Removing Old Paint: Blowlamp or Chemical Paint Strippers?
There are two main methods of removing old paint — burning it off with a blowlamp or using a chemical paint stripper. Both methods work by softening the paint film, making it blister and lift, so that it can be removed with a stripping knife or shave hook. In terms of time and trouble, there is not much to choose between the two methods —both are time-consuming and messy. And both methods can be dangerous if you are careless.
Using a blowlamp
First prepare the area by placing a nonflammable sheet underneath to catch scrapings (not always necessary outside) and remove extraneous flammable things from the vicinity of the flame. Keep an old washing-up liquid bottle filled with water handy just in case of a small fire. Place a ceramic tile on a horizontal surface within easy reach but well away from anything which could burn. Always stand the blowlamp on this when you are not using it. Before starting to strip, put on tough gloves— burning paint could fall on to your hands and cause a nasty burn.
After lighting the blowlamp, allow it to warm up for a few minutes before using it. Hold the blowlamp in one hand and a scraper in the other. Play the flame (which is invisible in bright sunlight) over the paint from a distance of approximately 150mm. As the paint begins to bubble, pull it off with the scraper. Two passes will probably be required to leave the surface fairly clean. Slight ridges and mottling of dried paint can be abraded off once the surface is cool.
Chemical paint strippers
Chemical paint stripping is the most versatile method of removing old paint and is particularly suitable for use on mouldings; other intricately-shaped painted surfaces, and near glass. Two different types of stripper are commonly used based on either dichloromethane (solvent strippers) or caustic soda (caustic strippers). All ‘Stint strippers may irritate the skin — if you get splashed wash the stripper off immediately and protect your eyes by wearing goggles. (Accidental splashes in the eyes should be washed out with plenty of water.) When using strippers, wear rubber or plastic gloves and old clothes. Cover up carpets and other floorcoverings well — using polythene sheets in preference to newspapers or dust sheets — and put your scrapings in an old tin rather than letting them fall on the floor.
Solvent strippers are the most common type and can be used on cellulose paint, emulsion paint and oil-based paints, though they work less well on polyurethane paints than on other gloss paints. Most are thick liquids or have a jelly-like consistency and should be applied by brush. After a few minutes the paint should start to blister. Leave it for a few more minutes and then remove it with a scraper. If you wait too long—over 10 minutes—the solvent evaporates and the blistered paint begins to dry making it difficult to remove.
Before applying a primer, all stripped areas must be washed down with water or white spirit —the container label should specify which — and allowed to dry thoroughly. Water soaking into wood can raise the grain, so stripped areas may also need rubbing down.
Caustic strippers can be purchased as a paste which is ready for use or as pellets which have to be dissolved in water first. They can be used on emulsion and oil-based paints but will not strip other cellulose paints. Caustic strippers may darken the natural colour of wood quite considerably, so you may need to use a bleach afterwards to restore the colour if you intend toit.
Usually with the paste-type caustic strippers, you have to put on a thick layer, cover it with a blanket (supplied), leave it for two to four hours and then scrape away the paste and softened paint. You can use caustic soda pellets dissolved in water as a cheap way of stripping large areas of paintwork or you can immerse objects in the solution. You may need to experiment with the strength of the caustic soda solution to ascertain optimum stripping times for different objects.
When stripping is completed, all surfaces should be washed with copious quantities of water containing a little acid — such as vinegar —and allowed to dry thoroughly before they are abraded flat and a primer is applied. Available with either aluminium oxide or tungsten carbide particles as the abrasive. Check the grades of the block and the coarseness of the particles before you buy.