Basic polyurethane question

[MikeMc]

Hi All,

I am into sealing my first piece with Polyurethane.

I used Minwax pre-stain, stained with minwax natural stain and have completed my 2nd coat of polyurethane - Minwax as well.

Now, the instructions recommend that you sand with 220 grit between coats. I applied the 1st coat to 6 drawer fronts.

3-4 hours later I sanded the fronts. I started with an electric sander with 220 grit but stopped after only 1 front because it seemed like I was taking the polyurethane completely off the drawer. I hand sanded the remainder of the drawers with 220 grit and completed a 2nd coat.

The finish looks better than the 1st but has some small defects such as brush strokes, small bubbles, etc.

Now, the instructions say to use 220 grit on subsequent coats but is that what most people do when finishing? I see grit much finer than 220 being used.

Also, what type of brush or applicator do you recommend for the final coat to minimize any brush strokes on the piece?

Finally, are there any techniques you have learned to make that final coat really look great?

Thanks in advance.

[TomP]

I have been using a sponge brush to apply my finish. In between coats I have been using "000" steel wool. I also use Minwax. I had to experiment at first and found this works for me....so far.

[Clint Brickl]

Before I finished my first project by brushing on poly I watched a video on the WOOD magazine website. He went through the process of brushing on two to three coats of poly and sanding in between. He recommends "tipping off" as a final brush stroke to minimize bubbles and brush strokes. It involves holding your brush almost perpendicular to the work piece and very lightly running the brush with the grain. I did this for my first few projects with pretty good results. I have now switched to using a wipe on poly for my projects. It takes more coats to get the same built up finish, but there are no brush strokes or bubbles.

[Dave F]

You certainly can go finer than 220 if you choose to. My usual finishing routine goes as follows.

These are my steps after I apply stain, if I use a stain..

1) Seal coat of standard poly or sanding sealer. (I use standard poly if it's a dark wood like walunt).

2) Sand with 180 or 220 with ROS. I just about take all the finish off. This coat is primarlily to seal the workpiece.

3) Apply one coat of poly.

4) Sand with 220 (power or hand sand, lightly)

5) Apply one coat of poly.

6) Polish with 000 steel wool.

7) Apply one coat of poly thinned 10%.

8) Polish with 0000 steel wool.

9) Apply one coat of poly thinned 10%.

10) Polish with 0000 steel wool.

11) Thoroughly clean with lint free tack cloth.

12) Apply quality furniture paste wax and buff.

[AceHoleInOne]

I am of the opinion its best to hand sand because there is not much finish to sand in the first place. Machine sanding can be to aggressive, your goal is to avoid sanding through into stain below. Sanding the mid-coats is only to smooth and level your finish taking care of high spots and nibs. I like hand sanding (more of a wiping action) with 320 foam backed paper.

Just curious, isn't the minwax Natural a "clear" color product (just a hint of amber or oil color which is the same tone as the poly, wonder if you could of just went straight to the poly topcoat first and saved a few bucks?) Usually the finish manufacture sell the "Natural" which is their tint base, meaning thinning other stains with it or making your own stain by adding your own tint and pigments. So I'm guessing when you machine sanded the first drawer down to the stain there was no issue with removing color?

-Ace-

[BillN]

IMHO the best way to achieve a beautiful finish with poly is to make it so you can wipe it on. You can either read the following or better yet, spend the few bucks for Marc's wonderful DVD on finishing. Although I had read about wipe on finishes, Marc's video made it simple and it changed the moment of terror at the end of the building into almost a moment of pleasure thinking about how (with no great skill) I was going to make this thing into something really nice looking. Why wiping? Because you will leave no brush marks. All the books I have read on finishing say that it takes a lot of practice to get good enough with a brush to have it come out near perfect. The first time I used a wiping technique it was almost flawless and I even made few mistakes. A wiping finish will require either thinning full strength poly or buying it already thinned for wiping. In addition, adding boiled linseed oil, or its equivalent makes the finish much warmer looking. Arm-R-Seal is already thinned with oil added. However, if you want to do it yourself, try this formula - one third poly, one third mineral spirits and one third boiled linseed oil.

