Removing exterior paint or stain is an important step before applying new coats of paint to the exterior of your home.  If you don’t remove problem areas where the old paint is failing, the new coat of paint will fail as well.  Top coats of paint are only as good as the undercoat or primer attached to the siding substrate.  You should also clean the surface to remove the chalky build up caused from deteriorating paint, dirt and pollution.  If the surface isn’t clean and mold free the new paint won’t adhere properly.

Identify cause for paint failure

Before going through the steps of paint preparation you need to figure out why your paint is peeling.  There are many factors leading to paint failure such as interior moisture migrating through the walls and breaking down the paint bond from within.  Another reason could be poor flashing installation around windows and doors causing moisture to feed behind the siding.  If these issues are not addressed it doesn’t matter how good the preparation is because the new paint will also fail.

Determining your causes for paint failure is an important step before deciding your restoration process.  You don’t want to spend thousands of dollars on a new paint job only to find out there are other issues at play causing your paint problems.

If you’ve determined your paint is failing because of poor preparation or product failure then removal and preparation of the surface will be sufficient before applying a new coat of paint. The following will describe some of the methods available and the methods we use as House painters in Minneapolis and St Paul.

The video below demonstrates the method we use 95% of the time for exterior paint preparation.  This method is also mentioned below in the “sanding and scraping” method.

Methods for paint removal

Thermal paint removal

Thermal methods are excellent for removing multiple layers of paint.  If the previous paint is peeling, cracking or alligatoring removal by use of thermal methods is often times the best choice.  The procedure for removing paint is fairly simple; heat the paint till it bubbles and scrape it away.  While you’re scaping away the paint move your heat source to the next area.  When using thermal methods for paint removal you’ll want to wear protective gloves, eye wear and a respirator.  You will also want to cover the ground with plastic to contain the removed paint.  Here are some common thermal paint removal methods:

1. Blow torch  – Using a blow torch has the advantage of speed and mobility but it’s dangerous and not recommended for any situation.  Old siding along with interior walls containing insulation, debris, etc. are highly combustible.  These materials can smolder for hours before an actual flame becomes present.
2. Heat gun –  Heat guns range in temperature from 200 °F to 1400 °F.  The ideal temperature range for removing paint with a heat gun is between 500 – 800 °F.  Temperatures over 1000 °F will vaporize the paint and it will also increase the chances of the siding starting on fire.  When removing lead based paint it is even more important to maintain temperatures of  500 – 800 °F in order to avoid harmful lead based vapors. Heat guns are most useful in removing paint on smaller intricate wood work such as trim and molding.  It is less useful in tackling large bodies of work such as siding.
3. Infrared heaters – Infrared heaters operate at temperatures between 350 – 600 °F.  The infrared heat will permeate through the top coat into the sub-coats making paint removal much easier and safer than other thermal methods.  If you’re removing lead based paint you have a significant cushion of 400 °F before you reach the 1000 °F when the paint will start to vaporize.  The other benefit to this system is the lead paint is removed in chunks and held in the paint chip vs abrasive methods which create fine dust.  Any paint removal method is going to be slow but if you’re removing multiple layers of paint on large bodies of siding, this is one of the better methods.  The Speedheater is an infrared heater developed in 2002 and sells for $499.00.  The manufacturer has a kit with supplies such as scrapers and ladder holders which aid in the removal process.  Or, if you’d like to save a little money you can build your own ceramic infrared heater for around $125.00.
4. Electric heat plate – Operates at temperatures between 500 – 800 °F.  This method can also be used successfully to remove paint on large areas but has become less popular with the introduction of infrared heaters.

Chemical paint strippers

The idea behind a paint stripper is the active ingredient penetrates the paint film causing it to swell, releasing it from the substrate. There are many different chemical ingredients used for paint stripping, some more dangerous than others.  You should always wear protective eye wear, clothing, gloves and respirator when using caustic or methylene strippers.  If Methylene or caustic stripping chemicals come in contact with your skin it will burn and cause sores.  Make sure you rinse with water as soon as possible if this happens.  Chemical stripping is messy and a safety concern so its not our preferred method for paint removal but that’s not to say others haven’t found them to be effective.

• One product worth noting is ready strip due to the fact that it’s environmentally friendly, biodegradable, non-flammable, odor free and cleans up with water.  The chemical make-up which cause most strippers to be hazardous is methylene chloride or caustic.  This stripper contains neither.  We recommend applying this product on a small test area before committing and buying it for an entire project.
• Another product worth mentioning is RemovAll.  Our company hasn’t used this product but others have found it to be successful at paint removal.  RemovAll is appealing to our company because you can spray it with an airless sprayer and its non-toxic.  It has a higher dwell time then methylene strippers but the safety benefits and speed of application make it a product we’d like to try.

