In vertical strokes, apply a uniform coat of primer on the metal door with a sponge roller. There are countless primer varieties available in the market. Use a primer specially manufactured for use on metal. Before the primer coat dries, brush out any sponge roller marks. Let the primer coat dry completely.
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Now you need to lay down a background coat of paint. Use latex paint instead of ordinary oil paint because latex paints have enhanced water resistant properties and will last longer in harsh climatic conditions. Generally, a yellow, tan or reddish latex paint coat is used but it is totally up to you which background colour you prefer.
Using a paint brush, apply a uniform layer of latex paint and give it time to dry. If necessary, apply a second coat of paint and let it dry before moving on to the next step.
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You need a smooth surface to apply the false graining. Using fine sandpaper, lightly sand the metal door until the paint coat you applied in the previous step is smooth.
Using a paint brush, apply a coat of gel stain on the metal door. Use gel stain instead of ordinary thin-bodied stain. Since the door stands vertically, ordinary thin-bodied stain will probably not stay and will eventually trickle down. Gel stain gives the false graining effect to the metal door.
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Create a graining pattern in the gel stain using a specialised graining tool. There are a number of graining tools available in the market which will allow you to make various graining patterns. Choose the graining tool which you think will make the best graining pattern. Wave or squiggle patterns are commonly created patterns when applying false graining to a metal door.
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Let the gel stain dry. To protect the false graining from climatic and other forms of damage, apply a mild coat of polyurethane.