Take a lint free cloth - old t-shirt material is very good for this -and fold it so you have a small pad with no creases or folds showing on the part you will use for application. Charge it (dip it) into some mineral spirits first so you don't suck a whole bunch of your finish into the pad, then dip it into the finish you mixed up. Apply it in long strokes with the grain. Use a bright light at a very low angle to reveal any missed spots. Let it dry. It will dry much faster than full poly because of the extra solvent. Put your wiping rag in a sealable plastic bag so it doesn't dry out. Apply another coat in 3-6 hours. Allow the second coat to dry THEN knock off any nibs with a very light hand sanding using 400 paper that is backed with cork on a board or one of those ones with a rubber pad. Use something (I like those microfabric tack cloths) to remove all dust. You can also vacuum it off. Wipe on another coat. Repeat nib removal and tacking. After 4 or five coats you should have an acceptable finish. Remember that each coat is much thinner than full strength poly so you need more coats. The good news is you can put them on quicker due to rapid drying. After the last coat first unfold and spread your wiping pad out in a single layer and allow to dry until it is stiff. One of my acquaintances failed to do this and burned down a whole apartment building! After taking care of the rag, WALK AWAY! Leave the project alone for at least a few days and depending on where you did the finishing (temperature and humidity), maybe a couple of weeks. This gives the poly time to fully cure and become very hard. Then, and only then, go back with fine steel wool or one of those white faux steel wools and rub out the finish. Finally, if you want to make it even prettier, apply some paste wax using the steel wool. Be prepared for some serious elbow work or get a pad to put on your RO sander and buff it out.

One more tip, prefinishing. If at all possible, do as much finishing as you can while the project is dissassembled. It is far easier to make sure you get finish where it is supposed to be and not have a mess if what you are finishing does not have interior corners and the like. If you're worried about the finish screwing up the ability to have glue bond properly simply mask over (with blue tape) those areas. I tape over or stuff something into all mortises and tape all tenons if I'm not using loose tenons.

Good luck.

[TomP]

Dave

What do you thin the ploy with. I'm still in the experimental stages of finishing.

[Dave F]

Any good quality organic solvent thinner. Mineral spirits are easily available at most paint & hardware stores. I prefer to use Methyl-Ethyl-Ketone (MEK) as it's a bit "cleaner" and evaporates faster than the mixture that is mineral spirits. I've used acetone in a pinch.

Whatever you choose to use, a little goes a long way, only use it in well ventilated areas, and keep away from fire or flame. NO SMOKING!

[Lawrence Brown]

You do know that MEK is now considered quite toxic, right? It's one of those that used to be available to anyone, now it's a more-or-less controlled substance. There was a Boieng subcontractor I used to work for out here years ago machining aluminum and such. When I started, we cleaned everything with the stuff. A year later it all had to change. The stuff was locked up and only the shift foreman had the key. My mother worked for 3M making sandpaper belts, and she told me about when they went through the same thing. (Other college kids got care packages of cookies. I got sandpaper belts and scotchbright pads!)

I agree though that the MEK is an awesome solvent. Nothing we switched over to after that worked nearly as well and always left a film. Just be sure you're wearing gloves and not breathing the stuff. Just for funzies, have a look at the MSDN:

MEK

Of course MSDN's make everything sound like it's gonna kill you tomorrow, but I like the part about it being a nerve toxin and mutagen

Then again, in high school I used to take the old chemicals from the science lab and burn them because we lived in the country and had a burning barrel and the teacher lived in town. Made some pretty clouds

[Dave F]

Thanks.. A bit about my background...

BS in Biology/BS in Chemisty, Illinois State Univ, '85.

MS in Biochemistry, U of Chicago, '89.

20+ years in lab work..

