Woodfinishers Weblog

Wood finishing forum for professional finishers

Bubbles in the finish

The following is a problem a follower sent in as a question, while it may be long I thought I should publish the diolog for all to have the benifit of: 

I am posting his question with out contact information for his privacy

 

From: Antonio  
Sent: Sunday, August 23, 2009 7:10 PM
To: info@annexpaint.com
Subject: needing advice and supplier

 

Hey guys,

We are a medium sized kitchen manufacturing firm based in the Bahamas.  Stumbled across your forums while looking for advice in solving some problems we are having which also haves us seeking new suppliers for professional finishing products.  Can you offer some input on the following problem?
For most of our darker Cabinetry finishes we stick with basic MagnaLac finishes, working from oil based stains to lacquer sealers then on to lacquer clear coats and the only problem is the occasional white cloudiness that is a pain in the a** to get out, usually this is when we spray in cooler weather, right now we still spray outdoors and have our drying racks indoors.

Now here is where the problem comes,  for our lighter colored cabinetry we stick with waterborne clear coats (minwax polycrylic) over water based stains with no problem but lately we have been trying to use the same clear coat system over waterbased paint.  For some reason we get constant bubbles.  We do everything by the books,  lacquer based (pratt & lambert) white undercoater, 2 coats of water based (benjamin moore) paint then after 24hrs of drying,,, the clear coat,,, and the BUBBLES!! We thought maybe it was reacting to the lacquer primer underneath so we re-prime with water based primer then final coat but still bubbles!! We use a basic compressor system with a devilbiss siphon gun (1.7mm nozzle). 

I know polycrylic is not exactly pro stuff but being a small island we are veryyy limited to the products we have access to, and would have to spend alot on importing tons of different products to test.  What do you think is causing the constant bubbles?  We spray polycrylic straight out the can.

any input would be appreciated.

AAntonio

Here was my reply:

Hi Antonio,

 Thanks for the data, that’s and interesting one, Bubbles come from a number of things usually it is because it is too hot and the top most layer is drying faster than the bottom of the layer which is still off gassing and so you have a gas trying to come through a layer of almost dry material which then forms a bubble.  The common solutions is to use a retarder or spray when it is not quite as hot. Out here in California there are a number of shops that do there spraying at 4 in the morning.

 You might want to try thinning the material down with what ever the manufacture recommends, sounds like just water will do, the next thing is getting a retarder for the material. I have found that regular Lacquer retarder works well as a retarder for water based products. That however is not a manufacture recommendation and would be something you would want to test first. Best Practice is to use the retarder the manufacturer recommends. As a point when adding a retarder to a water based material you should mix the retarder 50 /50 with water first and then add it to the lacquer. And you would use more than about 4% retarder other wise you are

 The White haziness is a similar thing, Moisture entrapment. As the lacquers is evaporating it is cooling down the surface and condensing the moisture in the air which them is trapped in the coating. You can do a few things for that, again adding retarder, or you can heat your materials i.e., the lacquer or you can move into a climate controlled space (sometimes not possible)

 Another thing that can cause bubbling is air pressure too high on your guns, another is a that you have seal leak on your gun on the fluid side that is letting air in to your fluid mix and frothing it up in the can. That doesn’t sound too likely.

Let me know how that goes and if you can send pictures and I’ll post it.

 If you want me to ship you materials I can do that.

 Greg Saunders
ANNEX PAINT
818-439-9297

August 25, 2009 - Posted by | Finishing failures and the fix, polyurethane

4 Comments »

  1. How about using an HVLP system off your compressor? I know
    there are a number of them on the market that will work.
    The Versa Max by Accuspray will work off a 2 HP compressor.

    Comment by Tom Smart | September 11, 2009

  2. Hi Tom,

    Sure you can do that. There are a few things you have to watch for, the first one being that you have to have a compressor that can keep up with you and that is usually bigger than the little five gallon portables, but if you are on a small job you can do a few passes and then let the compressor charge up, if you let it run down too far your gun will start to spit and not atomize the materials properly.

    The second thing you have to watch for in a small compressor is water condensation. Especially with polyurethanes and lacquers with even the slightest moisture you will give you a phenomenon known as Fish Eye in your finish. This is a very tiny dimple in the otherwise smooth finish and that caused by the contaminate getting into the finish and changing the surface tension of the materials you are spraying. The solution for that is to drain your compressor tank of any water and then put moisture traps on your compressor. there are also disposable moisture traps that you can plug in the the air line just before the gun.

    Professional paint shops and auto body finishing companies spend hundreds to thousands of dollars on special air “conditioning” and dryer units. just to give you a comparable magnitude on the importance of having moisture and dirt free air to the spray gun.

    You mentioned ACcuSpray, they have a unit that truly HVLP as in about 12psi you might have seen the guns that come with there own compressor that is filtered tat is then sent down the line to the gun through a large diameter hose, The model I used for a long time was the 4 stage turbine. that was great for small jobs and for situations where you were spraying in someones house and needed to watch the over spray.

    hope that answered the question

    Best,

    Greg

    Were you thinking of hooking up one of there guns to a regular compressor? I guess you could Jerry rig something for that but I wouldn’t recommend it as the guns are designed to work with that compressor.

    Comment by Greg Saunders | September 15, 2009

  3. What about when you use a canned spray paint such as Rustoleum and get bubbles that seem to grow like a fungus across your wood? I have a pair of chairs I am “trying” to re-paint but, is spots, I get these bubbles…tiny patches that grow as the paint is still being applied….even over bare wood or primed wood. The room I am working in is around 60 degrees so heat is not a factor. Any ideas?

    Comment by Renee | February 27, 2016

  4. Yikes, sorry I missed this posting and never replied. the bubbles are created from something that is causing gas to be trapped in the coating that then tries to escape but is caught in the paint. the colder it gets the thicker the paint is and the harder it is for the Gas (bubbles) to escape. warm up the room warm up the spray can and warm up the thing that you are spraying. and start out with lighter coats, spray on a coat that doesn’t cover enough and let it get tackie for about 10 minutes then another light coat and build it up. Greg

    Comment by Greg Saunders | May 25, 2016


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