I am making a series of pieces that are covered with a cherry veneer, and finished using Minwax’s Quickdry Polyurethane with no stain.
I am new to finshing with anything other than primer and laytex paint, so I am a total newbie here. I bought the Polyurethane in both the quart sized liquid can and a spray-paint style can. I followed the direction on the spray can, and laid down a thin coat of the poly over the whole piece. It said to wait no more than 2 hours, and recoat. (no sanding). Then wait 72 hours… sand with 220, then recoat.
Well… I did all that. except when I sanded, I had no idea what “light sanding meant.” The sprayed layers seemed to leave this rough feeling over-spray feeling that I knew I wanted to sand away. The lyers seemed so think, and since I’m a totaly newbie, I could not tell when I was still sanding poly, and when I had maybe gone through the poly to the cherry wood. I was literally baby-gloves careful. Almost no pressure. I did start out using a 3M sanding block, but then switched to just my hand to make sure I was barely just kissing the surface. But even with 220 sand paper, so many scratches appeared, that in order to turn the whole area “chalky” or get rid of all the scratches, I felt like I had to kinda sand more than what I’d call “light sanding.”
The problem is, every video from Minwax themselves, to television, to YouTune… all talk so much about each step, but then just say, “…and after a light sanding with 220 grit sp, apply another coat.” No idea what light sanding is.
So, after the sanding, I switched from the spray can to the quart sized liquid, to avoid a repeat of the weird rough overspray feel. I stirred it well to avoid bubbles, and I laid on a thin coat with a very small foam roller. I let that dry for 4 hours, then sanded again with 220 grit sp, and it’s drying now. I cannot tell if I am done, or if I need to sand and do another. I feel like each coat has been so thin.
Can anyone define “light sanding between coats?”
Replies
Between coats of finish you want to use 320 grit, not 220. In fact, with finish from a rattle can you might even want to go to 400 grit.
You just want to remove defects and just roughen the surface slightly. (Polyurethane varnish needs some "tooth" to grab for coats to bond well together. I would use a padded sanding block fingers will just follow dips and keep the surface wavy and not flatten it out as with a sanding block. To avoid oversanding, be sure you have plenty of raking (low angle) light.
Other than yelling at your work, I'd go with 320 + a sanding block for uniform pressure. Or wet/dry sandpaper + a water/dish detergent mixture.
Another idea; in Highland Woodworking's library there are articles by professional restorer A. Noel.
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