I’m finishing a set of bathroom cabinets. I’m having a real learning experience getting an oil-based enamel to go on smoothly via brushing.
I was using the varnishing technique – you know, that zen-like experience wherein the properly thinned varnish flows serenely onto the wood from the slowly moving china bristle brush.
NOT happening with enamel.
According to a Chris Minick article, paint, unlike varnish, is “thixotropic” meaning that it must be vigorously brushed back and forth to get it to lay out into a thin coat because it’s thick at rest, but tends to thin out (and flow) when energy is applied to it.
I’m hopeing that enamel is not “paint”, per se. I don’t remember this problem with the oil-based enamels that I used back in the 50’s (I know, I’m OLD), but I know that all things change and I’m willing to learn.
So, my question is – Is an oil based alkyd enamel “paint”? Must it be vigorously brushed back and forth like painting your house? Won’t the results be disheartenly “house paint” like? Is there a way to make this blank, blank enamel FLOW?
P.S. Chris’s article also suggests using a viscosity cup to accurately thin the stuff a bunch. Did you know that paint stores, even those that cater to the spray-finishing crowd, do not carry viscosity cups? When asked for one, the answer is “whut?”.
Replies
Are you thinning the paint? You gotta thin the paint. Here's a way to judge how much -- stir in some paint thinner, then pull up the paint stick and watch how the paint slides down. If it bunches up on itself, then it's too thick. It should sheet off evenly. I also add a splash of Penetrol, which makes the paint brush even better. It'll never be quite like a good varnish, but if you buy a good brush you will be able to lay this on with a minumum of brushing. Just enough to make sure you don't get runs.
Well, I'm already using about 10% Penetrol, but I'm for sure about to add thinner the paint.
I'll try your method of gauging the viscosity and try my resulting mix on a test board.
Good thing that I'm doing this for myself - the wife and I would have starved to death if I was counting on being paid for this when I get it done.
Oil based anything needs thinning these days, as the manufacturers leave out as much thinner as they can to help satisfy VOC regulations.
To eliminate brush marks, I "cross hatch" the strokes, brush in one direction, then at 90* direction. Works for oil and latex.
I think that it's possible that Sherwin Williams ProClassic oil-based Alkyd enamel is not compatible with Penetrol. It does help with the brush marks, but it also seems to substantially slow down the curing time of the enamel.
I let it sit for two days to dry thoroughly (24 hour recoating time on the can) and attempted sanding out the nibs and brush marks this morning. While doing so, I ran into a number of incompletely cured soft spots, particularly in corners, but elsewhere as well. So, I'll let it sit for another day before working on that piece again.
What I'm going to try next is to pick up a fresh can of the enamel (I foolishly added the penetrol to the can), and see how differently it responds (on another piece) to simply thinning it with orderless mineral spirits instead.
Mike D
Mike,
In my experience working with some of the finest painters on the west coast, rather than using penetrol or paint thinner, you need to use pure turpentine. It makes a difference. Stinky, but good.
Another indication that your paint is too thick is that it isn't drying.
Hal
http://www.rivercitywoodworks.com
My dad always used turpentine as well, as did I as a youth. However the local expert at the paint store says that he can't get really good quality turpentine anymore. Something about the resin content being way too high in modern turpentine so that it prevents varnishes, paints, and enamel from properly hardening.
By the way, while I was at the Sherwin Williams store, I asked the clerk to call their pro's help line and ask if their alkyd enamel is thixotropic or not. The answer was "...I don't really know, but I don't think so." I think that only Chris Minick knows what that word means - or cares. :)
Mike D
OK,
I've started over with another cabinet. This time, no Penetrol, and no dedicated primer. I thinned the enamel with about 25% oderless thinner to act as a primer, which, as one might imagine, darn well wetted the surface and flowed!
It looks good, is drying smartly, and promises to be ready to lightly sand and apply another coat of the enamel, this time thinned by only about 10%. A progress report will follow (gee, am I "BLOGING"? My grandchild will be thrilled.)
Mike D
Mike,
I hope it is going well.
Now we are on a different subject all together.
It is my opinion that you should use primer, rather than thinned paint for primer. They are totally different animals. You should see a big difference in your ability to sand, and in the ability of the primer & paint combination to do a better job of giving you a uniform surface in your finished product.
Hal
http://www.rivercitywoodworks.com
Hi Hal,
Well, it sanded out ok this morning, but the first coat of enamel didn't look as good over the coat of thinned enamel as a primer as it did over the coat of actual primer. On the good side, the 1st dress coat thinned with 10% oderless mineral spirits went down with much less fuss than a previous one thinned with 10% penetrol.
