Misc issues when spraying oil based paint

[Alex Horvath]

Hi,

I googled various issues related to the use of oil based paints and I get a lot of hits on this forum so I thought I'd better join...

I have re-trimmed my house and all of the trim has been painted with oil based primer and sanded. Walls currently have the builder applied latex and will of course be repainted with BM Regal (using brush/roller) after the trim. I have done some HVLP on stand alone projects using the Ben Moore oil based SI and I finally seemed to have found the formula for consistent results. Since this project was a near superhuman amount of work and I have never sprayed architectural trim I better ask a few misc questions-

1. When spraying trim I assumed I would have to mask the walls near the trim to avoid adhesion issues when I later paint the walls with latex. However, a seemingly very experienced painter using HVLP/oil told me he never bothers and has no adhesion issues with the latex over oil. I have tested latex over BM oil based SI (even w/o sanding the SI) and I could not separate the latex from the oil. However, I'm told there can be a long term issue. I'm guessing there are less issues with BM SI because it is a satin sheen which allows some bite.

So, being cautious, I would either mask the walls (a lot of work) or I could simply allow overspray onto the walls. Since I tape/cover the trim when I paint the walls, I could do quick rollover with the oil based Fresh Start as a tie coat between the oil based overspray and latex. This way I would not have to mask twice. I can't really sand the oil based SI overspray since my walls are textured. Is the latter method acceptable?

2. I have brushed the oil based SI and I get fantastic results on casing and crown however on wide, flat trim (i.e. jambs or stair risers/skirts) I could never get a flawless finish. That was my motivation for going to HVLP. Through much experimentation I found that I could use a 1.5mm, 1.8mm or 2.2mm tip with equivalent results but in each case I had to thin to 20% with mineral spirits to get good atomization.

I did not try my mil gauge when experimenting but it seems that the finish thickness is very thin when spraying as compared to brushing and thus the final product seems more susceptible to damage (this also seems to be true of the water based SI even when brushing). I plan to apply at least 2 coats. I always sand between coats but I find that it's so easy to sand through sharp edges using sandpaper. I have used the Norton sanding sponges extensively but it seems like they lose their effectiveness very fast.

Is there a better product to use between coats, perhaps the Mirka Abralon?

Thanks for any tips.

[Tom Veatch]

... However, a seemingly very experienced painter using HVLP/oil told me he never bothers and has no adhesion issues with the latex over oil....

This quote from http://www.thisoldhouse.com/toh/article/0,,212675-2,00.html supports that statement:


... Homeowners can safely recoat even many layers of oil paint with latex as long as the old paint is adhering well and is in good shape, says David Maurer, manager of product development and color delivery for the Gildden Co., which sold the first latex paint in 1948. "If, categorically, latex going over oil was a problem, I don't think we'd have any latex paint, or we'd have latex limited to new construction, and that's certainly not the case, " he says. "But I will say that if you have a lost of loosely adhering — and it is common on older houses to see oil paints fractured right down to the surface — latex paints can hasten the demise by putting pressure on the poor oil paint. ...

Personally, I wouldn't worry about the overspray.

[Larry Fox]

Alex, I agree with Tom. That said, if you are looking for a really nice finish that dries quickly and won't introduce any adhesion issues AND doesn't have the solvents you might want to look at tinted USL. If you are going white, Jeff Jewitt sells it at Homestead. I have used it for a couple of projects now and it is really a nice product. If you go that route, you might want to shoot the trim that you have primed with a coat of shellac as a bridge coat but you should not have to mask for that.

I have sprayed BM SI before and, in my experience, it makes a big mess as any overspray stays sticky for a bit and the gun is tough to clean. Leaves a nice result though.