Monday, 30 May 2011

Exterior house painting preparation.

The most important step in exterior house painting does not involve a paintbrush but rather paint scraping tools. Preparing the surface prior to painting your home will make or break your paint job. It is rarely the paint film itself that fails but rather the adhesion of the paint to the surface below (often called "substrate" in painting lingo). The reason paint fails to adhere is because the surface to which it was applied was dirty, wet or was loose itself. So making sure your paint surface is clean, dry, free from grease, oils and flaking or loose paint will give your primer and paint a good surface from which to bond. Painting the exterior of your house over a dirty or poorly prepared surface is like building a house on a bad foundation, and that's never been a good idea.

Let's review the tools you'll need to get byour house ready for a paint job that will last many years.

Difficulty level:
  • Average (Labouriuos)
Needed tools and materials:
  • Paint Scraper
  • Putty Knife
  • Sandpaper/Sanding Block
  • Stiff Brush
  • Heat Gun Paint Remover (optional)
  • Power Washer (optional)

With your home painting project you first need to work around the house before you can work on the house. So that nothing gets damaged, you need to protect surrounding landscape plantings, air conditioning units, BBQ grills and the like from cleaning agents, paint chips, paint splatters and other debris.

1. Turn off power to the air conditioner condensing unit.

2. Turn off gas to the BBQ grill and other appliances.

3. Using canvas drop cloths cover the exterior appliances, foundation plantings and other delicate plants that could be damaged. Don't use plastic tarps since they do not breathe like canvas and the plantings will swelter under the plastic sheets.

4. You may want to tie a cord around tall bushes near the house and pull the bush away from the home and stake it in the ground so the bush does not interfere with painting.


Once this is done, it's a good time to remove things affixed to the home.

1. Remove light fixtures, mailbox, shutters, decorations, etc.

2. Patch, repair and paint shutters and any other items. You'll replace these once the painting of the house body is complete.


The first step in paint surface preparation is to remove the loose paint. One method used to do this and clean the house at the same time is called "power washing." Some people love these tools and some don't. A power washer uses water from your hose and increases the water pressure as it leaves the wand to between 2,200 to 3,500 psi. In the hands of an experienced painting professional this tool can be useful. However in the hands of the inexperienced it can damage your home:

At high pressures the water jet can etch wood, even brick and blast mortar from joints.

Power washer will remove loose paint but may also lift or weaken the bond of good paint surrounding the removed loose paint.

Other issues with power washing include:

The high pressure water can soak the wall and requires time to dry out before painting.

Since the power washer does not fully remove all loose paint, the wall still needs hand scraping after the power washing and drying period.

In the end, power washing is no substitute for hand scraping.


I wish there were a way around this step but in the world of good paint preparation, removing loose paint and preparing the surface will always involve hand scraping and sanding. As mentioned earlier, even with power washing you will still have to scrape and sand to properly prepare the surface since not all loose paint is removed with a power washer.

1. Only work on removing paint and sanding when the paint is dry. There are several tools you can use including a paint scraper, putty knife, heat gun paint remover, sandpaper and sanding block.

2. To start scraping you find the weak link. Using a 6"-8" wide putty knife, find the loosest part of the peeling paint and get under it and lift and scrape.

3. Use the corner of the putty knife to dig and chip at corners of the bad paint to remove as much poorly adhered paint as possible. You can try wire brushes too, but I've found they work only on the looser paint and you need the hard edge of a scraper or putty knife to really remove loose paint.

4. A detail scraper is another scraping tool you may use to scrape away at loose paint in small detailed areas like around molding.

5. On wood siding make sure you don't gouge the wood with scraping.

6. A heat gun paint remover can be used to loosen thicker paint. Just make sure to keep the heat gun moving to avoid excessive heat build up. As the paint softens, scrape it loose with a putty knife.


Once the loose paint is scraped away and all remaining paint has good bond to the surface, the next step is to sand the surfaces where paint has been removed. It is important to feather or blend and minimize the hard edge visible at the seam of where paint has been removed and where it remains. Feathering is especially important on wood siding since siding is smoother than say a painted brick surface and surface irregularities are more noticeable on smooth siding.

1. Before sanding fill in any cracks, holes or gouges with exterior epoxy wood filler and let dry.

2. If you have large areas that need patching, either replace the wood or if it's not that serious, you can try an automotive body filler instead of wood filler.

3. With the paint scraped and the holes filled, you are ready to sand. Start with about an 80 grit sandpaper and an orbital power sander for larger areas.

4. For smaller sanding areas, a sanding block with hand sanding works well. Use about 120 grit sandpaper in these areas.

5. Sand areas smooth working to feather and eliminate all hard edges.


Once the surface is scraped and sanded and the surrounding landscape area is protected with cloth drop cloths, it's time to give your house a good washing. Cleaning the surface free of dirt, grease, loose or flaking paint is essential for the primer and paint to properly adhere to the substrate.

1. Remove your home's window screens, storm doors and storm windows and anything else that should not get painted.

2. If you have a power washer use it at the lowest pressure possible while still cleaning the surface of dirt. Use a wide spread fan tip and NEVER place the tip close to the wall surface. Remember, you can do serious damage to your exterior wall if improperly used.

3. If you're going to wash the house by hand it's worth it to get a car wash brush unit that gets attached to the garden hose to help make shorter work of this task.

4. Put on your eye protection and in a bucket mix water and trisodium phosphate (TSP) to clean the wall surface and degloss any existing paint. Be careful using TSP, it is a powerful chemical.

5. Work from the top of your house down. Rinse each section you complete with clean water.

If your house has any areas of mildew, you must kill the mildew with a mildew cleaner or make your own solution using bleach and water.


Once the house has been washed and cleaned, let the house dry. This is very important or else the paint will peel prematurely ruining the entire project. Not letting the house dry before painting is a common cause of paint failure.

If you're going to paint with latex paint, then wait at least one day. If you're using oil based paint then you need to wait at least one week before you paint. If you have used a power washer at high pressure to clean and remove loose paint, then you may have to extend these drying time recommendations depending how wet the wall surface became.

Caulk gaps around windows, doors, between siding, molding, columns, etc. If you have wood siding, look for nail heads that may be sticking up a little bit. If you find any, nail them back down using a nail countersink and putty the hole.

Once you've completed these tasks, you're now ready to paint with the confidence that you have done a professional job in paint preparation and your paint job will last many years.

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