Re penetrol usage, I was perusing books on finishing at Woodcrafts today, and came across an admonition that, while penetrol can be a useful and good thing, it should be limited to about a ounce a quart! So, depending on how smoothly things go tomorrow, I may experiment with adding a wee bit of penetrol to the mix.
Much to learn, here. I actually know better than to change more than one variable at a time when conducting an experiment, but sometimes one gets impatient (and then doesn't really know which change caused what outcome).
Mike D
I have not used Penetrol since about 1977 when I added it to latex house paint that was going over the very old, cracked paint on my old bungalow. It worked very well for that.
What is the advantage of using it with oil paint on your current project? I'm no expert but I would think that the chemists that formulated your paint probably knew what they were doing.
Also, you really should try the turpentine in your experimentation rather than paint thinner, if you can get it. I think it really makes a difference in the flowing out of the paint as it does not evaporate as quickly.
Hal
Hi Hal,
Actually, I'm aware of two commercial products designed to retard the curing of the paint long enough for brush marks to level out, or if spraying, long enough for the orange peel to level out.
The first is Flotrol (probably not spelled right). It is intended primarily for latex based "enamel" for house woodwork, and does in fact, retard drying (in the case of latex) long enough for most brush marks to level out.
The second is Penetrol (same disclaimer re spelling), which is designed to be used with oil based paints, and retards it's drying and curing long enough, again, for brush marks to level out. It works, but in the case of this Sherwin Williams enamel, it also really retards curing - not to a disastrous degree, but enough to stretch out this job.
Now, turpentine is what my dad would have used to accomplish that in oil based paints, and so would I have, 50 years ago. However, I have read and been told that the quality of today's turpentine is hugely variable. All that labeled "pure" is not necessarily so. As the story goes, the turpin refiners don't limit their raw material to one tree anymore. As a result, some batches of turpentine have a high "thinner" content with very little resin in it, and others, same label on the can, have much resin in it - so much so that it prevents enamel to fully cure over any amount of time. Again, as the story goes, the quality is so unreliable as to cause professional painters to now avoid the stuff like the plague. Thus my quest for the ideal % of penetrol.
As to chemistry, the manufacturers are hog-tied by the regulations of the Southern California Air Quality Management Board (nearly got that right). They can't use enough VOC's to make the darn stuff flow properly and still sell it. So we reckless fools add thinner (aka, VOC's) to the mix to make it usable - but that has the downside of making it dry faster, and if too thin, run, sag, etc. So, thin it a little less, add a little penetrol to it to make it flow better, and hope that your bathtub chemistry experiment doesn't ruin the cabinets you spent the better part of a week making.
Sorry for the essay - hope most of it is actually factual. :)
Mike D
Don't appologize for the essay. I never mind when I learn something.
I do know a local violin & guitar maker that boils turpentine down to make his own varnish. It's pretty scary to see a can of turpentine sitting on his barbeque boiling away!
Hal
Mike,
I am definitely not a finishing expert & haven't read Minick's article, but he must have been talking about latex paint as being thixotropic, not other materials. When you apply brush pressure to a film of latex, the brush can be moved more easily. That is thixotropy at work. It makes large areas like walls easier to coat. I don't believe that oil-based finishes have that property. If leveling is what you are after, I don't believe that thixotropy has much to do with that, however. You are probably on the right track by lengthening drying time. If you live in SoCal, weather is probably not a problem in that respect. It is for me since temperature & humidity vary to all the extremes. Varnishing on a hot August day is unthinkable & nearly impossible.
Cadiddlehopper
I am in Kentucky, now, and suffer the same variations in temperature and humidity! My reference to SCAQMB is because I retired from So Cal, and the SCAQMB's regulations tend to affect the rest of the country as well.
This has been a really interesting and educational posting for me. Lots of good input from lots of good folks. I know LOTS more about paints, varnishes, and painting.
Mike D
There are quite a few waterborne paint and finishes that are thixotropic, though I think it there may be some traditional resin formulations that also exhibit that property. (And the oil based gel stains and varnishes certainly are thixotropic.)
Where did you get the information that "the oil based... varnishes certainly are thixotropic?" I haven't spread any for a while, but I don't remember detecting that property. Do they possess it only for a few seconds or minutes, then it goes away?Curious Cadiddlehopper
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