I recently finished a small cherry cabinet. I used two coats of danish oil and topped it with minwax wipe on poly. I applied two coats of minwax to the entire cabinet but the top appears inconsistent, sides look great.
Maybe I did not sand the entire top consistently. It looks like some rough sanded areas. Should I just keep adding more poly coats till it levels out, sand and start fresh or live with the inconsistency.
Thanks
Humble Newbie
Replies
Two coats is not enough. Three coats of WOP is roughly equivalent to one brushed coat of full strength varnish. I usually end up with at least six coats when applying WOP. (This obviously depends upon the type of finish you want.) I would sand with 320 g and then continue applying thin coats, sanding lightly between coats to remove nibs. If the sand paper clogs, let the finish cure for 2 or 3 days before continuing.
Good luck, Tom.
Apply at least two more coats.
Yeah, 6 or 7 coats, light sanding or 0000 steelwool between coats. Make sure you clean the sanded nibs and/or steelwool bits off before the next coat.
I have also had good luck mixing wipe-on with up to about 40% solvent to dissolve the last coat better and blend in the previous sand-marks. I did this with a clear finish wipe-on, probably not needed with a satin finish wipe-on. Need more coats when you do this as each will be thinner, but they dried faster and collected less fuzz from the shop air / ceiling. Avoid doing anything while the finish dries as pretty much anything you do raises fine airborne bits that get in the finish.
Also had a bad experience with the final 3 coats coming from a new can of wipe-on that was different or contaminated somehow. Ended up having to remove all coats and start over on the wipe-on, what a pain. Combine / inspect all your cans before you start.
Wipe on varnish already has only about 20% solids, the rest is already thinner, adding more thinner won't cause it to dissolve into the earlier coats to any greater degree. That's because paint thinner isn't a solvent, just a thinner, for already dried wiping varnish. Perhaps a thinner with strong solvent power, such as toluene, could damage the previous varnish film, but not really dissolve it. When a varnish film has had 24 hours to cure, then it's best to scuff it with 320 grit to increase adhesion mechanically.
It's not like lacquer or shellac where the thinners are also solvents for dried finish. With those, each coat dissolves into the lower coats. Consequently, sanding between isn't needed.
Thanks for the additional info. This brings up a couple questions based on my observations.
First, if the thinner does not dissolve the poly, how can it thin it ? Does it carry tiny blobs of it around undissolved ? I have also used thinner to remove previous coats of wipe-on poly due to some contamination as I mentioned. I think there is some solubility there.
Second, pretty much everyone says to scuff sand, but when I do that on earlier coats of clear hi-gloss I see the scuff marks thru subsequent coats, even if I am super-careful and remove all loose material with a tackcloth. I actually see the sanding marks. If I use 320-grit I see 320-grit sanding marks, if I use 600 grit the marks are finer but still visible. This proved to be very frustrating. This method of adding more solvent (thinner) was quite successful in preventing this from happening, I have used it on my last 2 larger projects. Short of using shellac or lacquer which dissolves previous coats, what do people do for this problem (besides using satin finish ) ?
Polyurethane polymerises when it cures. The thinner can dissolve the monomer but not the polymer.Extreme example:
Polythene, the monomer is a gas - ethylene - the polymer is a solid which dissolves in hardly anything.
As Davcefai indicated, the thinning occurs when the varnish has not cured. Varnish, including varnish with polyurethane included, doesn't just dry. After the thinner evaporates, there is a chemical reaction that essentially creates a plastic that is the varnish film. The process takes some time--you can usually recoat after overnight, but full curing may take a month. That also explains why you may be able to remove some defective finish with mineral spirits. Something has gone wrong with the cure so it doesn't reach the point where it can be redissolved with the same thinner.
I'm not quite sure I understand why you wouldn't be able to obscure 320 grit sanding with normal wiping varnish. Are you hand sanding? You don't want thick coats, but wiping varnish should leave the surface looking wet, not wiped dry like you would finish off an oil/varnish mix finish.
Edited 10/12/2009 11:04 am ET by SteveSchoene
My experience with WOP has been very good.
I generally apply 6 coats, give or take depending on how it looks and the final finish I want. I don't sand between coats at all. I apply, let it sit in my workshop overnight with as little activity in the shop as possible to minimize the dust. The next day, I apply the next coat. But before I do, I wipe it down with a lint free cloth dampened with paint thinner to remove any dust that may have settled. I only sand when there are obvious imperfections in the finish, which is rarely. The only time I seriously evaluate sanding is just before the last coat. If I decide to sand, it is VERY lightly, then wipe down, then final coat.
The reason for not sanding is that the finish is not fully cured after 24 hours. So there is enough of a surface for the next coat to bond to. If I decide to sand before the last coat, I let the finish cure a couple more days before I do that.
I don't usually wait 24 hours for those thin coats. Two or three coats can be applied in a day if desired.Gretchen
When using wipe on, as others have said, you need many applications, especially for the top of the project.
I have often admoninshed newbies to wipe on that "don't give up by how it looks after two applications. It looks awful". I wipe on 8 coats for tops and 6 for sides.
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