters just had
brushes , rags & sometimes their hands.
They also had apprentices to do all the cleanup & rubbing.
You can get excellent results w/ spraycans, good brushes &/or mohair rollers.
for very fine imperfections , an old tip I used & have been passing on, is to use well crumpled paper grocery bags
for fine rubbing.
A final rub w/ a good hard pastewax does it.
Had to get paid for my work & used this basic method ( there are others) on some fairly pricey antiques..
If you are just doing a flat bar top , brushes or rollers are fine & a little light sanding in between is OK.
Maybe a little too much information, but you get out what you put in when finishing.
Best regards

Answer 2

Hello Mark G.
You want to sand between coats to 'break' the gloss. This will help the new layer adhere to the first. A neat little trick you may want to try is to thin (reduce) your varnish to where it is about twice as thin as normal, less if you can still work with it, for your final coat (only). Do NOT sand it. You will get a glassy, high gloss final finish.
If you are using spray varnish, there is another method which will allow you to do the job without the need to sand between coats. Important: using this method it is very important to use very thin coats. Let the 1st coat 'set-up' to a dry state but (just barely) tacky then spray a second ,very thin coat. Again, let it dry to until just barely tacky and spray a third very thin coat. You want each 'under' coat to be almost hard enough to sand but not quite. The idea is to have the surface of the 1st coat hard enough to support the 2nd but still be able to re-liquefy and merge with it. This in effect joins the coats into one solid coat. Practice this method on scrap material before using it on anything valuable as it ABSOLUTELY requires a developed technique. Start by trying 3 coats without any sign of 'crinkling' when dried and work up to the same with 5 coats. It works.

Regards,

Lenny.

Answer 3

The primary reason for sanding between coats is to remove any dust and dirt specks that can get stuck in the paint or varnish. You should use 220 or 320 grit paper for this and sand very, very lightly and then tack cloth the surface.

How long you wait between coats depends on the paint or varnish.

I use a lot of wipe-on poly and you don't have to wait but 4 to 6 hours between coats. Many times it is so smooth and speck free that I can put on three coats before needing to sand. Because it dries fast, it traps less dust and dirt specks.

Answer 4

It smooths out any lumps or streaks from the previous coat and helps the new coat adhere better. Also, make sure you wait a coupla-few days between coats to let the previous coat cure completely. If you apply it too soon, the solvent in the next coat will cause the previous coat to crinkle and you'll have to start all over again.

Answer 5

To make the next layer adhere better.

PS: Read Paul's comment about time between coats, he's right on with that!!

Answer 6

when you sand between layers of varnish, it give you a better and clearer finish.

Answer 7

it puts what is called tac to the finish allowing the next coat to adhere beter it is just the best way to get a top grade finish.