Wednesday, June 10, 2009

Project Laxity

I have been lax in posting about my projects - indulging in the engineering tendency to do rather than to document. So, for a while at least, things are going to be more historical than contemporary. In February, I picked up a replacement frame for my bike and stripped it with methylene chloride and acetone in preparation for repainting it.

Before I get into describing this project: methylene chloride, and any corresponding gel- or liquid- paint stripper is nasty stuff. MINIMAL PRECAUTIONS INCLUDE: Chemical gloves: (not latex gloves, not dish-washing gloves, not leather gloves, but cloth-lined chemically resistant chemical gloves (shown below). Proper ventilation: you really should work outside. If you must work inside, work in a large area with huge fans (even for small projects). Fumes are hazardous to pets, your eyes, your brain and your home decor. Proper respiratory protection: Comfort masks won't cut it here, and dust respirators won't filter out the organic solvent fumes. You'll need to use a bona-fide paint and insecticide respirator. Decent respirators are available from the Home Despot for less than $40 and the cartridges need to be kept in an air-tight bag when not in use (they have a limited lifetime of less than 10 hours after being exposed to air). Protective clothing: When working harsh and destructive organic solvents, you'll want to wear eye protection, full sleeves, overalls and boots that you don't mind trashing. Common sense: Your work surface should be protected from the stripper gel. You should have an exit strategy in case you get gel where you weren't expecting it (like on your skin or face). Have shop towels and acetone around to clean up spills. Have a plan for how you'll dispose of the used materials (like putting your scrapings and used towels in an empty paint can and traipsing it over to your local DPW on hazardous waste collection day).

The obligatory disclaimer is that there are more environmentally-friendly ways to strip paint and enamel off of metal. You can sand-blast, use a rotary wire brush, resort to "green strippers", etc. The truth of the matter is, however, that none of these alternative methods are as fast and effective as using organic chemical stripper and trying not to breath too deeply.

Step 1: Prep your materials. I worked on my deck. I started by zip-tying a platform together from four milk crates and then affixing some 3-mil thick contractor waste bags to act as my work surface. For my stripper, I used 5f5 that contains, among other solvents, methylene chloride aka dichloromethane. I used a wire brush for both stripper application and paint removal. I used a metal container to hold the 5f5 while I applied it in small batches and a small quart paint can to dispose of the paint scrapings.

Step 2. Clean the frame of any debris and remove the decals (scraping with a knife or exacto blade).

Step 3. Apply gel stripper to a portion of the frame in a thick and even coat. You can see my entire set-up in the photo.

Step 4. Wait. The directions on the stripper recommend waiting 10-15 minutes per application, but that varies with humidity, temperature, the type of paint and the base material. When the paint is ready to be scraped, it will have begun to bubble up if not slough off outright. This beautiful degeneracy is illustrated perfectly on the head-tube.

Step 5. Scrape. Use the wire brush to remove the paint. As it collects on the brush (or on the work surface) scrape it off into the waste container. As the solvent dries, the paint will re-adhere to whatever surface it happens to be on. This adhesion is fairly weak, but it makes clean-up bothersome.

Step 6. Repeat over the frame. Limit your working area to a size where you can apply the solvent, step back, breath some wholesome air, and then scrape the entire area clean before the paint re-dries.

Step 7. Clean the frame with acetone (on shop towels) to remove remnants of both the paint and the methylene chloride. I also cleaned my work area in-between applications of stripper to prevent removed paint from getting back onto the clean frame. You can see in the photo below that the frame is looking pretty good after one go-over. Methylene chloride is as effective as it is dangerous.

Step 8. Repeat as necessary. It took two applications of stripper to get my frame and fork pefectly clean. I then wiped down the frame with acetone, followed by water, and cleaned up my workspace.

Now I have a bike frame ready for primer, color and top-coat.

No comments:

Post a Comment