painting over stain and polyurethaned trim/doors

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Old 02-27-11, 09:14 AM
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painting over stain and polyurethaned trim/doors

What is the best way to paint over stained and polyurethaned trim and doors...what primer should I use?
 
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Old 02-27-11, 10:15 AM
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First you need to sand the poly, you don't need to sand it off, just rough it up [scuff sand] to help the primer bond. A pigmented shellac like Zinnser's BIN is best although most oil base primers will also do a good job. I'd shy away from any latex primers.

No matter which primer you use, you can top coat it with latex, oil base or waterborne enamel. I prefer the waterborne - it dries fast and hard, doesn't yellow like oil base enamel does...... but it's also the most expensive

Expect to apply 1 coat of primer and 2 coats of enamel in order to get full coverage. You may also want to caulk the joints for a nicer looking job.
 
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Old 02-27-11, 07:41 PM
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Nydiylady:

With utmost respect, I have to disagree with Marksr on this one.

I agree that you need to sand down the poly for the primer to stick better to it. But, I don't see why you need to prime over that sanded polyurethane. The only reason why paint sticks better to primer than it does to paint is because primer dries to a rougher surface than paint ('cept possibly a dead flat paint). By sanding down the polyurethane, you already have a rough surface for your paint to stick well to. Why prime over that rough polyurethane surface only to replace it with a rough primer surface. If it wuz me, I'd sand down the polyurethane, remove all the sanding dust and then paint.

Are you SURE it's polyurethane on the doors, and not varnish? If the doors are original to the house, and the house was built prior to 1956, they have to be varnished. That's because Bayer (the Aspirin people) didn't take out the patent on "urethane modified alkyd resins" (which we know as "polyurethane") until 1956. So, anything prior to that has to be varnish.

If they're varnished, then you can save yourself a lot of work by cleaning the doors with a strong solution of TSP instead of sanding them. The only reason why people clean walls with TSP prior to repainting them is because TSP dulls the gloss of true drying oil based coatings, like Linseed oil based paints or Tung Oil or Danish Oil. Real varnish is nothing more than linseed oil with dried up natural plant resins (like amber) dissolved in it. Since varnish and linseed oil based paints are chemically very similar, you can use TSP to dull the gloss of varnish as well. So, if you have some TSP handy, try cleaning the surface of the door with a strong solution of the stuff and see if it dulls the gloss. If it does then you have varnish, not polyurethane. And, cleaning with TSP is a lot easier than sanding. Rinse the TSP off well with clean water and allow plenty of time to dry before painting.

Nowdays, even some people working in paint stores will tell their customers to use TSP to clean walls painted with latex paint, and that's nonsense. TSP doesn't dull the gloss of latex paints the way it does the old linseed oil based paints. If your walls are painted with latex paint, you're better off using a half decent cleaner like Mr. Clean or Fantastik. At least then your walls will be clean when you paint over them.
 
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Old 02-28-11, 04:32 AM
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TSP like most any cleaning agent would need to be rinsed off well so there are no bonding issues with the coating that is applied over it!

You might get away without a primer if you use an alkyd enamel but I wouldn't trust a latex enamel to adhere long term to poly, varnish or shellac no matter how well it is cleaned.
 
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Old 02-28-11, 12:33 PM
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Thanks for all the great info. The house was built after 1956...does that mean it could also be varnish? How can I tell the difference between poly and varnish? Do you know if poly is toxic when released in the air?? I read that someplace. Thanks
 
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Old 02-28-11, 12:45 PM
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About when was your house built? I've painted a lot of new houses over the years and we rarely ever used poly. Varnish is easier to use and is compatible with both sanding sealer and japan drier - most polys are not. Poly dries to a harder film than varnish which also makes it harder to sand. The majority of stained woodwork in houses built from the 60s to the end of the century were coated with varnish. Shellac was mostly used before varnish became popular.

