I'm in the process of finishing a piece of butcher block for an aquarium cabinet and need some advice on applying the polyurethane. I applied two coats of stain, with a light sanding (220 grit) in between coats, and I'm happy with the result. Now I need to seal it with a polyurethane. I plan on using a clear water-based polyurethane with matte finish. The can says to sand in between coats. I applied a coat of oil-based poly to a sample piece, let it dry for 24 hours, then sanded it lightly with 220 grit, but it appears to have removed all of the polyurethane and I took a little of the stain off as well. Did I sand too hard or is 220 grit too aggressive? I was probably a little more aggressive than I should have been because there were bubbles in the poly. I didn't shake the can, I only stirred, so I'm not sure why there were bubbles. Is the oil-based poly more prone to bubbles? I used a paint brush to apply it. Would a foam brush be better?

 

You don't sand between coats of stain. Generally your first coat should be a sanding sealer. I like Zissner Seal Coat a lot. And you just lightly sand (once over) so there is no way you should sand through the poly. You obviously shouldn't sand so hard that you get down to bare wood. You should be using a China bristle brush to apply poly. I only use oil base, I have zero confidence in the durability of water based poly... plus IMO water based dries too fast which makes things prone to brush marks.

 

This is my first attempt at staining anything and I was following the advice of a couple You-tubers. The reason was after the first coat, the grain raises up, so sanding it knocks it back down. Does this not happen when using a sanding sealer? Also, the can of poly says to apply three coats, but maybe this is only if you sand between coats?

I should also mention I stained the wood with a charcoal gray stain, so I want to maintain this color. I've heard an oil-based stain can turn amber colored over time? I also don't want the finish to be shiny. Not sure if oil-based vs. water based makes a difference as far as sheen.

Why did I get so many bubbles? I gently stirred the poly and used a bristle brush.

 

That is what sanding sealer is for. And you always sand lightly between every coat of finish. I'm guessing you were using a brush for latex paint and over brushed it. Use China bristle only. Work fast then let it settle.

If bubbles appear out of nowhere then your stain probably wasn't dry.

 

You have to sand between coats of poly to get good adhesion of the layers but you're not trying to remove any significant material, you're only trying to create nooks and crannies for the next coat to flow into. 220 is the right grit, I think you applied too much elbow grease.

 

Okay. Thanks fellas. I'll post a pic of the final result.

 

Here's a pic after the first coat of poly (still wet in areas). Turned out pretty nice! Put the final coat on last night. The China brush worked out much better

https://www.mediafire.com/view/lldsd...15237.jpg/file

 

BTW, I lightly sanded with a 320 grit sponge in between coats, which appeared to work well. This is my first time finishing a piece of wood this size, so I have no clue if it would have made any difference if I had not.

 

Normally a light scuff sand with 220 grit is recommended. 320 will probably be fine.