Blistering and Peeling Paint Problems

Ideally, exterior paint should fail by erosion or fading to the point that it no longer looks good and therefore requires a repaint.

But, in the real world, the reason most house exteriors are repainted is probably the issue of peeling and blistering paint.

Most home owners expect the paint to eventually peel (understandably so) on an exterior wood house. Wood is tough to keep paint on because

of the expansion and contraction of the substrate and because ot the swelling that occurs with moisture / humidity uptake into the wood. Add to this the fact that wood allows moisture (in the form of vapor) from inside the house to pass through it to the exterior which causes another whole set of problems sometimes.

A lot depends on the substrate

Aluminum or vinyl sided houses that have been painted will far outlast painted wood because those substrates are more stable and do not allow moisture to pass through (this is why these materials have holes or venting slits in them). Can you keep paint from peeling on an exterior wood house? It really depends on the age of the substrate, and what type of paint was used on it. A new rough sawn wood house that has been painted with latex primer and paint will probably not peel as a rule. A older house that has a number of oil based paint coats built up on it probably will - in time.

What type of peeling is it?

Not all peeling is alike. There are quite a few causes of paint peeling and blistering. You should try to determine why the paint is failing so that you can take corrective measures to prevent or delay further problems.

Inter-coat peeling

Where the paint is peeling will tell you a lot about why it is peeling. Paint that is peeling between two coats of paint, is called "inter-coat peeling". This type of peeling tells you that the problem is with the

paint adhesion between those two coats of paint. With inter-coat peeling you will see where the paint has peeled off is exposing another color or coat of paint.The paint chips or peels that have come off need to be examined on the bottom or inner side of the paint chip. There may be two more coats over the problem coat of paint, so you must look at the inner side of the paint chip to determine which coat is not adhering to the exposed coat of paint.

Some of the more common causes of inter-coat peeling are:

1. Painting over a glossy surface.

As a rule paint does not adhere well to glossy surfaces. This is especially true with latex paint. Glossy paint does not allow the subsequent coat of paint anything to grip to resulting in poor adhesion. I don't reccommend deglossing exterior surfaces as a rule becase it is not very practical. In some circumstances deglossing is feasible, but as a rule you will need to use a "bonding primer" for glossy surfaces before applying the finish paint.

2. Painting over a chalky surface

Again, latex paint in particular has a hard time wetting or penetrating a chalky coat of old paint. The best way to prepare chalky surfaces (post 1978 homes only) is to clean the chalk off by pressure washing. If you can't do this, you can sometimes bind moderate chalk with an long drying oil based primer or by adding an oil additive called "Emulsa - bond to the first coat of your latex paint. Always do a few spot adhesion tests to be sure the primer or EB paint mix are binding the chalk and wetting through it. If not, you will still get peeling. Usually one of these two options will work, particularly for light to moderate chalk.

3. Surface contamination

This is more of a problem with metal or non porous surfaces. Sometimes there is oil contaimination that will repel the paint. Other times there may be silicone caulk smeared by a well meaning individual on the surface to prevent air or water leaking. Surface contaimination as a rule should affect isolated areas only, rather that the whole house.

4. Misc.

Some other causes of inter-coat peeling or blistering are:

Moisture blisters on a new latex film. Latex paints take a while to cure and for the paint to form a tight and complete film. This process called "coalescing" can take three or four weeks to occur. During the interim, latex paints are sensitive to high humidity and rain. Depending on what type of substrate and primer or paint that the new latex paint is applied to, often a freshly applied latex paint will form (usually small) blisters whenever exposed to high humidity (often that is every morning dew, or from rain). Usually you will find blisters in the paint that has been exposed to the high humidity, which will as the sun comes out, disappear, only to reappear upon exposure to high humidity again. This blistering cycle will diminish over the following weeks as the paint cures, and finally the paint will stop blistering altogether.

Brittle paint applied over softer more flexible paint

Particularly on the exterior where there is a lot of expansion and contraction with temperature changes, inflexible, brittle paint films can delaminate or crack over flexible films that have no problem moving with the substrate. There are different scenarios where this can happen. One instance is where an interior (only) short oil, quick drying primer (which was not intended to be used on an exterior) is used over soft flexible exterior latex paint.

Please read lead paint warning if your house was built before 1978,

Paint Problems

Peeling Paint and Paint Blisters

part one

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