Tiny Bubbles

[smallboatshop]

Lately during painting, I've had problems with tiny bubbles that do not go away, leaving the smooth surface with a fairly even distribution of these sand-grain size bubbles. I use roller and tip method with foam roller and have tried both bristle and foam brushes for tipping. I have also adjusted the viscosity of the paint with the thinner appropriate to the brand ( have tried both Kirby and Epifanes).

Any suggestions?

Dan

 

[Douglas Ingram]

What is your situation regarding dust? Dust is the enemy. Track down any possible source of dust, surface, air, brush, paint.

Are the bubbles evenly distributed over the surface, or in spots? Are the actually bubbles? or particulate?

Try another paint using the same technique. It doesn't have to be on the canoe, but it can help determine whether its your tools, technique, or the paint as the source.

It could also be due to the cooler weather. Cold makes the paint more viscous, thus not allowing air bubbles to break the surface tension of the paint.

 

[smallboatshop]

Thanks for your reply, Doug. I have pretty much narrowed the problem to bubbles which I can break with a bristle from the brush. And I've tried different paint so it must be my technique. Temp in the shop is in the 60's.

I have no curtians (sags), no holidays and no orange peel so the self leveling seems under control; but I do have these rotten little bubbles that are driving me crazy. What am I doing wrong??

 

[Douglas Ingram]

How was the paint mixed prior to using it? How long did it sit between mixing and use? If the paint was aggressively mixed, was cool, and used right away, that could be your answer. I always like to warm the shop up some before painting, enough that the canoe and the paint is warm. 20C minimum, 25C is better.

Sorry, I have no clue what that is in F.

BTW, nice shop.

 

[Kathryn Klos]

20C= 68F

25C= 77F

Toasty, compared to what it is outside here now!

 

[garypete]

Heat Paint to Eliminate Bubbles

I learned long ago from an expert varnisher to heat varnish before applying. The same seems to apply to paint.

Your shop must be 70 F or warmer, as must the object you're painting. The best heat source I've found is the warmer plate from a Mister Coffee or similar coffee maker. My Mister Coffee warmer plate fits a quart can perfectly.

Heat the can until the liquid is warm to the touch but you can still hold the can comfortably with a bare hand. At that temperature, flow-out is even and without runs on horizontal surfaces. You'll need to brush the paint a little thinner on vertical surfaces as the warm paint is less viscous and will run with a heavy coat.

Enjoy.

Gary

 

[MikeCav]

Let me ask an off the wall question, Dan. Have you recently switched sandpaper brands or used a drycoat rust preventative on any of the tools near your painting area? I'm wondering about contamination.

 

[garypete]

Silicone contamination

As Mike suggested, your problem may be contamination of your shop with minute particles of silicone.

This silicone contamination often occurs if you have sprayed WD-40 in your shop in the recent past. The contamination shows up as "fisheye" spots in paint or varnish applied in the same room. It's especially noticeable when you are using a spray gun to apply paint or varnish.

I formerly used WD-40 as a blade lubricant on days when I was ripping cedar strips on my table saw. When I started to get fisheye sprayed finishes, I asked questions on an automotive-painting website and found out about the problem I had caused by spraying silicone-containing WD-40 in my shop.

A good spring cleaning of the shop and time cured the problem. I now use a stick blade lubricant on my table saw blade on ripping days. Works great, no silicone.

This still doesn't explain why you're getting actual air bubbles in paint that are large enough to puncture with a paint brush.

Gary

 

[Dan Miller]

As Mike suggested, your problem may be contamination of your shop with minute particles of silicone.

This might be true....

caused by spraying silicone-containing WD-40 in my shop.

This is not true. WD40 does not contain silicone.

 

[smallboatshop]

I found a lot of information on the web about fish eyes. One interesting point is that the paint additive to prevent fish eye inhibits the adhesion of the paint. There was also a site that talked about causes of fish eye and besides the silicone there were other oils including workers who were snacking on chips and transferring the oil to the work.
I painted a piece of mirror on the bench in the shop and then took into the house when dry and looked at the dots through a jewelers loop. Sure enough there was a dot of light at the center/top of each dot.
I am still looking for the source of this contamination.

