Episode #125 of the Stack Overflow podcast is here. We talk Tilde Club and mechanical keyboards. Listen now
20

When you apply multiple coats of urethane, any dust or small flaws will be amplified with each new coat. If you want the smoothest finish possible, then wait until it is dry, very lightly sand with very fine paper (220 or finer) to remove any dust bumps, wipe it clean with a slightly damp cloth or tact rag, let it dry or buff it dry with a dry cloth, then ...


17

According to FDA regulations, the typical clear wood finishes that dry to a hard film, including polyurethane, are considered food safe. Wait to use the surface until the finish is completely dried, and clean it before allowing food contact. Polyurethane is a fine choice to use on a counter, as long as you don't use the counter as a cutting board. If you ...


13

The sanding of coats in-between is to give the new coat something to adhere to. It roughs up the surface just enough to give it a bit of grip. Multiple coats is the same as anything else. Multiple coats makes the coating thicker, stronger and more lustrous. Cars have multiple coats of paint to protect the body; you paint your walls with multiple coats to ...


12

For starters, I am going to guess you used a water based urethane instead of an oil based product? I have never seen a good oil based product react as you described to simple spills. I have seen some damage caused by very hot items being placed on a urethane finish, but normally, liquids will bead up and not penetrate the finish. Even though the water based ...


10

Surface finishes are notoriously difficult to get smooth when the process is interrupted. The glossier the finish, the harder to have sections blend. If you are talking about preliminary coats, especially if they will get a light sanding between coats, this is probably ok. For the finish coat, I would strive hard to do it all in one shot. If you simply ...


8

It's all about adhesion. When you recoat after 2 hours you get a chemical bond between layers. If you let it go longer than that, you need to wait 24 hours so it's hard enough to sand and get a mechanical bond. I sand before the final layer. That gets it smooth without danger of sanding through.


7

To elaborate a little more. When you apply a finish like poly or even paint, it doesn't just instantly go from a liquid to a solid after an hour or whatever the dry time is for the product. When it's exposed to air it slowly starts to solidify. As this happens the physical properties of the finish change. Most importantly it's workability changes. If you ...


7

I had two floors to do once and between coats I used a broom with 3 bits of fine sanding paper taped to the broom head - cheap, cheerful and effective... Also, had to punch down the floor brads (nails) so they were below the surface... Those floors came up magic but also vacuumed after sanding to remove the dust...


7

You could use a hand-held orbital- like you mentioned the biggest downside is time. But you're correct, sanding between coats of poly isn't stripping an old floor- it's just scuffing up the previous coat of poly in preparation for the next one. Even easier for this step though would probably be a pole sander- like the kind for drywall seams. Use a fine ...


6

Doesn't make any difference, really; the question is number of coats per surface, not order they're applied in. The thing to watch out for is that there will be a tendency for drips to run down the edges and onto the other face. You may want to use masking tape or other techniques to guard against that, though going with multiple thin coats rather than ...


5

I generally spray-finish when I want to have a true satin sheen. I find that it's much easier to manage the application when I'm trying for a Satin finish, even if I'm just using a rattlecan, especially for the final coat. I might just suck with a brush, but I tend to find that I leave either brush strokes, tiny bubbles, or areas of uneven thickness that ...


5

The gloss in clear finishes is reduced by flatting agents which are suspended in the clear finish. Flatting agents are tiny particles that reflect some of the light back, thereby reducing the sheen of the finish. If they settle out or are not mixed well, then the finish will be more glossy, so it's possible you did not mix the finish as well the second ...


5

Can exposure to heat in the can or while drying affect the sheen of polyurethane? No. Is there anything I can do to compensate? Yes... As a hardwood flooring installer for 4 years, I often recommended against any kind of gloss finish (It looks great at first, then it looks horrible for awhile, then it looks okay - but isn't glossy anymore). I often ...


5

There's no need to stain if you like the color as it it. Staining won't do anything for you and will just take more time. Chances are that your boards might already be pretty smooth, so I'd start with fine sandpaper (200 and above), not rough like 60 grain, except on edges that have been cut. If you use 60 grain on a surface which is already smooth you'll ...


