Furniture, Wood and Cabinetry Finishing - Polyurethane finish troubles

Someone Help!!! I am in the process of refinishing my kitchen cabinets which are veneer finish. In the past, I had trouble with getting flat spots and brush marks with the final polyurethane finish and couldn't figure out why. A local hardware store suggested that I use a sanding sealer before applying the poly. I sanded the facing and doors clear down to the wood grain but only used course and didn't use medium or fine grit. After cleaning the surface with denatured alcohol and tac cloth I proceeded to use the sanding sealer. I did two coats and inbetween I used 220 grit paper to smooth out the finish. I noticed the problem with the finish at this point but I thought the polyurethane would smooth it out to which I was very WRONG!! It only made matters worse! I made sure that between each coat I cleaned and used a tac cloth and used a high quality brush. I seem to be getting flat spots in areas which I thought the sanding sealer was supposed to even it out. I am also getting brush marks and at night when the kitchen lights are on it shows every defect in the finish and looks terrible for the amount of time I spent doing them. Could the problem be my sanding without the medium and fine paper from the beginning and also would using a foam brush cut down on the brush marks? Thanks---Vince

Vince:

I always advise a foam brush for either polyurethane or regular varnish. Buying enough to finish a project is a small price to pay to avoid aggrevation like yours.

Now about the 'flat' spots. If you're talking about sheen are you stirring the poly thoroughly? You obviously don't put it in a shaker at the paint store, but it does need to be well stirred. Even gloss poly has some flatner in it, and this must be stirred in, or you'll get an uneven sheen - glossy in spots and dull in others.

A thorough sanding at this point to level the surface and get rid of the 'nubbies' is in order. Apply the poly with the foam brush and DON'T OVERBRUSH. When I first got in this business a kind old gentleman told me a trick about finishing with varnish, which also applies to polyurethane: "If your brush goes over the same spot more than 3 times, that's too much".

Take a door down and try your revised technique on it and let me know what happens.

--------
George T.

i agree with george.the same think happened to me i wasnt stirring the varnish..good luck

I also had some trouble with polyurethane. I found that if I put my first and second coats on with a mix of 50% poly and 50% mineral spirits I got a much better finish.the third coat was straight poly. Sanding between each coat with 220 grit sandpaper, I got a really smooth finish without brush strokes or flat spots.

I wasn't aware that you could dilute polyurethane 50/50 with mineral spirits? Is mineral spirits considered the same as paint thinner( you can tell that I'm a novice )? Thanks for your input! It's always nice to have suggestions from those who have had the same troubles at one time or another! Thanks again----Vince

Yes...I think the mineral spirits act like a thinner. I got the information from an article written by a person that refinishes furniture for a living. I found that if that first coat of poly goes on smooth, the rest go on more evenly. I keep a jar of the 50/50 mix and always use it as my first coat.

Lairmore is correct. For an oil base polyurethane mineral spirits can be used as a thinner. Mineral spirits and the product commonly labeled paint thinner are the same thing. Many products labeled as paint thinner have in parentheses right below "Paint Thinner", (Mineral Spirits).

The advantages of a thinner are:

1- The finish flows more smoothly.
2- The finish generally dries slightly faster.

The disadvantages of thinning a finish are:

1- The possibliity of runs on a vertical surface is increased.
2- The coats are thinner, so you need more applications (possibly) to build up the finish you want.

------------
George T.