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Helpful Information

Pre-Finishing Study

Primed siding is gaining in popularity for sound fundamental reasons. The USDA Forest Products Laboratory has studied and proven the damaging affects of sunlight on bare wood and its severe adverse affect on coating adhesion after only a couple of weeks of exposure. Pre-priming can realistically double or even triple the life of the coating. That means low-maintenance. This study shows how.

Type of Exterior
Wood Surface

Water-Repellent
Preservative and Oil

Semi-Transparent
Stain

Paint and Solid
Color Stain

Semi-Transparent
Acrylic

Pre-Finisher


Suitability

Expected Life
(Years)

Suitability

Expected Life
(Years)

Suitability

Expected Life
(Years)

Expected Life
(Years)

Expected Life
(Years)







Paint

Solid Color
Stain









1 Coat

2 Coats

1 Coat


2 Coats

Siding

Cedar and Redwood

Smooth (vertical grain)

High

1-2

Moderate

2-4

High

4-6

---

3-5

3-5

10-15

Roughsawn

High

2-3

High

5-8

Moderate

5-7

---

5-7

5-7

15

Pine, Fir, Spruce

Smooth (flat-grained)

High

1-2

Low

2-3

Moderate

3-5

7-10

3-4

5

10-15

Rough (flat-grained)

High

2-3

High

4-7

Moderate

4-6

8-10

5-7

5-7

10-15

Shingles

Sawn

High

2-3

High

4-8

Moderate

3-5

---

3-4

4

10-15

Split

High

1-2

High

4-8

---

3-5

---

3-4

4

10

Plywood (Douglas Fir and Southern Pine)

Sanded

Low

1-2

Moderate

2-4

Moderate

2-4

5-7

2-3

5

10

Textured (smooth)

Low

1-2

Moderate

2-4

Moderate

3-4

6-8

2-3

5

10

Textured (roughsawn)

Low

2-3

High

4-8

Moderate

4-6

6-8

3-5

5-7

10

Medium-Density Overlay

---

---

---

---

Excellent

6-8

8-10

5-7

5-7

10

Plywood (Cedar and Redwood)

Sanded

Low

1-2

Moderate

2-4

Moderate

2-4

6-8

2-3

5

10

Textured (smooth)

Low

1-2

Moderate

2-4

Moderate

2-4

6-8

2-3

5

10

Textured (roughsawn)

Low

2-3

High

5-8

Moderate

4-6

6-8

3-5

5-7

10

Hardboard, Medium Density

Smooth

---

---

---

---

High

4-6

8-10

3-5

---

10-15

Unfinished

---

---

---

---

High

4-6

8-10

3-5

---

10-15

Pre-Primed

---

---

---

---

High

4-6

8-10

5-7

---

10-15

Textured

---

---

---

---

---

---

---

---

---

---

Unfinished

---

---

---

---

High

4-6

8-10

3-5

---

10-15

Pre-Primed

---

---

---

---

High

4-6

8-10

5-7

---

10-15

Millwork (usually Pine)

Windows, Shutters,
Doors, Exterior Trim

High

---

Moderate

2-3

High

3-6

7-10

3-4

5

10-15

These data were compiled from the observations of many researchers. Expected life predictions are for an average location in the continental United States; expected life will vary in extreme climates or exposure (such as desert, seashore, and deep woods).

Development of mildew on surface indicates need for refinishing.

Expected life of two coats, one primer and one topcoat. Applying a second topcoat (three-coat job) will approximately double the life. Top-quality acrylic latex paints will have the best durability.

Medium-density overlay is generally painted.

Semi-transparent stains are not suitable for hardboard. Solid-color stains (acrylic latex) will perform like paints. Paints are preferred.

Two-coat systems consist of one prime (4 sides), and one topcoat of approximately five to six wet mils.

Pre-finished (KTA Tator/PPG Industries Forest Products Laboratory) (6).