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Last night, I applied the third coat of General Finishes Semi-Gloss Polycrylic to a keepsake box. In retrospect, I wish I'd have used a high-gloss finish, but it's too late now. I'd really like this project to shine, so I was wondering if anybody has ever rubbed out polycrylic before. What would be the procedure for this?
Thanks!!
- Keith
Once the finish is fully cured...like a month from now...you should be able to rub it out like any other. Do note that any finish containing polyurethane is not going to rub out as nice as one without that stuff in it. Polyurethane's claim to fame is abrasion resistance and rubbing out is...abrasion. But as Steve mentions below...and I missed in my original edit of this post...satin is not going to be gloss even with rubbing out. Top coating with a gloss version may help and you might then rub that back a little to insure it's not "too shiny"...
You can get some of the way there, but rubbing out a satin finish will never get to really high gloss. The dullness of the satin finish has two (at least) components. The most important source is the surface roughness created by the flatting agent. This can be mostly dealt with by rubbing out. However, a meaningful amount of the dullness brought by the less than fully transparent nature that the flatting agent brings. This is embodied in the finish and is not susceptible to change by rubbing out. The more coats of satin (versus initial coats of gloss followed by a satin coat0 the more you are stuck with this, short of stripping and starting over.
The semi-gloss or satin looks are achieved with "stuff" being present in the material. You can buff out the surface and get a bit more reflection but the view 'through' the finish will (or should) stay "semi".
When I am building a thick film finish that is to be satin, I build with gloss or clear and then use the satin only on the final finish. This keeps a required thicker film from looking milky. On one or two coats (like over a shellac sealer) I go straight to the satin.
As I mentioned in my first post, I used a semi-gloss polycrylic. Is this close enough to satin to actually call it satin? If I apply a couple of coats of GLOSS polycrylic, like Jim mentioned, and let it cure, would I then be able to rub it out a bit?
- Keith
is polyurethane the same as polycrylic? Any substantial differences?
Thanks,
Bill
Polyurethane isn't a complete description of any finishing product, it is only one kind of resin. That resin can be used in a number of ways. What DIYers tend to see is single part oil based varnishes where usually the resin is an alkyd and polyurethane combination. So basically oil based polyurethane is just one kind of varnish, quite similar to alkyd varnishes or phenolic resin varnishes. All these varnishes can be applied in exactly the same ways with only minor differences. Single part polyurethane varnishes do tend to have more problems in adhering to certain stains and other finishes, are a little cloudy, and probably most significantly are more difficutl to rub out to an even sheen. The benefit is a small degree of extra abrasion resistance, a benefit only worth having for floors. Some tell us it is cheaper to manufacture than alkyd varnishes, but I can't confirm that.
Polycrylic is a brand name for a waterborne finish where the resin is mostly acyrlic with some polyurethane added. So waterborne finishes, with or without the addition of polyurethane are more like each other than waterborne finish with added polyurethane is to oil based polyurethane varnish.
There are also two-part finishes which use only polyurethane resin, typically by combineing a isocyanate (TDI or MDI) with a polyol to create the polurethane reaction when the parts are mixed. Most of these are suited only for professional application.
The solids that make a satin finish satin (or semi-gloss) do not affect the clarity, transparency, or color of the finish; they only affect the reflectivity of the surface. So, if you spay four coats of satin and then spray a coat of gloss over it, those solids are not at the surface, and only the gloss solids are at the surface reflecting the light. Therefore, it looks exactly the same as if you had sprayed five coats of gloss. (You can look it up or try it yourself; either way, it's true. I've done it many times.)
You don't need to "rub out" the poly to change the gloss. just sand the surface with 320 paper and apply a gloss version of the finish. The surface will take on the gloss of the final coat applied.
As Flexner has stated in his book, (page 110) a non-gloss finish is created by adding flatters to a gloss varnish. The flatters are glass clear. When the finish cures the flatters create a somewhat uneven surface that causes the light to be scattered when reflected causing the gloss to disappear. In other words it create an uneven surface.
Think about when you let a gloss finish fully dry and then sand it with 320 or 400 paper. This sanding creates a non-flat surface very similar to that created by the flatters. When you apply a fresh coat, the hills and valleys are filled with new finish. If the new finish is a gloss, the resulting the resulting finish will be a gloss.
Look it up in Flexners book and or, give it a try.
As a universal statement, I disagree that putting gloss over several coats of satin will look the same as an equal number of coats of gloss. With all due respect to Mr. Flexner, flatters may be glass clear but they do not have the same refractive index as every resin they may be used with. He may be right in certain cases where the flatter and resin do have the same refractive index, or are very, very close, but for all other cases it won't hold true. In my own work, I've seen how cloudy applying 4 or 5 layers of satin wipe on poly can be and topcoating with a layer of gloss gave me a nice glossy surface that was still cloudy underneath.
John