Typically, we use chemical strippers to remove clear coats on furniture or woodwork followed by sanding.  They seem to work well when removing single coats of varnish or paint.  We haven’t found them to be consistently effective when removing multiple layers of oil and latex paint despite claims made by the manufacturer.  Estimating project costs for a homeowner is difficult without a measurement of consistency so that is why stripping is not our preferred method for paint removal.

Abrasive – sanding, shavers, scraping

For exterior paint preparation, scraping followed by sanding is one of the more commonly used methods by our Minnesota painting company.  Entire paint removal is not necessary in most cases so scraping and sanding is the most cost effective solution for prepping the surface.  You can also use paint shavers if you’re planning on removing all of the exterior paint at fairly high sq foot per hour.

1. Sanding/scraping – We use scrapers followed by orbital sanders to remove paint and feather sand the edges where the paint is peeling.  We don’t use this system for total paint removal but this system works excellent for prepping spotty areas followed up with peel bond or a good oil based primer on the exposed wood.  This system should only be used if the current paint thickness is less than 15 – 20 mils.  If the paint is above 15-20 mils in thickness additional coats of paint will result in alligatoring because the undercoats are hard and don’t flex with the siding.  With age and oil based paints, the undercoat will become brittle and break (alligatoring) as the siding expands.  When the undercoat fails the top coat fails as well.  In addition, if you use this method on thicker paint you will see a clear definition between the sanded area and the area where the old paint isn’t removed.

1. Shavers – Paint shavers remove layers of paint much like a plainer removes thin layers of wood.  Shavers don’t use pads of sandpaper which can clog easily from paint but instead use carbide blades cutting through the paint.  After a couple passes with a shaver the surface should be lightly sanded with 80 grit paper because shavers tend to leave the wood frayed.  Paint shavers really only work on non patterned siding like clap board.  Any texture to the siding will be destroyed if you are trying to remove paint with a shaver.  Nails should be set prior to using a shaver because the carbide blades will rip the nail head off or tear the nail right out. We’ve found the paint shaver pro to be one of the quicker methods for paint removal on smooth surfaced siding like clap board.  Another shaver we haven’t used but heard good things about is the metabo paint remover.  Either system will have the ability to attach a HEPA vacuum to the unit aiding in disposal of lead dust.  Keep in mind, not all dust is contained in this system and a HEPA respirator should be used when removing lead paint.  Benefits of shavers are their speed.  Negatives are their inability to be completely dustless in lead removal, inability to perform on patterned siding and the loud noise caused from the machine.

Blast Media

Our company doesn’t use blast media for paint removal.  However, in keeping with the theme of this post we figured it would be good to talk about blast media as a method for paint removal.  Keep in mind, this information is based on research and not actual experience using these materials.  With that said, blast media comes in several different forms from highly abrasive steel grit to less abrasive dry ice, corn cob, walnut shell media.  Most blast media is not recommended for use on a wood substrate, especially for historical restoration because it will leave the surface marred.  I’ll be talking about the less abrasive and relatively new method of dry ice blasting.

• Dry ice blasting is a delicate blast media which can be effective at removing thinner layers of paint.  Depending on the bond between the paint and the substrate dry ice has the capability of removing paint up to 300 sq ft per hour.  However, it doesn’t look to be as effective in removing thicker layers of paint or paint that’s adhered to surfaces with a high degree of porosity.  Dry ice blasting works by freezing the paint extremely fast causing it to shrink and release from the substrate.  Once the dry ice hits the substrate it turns into a gas upon impact releasing a wave of kinetic energy.  The kinetic energy forces the paint off the surface.  The benefit to dry ice blasting is you don’t have chemicals or other blasting medias to dispose of along with the paint you are removing.  Manufacturers state dry ice blasters can remove lead based paint.  However, I am not sure how the lead based paint can be contained cost effectively since the “blasting” affect clearly blows the paint everywhere.  Dry ice blasters range in price from $15,000 to $25,000.  Previously owned units are available as well as rental units.

The appeal to dry ice blasting is it removes the paint from underneath.  Abrasive medias like sand, corn cob and walnut, chip away from layer to layer until the substrate is exposed and will continue to chip away at softer substrates after the paint is removed.  Like anything blast media takes experience so the use of abrasive methods like corn cob and walnut can be effective for preparing wood for stain or paint, especially to prepare log siding.  From our research, abrasive media tends to work better on harder substrates like metal.

Pick your tool and clean

All of these methods for paint removal and preparation should be considered as tools in your tool bag.  Choose the best method that considers the following:

• Number of layers of paint your removing
• Type of paint your removing
• The substrate you’re removing paint from
• Cost of removal
• Safety concerns
• Extent of paint failure

It’s important the surface is clean, dull and dry before the paint is applied.  Once the paint has been removed the surface should be cleaned to remove dust, chalky build up, dirt and pollution.  We use a pressure washer in combination with solvents to clean the surface.  For especially difficult to remove chalky build up we may prime with oil or use an additive like EmulsaBond.  Latex paint won’t adhere well to chalky build up.  Slow drying oil primers are able to penetrate the chalk and form a bond to the undercoat.