I'm another newbie with a boat that needs refinishing, so I thought I'd post here before I start a whole new thread. The finish looks okay in some parts, but is worn off an grayed in others. I am not sure if it currently has varnish or Cetol on it. I'd like to refinish - I plan to use Oxalic Acid, I have a sander, and will recoat with Cetol Natural Teak. I'm just not sure about the order of events -- do I need to use something else first to remove all the existing varnish/cetol? Any recommendations? And then do I use oxalic acid, or sanding first? (I've seen some people say acid then sand, and others say sand then acid.) Thanks in advance!
Kind of like booze, different folks' preferences vary when it comes to finishing wood. Here's what I'd recommend based on my own experiences.
First for Cetol you'll need to strip it down to bare wood. You've got several choices -- sand it off; scrape it off; or use a chemical stripper. Of the three I prefer to scrape when possible, but sometimes sand or strip depending on the situation. Chemical strippers are relatively quick, but leave a fair amount of gooey mess. Sanding works, but can become tedious after a while.
Scraping -- using a sharp scraper and sometimes adding a little heat from a heat gun -- works in 90% of the spots you'll encounter. Google "cabinet scraper" and you'll get a good number of hits. Look for the videos that show using one, and those on how to sharpen them. If you don't want to buy a "real" cabinet scraper, you can make one using the side of a putty knife, the back side of a hacksaw blade, etc. The key is to keep the scaper sharp.
Using a heat gun along with the scraper can make it go quicker. Just remember that you're not trying to "burn off" the old finish, just heat it up enough to make it soft. You've got to be very attentive to make sure you don't char the wood.
Sanding off a finish will work, but takes time. The finish will clog the sandpaper fairly quickly (depending on the quality of the paper), and you'll go through a fair number of sheets before you're done. I'd leave the sander in the tool garage except for large, flat areas. Sanders and round edges just don't play well together. To strip off the finish, start by hand gently with 80 grit paper on a stiff sponge or a block of wood. After a while you'll get a good feel for how much pressure to apply to get off the varnish without taking off too much wood. Once the finish is off, switch to 180 grit paper and go over it again.
Chemical strippers work great, but I only use them on pieces I can remove from the boat. Citrus Strip works OK, and is friendlier on you than others you may encounter. Lay it on fairly thickly, and let it work. Scrap off the loosened finish with a plastic scraper, then give it a scrub with some bronze wool (not steel wool) and mineral spirits. If there's wtill any finish left on the wood, repeat the process. After all the finish is off, wash it with soapy water and rinse well. Let it dry, and then sand it smooth with 180 grit paper.
If you're going to use the oxalic acid, do it between the rough sanding (80-100 grit paper) and the finish sanding (180-220 grit). You want to have bare wood for the oxalic acid to achieve a uniform finish. The water will raise the grain of the wood, which you'll need to knock back down before you apply the finish.
Best of luck!