Restoring cedar strip--removing poly

[ace065]

Hello, everyone-
This is my first post here. A little background .....in 1993 I decided to build a cedar strip canoe. I have always been good at working with wood and thought it would be fun. I purchased 20 ft pieces fo western cedar and had a friend who owned a cabinet shop to cut into 3/4 inch wide strips. I purchased plans for an 18 1/2 ft canoe and, nine months later I had a beautiful canoe. A friend and I canoed in my creation several times over the next 2 years and I discovered that building the canoe was more fun than using it. It has been unused since 1995. It has been exposed to the sun on and off since then. I have decided to restore the canoe since I have the time now, being retired. The boat is in very good shape, with only three small spots of epoxy/fiberglass delaminated from the strips. Since I had history refinishing wooden golf clubs, I used Deft exterior poly on the canoe. Talk about tough!!! I am trying to remove the poly to prepare for recoating. I have an orbital air sander that takes a round 6 inch disk. Using 180 grit is a slow go. What grit should I use? Also, should I remove the poly that isn't peeling? It seems that one side is peeling and the other is in pretty good shape. The inside is not peeling. Should I just sand the good spots lightly and remove the peeling places from the bad spots? And what coating should I use...poly or spar varnish? Thanks for the help.

[MoMan]

Have you tried a nice sharp cabinet scraper instead of sanding? Might be more efficient.

[Todd Bradshaw]

The last one I did that to, I used 100 grit disks on a 5" random orbit sander. It's still a fairly slow process, but that's about as much cutting power as you want in order to have time to stop before you start cutting into the glass. A scraper might certainly be worth trying and very well could be more efficient once you get the hang of it.

p.s. if you hit birch bark, stop sanding

[ace065]

Didn't think about a scraper. Might try it but won't I need to also sand after scraping? What about the places where the poly is not damaged? Sand/scrape or just lightly sand and coat. Also, poly or varnish...which is best?

[Canoez]

Have you tried a nice sharp cabinet scraper instead of sanding? Might be more efficient.

Works like a charm.

Also, if you're making a cedar-strip canoe and you wind up with some "orange peel" from rolling the epoxy on, the cabinet scraper makes quick work of that, too.

[ace065]

Could someone give me an idea of what type of scraper I need? There seems to be several different kinds. This poly has dried very hard and I can't see how a scraper would work, but you guys are the experts. If I knew how to do it, I wouldn't be asking, wood I?

[Todd Bradshaw]

Most scrapers just have a steel blade with a clean, sharp, square edge and it's a matter of finding the proper angle to drag it across the surface - removing, but not gouging. You may want to invest in a few different sizes and shapes if you try one and it seems to work well. Whether or not the surface needs much sanding after scraping will depend on the surface quality left behind, but it should need a lot less sanding than it would have needed without scraping.

There is a pretty good chance that the old polyurethane has darkened to an extent. If you remove part of it and leave other parts with just prep sanding there may be color changes where the different sections meet, so you probably should be prepared to remove it all if you want even color. You can usually wipe areas down with a wet sponge and get a brief preview of how they'll look when revarnished while the area is still wet. Look for color shifts, deep scratches, sander swirl marks or other less than ideal looking spots that might need a bit more or finer sanding. Varnish cans will usually tell you how fine of a sanding grit to prep with. We will sometimes go another grit or so finer for clear stripper finishes, but there is no advantage of sanding too much finer than that as you may start to lose bond strength if the hull is too smooth. Most folks are using high quality marine varnish as it seems to have the best protection from UV - and protecting the epoxy from UV is critical on clear finishes. The price of real marine varnish is getting crazy these days, but once you bite the bullet and buy some they generally work quite well.

[ace065]

Just tried to scrape the poly off my canoe and I just don't believe it is going to be any easier than sanding. This poly is very hard and is curled up in small spots, I can sand off the ridges and still have tiny spots that the poly is firmly attached to the glass. I thought a scraper would just remove the poly in strips the width of the blade. Just isn't happening. Will try to attach pics if I can figure out how to do it.

[ace065]

Hey Todd-
Just tried to scrape my canoe with a razor blade. It actually works!! So....... it stands to reason that the right cabinet scraper will work much better. I think I know what type of scraper will work..one with a very sharp, flat blade. Probably how all of them are made I guess. Will have to sand some after scraping but maybe just block sand. Thanks for the info.

[Rich Jones]

I just took my bright finished pulling boat down to the wood. Used a heat gun and scraper. It doesn't take much heat to bubble the varnish (poly in my case). Holding the heat gun in one hand and the scraper in the other, the stuff comes right off. Be careful, though, because too much heat will mess with the epoxy. The scraper was only one and a half inches, but I made quick work of it.

[ace065]

Opinions on using heat gun along with scraper? Sounds like it might make the job easier, but is there a possible price to pay? I sure don't want to create more problems by making it easier. Would like some opinions about this, along with personal experiences, good and bad.

