Paint Incompatibility - Causes & Solutions

A common error made by novice painters is applying incompatible paints. The primary cause of this error is the application of latex paints over oil-based paints. The chemical composition of these paint types cause poor adhesion between the surfaces and can internally corrode both layers. Solving this problem requires either the complete removal of one of the paints (usually the oil-based layer) or the application of an intermediary surface such as primer.
 

Causes

Oil-based paints form a hard "shell" surface when they dry. This surface makes oil-based paints highly resistant to weathering and easy to clean. But this surface also resists the adhesive qualities of new paint. Latex paints are more pliable; they can expand and contract with changing temperatures or structural movement in the subsurface, but when latex paints do achieve good adhesion with an underlying layer of oil-based paint, the expansion and contraction of the latex paint can "pull" the less pliable, oil-based paint away from the subsurface.
 

Solutions

There are two solutions to the problem of paint incompatibility. The first is to remove one of the types of paint. Since oil-based paints are typically older and replaced by latex paint, removal involves scraping and sanding the original paint, and applying the new paint to the raw surface of the substratum. This is time-consuming process. Anyone can apply a coat of primer to the oil-based paint surface to provide far greater adhesive power between the layers and also to operate as an intermediary surface to accommodate the expansion and contraction of the latex layer.

Paint incompatibility can ruin any paint job and frustrate homeowners. Watching out for the chemical composition of different paint types can prevent this frustration. Remedying the problem after it occurs requires more effort, but is essential to a quality finish.

Primers and Finishes

Priming is essential for better adhesion, sheen uniformity, mildew control and durability. 
Select a top quality exterior paint in the color and sheen of your choice.

Substrates, Primers

Substrate: Wood 
Primer: 220 Weather Shield Ext. Alkyd Primer 
Finish Coats: 1240 Acry-Shield Exterior Flat Finish 
1245 Acry-Velvet Ext. Low Sheen Finish 
1250 Acry-Lustre Ext. Semi-Gloss Finish 
1235 Seasons Ext. 100% Acrylic Flat 
1236 Seasons Ext. 100% Acrylic Low Sheen 

Substrate: Masonry 
Primer: 239 Kel-Bond II Surface Conditioner 
Finish Coats: 1240 Acry-Shield Exterior Flat Finish 
1245 Acry-Velvet Ext. Low Sheen Finish 
1235 Seasons Ext. 100% Acrylic Flat 
1236 Seasons Ext. 100% Acrylic Low Sheen 

Substrate: Metal 
Primer: 1711 Kel-Guard Rust Inhib. Primer 
Finish Coats: 1240 Acry-Shield Exterior Flat Finish 
1245 Acry-Velvet Ext. Low Sheen Finish 
1250 Acry-Lustre Ext. Semi-Gloss Finish 
1235 Seasons Ext. 100% Acrylic Flat 
1236 Seasons Ext. 100% Acrylic Low Sheen