How do I prevent air bubbles when apply polyurethane on painted table?
Question:I purchase a flaw stain table. I sanded the table down, primed with bond primer in gray and painted it with latex flat black. To practice, I used water based acerlic polyurathane under the table, but it kept bubbling up. I applied with paint brush and sanded it with 220 grits sandpaper after each coat. After 3rd coat, I still have bubbles. I stired the can as directed. I didn't like the result so I decided to use min-wax satin finish fast drying spray can on 2 table leaves tops and 4 legs. Well no bubbles but it has a rough touch and uneven, no drip. I did 3 coats without sanding and within 2 hours between each coat as directed by manuf. Now I'm to afraid to do anything to the main piece table top which is the biggest piece. How do I fix the rough finish on table leaves and legs? What I should do with table top? I planned to use it as a kitchen table so I need durability. That's why I decided to use poly on top of paint. How long I need to wait to put poly after paint dry?
Answers:
Not sure why your getting those paint bubbles, did you try a non-water based poly? Also very very very important, make sure there is no dust around it will cause alot of issues. Make sure you are letting it completly dry between coats, and make sure that it is compatable with the paint you've used.
I have a lot of experience with oil based polyurethane, which is more durable than the water based, a big advantage on a table top, and have never had bubble problems. The down side though it that it cures slowly so if there is dust in the air, it will be in the finish. A little poly film tent will help.
Shaking instead of stirring can cause bubbles in types of poly. Aside from that, I have never had a bubbling problem.
It may well be in your brushing technique, and in the brush that you are using. First - purchase a brush intended for use with polyurethane or stain. This brush will NOT be cheap, however, for a few dollars more, you have a brush that could last you a lifetime with proper care. Second, ALWAYS maintain whats called a "wet" brush when applying the poly. Don't scrimp...brush from the "wet" poly you just applied to the unfinished area. Keep plenty of poly on the brush. Don't allow it to "drag" (if it drags, it's too dry). Honestly I'd use a high-gloss oil based polyuethane, it'll take the pounding that tables take much better than the water based products. Allow each coat to dry per the manufacturer's instructions on the poly can, lightly sand with #000 steel wool between coats - this will remove slight bumps, bubbles, etc. Face it - it's NOT going to be perfect but if you follow the above directions, it will look very good.
Sounds like the underside of the table was contaminated. This could be a lot of things ,from wax to bug spray( I do not know how old the table is). No finish will adhere or cure properly to a finish that some level of oil , wax or silicone. Sand thoroughly, try finishing again. The finish on the parts will probably need wet sanding with 320, then 600, to 1000, then polish with auto compound . Wipe excess completely. Polish with clean cloth. This is a lot of work unless you can handle an electric buffer. If you do it by hand, be patient, it will shine.
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