 

[Todd Bradshaw]

Sand-grain-sized sounds a lot more like bubbles to me than fish-eyes. Bubbles during roll-and-tip painting are caused by the roller and it's the job of the tipping brush to remove them. Cold temps, the wrong brush or inadequate tipping can leave them on the surface. Some paints also flow out better than others. Assuming that there is nothing (air, solvent fumes, etc.) bleeding out of the surface and lifting the paint after application, the bubbles are present after rolling and simply not being removed.

Fish-eyes are usually larger than sand grains and generally form after you've already passed that portion of the hull in the painting process - sometimes five to ten minutes later. What originally looked like a perfectly fine roll-and-tip job suddenly begins to show small round gaps where the paint has parted and flowed away, leaving a hole in the paint coverage.

Another factor can be the grit used to prep the surface. Most enamel manufacturers specify sanding the surface to a grit range of 80-120, which is smooth enough to provide a good base, but which has enough tooth for the paint to bond properly and perform as it's supposed to. Some builders sand to a much finer grit in an effort to get a perfectly smooth hull and it's generally a mistake. The adhesion of the paint is reduced and it can also make for application and coverage problems.

 

[garypete]

[/QUOTE]Another factor can be the grit used to prep the surface. Most enamel manufacturers specify sanding the surface to a grit range of 80-120, which is smooth enough to provide a good base, but which has enough tooth for the paint to bond properly and perform as it's supposed to. Some builders sand to a much finer grit in an effort to get a perfectly smooth hull and it's generally a mistake. The adhesion of the paint is reduced and it can also make for application and coverage problems.[/QUOTE]

Todd, I'm exonerated from Sanding Guilt! Thank you!

As I age further on the wrong side of 50-years-old, I find I have less patience with my former tedious sanding regimen of 60-100-150-220 grit preparation before paint. So I've been shortcutting and stopping at 100 grit...and feeling lazy. But it seems like I get just as good or even better results with less sanding. I was feeling guilty for not sanding finely enough, but I now see it wasn't laziness but rather accidentally doing the right thing.

My Sanding Guilt is gone and I'm a free man again!

Gary

 

[Todd Bradshaw]

I generally sand to 100 grit on the random orbit, wash the hull with water, let it dry and paint. This is Interlux Brightside enamel rolled and tipped-out in my driveway, scotchbrighted between coats. No thinner, Penetrol, or other additive was used - it's straight out of the can. By the time this photo was taken, the paint had already been on for two years and the boat had been out on a mooring for a full season. It was back for spring clean-up and to touch up some scratches on the bow caused by bumping the mooring buoy.

 

[Jpatten]

I painted a jeep with a foam roller and rustoleum paint and had the same problem with bubbles. I found that if I thinned the paint to almost water consistency the bubbles would settle out after about 5-10 minutes of being rolled on. Making the paint this thin means that you have to put on about twice the coats of paint that you would normally do but it works great. By the way you don't need to tip it with a brush after you roller it. The paint being this thin ends up settling out very smooth. One thing to be careful of is painting the sides of the canoe/vertical surfaces. Need to be thin coats so it doesn't run.

Have not had the chance to try it out with a canoe or Kirby paint yet but I would assume that it would work very similar.

 

[Pete Mathews]

One way to determine if you have bubbles or contamination is to spread a small amount of the paint or varnish on a piece of glass. This can be done in the house (away from dust) and even dried in an oven at a low temperature. Once dry you should be able to tell by looking at either the front or back if it's dust or bubbles.
Mixing a little recommended thinner does help if it's bubbles. It's best to stick with the manufacturers recommended solvent, and rate of dilution. Penetrol can be used in most marine paints.
"Fish Eyes" can identified by what looks like a small dot in the center with the paint drawn away from it to form a crater like appearance. This is usually caused by surface contamination. Check to make sure the adhesive used to bond the grit to the paper isn't a silicone base. Some aluminum oxide sandpapers can cause this problem. They can leave silicone particles on the surface. Also pressing too hard with a tack cloth can do this, but if you're experiencing it over a large area it's probably not that. If you've tried several different brushes and rollers as mentioned, I'd look first at particulate matter in the air (what's changed recently?) or surface contamination (any new products introduced lately?) It is possible that you've gotten a can of paint or varnish with contamination supplied by the factory: It does happen. On occasion some weird chemical things happen which will cause the paint/varnish to from particles in can after being filled. This too is also rare, but does happen. The painted glass will indicate that.
The sanding grit shouldn't really have any influence on bubbles or contamination as long as good cleaning practices are used. The grit will effect gloss and adhesion of course.

