Techniques > Briefs > Exterior Paint > Selecting the Appropriate/Safest Method to Remove Paint >

Chemical Method

Ddf po fnjdsfo nof n dsjfo foef noC N fNokfs fno dj fj s jjfs sfdjjf fjk dfj d dfj gjkx;fg gzpdjg jg av j dsfjp jpd fjp fjp fdj d fjp gjapf gjap.

With the availability of effective thermal methods for total paint removal, the need for chemical methods — in the context of preparing historic exterior woodwork for repainting —becomes quite limited. Solvent-base or caustic strippers may, however, play a supplemental role in a number of situations, including:

  1. Removing paint residue from intricate decorative features, or in cracks or hard to reach areas if a heat gun has not been completely effective;
  2. Removing paint on window muntins because heat devices can easily break the glass;
  3. Removing varnish on exterior doors after all layers of paint have been removed by a heat plate/heat gun if the original varnish finish is being restored;
  4. Removing paint from detachable wooden elements such as exterior shutters, balusters, columns, and doors by dipstripping when other methods are too laborious.

Recommended Chemical Methods (Use With Extreme Caution)

Because all chemical paint removers can involve potential health and safety hazards, no wholehearted recommendations can be made from that standpoint. Commonly known as "paint removers" or "strippers," both solvent-base or caustic products are commercially available that, when poured, brushed, or sprayed on painted exterior woodwork are capable of softening several layers of paint at a time so that the resulting "sludge" — which should be remembered is nothing less than the sequence of historic paint layers — can be removed with a putty knife. Detachable wood elements such as exterior shutters can also be "dipstripped."

Solvent-base Strippers
Ddf po fnjdsfo nof n dsjfo foef noC N fNokfs fno dj fj s jjfs sfdjjf fjk dfj d dfj gjkx;fg gzpdjg jg av j dsfjp jpd fjp fjp fdj d fjp gjapf gjap.

Solvent-base Strippers: The formulas tend to vary, but generally consist of combinations of organic solvents such as methylene chloride, isopropanol, toluol, xylol, and methanol; thickeners such as methyl cellulose; and various additives such as paraffin wax used to prevent the volatile solvents from evaporating before they have time to soak through multiple layers of paint. Thus, while some solvent-base strippers are quite thin and therefore unsuitable for use on vertical surfaces, others, called "semipaste" strippers, are formulated for use on vertical surfaces or the underside of horizontal surfaces.

However, whether liquid or semipaste, there are two important points to stress when using any solventbase stripper:

First, the vapors from the organic chemicals can be highly toxic if inhaled; skin contact is equally dangerous because the solvents can be absorbed; second, many solvent-base strippers are flammable. Even though application outofdoors may somewhat mitigate health and safety hazards, a respirator with special filters for organic solvents is recommended and, of course, solven-tbase strippers should never be used around open flames, lighted cigarettes, or with steel wool around electrical outlets.

Although appearing to be the simplest for exterior use, a particular type of solvent-base stripper needs to be mentioned here because it can actually cause the most problems. Known as "water-rinsable," such products have a high proportion of methylene chloride together with emulsifiers. Although the dissolved paint can be rinsed off with water with a minimum of scraping, this ultimately creates more of a problem in cleaning up and properly disposing of the sludge. In addition, these strippers can leave a gummy residue on the wood that requires removal with solvents. Finally, water-rinsable strippers tend to raise the grain of the wood more than regular strippers.

On balance, then, the regular strippers would seem to work just as well for exterior purposes and are perhaps even better from the standpoint of proper lead sludge disposal because they must be hand 'scraped as opposed to rinsed off (a coffee can with a wire stretched across the top is one effective way to collect the sludge; when the putty knife is run across the wire, the sludge simply falls into the can. Then, when the can is filled, the wire is removed, the can capped, and the lead paint sludge disposed of according to local health regulations).

Peel Away Paint Removal System, Dumond Chemicals

Caustic strippers: Until the advent of solventbase strippers, caustic strippers were used exclusively when a chemical method was deemed appropriate for total paint removal prior to repainting or refinishing. Now, it is more difficult to find commercially prepared caustic solutions in hardware and paint stores for homeowner use with the exception of lye (caustic soda) because solvent-base strippers packaged in small quantities tend to dominate the market.

Most commercial dip stripping companies, however, continue to use variations of the caustic bath process because it is still the cheapest method available for removing paint. Generally, dip stripping should be left to professional companies because caustic solutions can dissolve skin and permanently damage eyes as well as present serious disposal problems in large quantities.

If exterior shutters or other detachable elements are being sent out (6) for stripping in a caustic solution, it is wise to see samples of the company's finished work. While some companies do a first-rate job, others can leave a residue of paint in carvings and grooves. Wooden elements may also be soaked too long so that the wood grain is raised and roughened, requiring extensive hand sanding later. In addition, assurances should be given by these companies that caustic paint removers will be neutralized with a mild acid solution or at least thoroughly rinsed with water after dipping (a caustic residue makes the wood feel slippery). If this is not done, the lye residue will cause new paint to fail.

Caustic strippers

Ddf po fnjdsfo nof n dsjfo foef noC N fNokfs fno dj fj s jjfs sfdjjf fjk dfj d dfj gjkx;fg gzpdjg jg av j dsfjp jpd fjp fjp fdj d fjp gjapf gjap.
Ddf po fnjdsfo nof n dsjfo foef noC N fNokfs fno dj fj s jjfs sfdjjf fjk dfj d dfj gjkx;fg gzpdjg jg av j dsfjp jpd fjp fjp fdj d fjp gjapf gjap. Ddf po fnjdsfo nof n dsjfo foef noC N fNokfs fno dj fj s jjfs sfdjjf fjk dfj d dfj gjkx;fg gzpdjg jg av j dsfjp jpd fjp fjp fdj d fjp gjapf gjap.

Summary of Chemical Methods

Recommended, with extreme caution: Solvent-base strippers, caustic strippers.
Applicable areas of buildings: decorative features, window muntins, doors, exterior shutters, columns, balusters, and railings.
For use on: Class III Conditions.
Health/Safety factors: Take precautions against inhaling toxic vapors; fire; eye damage; and chemical poisoning from skin contact. Dispose of lead residue properly

(6) Marking the original location of the shutter by number (either by stamping numbers into the end grain with metal numeral dies or cutting numbers into the end with a pen knife) will minimize difficulties when rehanging them.