# Overzealous sanding between coats



## Chazmania (Feb 9, 2009)

This is a great site, I'm glad to newly join. I have a question I couldn't seem to answer via searching:

I'm finishing my first woodworking project of substance- a red oak bench matched to existing store-bought dining furniture. The inspiration came from DJMarks' mission-style ottoman: http://www.djmarks.com/woodworks/106.asp

My question is about finishing: After sanding to 220 I stained the oak with a pigmented stain (minwax), followed by a couple coats of wipe-on polyurethane. Each finish step was a day or two apart. When I started sanding (320 grit, light) between coats of polyurethane, I realized (a bit late) that my sanding was removing stain color pigment irregularly, turning my uniformly stained project a bit blotchy. After the work to get to this point, I was a bit dismayed. I've avoided the issue for about 6 months (winter).

How would you resurrect this project? Re-stain on top of existing polyurethane, to filll in the removed stain? Just add more poly and chalk it up to a 1st time mistake? Strip the whole thing and start over?


----------



## ent (Feb 10, 2009)

Hi, for in between coats of poly, use 0000 (say four-ought) steel wool. You should not have any problems with blowing through the finish using the wool. Pros do use paper as it is cuts faster and does not round dust nibs, but you need to use a higher grit and a good touch. 0000 wool is roughly 600 grit, but I would still use the wool.

Now for the issue. If you just poly over, I think you will be disappointed for the long term. When the light hits the piece it will magnify the rub throughs.

If you try to restain, your mileage may vary as the poly might prevent the stain from absorbing as it should. I have done this successfully for glue spots found late in the finishing process. If you only have a few, you might be able to get away with it.

To be 100% sure, you might want to consider sanding the all the poly back and just restaining. You probably don't need to go to bare wood for good results, but I do think you need to get the poly off. Since you only have a few coats, it might not be bad.

Good luck and get that piece finished!

Frank


----------



## Al_Killian (Feb 15, 2008)

I would strip the top and start over. Take off all the poly and when the dust turns the color of the stain, STOP. Now you can hit it with a quick coat of stain and start aplling poly. Are you useing wb or oil poly? If wb(water bourne) do not use wool as it can rust if any littlslivers get left on/in the finish.


----------



## North40 (Oct 17, 2007)

What do the instructions on the can of poly say? I'd use whatever grit the can recommends. We talk about sanding between coats, but you aren't trying to remove anything, you are just trying to create a little roughness on the surface. I use a foam sanding block, and just use the weight of my hand - no extra pressure - and I try not to go over any single spot more than three times.

I'm with Frank on the color - you might get away with re-staining now, but it sounds like you're well on your way to removing the poly anyway, so I'd suggest just sanding the rest off. One other option would be to even out the colors with glaze.


----------



## SCOTSMAN (Aug 1, 2008)

OK look why do we need to sand between coats? simply to achieve an undercut rougher area to take the next layer of cover.If we do not do this and I am sure we have all seen paint varnish etc come off in big strips because it is applied over a very smooth surface like water on glass if we watch water run of glass because it is highly poilshed we can understand that if wee roughened the glass the water would hold better and not run off so well millions of small microscopic grooves to catch in thats it you only need a light touch thats all you don't want to go through to the previous layer just scrtach the one your working on hope this helps Alistair


----------



## Loren (May 30, 2008)

I would probably scrape it back and re-finish. Live and learn.

If you let the varnish cure too long between coats you have to
rough it up more to get a good bond. There is a sweet spot where
you barely need to sand at all - but it varies on your climate and
other factors.


----------



## North40 (Oct 17, 2007)

Loren is right - there is a window of opportunity between "set" and "cure" where hardly any sanding is necessary. In fact, I read an article recently that suggested you find that "sweet spot" and re-coat without bothering to sand, and only sand before the final coat. I've done this a couple of times without any problems, but it's not my standard practice, and I wouldn't recommend it unless you are very experienced with your finish.

Alistair is right, too - a cured and unprepared surface can reject the next layer, but there may be other causes for rejection too. I've only had varnish rejected twice, and both times the previous layer had been sanded.


----------