[MikeMc]

You do know that MEK is now considered quite toxic, right? It's one of those that used to be available to anyone, now it's a more-or-less controlled substance. There was a Boieng subcontractor I used to work for out here years ago machining aluminum and such. When I started, we cleaned everything with the stuff. A year later it all had to change. The stuff was locked up and only the shift foreman had the key. My mother worked for 3M making sandpaper belts, and she told me about when they went through the same thing. (Other college kids got care packages of cookies. I got sandpaper belts and scotchbright pads!)

I agree though that the MEK is an awesome solvent. Nothing we switched over to after that worked nearly as well and always left a film. Just be sure you're wearing gloves and not breathing the stuff. Just for funzies, have a look at the MSDN:

MEK

Of course MSDN's make everything sound like it's gonna kill you tomorrow, but I like the part about it being a nerve toxin and mutagen

Then again, in high school I used to take the old chemicals from the science lab and burn them because we lived in the country and had a burning barrel and the teacher lived in town. Made some pretty clouds

I just bought a thing of this from home depot suggested to clean the resin off my router bits..

[Lawrence Brown]

Thanks.. A bit about my background...

BS in Biology/BS in Chemisty, Illinois State Univ, '85.

MS in Biochemistry, U of Chicago, '89.

20+ years in lab work..

Cool. Well, you know what you are doing then. Yeah, I don't know how much of those changes I mentioned were the employer suddenly realizing the stuff was bad or the government saying, "we've decided you now need to do this."

[Lawrence Brown]

I just bought a thing of this from home depot suggested to clean the resin off my router bits..

Wow. Didn't think they'd have something like that. Good to know. I definitely won't argue with how good the stuff works.

[MikeMc]

Wow. Didn't think they'd have something like that. Good to know. I definitely won't argue with how good the stuff works.

I have been too concerned to try it. If it removes epoxy resin then what is it going to do to the paint on the router bits?

You can never be too sure about the advice from home depot...

[Dave F]

I wouldn't go out of my way to say that ANY of the thinners or solvents are good for you. They each have issues. Acetone is every bit as bad as MEK. Mineral Spirits is a mixture of short chain hydrocarbons such as MEK, acetone, toluene, benzene,... all sorts of nasties. That's why I like MEK better anyway, it's just MEK. With mineral spirits I feel like Mama Gump may as well have canned it "Ya never know what yer gonna get"..

In all cases I triple glove with LATEX surgical gloves prior to even opening the can. I work outside when I can or at least in the garage or shop with the doors wide open. I use latex gloves due to the fact that all of these solvents will disolve vinyl gloves in a minute or two.

Speaking as a life long woodworker and chemist, be careful with all of this stuff. We spend a lot of time and effort talking shop safety with regards to getting splinters in your eyes and chopping off appendages, but in all seriousness, finish chemicals may be some of the most dangerous things we touch on a regular basis.

Be careful out there...

[Lawrence Brown]

Aha. Thanks for the tip on the mineral spirits. I was never really sure of that one.

[TomP]

Any good quality organic solvent thinner. Mineral spirits are easily available at most paint & hardware stores. I prefer to use Methyl-Ethyl-Ketone (MEK) as it's a bit "cleaner" and evaporates faster than the mixture that is mineral spirits. I've used acetone in a pinch.

Whatever you choose to use, a little goes a long way, only use it in well ventilated areas, and keep away from fire or flame. NO SMOKING!

OK, I will stick to mineral spirits. The other makes me twing.

[Lawrence Brown]

Now we're starting to complicate things (see what happens when you don't go to WIA?), but if it's as Dave F says and mineral spirits can also contain MEK and benzene (another known carcinogen), then I guess it doesn't really matter as much. Not in the sense that the stuff isn't dangerous, but in the sense that we seem to be screwed no matter what, so just like anything else dangerous that we deal with, it comes down more to the precautions we take. I'd just follow Dave's directions of "don't get any on ya or in ya".

[Jtblckmaro]

Is oil based stain ok to be in the mix instead of BLO to add some pigment to the mixture? I've seen Norm use a poly stain mix and have been wondering.

[AceHoleInOne]

Naphtha is another choice, a little hotter than the mineral spirits, so it drys faster.

-Ace-

[jasonjarrard]

how about turpentine