Chestnut varnish?

[mccloud]

I have been attempting to strip the varnish from a 1950's vintage Chestnut, which has proved to be very difficult. I do not see evidence of multiple coats, so am guessing this is the original varnish. About 70% of the inside of the hull was still covered, which looks shiny and is hard, when I started this project. I've tried using my last can of DCM-containing stripper which is not highly effective, and have tried Citrus Strip, which is slightly more effective if I wait for an hour or so before scraping. I've tried both on the same spot. I've been over most of the hull 3 times now and still some areas have varnish. The hull has been washed with hot, soapy water and a stiff bristle brush, and with TSP solution, yet spots of varnish remain. The edges of the ribs are a particular problem. It looks like I will be spending many, many hours sanding unless someone has a trick for getting this varnish off. Does anyone know what formulation of varnish Chestnut was using near the end of their life? Are there tricks other than the usual strippers for getting rid of this varnish? Tom McCloud

 

[MGC]

Don't rule out the possibility that you are dealing with a polyurethane finish. It's possible that polyurethane might have been cheaper/more available than a proper spar varnish at the time that hull was finished. I've had to resort to lot's of sanding whenever I've encountered polyurethane. It's funny, it either bubbles up or it sticks so hard that you can't get it off....
You may have taken one for the team. Based upon your struggles I now plan to sand and re-varnish my 50's hull instead of trying to remove the old finish. As yours, mine is also original but blessedly has not failed anywhere.

 

[Rob Stevens]

Did you try heating it?

 

[1905Gerrish]

Tom,
Trying using maroon scotch-brite pads in combination with the stripper when you need to scrub. I always cut the full sheets in quarters. I plan on a box per canoe. Never a fun job!
Zack

 

[mccloud]

Heating with a heat gun DOES soften the varnish enough to scrape off the top layers, leaving some residue which will be easier to sand away. Thanks, Rob. Since I've been working outdoors at 45F, extra heat is a good thing. Will continue to experiment with solvent and scrubbing pads. TM..

 

[Todd Bradshaw]

Keep in mind that one of the most limiting factors when using chemical strippers, and despite the efforts of their manufacturers to prevent it, is evaporation. The faster the stuff starts to dry out on the surface you are trying to strip, the less effective it becomes. This is what causes the condition where you try to remove it and the stripper has pretty much liquified the top surface, but the farther you get down into it, the more gummy the old finish is - and you may even get down to a level where it is still plenty hard before you ever approach bare wood. The RX for this is messy at times, but involves applying the stripper in a fairly thick layer and then immediately covering it with plastic sheeting. Then you give it plenty of time to work without evaporation diminishing the stripper's ability to do the job. It's not a perfect solution, especially when draping plastic over complex shapes and trying to get it down pretty tight, but it can make a serious difference in just how well the stripper can work.

 

[mccloud]

Continuing with this project, since the standard strippers did not work well I wanted to try something else. If the varnish is a urethane varnish, then a varnish thinner or cleanup solvent might soften it. There is no standard formulation for varnish thinner, but they would generally be composed of a lot of acetone with lesser amounts of aromatic organic solvents such as toluene ( and others). These are more volatile than strippers and more flammable. So as an experiment I bought a can of KleanStrip Paint stripper after wash, poured some onto a heavy winter sock, and laid that up under the deck where it is difficult to reach. After 15 minutes or so I took a look, and saw some 'bubbling' of the varnish, then following with a scraper, about 70% of the surface came clean quite easily. So if you have an intractable varnish removal problem where the usual strippers haven't worked, give a stripper afterwash or varnish thinner a try.