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What paint should I use to paint front door? The paint would go on two surfaces: steel or aluminum (door) and frame (wood). The door appears to have been painted previously with Comex Flex Glow (Acrylic Enamel).

A colleague of mine was telling me that I should use “Sherwin Williams Emerald Urethane Trim Enamel” (https://www.sherwin-williams.com/ProductDisplay?storeId=10151&urlLangId=-1&productId=312501&urlRequestType=Base&langId=-1&catalogId=11051#data-sheet). I have painted my house and garage door with Sherwin Williams Emerald Siding Flat/Satin. I was planning to use the same paint Sherwin Williams Emerald Siding Satin to paint the door.

What is so special about Urethane? Why "Emerald Urethane Trim Enamel" would be better? Would I be able to use “Emerald Urethane Trim Enamel” on top of the Acrylic Enamel? Should I just continue with the paint I used for siding and garage door?

The world of paint is confusing... Thank you for the help!

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The world of paint is intentionally made confusing by people trying to sell you stuff. (a lot like the world of investing.)

One of their favorite tricks is taking buzzwords from better paints, and finding the minimum possible way to legally use those words in their product. Like spar varnish - it's for spars. Or Epoxy, which is 2-part by definition - as is Polyurethane -- Imron, Nason, Interlux and Awlgrip are examples of bona-fide 2-part polyurethane paints. Your car and any commercial jet is painted with it. They work because the cure happens in-situ, at full strength and without the need for air or moisture to cure.

Any 1-part paint is simply already-cured epoxy or urethane, ground up and mixed into the paint. The material is tough and does help - but not near as much as the real deal.

They won't sell you actual 2-part urethanes or epoxies because the B-part is a toxic immune system irritant until cured. It requires careful mixing and extreme "moon suit" grade protection when spraying. (brushing is safe.) They will sell you 2-part garage floor paint because nobody sprays that.

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The urethane paint contains a harder resin which should increase durability on surfaces that are touched or washed often. It's "nice" rather than essential. Most people paint the trim and siding at the same time, so a longer lasting paint on the trim just makes things look nicer towards the end of the paint's life.

"Trim Enamel" is a result of all paints being water based. At one point it was very common to do walls and siding in latex and trim in an oil based enamel, which was harder (durability again) and generally had better color. Trim enamel is telling you the paint is tailored towards accent work.

One word of caution, water based paints will not adhere to metal unless they are specifically labelled direct to metal. You should be fine because of the existing coats of paint, but if you take anything down to bare metal while preparing the surface you'll want to go over it with a primer. (Latex primers typically do adhere to metal, but it's always worth checking the directions first.)

  • Thank you Matthew. So if I understand you well, tant special paint inst really required, right? Would the special front door paint be easier to apply? How do I make sure that there are no brush mark in the end result? – Martin Jul 28 '17 at 2:11
  • The trim enamel will look a little better and be slightly more durable than the emerald siding. Exactly how much your front door contributes to curb appeal and whether that justifies a special paint is a mostly subjective question. I regret that the only actual advice I can offer on technique is that you should use a brush with synthetic bristles for latex paint. I generally find explaining how to paint similar to explaining how to ride a bike, or completely impossible. – Matthew Gauthier Jul 28 '17 at 3:05
  • @Martin the point that I think that you're missing, is that different paint is often used where a harder more durable paint surface is needed. Front doors get rubbed against by people and pets constantly, siding not so much. – Tyson Jul 28 '17 at 14:44

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