Prepping Door

I'm needing to reseal my front door. It has Polyurethane on it right now but i want to put on Spar Varnish since it gets a lot of sun light and when it rains it hits the door. What prep do i need to do to make sure the Varnish adheres properly. I'm not wanting to remove the stain. Thanks for any advice.

I use large amounts of both products. Poly is good for flooring but not for exterior door applications. Spar varnish is excellent for furniture and exterior doors.

I would do a deep sanding on the door (200 grit). Follow with a thorough scrub down with a fibre scrubbie (green pad) that is saturated with acetone. (use chemical gloves and do not pour the acetone on the wood directly) This removes more of the original finish and any remaining oils. Finish sand with 300 grit or finer. Rub down with tack cloth to remove remaining dust.

DO NOT shake the spar varnish. This introduces bubbles into the varnish which can transmit to the door surface. Use a dense foam brush to trail the varnish onto the surface being careful not to move so fast that it causes bubbles via cavitation. Work the length of the wet area to help remove any brush marks. Apply one light coat. Allow a day to dry sand >300 grit, tack cloth, then next coat.

I apply three coats. Here is a hint to get the varnish to lay down even better ... Heat a pot of water to tiny bubbles but NOT boiling. Just pop open the spar varnish a bit and set the can in the pot of water off the stove for a few minutes. This will heat the varnish and it will become even more fluid. Adjust your brushing technique accordingly and keep the coats light each time.

BTW ... Am installing a new walnut entry door with a sidelight today. It is unfinished so this project will be soup to nuts. Will try to take pics.

This is how it might look when done ...

Thank you for the response. I will follow those steps. How long do i need to keep the door open till i can close it between coats? Also on that door is that the satin finish.

Additional question about the varnish. I have a computer stained computer desk that i use everyday. I put poly on it few months back and its already starting to wear down in spots. Would the varnish be a stronger finish to handle everyday use?

I keep the door open as long as possible, no less than 2-3 hours. In one case, we plastic sheeted the outside of the entry and left the door cracked overnight.

I ran by Sherwin Williams to get some stain to touch a few places. They are having a big 40% off sale. I was going to get the Spar Varnish but all they had was Spar Urethane. Whats the difference between them. Should i stick with the Spar Varnish?

Want a finish that has far more UV protection then any Spar on the market?
Drys fast enough to get three coats on in one day.
Self leveling so no sanding between coats.
Then use this.
http://bristolfinish.us/
No it's not cheap but it's what pro antique boat restores have been using for many years.
It has 5 times the UV protection that Helmsman Marine Spar has.
Extreamly high build up. Hardens like glass.

The urethane product is excellent ... Here are the important steps, INCLUDING SANDING between coats ...

- Apply a thin coat of Helmsman® Spar Urethane using a high quality natural bristle brush. On unfinished wood, apply sufficient material to seal open joints, edges and end-grain.

- Let dry at least four hours, then sand entire surface lightly with very fine sandpaper (220 grit) to ensure an even finish and proper adhesion of additional coats.

- Apply second coat. If a third coat is desired, repeat previous step before applying. Note: For exterior surfaces or for previously unfinished wood, three coats are recommended.

- After final coat, allow 24 hours before normal use.

CLEANUP: For easy clean-up use mineral spirits or paint thinner.

Will the Urethane still give it that glass type appearance?

Urethane will certainly do that if you choose the gloss version. You can choose anything from that to as low as a matte finish. Here is one of a set of tables we built for a restaurant. The finish is almost mirror quality. The reflection you see in the pic is the trees above the table top. The urethane was applied with the high quality foam brush and slow application speed to minimize bubbles.