Most any solvent based coating is slightly toxic when sanded [no big worry unless you already have breathing difficulties] I've never heard of lead being used in varnish/poly but I don't know for sure
 
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Old 02-28-11, 06:53 PM
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If your house was built after 1956 it could be either poly or varnish. The easiest way to tell is to clean an inconspicuous area of the door with TSP and see if it dulls the finish. If so, it's varnish. If you change your mind about painting the doors, you can always simply dilute some polyurethane in mineral spirits, and go over any dull spots with a rag dampened with that dilute poly. Several coats will restore the gloss to it's former level.
Keep the rag wrapped tightly in a plastic bag between coats to prevent the poly from drying out between coats.

No, sanding polyurethane doesn't present any greater danger than sanding modern oil based paint.

The lead that was used in paints prior to 1974 was in the form of lead carbonate. Lead carbonate is a soft white solid that is easily ground down into a fine white powder. It is this white powder that was used as the high hiding white pigment in paints prior to 1974, and is the reason those paints were said to have "lead" in them. I'm not sure if there were other lead based pigments used in paints back then or not.

When they banned the use of lead carbonate in paint, they replaced it with titanium dioxide, which is still the high hiding white pigment used in paints today. Since varnish and polyurethane are intended to dry as clear as possible to display the beauty of the wood, they wouldn't have used lead carbonate in varnish or polyurethane because it would have turned the varnish or polyurethane white.

Lead carbonate was only banned in house paints. You can still buy lead carbonate powder and lead carbonate white paint in any artist's supply store. Just ask for "Flake White" or "Lead White".
 

Last edited by Nestor; 02-28-11 at 07:20 PM.
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Old 03-01-11, 05:00 AM
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Thanks for all the help! The house was built in 1979. Will test the doors when i buy TSP. If I decide to use the oil based primer zinnzer BIN do I have to wear a respirator?
 
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Old 03-01-11, 09:40 AM
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While Zinnser has several different oil base primers, BIN is not one of them - it's a pigmented shellac sealer which is probably the stinkiest paint/primer a homeowner is likely to ever use. A respirator isn't mandatory but it would be nice, fresh air ventilation is also a good idea. Compared to latex paint, oil base also has a good bit of odor but probably half of what the BIN does.
 
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Old 03-01-11, 07:06 PM
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ok so the zinnzer BIN would be the best to use...and an oil based primer 2nd best(less stinky) is there is one you would recommend?
 
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Old 03-02-11, 04:10 AM
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Oil base Kilz would be bare minimum. Zinnser's oil base bullseye primer would be good along with SWP's multi purpose oil base primer just to name a few.
 
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Old 03-02-11, 04:38 AM
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A rare, unexplained phenomenon: One time I used BIN on extremely dark stained trim (almost ebony); the trim had barely a coat of poly on it; The stain bled through the BIN primer slightly and through the 2 oil finish coats ugh! My 2 cents worth!

BIN is still a great friend of mine, especially for my basement walls and stains in general.
 
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Old 03-02-11, 05:01 AM
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That is odd. Only once did I have a problem with pigmented shellac not sealing a stain. That was about 40 yrs ago. There was an ink stain on a steel post, after multiple coats of primer we wound up stripping the post down to raw metal and starting over
 
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Old 03-02-11, 05:23 AM
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Fixing varnish.

We have a varnished front door I don't want to paint. There are light spots that need doctored up. How do I "fix" them? And for final finish coat do you really recommend poly or is it really better to stick with the varnish? Can I get a satin finish with the varnish product also?
 
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Old 03-02-11, 06:15 PM
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Both poly and varnish come in the 3 basic sheens; satin, semi-gloss and gloss.

Poly dries to a harder finish than varnish so it might be preferable. If it's the exterior side you need to use a spar varnish/poly. Minwax's Helmans Spar Urethane is one option for the exterior.

You'll need to lightly sand the door with 220 grit. Then wipe it down with a wet thinner rag. Pay attention to how the light spots look while wet - that's how the door will look with a fresh coat of poly. If that makes the 'spots' ok, your are good to go. Stains can be tricky to touch up so lets hope we don't have to go there although adding a little stain to the poly will often disguise those types of spots.
 
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