Hull scraping 101 questions

[Anastasia]

So I have embarked on my first dry dock and am exploring the history of my boat's hull. I've got my heat gun in one hand and Pro Prep handy dandy scraper in the other. I heat the paint up to bubbling by moving the gun in six inch sweeps.

Here are some of my questions:
1. The top layer of glossy green paint comes off easily and underneath is a matt white layer which either chips or hangs on with great tenacity. I get it to bubble a bit, but it's quite stubborn and I'm worried about burning the wood. Have I hit a common undercoat layer that just takes a bit more side to side scraping effort or what?

2. I am supposed to run the scaper in the direction of the grain of the wood like when I sand, right?

3. Should I worry about too much heat on copper riveted areas. Copper is a good conductor, isn't it?

4. Can anyone give me advice on the proper way to sharpen Pro Prep blades?

5. Should I attempt to round the sharp corners of the Pro Prep blades to lessen the possibility of gauging the wood. If so, is there a good way to do this?

6. I have a mask, leather gloves, and overalls on and a drop cloth underneath to catch the paint flakes and I'm outside in the fresh air. Should I have any other concerns?

Thanks for your help!

[Keith Wilson]

Well, I'll give it a shot. Here's what works for me; others may have better methods.

1. I've found that there are some primers which don't strip easily. That's the point of the primer, I guess, to stick tight, while the topcoat looks pretty and resists weather. Don't worry too much about getting absolutely all of it off; if it won't come off with heat and scraping it will probably stay on in service. This assumes that you're not contemplating some radical change in paint type, and that the new paint is compatible with the remnants of the old primer.

2, Yes, mostly. Sometimes it works better at an angle, and sometimes you can't fit your hand in that way. Cross-grain scraping gives a rough surface, and you have enough work ahead of you already without making more.

3. Not a problem as long as you don't go absolutely crazy with the heat gun.

4. At this I'm certainly experienced, if not an expert. I use a small fine-tooth file. File the face of the blade away from the handle (the face with the bevel). Always file "out", that is, from the center of the blade out into the air, at about 45 degrees to the plane of the blade. A couple of strokes of the file will usually do it. There will be a burr on the back edge of the blade (the face attached to the handle), but that's fine, it helps. It's hard to explain this in writing; I could show you in about 10 seconds. Anyway, sharpen often. It's a good excuse to straighten up and rest your back, and the work goes faster.

5. Yes. I round the corners of all my blades slightly with the file. I also try to file a slight crown in the cutting edge of the blade as I sharpen.

6. Good Lord, you're safe from anything but nuclear attack. I don't use any of that except safety glasses and usually a mask.

I just did a quick search and found this site (http://rogcad.com/pbook.htm) about removing house paint that describes the sharpening business better than I did. It's about removing house paint, though, so some of it doesnt apply. He has an interesting idea to tape two or three electric heat guns together; I may try that.

[ 09-23-2003, 11:43 AM: Message edited by: Keith Wilson ]

[Nicholas Carey]

With the pro-prep scrapers, usually you touch the blades up with a file a couple of times (I'd dismount the blade and clamp it in a vise while sharpening just to be safe, so you don't slash your hand on the blade.)

They are made of awfully hard steel and consquently difficult to really sharpen well in my experience. They're designed to be replaceable and they hold their edge a good long time. Once they get seriously dull, just toss the blades and replace them.

I probably wouldn't round the corners of the blades, 'cause I think it would dull the factory edge (which is awfully good). the pro-prep people make a ton of different blade shapes. We usually use a channel blade like this

http://www.prginc.com/Clean&Rmv/scr-phc03.gif

so one corner is rounded anyway.

That's my 2 cents worth anyway.

[Wild Wassa]

Anastasia, With the softening of the paint, it takes a bit of time to find the temperature that is best, sometimes a few minutes, other times hours, I find. The different media, strip differently. And a day or two later I'm often stripping differently, even differently in places close to each other.

I like to bring the temperature of the paint up slowly (but changable) and I'll start scraping before the temperature is up to speed, so that I'm scraping at the coolest temp, not the hotest. Often I've had the paint soft, only to find that I've set the paint harder, with too much temp or taking too long. There can be a fine balance between heat softening and 'case hardening the paint'. Some of the plastic paints wont allow a second heating after the top coats have come of easily. It can pay to try to take all coats off at once, Skipper.

Some types of paint strip better at lower temperatures. I'm also finding with enamel over assorted stuffs(?), I can make the stuff unmovable, again too much heat, especially if one works slowly. I find some of the white primers don't scorch but the wood underneath does, this is scary.

Stripping the individual layers of paint, 'individually', seems to be the norm unfortunately and definately supports the case for 'not mixing the media' when painting and repainting a boat, if at all possible.

A sander/grinder removes difficult paint from hulls and like the heat gun, ... keep the grinder moving. Good luck.

Warren.

[ 09-23-2003, 04:57 PM: Message edited by: Wild Wassa ]

[Keith Wilson]

Here's what I do to my Proprep blades - curves somewhat exaggerated, and I think a slight crown helps even for hot scraping.

http://rogcad.com/bladetxt.jpg

I don't find the blades to be particularly hard, certainly not as hard as a grade 8 screw, much less a plane iron. They're not hard to sharpen with a file, and touching them up every five minutes or so works best for me.

[ 09-23-2003, 03:40 PM: Message edited by: Keith Wilson ]