Tiiiinnny bubbles.... In my Rockhard varnish


Sorry, I know, another dining-room-table-finishing post... My question is how to best apply Behlen Rockhard tabletop varnish without leaving bubbles. Background: brand new table had some very thin coat of finish on top, over an oak veneer, which I dry-sanded with 320 grit then wiped with a tack cloth. I bought what I thought was a nice brush (china white bristle for stain/varnish), didn't shake the can, and brushed on the varnish slowly, and I still got quite a few bubbles. Most of them "settled" out and disappeared as the coat of varnish kind of spread out/flowed on the table, but several are still there. It was fairly humid, which I thought would be good to prolong drying time and allow more bubbles to pop without leaving a mark. I plan to let this dry several days, dry sand again with 320, and then add a second coat of Rockhard. Would thinning with mineral spirits help reduce bubbles on the next coat? If so, would 10-25% min spirits make a difference, or should I go for 50%? Should I apply this with a rag, thinned or unthinned? Finally, what difference does it make to wet-sand, and does that involve water or mineral spirits? Does wet-sanding help at all between coats, or only at the end? Thanks very much for your advice and opinions, Andy
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Andy,
I've not had to thin my varnish. So I don't have experience with that. The biggest point of entry for bubbles is through the brush if you haven't shaken the can. The angle of the brush while spreading the varnish is probably the main reason for the bubbles. Hold at a realatively high angle and let the varnish drain out of the brush. Don't push down on the brush to hard. The flatter the brush on the surface the more turbulance is created within the brush causing bubbles within the brush and at the tip that are released onto the surface.
What happens is most people push down harder on the brush as the brush dries out. They are trying to get the most out of the brush without going back to the bucket or can. Avoid this habit. As the varnish runs out while holding the brush high go right back to your container. Be very careful not to create bubbles by pulling the brush over the edge of the container. Instead lightly squeeze the flat brush against the side of the container.
I think you will find fewer bubbles on the surface.
The finer grade sand papers clog easier. Especially on varnish. So Wet-Dry Sand paper used with either water (my choice) or mineral spirits is the best choice. The moisture help the sandpaper stay open longer.
Good Luck in your finishing.
Roy
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Hi Roy, I hope that you don't mind an off-group query regardy your suggestion below. How to you proceed when you're dealing with a full can? I have used a clean piece of wood but it dries me nuts to lose the material to waste. TIA, Chiz

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Well now, that didn't work out at all like I planned - Ha!! Some days I've gotta wonder... about myself. Apologies to all.

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C & M wrote:

I tried his tips on the last Varnished rail I did -- worked fine -- fwiw.
I used steel wool for the abrasive between coats -- not much in the way of bubbles to knock down.
-- Will R. Jewel Boxes and Wood Art http://woodwork.pmccl.com The power of accurate observation is commonly called cynicism by those who have not got it. George Bernard Shaw
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Really, you should not use the can anyway. It is best to pour out what you think you might need into small paper bucket or plastic bucket (or cup) size depends on quantity. The reason for this is that you don't want any more then is necessary to be exposed to the air for long periods of time.
Beside that ridge on the top of the can is to tempting to use to pull off the material.
Roy
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Another source of bubbles is varnishing in a situation where the piece gets hotter after laying the varnish on. Air in the wood expands and makes bubbles. This is often a problem with work that has to be done outdoors (boats). I suppose it could happen in a shop that heats as the day progresses. Good luck. Dave
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