[Todd Bradshaw]

If you want to preserve the resin (either epoxy or polyester) I wouldn't go near it with a heat gun. As little as 140 degrees can start to soften epoxy and that's how we remove it - by destroying it. Not a good idea.
Another thing that can happen to clear-finished strippers is that the wood itself can heat up, expand, and actually stretch the fiberglass layers. This can cause a network of fine, white-colored micro-fractures down inside the weave of the cloth. They not only show, but a once smooth surface may suddenly get covered with cloth texture, telegraphing the weave to the surface.The fractures aren't usually a structural problem, but they can't be removed or hidden without tearing off the glass and replacing it. I had one stripper do this to me one summer just from hanging in the rafters of a garage where it got hot on sunny days.

There are ways that you can "bake" freshly applied epoxy to increase its heat tolerance, but most folks don't happen to have an autoclave in their garage big enough to hold a boat. For those of us in that position, it's a good idea to avoid heating any fiberglass layers that you would like to keep.

[P.I. Stazzer-Newt]

There are a number of different things called "scrapers" - many with handles, but the classic Cabinet scraper is not quite a square edged piece of steel - the cutting action relies on a series of subtle burrs formed on the edges (eight on a square one).

They are a revelation the first time you meet one which has been properly set.

http://woodgears.ca/scraper/index.html shows one way to do it.

http://www.stewmac.com/freeinfo/Repa...ed/i-3416.html < the other method.

[wizbang 13]

I agree with Todd, 100 grit on a DA.

[ace065]

Just read sites suggested by Stazzer and found them enlightening and a little confusing. Don't want to spend more time sharpening the scraper than stripping the poly. Since the scraper, in my case, will be used to strip off a thin layer of poly and not go deeper as it would with wood grain, don't I need to be careful to get the correct scraper? I do not want to cut or shave into the epoxy. At Todd's suggestion, I think I will use a scraper CAREFULLY and finish off the 100 grit on my DA. Either way, my next couple of weeks are obviously planned.

[wizbang 13]

weeks? an hour or two.

[Rich Jones]

If you want to preserve the resin (either epoxy or polyester) I wouldn't go near it with a heat gun. As little as 140 degrees can start to soften epoxy and that's how we remove it - by destroying it. Not a good idea.
Another thing that can happen to clear-finished strippers is that the wood itself can heat up, expand, and actually stretch the fiberglass layers. This can cause a network of fine, white-colored micro-fractures down inside the weave of the cloth. They not only show, but a once smooth surface may suddenly get covered with cloth texture, telegraphing the weave to the surface.The fractures aren't usually a structural problem, but they can't be removed or hidden without tearing off the glass and replacing it. I had one stripper do this to me one summer just from hanging in the rafters of a garage where it got hot on sunny days.

There are ways that you can "bake" freshly applied epoxy to increase its heat tolerance, but most folks don't happen to have an autoclave in their garage big enough to hold a boat. For those of us in that position, it's a good idea to avoid heating any fiberglass layers that you would like to keep.

My boat is glued lap with no fiberglass. The laps are held together with epoxy and that's why I was very careful with the heat. I wasn't aware that so little heat could mess up the weave in fiberglass.

[ace065]

Wizbang-
I am a retired 65 year old with ADD. Seriously, if I finish this project in two weeks, it will be a miracle.

[ace065]

Richard-
I read about your ordeal with your boat. Nice to hear that you recovered so well. Obviously, I have a different type of boat so I won't be using a heat gun on it. Nice to have people to share their trials and tribulations and also nice to have experts like Todd to keep you on the right path.

[ace065]

Well guys, it's been over a month since I began my restore project on my cedar strip and the progress is slooooow. I admit that I haven't spent very much time on it but the time I spend is yielding little progress. I bought six cabinet scrapers and they work very well. Each time I make a pass I get a roll of poly off the boat. Still, I know that to get all of the poly off this canoe is going to take a long time. Todd- if you are listening- I have a question. Is it necessary to remove ALL of the poly? In the places where I apparently have removed all the poly, I can see little white dots. I believe that is okay, isn't it? What happens if I remove all the poly until it is smooth, with no blisters of poly showing but leave some on the canoe? Then apply poly or varnish over the smoothed out poly. I used Deft exterior poly on this boat and it is hard as steel it seems. Any opinions will be appreciated.

[Todd Bradshaw]

Assuming its surface is sanded for good adhesion of the new layer, about the only real danger I can think of might be some moderate color blotches if the old stuff has yellowed over time and is sitting next to spots with all new varnish and no old undercoat. About the only way to preview this is to wet down the hull to simulate new varnish and see how it looks when wet. The old spots may or may not show up.

The little white dots are the tops of the woven fiberglass yarns as they pass over and under other yarns. When you start seeing them you generally want to stop sanding on that area, since you don't want to sand into the weave and weaken the glass layer. The spots will usually disappear when the new varnish is applied over them.