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bubbles - how can I fix it?

Posted by rosegarden3 (My Page) on
Sun, Oct 7, 07 at 19:43

Ok I did a search and could not find anything on what to do. So if this has been answered before I'm sorry.

I bought a solid oak table with 4 chairs at a yard sale. The table and chairs are large and solid. The table top was beat up and scratched but the rest of it looks great. So I just wanted to refinish the top. I striped it and sanded starting with 80 and went through to 220. I used minwax stain thankfully it matched great. So then I used minwax poly. I put the first coat on and got a few bubbles, after I sanded it looked good. The second coat I got lots of bubbles. I stirred very slowly, used a natural bristle brush(as the can recommend a natural brush or a sponge brush) I got lots of bubbles so I switched to a foam brush and still got lots of bubbles. So now I have 2 coats of poly on and lots of bubbles. Is there any thing I can do to fix this without striping it down and starting over?

Thanks
Rose


Follow-Up Postings:

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RE: bubbles - how can I fix it?

Sand the bubbles out---poly is not repairable, it has to be replaced.

Now, get a really good brush---I prefer Purdy brand. Get a man made bristle model in a 3" width---that is a good all around size. The more you overbrush poly---the more problems---like bubbles and thin spots.

Application procedures differ for oil based poly and water based poly. You can use the same brush for either. Water based is easier to apply smoothly as it is less viscous, you can apply it in large areas ---oil based is thicker and must be applied in smaller amounts and smaller areas.

Never use more than one inch of the bristles of the brush, and watch the surface to make sure you get complete coverage---you can brush over a spot several times and leave bare spots.

The trick to applying poly is to do so at relatively high temperatures---80 to 90 degrees, this allows the poly to flow better. Use a minimum of brush strokes---no more than three passes over any area---slower strokes is better for coverage---don't worry about a few ridges, at 80 degrees, poly will self level. The last(third) stroke in an area should be from new to previous coverage---that blends the new to the old better as you lift the brush to end.


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RE: bubbles - how can I fix it?

thank you! what grit sand paper do I use, 220?


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RE: bubbles - how can I fix it?

Depends on what sander---220 is ok for hand sanding. 150 for power sanding(NOT a belt sander!!!!!!!)---but DO NOT press down on the sander. 220 with power sanders---random orbit or 1/4 sheet finish sanders---will clog up rapidly and cause big scratches.


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RE: bubbles - how can I fix it?

Suggest also you brush slowly: let it flow from the brush. Applying fast always seems to make more bubbles. Make sure after stirring the can that there are no bubbles before applying too. If using oil-based poly I have found it useful to cut it by 1/3 turpentine (real turpentine, not paint thinner). I feel the body is too heavy otherwise. Brushes more easily, dries faster, levels faster, reducing the temptation to overbrush to smooth out. I don't care if I have to add more coats if the result is smoother and dries faster. Not with varnish, just oil poly.


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RE: bubbles - how can I fix it?

Practice on some scrap wood.
It sounds like you may be 'scrubbing' the finish on.
Clear finishes are usually put down with a single brush stroke in one direction.
You do not go back over the previous area.


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RE: bubbles - how can I fix it?

Depending on what type poly it is... water based or oil based.. you can sometimes cure the bubbles with a heat gun. A hair dryer isn't hot enough and a torch is a bit dangerous, but a heat gun usually works. It expands the bubbles and they break. I've used this on furniture and floors a few times so I know it works.

In your case though, I'm sure the poly is dry. And so as has been said, sanding is your only choice. Just have a heat gun handy when you reapply the poly. :)


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RE: bubbles - how can I fix it?

I have a quaestion on your original prep sanding. Did you use 80 grit and go directly to 220? If so some of the bubble issues you are having is caused by voids in the wood fiber. I have done a lot of production work and found that bubbles are also common in sealer stages even if you are using a spray gun. The sand proceedure I would recommend if you start with an 80 grit is go to 120, 150, 180 then 220. If the surface area is small enough do the sanding by hand. If not then a hand sander is fine and go from 80 grit to 120 to 180 then to 220. Typicly production will follow the same proceedure. Another trick is to use a sealer with about a 10% reduction with either solvent or water depending on the system you use. If you use a solvent to reduce the material, check the label on the side of the can, there you will find a list of components used to make the product. Select the predominant solvent (i.e. Miniral Spirits, VM&P Naptha, Xylol or Lacquer Thinner. The purpose of additional solvents in the sealer stage or first coat, is to allow the base coat to absorb into the fibers of the wood and allow the air to escape. Another issue with bubble of foaming is that the product is trapping air due to the application method, again a 5 to 10% reduction should eliminate the problem. I hope this offers some additional information.


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