Milk Paint Question/Problem

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Several years ago, while I was a student in the RCC woodworking program, I made a Windsor chair which I painted in milk paint. I used 2-3 coats of fresh-made milk paint and then used Minwax Natural as a top coat. I chose a dark blue color (Federal Blue I think it was called) and mixed 10-20% black paint into the blue to darken it. Within a day or two of finishing, a white stain developed on the paint surface. The stain could not be rubbed off and was not soluble in paint thinner, alcohol, or lacquer thinner. I'm attaching a couple of photos to show what this stain looks like.

The instructors at RCC had not seen a stain like this before and couldn't offer any suggestions on its cause. I want to refinish the chair and would like to use milk paint again, but I'd like to know what might have caused the first problem so I can avoid it on the second try. Has anyone seen anything like this before or any thoughts as to what might have gone wrong?

Any suggestions for other paint that might look like a milk paint finish and still be durable and appropriate for a chair?
 
Was the paint 100% dry when you top coated?  I suspect there may have been water trapped under the minwax natural(is that poly?)
 
That looks like a lime stain to me. Since Milk Paint is made from lime, I'm thinking that you may have gotten a bad batch or that the powder wasn't fresh (or maybe the packaging wasn't air tight). I would be really interested to see if C.L.R. or LimeAway would have any effect on it. I have no idea what it might do to the paint though. But if it is indeed lime residue then the CLR or LimeAway should remove it. Was this "Old Fashioned Milk Paint"? Was the black paint also milk paint?
 
Hi Preston, I have not seen that type of problem in the past, so no help there. Have you contacted either of the two current manufacturers of the milk paint for an answer? I do know that General Finishes has what they label as milk paint, it is more of a latex paint I think,, but does give the final "results " in the colors I have used in the past.  Rick
 
Both the blue and black were Old Fashioned Milk Paint brand. The blue paint was made from newly-purchased powder. I prepared the paint under the "direction" or my grade-giving instructor and  I don't recall any of the details of the preparation, so I'm pretty sure I prepared it according to the instructions. The black paint was already-mixed old paint that I borrowed from a student in the previous year's class, so it was a year old. I realize that could have caused the problem, but since there was so little black in the mixture (1-2 oz. in 16 oz), I've discounted that possibility and thought the problem lay elsewhere. I was curious if anyone else had seen a problem like this.

I'll look into the General Finishes paint. I want a darker blue than any of the standard colors so I'll probably need to mix blue and black again.

As to checking on the LimeAway idea, I've already carried the chair to have the old finished stripped off. The stripper-guy said I probably could paint over the old finish and didn't really need to have it stripped, but I didn't want to take any chances and thought it best to start with a bare chair.
 
Preston - I suspect your problem wasn't with the milk paint - it was top-coating with Minwax (minwax anything).  Most Minwax formulations contain polyurethane, and polyurethane is incompatible with pretty much everything.

The typical finishing schedule for milk paint is milk paint followed by a) nothing - leaves a "dry paint" surface that some like as a close approximation to the look of really old oil-based lead paint, or b) boiled linseed oil.  the linseed oil treatment will provide some resistance to water spills, and overall will darken and even out the look of the milk paint.
 
The Minwax product I used was Minwax Oil Finish which I think is a linseed-like oil finish. As I recall, the reason for using that was as you point out: some protection of the paint surface. I don't remember whether the gloss of the finish was an issue in using the oil coat or how much gloss the oil added. I do recall applying 2-3 coats of the oil. I did wonder about applying a "penetrating oil" topcoat to a painted surface, but as a student it was "not ours to reason why".
 
Preston,

I've top coated milk paint with a wipe on tung oil without any bad effects but I do not remember which TO.  I did it 20+ years ago and the chairs still look great.  If you top coat the milk paint with a water base varnish you should not have any problems.  Another professional furniture maker friend applies a wax over the milk paint and sometimes shellac all with no bad effects.  He also has used TO with no bad effects.  I suspect it depends on the brand/type of TO.  Experiment!

Dennis Bork
 
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