OT-whats the secret to varnishing wood?

Rkh

Member
Decided to start putting polyeruthane on all the doors & windows-how do you keep from streaking? I used a powerful dual light so i could see better, but still get streaks once in a while where it looks like you missed covering with polyeruthane?
 
I had that same problem when I started woodworking. When I apply polyurethane with a brush, I apply the poly and then wipe it off with a clean cloth or paper towel so it doesn't have streaks. If I want a thicker coat, I apply and wipe down a second or third coat.

If I an working on a flat. horizontal surface, I often use a spray gun and can apply several coats without having to wipe off the excess (unless I really mess it up).
 
Some good tips
Natural bristle brush specifically designed for use with oil-based clear finishing products is a must.
Choose the right brush.

Use natural bristle for oil-based finishes and synthetic filament (polyester, nylon, or a blend of the two) for water-based and water-based oil-modified finishes. Don't use rollers or foam brushes?they create bubbles.
Dampen the brush with a solvent.

Your brush will be easier to clean, and will go longer between cleanings, if its bristles are dipped first in mineral spirits, if you're using an oil-based poly, or in water, if the finish is water-based. Before using the brush, rapidly roll the handle between your hands inside a cardboard box to eliminate excess.
Pour some finish into a clean container.

Working from a separate container prevents the dust and other particles picked up by the brush from contaminating the finish in the can.
Tap, don't wipe.

After dipping about one-third of the brush into the finish, gently slap it against the inside of the container. Scraping the bristles over the edge of a container leaves the brush too dry to apply a coat of the right thickness.
Always brush or wipe with the grain.

It's the best way to work the finish into the wood pores and ensure an even appearance.
 
When you say polyurethane I hope you mean you are doing interior doors. An exterior polyurethane is pretty much only available at a professional supplier. For an exterior door a marine grade spar varnish should be used.

Are the streaks brush marks? The best way to eliminate brush marks in oil based polyurethane is use some Flood Penetrol in the varnish and use as soft of a paint brush as you can find. Then apply the varnish as thin as possible with as few strokes as possible. The more you brush it the faster it sets up and the finish needs to flow together before it sets up. The Penetrol will slow down the drying time a little so it has a better chance to flow together.
 
The spots you missed are called "holidays". Or at least that's what yachtsmen call them.

There is a trick to brushing varnish. The brush needs to have enough varnish in it to ensure it is "wet"; that prevents holidays. But you need to brush lightly so you apply a very thin coat. The more varnish on the surface, the more likely you'll have runs if it's not a horizontal surface. Brush the varnish out only enough to eliminate runs.

Always sand between coats. That will give a better, smoother finish, and it will make it easier to apply subsequent coats. The sanded varnish will stand out like a sore thumb if you leave a holiday.

Here's some good information from the yachtsmen; it's intended for spar varnish, but it's applicable to urethane as well.
Varnishing tips
 
(quoted from post at 15:35:13 06/29/16) The spots you missed are called "holidays". Or at least that's what yachtsmen call them.

There is a trick to brushing varnish. The brush needs to have enough varnish in it to ensure it is "wet"; that prevents holidays. But you need to brush lightly so you apply a very thin coat. The more varnish on the surface, the more likely you'll have runs if it's not a horizontal surface. Brush the varnish out only enough to eliminate runs.

Always sand between coats. That will give a better, smoother finish, and it will make it easier to apply subsequent coats. The sanded varnish will stand out like a sore thumb if you leave a holiday.

Here's some good information from the yachtsmen; it's intended for spar varnish, but it's applicable to urethane as well.
Varnishing tips

Holidays are also the narrow strips that are missed when mowing a hay field. Having the wood sanded adequately so that the surface is uniform helps the urethane to evn out better.
 
I age used some of this newer water based stuff and yes it is hard to apply. Only good advice I can say is use a good quality brush the rest is in your technique and you will figure it out as you go. The water based stuff is great due to low odor and fast drying.

Last time I did a lot of trim I used Arm R Seal from general finishes. It's a wipe on poly and takes 3 coats to get good build but it sure saves time since it's a wipe on product.
 
Last winter I put twelve coats of urethane on a kitchen table I made. It was so frustrating trying to get the perfect flawless finish but I did win out. The proper natural bristle brush suggestion is very good advice. What I will add to that is to buy a GOOD EXPENSIVE brush that does not lose bristles, depositing them in the wet finish. For handling the holidays I looked over it very closely using a bright light and reflection immediately after brushing while the urethane was still good and wet so I could re-brush the holidays and still have it blend in. Lots of brush strokes with a wet brush is important. I sanded thoroughly with 2000 grit the next day, then put on another coat. The first couple coats were brushed with a cheaper brush that left bristles in the urethane (Grrr). Then I sprayed on six coats but I wasn't completely satisfied with the results from spraying no matter how far I thinned it. I finally did the last last four coats with a high quality bristle brush using mildly thinned urethane and ended up fairly happy with the results. This was gloss urethane over a large horizontal surface so it was a different ball game compared to semi gloss on window and door woodwork. It seemed to me thinner urethane didn't tend to have as many holidays and holidays will happen in the first or tenth coat or anywhere in between.
 
What I've learned that works very well is to cut polyurethane 50/50 with mineral spirits and apply with a sponge brush. Flood it on and scuff with 400 paper between coats. I typically use about 6 coats. I've only done this with satin finish.

Here's an article on this technique - I've found it works great!
wiping varnish
 
I use pre-hung doors. Use spray gun and mix 10-15% mineral spirits. Take doors outside, Spray the urethane on in thin coats.

One Christmas I made gifts for sister that needed urethane coat. It was about 30 degrees outside, snow on the ground, sun was shinning.

You would have to do this to believe it, but the sunlight dries the urethane in about 30 minutes, thin coats, in 30 degrees. Scuff sand if needed, usually after the first coat of two.

Windows inside a house, you will have to use the sponge idea, they do make sponge brushes.
geo.
 
The Arm R Seal has been the only wipe on I have used and I got hooked on it after a bottle was given to me for another project. For being a wipe on product and the time it saves I cannot say enough good things about it. Trim is a bear to finish with a brush especially if its already in place with the drips and runs off the brush while finishing the top (upside-down) of the window. I do remember having to watch closely for runs but if you catch them right away when things are still wet they were easy to fix.
 
That's fuuny . I didn't know that is what yachtsman call them. That is what gilders call missed spots in gold leaf size which gets used on a lot of boats. That is an old sign painter term.
 
What I was taught years ago by a finish carpenter was: 1st coat 50/50 poly/ mineral spirits, 0000 steel wool when dry, 2nd coat full poly, steel wool when dry, 3rd coat 70/30 poly/ mineral spirits steel wool, if subsequent coats are needed they are same as 3rd coat. Flows on nice, great consistent coverage. Takes time but not too much time.
Dave
 

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