Furniture, Wood and Cabinetry Finishing - Polyurethane Question

Hi, I am in the final stages of finishing an aquarium stand. In most areas, it looks great, but in a few, the polyurethane has turned yellowish white instead of clear. It appears to occur in specific areas of the wood, like corners for example, an insome cases follows the patterns in the wood. Any ideas as to what the problem is? Is the only way to fix it to completely sand off the finish and start over in those areas?
Thanks,
Clay

It sounds like the wood might have to much moisture. What kind of wood are you using? Also, for your application, I think you should be using a spar poly.
Anyways, yes, the only way to fix is sand it off and re-finish. But if it's moisture it may just do it again.

Thank you. If I were to put a layer or 2 of spar poly over the poly, would that be almost as good as just using spar poly?

Spar varnish/poly is for marine or harsh enviroments. If you expect the stand to get wet [other than rare occasion] it would be better to use spar although several coats of regular poly will likely be fine.

Oil base varnish/poly always slightly yellows the surface it is applied to. I suspect you are noticing it in certain spots because it was applied heavier there. Sanding should take care of it, I doubt you would need to sand it off completely.

I just reread your post, I didn't notice the white reference the first time. White can be a moisture issue. Sand it down and wipe with paint thinner - if it looks OK while the thinner is wet it should be good to recoat.

Great. It will not get wet other than the occasional spill, so I will stick with the poly. This is the first time I have done finishing myself, and I think it looks great. I have always been a fan of unfished furniture because it is solid wood, as oppesed to all the particle board that is sold now days. It seems that even the good furniture stores use particle board in some fashion.

I have a new issue, but same general question. I am in the very final stages of finishing a desk. I put sveral coats of high gloss poly on it and it looked great. I sanded it with a 400 grit sand paper, and now it is dull and streaked, grayish in areas (I did clean off the dust). Did I sand to hard? If I put another layer of poly on, will it clear up?
Thanks

You have just taken the sheen off of it, another coat will shine it right back up.

The only time you really want to sand over the final finish is when you want to tone down the gloss, maybe give it a hand rubbed finish. I would suggest repainting with a thin coat of poly and call it done.

Thanks for the replies, I will give it another coat tonight. What kind of brush do you all recomend for putting the poly on? I have been using cheap bristle brushes from Home Depot, and see pretty good results, except some bristles fall off. Do you all use better / more expensive brushes? If so, what is the best method for cleaning them?

Quality brushes are always easier to use than the cheap ones. It is always best to use a natural bristle [either white or black/china] with oil base paint.
All bristle brushes will shed a little but the cheaper ones may be worse. I always take a new brush and work the bristles around with my fingers which usually works loose any unglued bristles.

You always clean the brushes with the recomended thinner. With oil base this would be mineral spirits or paint thinner. You can also use kerosene or even gas in a pinch. After raking all the excess paint from the brush pour some thinner in a work pot/bucket and work the thinner through the brush. If there is any dried paint [or just stubborn] on the brush a wire brush is used to both clean this and comb the bristles in the correct direction. It usually takes 3-4 rinses, each with clean thinner, to get the brush clean.

Okay, thanks for the replies. Now 1 more question. I notice in the polyurethane that it appears that certain areas of polyurathane are a little bit thicker than in other areas / or it appears that there are brush marks in the poly. How is poly applied so that this does not occur? Is it possible to use a paint roller? Thanks

Poly can be rolled but you would either need to 'tip out' [with a brush] over the rolled poly [to eliminate the roller stipple] or live with the orange peel.

Poly should always be applied evenly. It sounds like you are applying more material in some spots and less in others. It may be benificial to thin the poly slightly. No matter what type of paint/poly you apply it always looks best if applied evenly. You should paint 1 section at a time - 1 side, top , panel etc.