There are two kinds of paint strippers: 1) solvent-based, like methylene chloride, which pose environmental, health and safety dangers, and 2) the so-called "safe" strippers based on less threatening chemicals that still require special care and handling.
WARNING! There are extreme health hazards associated with sanding and stripping lead-based paints. If there's any chance the paints you're dealing with were made before 1978, treat them as if they have lead and/or have them tested. For more information, see Lead-Based Paints in our Healthy Homes project.
Methylene Chloride Strippers
Methylene chloride strippers come in either liquid or semi-paste form. Both forms should be treated with caution and used under controlled conditions.
These strippers are caustic, so they'll burn skin and lungs. They're also flammable and not safe for ordinary disposal. With all these hazards, people still use them because they work on old finishes faster than anything else.
If you choose one of these products, make sure to work in a well-ventilated area, wear gloves, a face mask and eye protection and collect all the waste in a suitable container (metal, not plastic which the stripper will dissolve).
Using Semi-Paste Stripper
Before applying stripper, make sure the area is well-ventilated. Use eye protection, rubber gloves and don't stay exposed to the stripper's fumes. Take frequent breaks away from the area while the stripper does its work.
In semi-paste form, strippers are usually applied with an old bristle brush or foam applicator. Spread about an 1/8" thick, stripper generally dissolves the exposed layer of old finish in 5-15 minutes. Scrape away the residue and collect it in newspaper for proper disposal (see below).
NOTE: You may not want to use metal scrapers on the wood because the metal edge can gouge the soft wood fibers, leaving noticeable marks.
If you use a metal tool like a putty knife, push gently and gradually while controlling the scraper with both hands. If you're concerned about gouging, consider using stripping pads or plastic putty knives. However, they won't shave off the old stripper as well as a metal scraper
If any of the old finish remains after the first coat, another one can be applied to finish the job.
If you're removing a clear finish, you might choose a liquid stripper rather than a semi-paste. They're generally brushed on the same as a semi-paste, and the residue is removed the same way.
Using "Safe" Strippers
"Safe" strippers are often described as having no harsh chemicals, being biodegradable, water-based or environmentally friendly, but you should still take precautions when using them.
Work in a well-ventilated area with gloves and proper eye protection. Application is the same as with a methylene chloride semi-paste: brush it on thickly (about an 1/8") and allow it to work its way into the existing finish.
Remember, the residue pulled off by either "safe" or methylene stripper may contain lead-based paint, so disposal should be handled the same way.
The residue left over after stripping shouldn't be thrown into the household trash container. It's considered a household hazardous waste and must be handled accordingly.
It's best to check with your local health and safety officials about the approved method of disposal in your area. In many areas, it's recommended that the waste be placed outside to dry on old newspaper, packed and labeled in separate trash bags, then taken to an approved disposal facility.
Again, if you're not sure about disposal procedures, contact your local or county hazardous waste department or state department of environmental health.
Covering Stripper Overnight
"Safe" strippers take longer to work -- although newer products are now approaching the speed of methylene chloride. Some products can actually dry out before they've fully stripped the old finish.
Once you've spread the stripper, it's a good idea to then cover it with plastic. That keeps the stripper moist and allows it to finish the job, which sometimes takes up to 24 hours.
In many cases, much of the spent stripper and the old paint will pull off the wood when you pull off the plastic covering. It can get messy if you're not careful.
Scrape away any remaining waste with a putty knife, while avoiding gouging or denting the wood.
If you're lucky, one coat will suffice, but that's usually not the case. If any old paint remains, reapply stripper as often as needed to remove all the old finish.
Stripping Detailed Trim
Whether you're using methylene chloride or "safe" strippers, it's always a challenge removing old finish from the crevices and curved surfaces of detailed trim.
Brass bristle brushes are also useful in reaching otherwise inaccessible details, and other specialty tools (like dental instruments) can probe narrow gaps and scrape rounded surfaces clean.
As with any scraping tool, take your time and be careful not to gouge the wood or splinter any delicate details you're trying to restore.
Cleaning Stripped Wood Trim
After scraping away the stripping residue, the wood should be wiped clean with a damp rag.
TIP: Try to avoid over-wetting the wood with water because the surface fibers absorb the moisture and expand beyond their normal size, raising the wood grain and creating a surface that feels rough to the touch.
In fact, we often wipe the surface with denatured alcohol rather than water, because it evaporates quickly and keeps the grain from rising.