Finishing Question

[Scrappile]

I am finishing a little project and not real sure about finishing process.  It is red oak.  I stained it with Watco Danish Oil.  Sprayed it with two coats, so far, with Miniwax Fast-drying Polyurethane.  Here is my question.  The instruction say to re-coat within 2 hours and if you can't, wait for 72 hours to apply another coat.  I am assuming that if I want to sand it lightly before the final coat, I need to wait the 72 hours.  Is that correct? 

[MTCowpoke22]

That's the way I've understood it. I usually try to make sure I'm going to be around the house for awhile when I start spraying poly. It usually only takes 15-20 minutes for it to set up enough for another coat. And I can do something else while waiting on it.

[oldhudson]

I'd wait.

[Scrappile]

Thanks, I agree.

[stoney]

Paul I guess that is one reason I don't use Polyurethane.   I don't like waiting that long to finish a project.   I usually use oil based stain and follow  up with light sanding then Krylon acrylic rattle can with light sanding between 2 coats.   The Krylon dries in around 10 minutes each coat unless the humidity is high.   I think it provides a nice finish.   If you haven't tried Krylon give it a try you might like it.   

[Scrappile]

Thanks Al, I have some Deft Clear,  it dries about as fast.  Maybe I will try it next time.  I have used Krylon in the past to seal decals the color in then does not run when you put them in water.  This is after printing them on a laserjet printer.  Maybe I can find it. 

[JTTHECLOCKMAN]

I too use Deft lacquer. I stain with Watco stains and let dry at least 24 hours usually 48. Top coat with about 4 to 6 coats of lacquer. If the project is large or I am doing many items with the same process I will break out the compressor and HVLP gun and spray a water base lacquer. No sanding needed between coats and a beautiful finish every time. 

[spirithorse]

Hi, Paul,
I hope not to hi-jack your thread but, I have a question along the same lines.
Why sand between coats of polyurethane at all?
I seem to have good success with a wonderful finish by applying the coats of
polyurethane, allowing it to absorb into the wood and get fiarly well dry, and then
applying additional coats. After about 3 or 4 coats, I let that dry over-night and
apply the final coat.
The instructions on the can never made sense to me that it can be re-applied
WITHIN 2 HOURS but, if you don't  re-apply that quickly let it dry for 72 hours.
That doesn't sound like quick drying to me.
God Bless! Spirithorse

[Bill WIlson]

Polyurethane does not adhere well to itself.  The manufacturer wants you to recoat within 2 hours, because that is the window within which the material will bond best to itself.  If more than 2 hours have passed, it's necessary to do a light sanding in order to provide tooth for subsequent coats to adhere to.  They recommend that you wait 72 hours, because the poly hasn't cured sufficiently to sand, before that.  Poly is somewhat unique in this way.  Other finishes, like lacquer and shellac do not have this restriction, because each new coat literally melts into the previous one, so sanding between coats isn't necessary.

[SCROLLSAW703]

what bill said. Two hours really isnt long enough between coats for the poly to dry hard enough to sand, you'll have a gummy mess, scrappie. You'll leave deep scratches in it, & your next coat will make those scratches show. Poly has to harden before you sand it in order for the next coat to adhere to it. When you sand poly, you should get a white dust from it when its dry & cured. And do not sand with any thing less than 220. most of the time, I'll go over it lightly w/220, then smooth it out with 400 or even 600, depends on the project. But I wouldn't go over 3 coats of poly. You'll have a built up look you may not want, & poly is self leveling. So spray lightly, & evenly. I don't use poly out of the rattle can. I use my hvlp sprayer to spray it. I've never had any issues.

Edited June 16, 2017 by SCROLLSAW703

[RangerJay]

Not sure about others but I have always stayed incredibly loyal - (others might say obsessive) - to my finishing products and processes.  Think that grows from the "if it ain't broke don't fix it" philosophy of life ...... and a literal fear of experimenting with something different on a piece of work that I have spent a lot of time and effort on .....

Having said that ....

My own go-to finish is Minwax semi-gloss rattle can polyurethane.

I do not adhere to the 72 hour rule.  

If I can I do work to apply at least 2 coats within a two hour(ish) window (no sanding between) - if I can't hit that window (usually because it's time to call it a night) then I wait till the work is dry and hard enough to be sandable - this is usually just overnight and is easy to determine.  To help the drying effort I have adopted the habit of turning a small fan onto the drying table as soon the finish is sprayed - I do not recall ever having to wait more than overnight (the exception to this may be when the first spray coat is applied over stain).

Sanding effort is thorough but very light. My sandpaper between coats is 220 and on the last coat I will use 400 before the final spray.

Each coat is applied with 4 passes from 4 directions. I will use between 4 and 6 coats of finish - the number dependent on the species of wood - less for closed grain (i.e. maple) more for open grain (i.e. walnut).

Not sure whether this has any great bearing on drying time - but I also keep a de-humidifier going in the shop during humid summer times - this is more for my own comfort and that of my tools - but I think I can imagine that a drier shop environment is also better for drying finishes.

Should also add that I "finish" the "finish" with a top-coat of furniture wax that has been applied with 0000 steel wool - this gives the piece a very smooth, soft lustre.

With the exception of a switch from a brush to a spray can about 5 years ago I've followed this process for decades and I do not recall there ever being any subsequent issues with the finish.  

 

Jay

Edited June 16, 2017 by RangerJay

[Bill WIlson]

I'm sure there's an element of safety built into the 72 hours figure.  The manufacturer can't know all the variables in any given application, so they probably base the recommendation on the worst case scenario.

[Scrappile]

Thanks all for the great input.  It appears I have not done anything wrong on this piece yet, but I picked up some info here that may speed up the process a little.  I hope to get time to sand it this evening, and then spray again,  maybe not, family is coming to let us have our grandson and their dog for a week.  This is the first time he has stayed with us without his mom and dad so it is going to be interesting.  I can't wait.  I'll have him shooting guns, spitting tobacco, swearing, drinking whiskey and scrolling before the week is over.... He is six and a pretty darn good little boy. 

Anyway thanks again for all your input.  I have a lot to learn about good finishing.

 

 

[stoney]

I guess I should further explain what I mean by light sanding.   What I am actually doing is knocking off any tiny dust nibs with a piece of brown paper bag which is supposed to be about the same as 800 grit sand paper.   This gives the finish a smooth satin appearance.   Seems to work well with Krylon acrylic.   Works well for me and after waiting the 24 hours for the oil based stain to dry I can complete the finishing in a very short period of time.  

Edited June 16, 2017 by stoney