Sanding with 220 grit with only a few passes it looks like I sanded through the two coats down to wood!? Ignoring that it's not needed for adhesion what it does is pointlessly remove varnish you just applied, only to be replaced by more varnish in the next layer(s)! There are uncountable examples of this to prove the point, as Bob Flexner makes some reference to in The 7 Myths of Polyurethane on Popular Woodworking. What happens if you forget to sand between polyurethane coats? How do rationalists justify the scientific method. Thanks for the article. You can certainly "build" varnish quite deep, if you want that look, but unless you're finishing a bar top or some other surface expected to get a lot of wear and moisture you shouldn't need it. Try to get the "non-filling" type, like the waterproof or aluminium oxide. @bowlturner I updated the title. Bear with me. Although some sanding between coats is needed for some users, it's actually a very self-serving direction on the part of the manufacturers as they're assuring you use more of the product than needed. Is it bad to sand extra-fine before applying Poly? I don't know where the confusion arose but the 21 coats refers to a traditional drying-oil finish, not varnish. Stack Exchange network consists of 176 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. The sanding between coats accomplishes two things: It removes defects from the applied urethane as well as small dust particles lodge in the dry finish. Polyurethane dries slowly, so there are always dust nibs that should be sanded out before the next coat is applied. I did 2, what I thought were, thin coats 3 days apart and the last one was 2 days previous to now. Never sand a tacky surface as the grit of the sandpaper will quickly become clogged with the polyurethane material. site design / logo © 2020 Stack Exchange Inc; user contributions licensed under cc by-sa. It only takes a minute to sign up. [Useful trick while I'm here: After the varnish has really cured, a brown paper bag is just abrasive enough to knock loose dust specks caught in the surface and polish it a bit.]. Coat the entirety of your workpiece, but don't brush excessively or you'll create areas with too little polyurethane. My problem involves quoting the instructions on the can and giving some background into my process. Clean the surface with the tack cloth. Typically the sandpaper should be run over the surface in the same direction as the wood grain. For the rest of the project I skipped the sanding, but I would like to know what I did wrong. It immediately took off the thin coat I had applied, even with just a very light sanding, and even took off some of the stain I'd applied underneath. How do I prevent stain from being removed during sanding? Sand with 220 grit after first coat and wipe down with a tack cloth. Which would be an issue except they pissed on the table in several places. Quick link too easy to remove after installation, is this a problem? This depends on the specific varnish -- viscosity varies and some build faster than others -- and how you apply it (padding typically puts down a thinner coat than a well-handled brush) -- but three-to-five coats should give you as much protection as most things will need, and can give you quite a nice shine. No one I know of has ever suggested 21 coats of poly. The most egregious part of this is that sanding is not needed to ensure adhesion between fresh coats of poly. Was the theory of special relativity sparked by a dream about cows being electrocuted? rev 2020.11.24.38066, The best answers are voted up and rise to the top, Woodworking Stack Exchange works best with JavaScript enabled, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site, Learn more about Stack Overflow the company, Learn more about hiring developers or posting ads with us. Even so, I still advise that you sand between the coats when applying polyurethane as this will help increase the adhesion between the layers to give you a more level finish. Cutting out most sink cabinet back panel to access utilities. Fortunately, I started on a part that was easy to quickly repair. I've been using polyurethane for 40 years or more. You have to sand those with very light sandpapers. Sanding Between Coats by Alan Noel Professional Wood Finisher When applying several coats of finish to a project it becomes necessary to sand between coats to not only remove any trash that has settled into the finish but also to promote good adhesion between the layers of finish. And actually it's not needed between coats of any varnish and never has been. Apply a final coat of polyurethane within 48 hours of the previous coat. Is the word ноябрь or its forms ever abbreviated in Russian language? Why would they suggest I sand with that grit if it takes away the coats to begin with? To start the project, sand the wood surface with a 320 or 400 grit sandpaper to remove minor surface defects from the wood. The sanding between coats accomplishes two things: It removes defects from the applied urethane as well as small dust particles lodge in the dry finish. Sanding with 220 grit with only a few passes it looks like I sanded through the two coats down to wood!? home | projects | blog. Polyurethane Book Case is Rough, Sand in Place? where varnish is applied in a clean-air environment, sanding between coats is never done as far as I'm aware. Let dry 4-6 hours. Obviously they didn't intend for that to happen and I am doing something I am not supposed to do. Put on a second coat forgetting to sand it between. It seems to work better if done right after the first coat has dried, perhaps because it's still polymerizing. Wiping down with warm soapy water would have probably been the first thing I would have tried :-). I get the best result building or refinishing furniture when I thin oil based urethane 3 parts urethane- 1 part mineral spirits for the first coat. If manufacturers were truly interested in helping their customers to apply the product most effectively, as they say or imply, what they would do is give people specific tips on how to apply smooth, even coats of varnish such that no sanding would normally be required (except to de-nib). I had earlier oil questions and, while I never said poly outright, I was reading the answers like there were talking about poly. Possibly, but I think you should have first tried a non-sanding approach. From other answers on WW I understand that applying only a few coats of poly can be sufficient but traditionally you could use as many as 21 over the course a year. I got confused since poly is a oil based product that I thought it was like tung, blo or something in that vein. G.K. Bayne is a freelance writer for various websites, specializing in back-to-basics instructional articles on computers and electrical equipment. On the other hand, polyurethane stains require something different. Why can't I shake my can of polyurethane? I'm shocked that you would implicate the manufacturers in attempting to get you to use more of their product than necessary!


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