5

When I looked into this question in the past, I reached the same conclusion as JayL, plus one additional handy rule: If I can smell the finish at all, it is not completely cured yet. So when my thinned poly coats feel cured to the touch, I lean in and take a deep breath. Usually there will still be a faint whiff that lasts up to a couple more weeks.


5

I would keep them the same if it's not too inconvenient. Different manufacturers (and even different batches from the same manufacturer) may have different drying properties (the Satin may come out differently). They may also have trouble adhering to one another which would lead to cracking between layers and may also yellow differently, producing a ...


5

First of all, I'm assuming you already sanded the surface smooth enough before you started. If you put polyurethane on a rough surface you will get a rough finish. Second, as @keshlam says, make sure there is no dust at all on the surface before you apply the finish. A slightly damp cloth can help pick up anything remaining (but make sure the wood is dry ...


5

The first coat of finish will raise the grain of the wood, so you need to sand it down with some sandpaper (220 grit or so) before you put on the next coat. This is mentioned in the directions.


5

Depends on the quality of the existing finish... if it's as flat as you want it to be, then I'd kiss it with 150 on a pole sander. Link for illustration purposes only: there are many out there... If you need to knock down blobs/ runs/ etc, then start with 120 on the handheld random orbit sander. Work your way up to 150/220. Vacuum and then wipe with a ...


4

Lots of good answers here. I was a finisher in a cabinet shop for many years and this is how used to do it. Avoid anything with silicone to get on your hands or near your wood project. It causes fish eye dimple defects in your clear coat and will ruin the finish. Such items with silicone include lubricants, water repellent sprays, etc. Wash your hands ...


4

What you're looking for is Spar Urethane. Polyurethane is not good for outdoor use. Spar urethane will hold up the UV rays better.


4

Spray foam insulation for large areas with a closed-cell foam tends to be a job performed by professionals. They will mask off the area being sprayed, and bring in a bunch of specialized equipment to do the job fast. The result doesn't require a separate vapor barrier since closed cell foam is a barrier. It does have the downside that any future repairs or ...


4

It simply means that the edge of the finished area should not be allowed to dry out, so you're not putting wet polyurethane over dry.


4

I normally would not recommend thinning urethane. If you have a new can of fresh urethane, it should be ready to go. I would try to apply it thin rather than a thicker coat. If you feel you really need to thin it, just slowly pour some in another container and add a small amount of thinner at a time. Stir it slowly and you will have no issues with air ...


4

If I may add something here: they sell polyurethane that is pre-thinned. One brand I've used is Min-wax Wipe-On Poly. It's intended to me wiped on with a rag and I've never had any issue with bubbles. This is actually all I use any more. I have not examined the cost though; it could be that this product costs more than simply buying poly along with a ...


4

The drying times on the can are usually very optimistic in my experience. They sometimes state the drying conditions the times are intended for, like 78 ºF and <20% humidity. If you are colder and/or more humid you will have to wait longer. Definitely do not sand if the finish is tacky. There's no harm in giving it extra time to dry. At this point I ...


4

I would use a dual action orbital sander and wet/dry paper @1200 grit a very wet sponge to dampen the area dont press down let the sander float and as the streaks are cut out the residue will turn milky, keep wiping and moving this high grit with water will leave a mirror finish, I have used 800 & 1000 to remove larger imperfections but the 1200 works ...


4

The following is a carry over from a CNC video I saw many moons ago, but have lost the link. Give the selected adhesive a sacrificial material on which to bond. Your thoughts of using plastic bags aren't far off, but let's add in a layer of adhesive that you can remove. If you cover the clamping boards with wide painters tape where the glue is going to ...


4

Bonding anything together without sanding either down to bare wood grain, or at least scuffing the finish surface prior to bonding, will be tenious at best. Having said that, if all you are trying to do is glue them together so one for not move, the bonded material is not weight bearing or subject to vibrations....it might work for a while. Your choice of ...


4

As Harper mentions old poly can be a problem, but poly that is not well mixed (stirred not shaken) can also be an issue. If you sand you may well have scratches but don’t strip again--you need more coats and a very fine sand paper or fine steel wool between coats for best results. I have put more than a dozen coats of poly down for a gorgeous finish. ...


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