 

[smallboatshop]

" Check to make sure the adhesive used to bond the grit to the paper isn't a silicone base. Some aluminum oxide sandpapers can cause this problem. They can leave silicone particles on the surface."

Hi Pete, Thanks for your input and to all who have contributed to this thread. I do use 3m sandpaper which their website describes:
"3M™ Wetordry Tri-M-ite Sheet, 9 in x 11 in

Use wet or dry for sanding old finishes, fine featheredging plus surface work. It is a silicon carbide, closed coat product bonded with a waterproof resin."

Could this be a source of contamination? What do others use?
Dan

 

[Dan Miller]

Silicon and silicone are not the same thing. Silicone happens to have the element silicon in it, but then, so does traditional canvas filler.

 

[Pete Mathews]

About the silicon/silicone issue:
I've never heard of a silicon carbide paper causing problems or 3M Tri-M-ite specifically either for that matter. That doesn't mean it couldn't happen. All it would take would be the manufacturer to change the manufacturing process slightly to possibly cause somthing like that to happen.
Silicone, on the other hand, is finding it's way into a great many products these days, from cleaners and waxes to sealants (above the water line) and a myriad of other products and is death to any refinishing project that it comes in contact with it. That said, it usually causes either "fish eyes" or a "crawling" of the finish that comes in contact with it and usually would not be confused with dust or particulate matter on or in the finish.
Solving this will probably be a process of elimination, hope this has provided some.

 

[Michael Grace]

Silicon dioxide is used as an abrasive because of its regular crystaline structure- silicon dioxide or silica is sand, hence the name sandpaper. Because of its crystalline structure, its relatively inert nature, and the fact that it is polar (and so won't repel other polar or charged compounds), silica doesn’t contaminate surfaces except as dust- it does not readily adhere and interfere with subsequent coatings.

“Silicone” on the other hand, is a very different beast. It is derived from silica- through smelting with carbon, silicon dioxide (sand) is reduced to elemental silica and carbon dioxide. Elemental silica is then chemically converted into any number of silane products through combination with organic (carbohydrate-based) chemicals such as methyl chloride. These silane polymers possess properties that are very different from silica. Silicones are silicon-based polymers that are hydrophobic, which means that they do not like to interact well with water. Because silicones are long-backbone polymers with un-charged methyl side chains, they exhibit little interaction with uncharged and non-polar molecules. This means they exhibit very low surface tension. Thus, they have important functions as water repellents, antifouling agents, mold releasers, etc. (think Rain-X).

Silane-based products have a wide variety of important uses, and they are not to be terribly feared. A few molecules floating around a shop will not kill the possibility of finish coats adhering well. But treating a surface with such products prior to finishing certainly will. That said, the large size of polymeric silane molecules should prevent them from migrating into the surface of a finish, so even materials treated with these products should be renewable to accept finish coatings simply through a thorough and complete sanding.

Which brings us to sandpapers… For effective coating of surfaces, polymeric silane products like Rain-X are generally provided as molecular suspensions. Their use in sandpapers should not contaminate a surface because they are bonded in place on the sandpaper. And there is a logical marketing-based reason not to fear your sandpaper. Because sandpapers are used to prepare surfaces for finishing, a manufacturer would be committing suicide by treating their products with a transferable form of silicone.

 

[H.E.Ross]

silicone rejection

I had a run-in with silicone after I had a canoe lettered and striped by my sign painter. It is my practice to top coat this work with varnish. After completing my job I was horrified as the fish eyes began to appear. I called my sign painter and asked if he had changed paints. He assured me that it was the same paint he had been using for years (ONE SHOT). After an afternoon on the phone I finally spoke with the chemist at the factory. He informed me that the paint had been reformulated with silicone just recently. There was no indication or notice on the product however. The fix was to sand ever so carefully as to not ruin the custom striping and then recoating with varnish treated with anti-fisheye agent (silicone additive). I'm not sure if my experience will help with the problem at the start of this thread but I thought it related to the ongoing discussion.
Best-Hank