Troubleshooting a Rough Finish Inside Drawer Boxes
Here's a long thread full of advice for spraying the insides of drawers. October 20, 2013
Question
(WOODWEB Member) :
I am spraying dovetail drawer boxes with a HVLP cup gun, and having a bit of a problem with what I assume is overspray. On the second and final coat, once everything is dry, I run my hand over the inside walls and they feel gritty.
I am using pre-cat self-sealing lacquer from Valspar, adding 15% thinner. My technique is to spray the bottom first, both directions, then top, then inside walls and last outside walls. When I spray the inside it is like a cloud after it hits the walls. Am I spraying too slow and letting it dry too quick? Is my equipment not good for drawer boxes? As far as equipment, I am on a bit of a budget.
Forum Responses
(Finishing Forum)
From contributor J:
When this happens to me, I usually thin out my mix and turn down the air as low as I can.
From the original questioner:
Sorry for the ignorance, but this was the second order I have sprayed, with no training. When you say thin it, do you mean add more thinner? I already used 20% for the first order and had the same results. Do you mean turn down the pressure on the hose or on the gun? I am running the line at 50psi.
From contributor J:
You are already thinned out, so turn your air down at the gun. Turn it way down and adjust up until you get a decent spray. Make sure you are not getting water in your air also.
From contributor M:
You are not doing too bad for spraying so little. Any gun will work provided it atomizes the material properly. That is, it looks like a nice fan pattern. I believe your pressure is too high - I never spray above 22 psi, however your gun may work best at a higher pressure. The higher the pressure the greater the chance for orange peel, which is I think what you are feeling.
I do not like self sealers - they do not sand as well as sealers. I would not thin my material more than 10%.
When I spray drawer boxes, I first spray the inside walls twice, then the bottom, then the outside and finally the top edges. In order to eliminate that grit you feel, you have to keep a wet edge. Meaning the box is equally wet when you are done.
From the original questioner:
I have another order to finish tomorrow. I am going to take this advice and see how it turns out. I also need some feedback about equipment. I am starting with an hvlp cup gun from Princess auto and not sure what direction to head in. I know the cup gun is a bad idea since I already ran into a problem with tall drawers.
From contributor E:
I agree with using a sanding sealer, especially in the tight confines of a drawer. Sands way easier than the self-seal stuff. After sanding, take the time to blow out or vacuum out the sanding dust well. If you still have some grit, sometimes a little 0000 steel wool or very fine paper followed by spraying a little lacquer thinner can work. This trick used to work great before pre/post cat lacquers, but can still help to a lesser degree on those finishes if you do it fairly soon after spaying your finish.
From contributor L:
You don't want to add more thinner, you want to add some retarder. This will slow down the drying and keep a wet edge. I spray mine in a different order than you do. I spray and outside and then the opposite inside. I go around the drawer until the 4 inside and outsides are done and then I spray the bottom.
From contributor A:
I only spray post-cat but this also works with pre-cat (I've done it in the past).
1) Use a very slow drying thinner. Butyl acetate is what I use (Flow Enhancer 2 for many Campbell products).
2) Thin it at least 20% but follow your manufacturer's maximum recommendation. There are some solvents that are far too slow to use at 20% (butyl cellosolve for instance, I wouldn't use it in this case).
3) Stand your boxes up on their back end (who cares if the back of the back isn't finished?). Let the overspray fall down and out.
4) Air pressure lower. Start with half your normal amount of air pressure.
5) Try not to spray the individual walls on the inside one at a time - this makes for drip-hell. Do the back, bottom, and front in one stroke, arcing your hand, as if you were spraying the inside of a large bowl. A quick spritz on the right and left.
6) Spray lightly. Not a place for spraying too much.
From the original questioner:
Does thinner effect the consistency only or does it affect drying time also? If I use sealer for the first coat, do I still use 320 grit for sanding? Also sealer is cheaper right? People just don't want to use it because that just means more cleanup between coats? Good to get advice from people that aren't thinking to convince me to make a sale. Hardest thing is that everyone has a different approach. Not to say one is better than the other, just got to find the one that works for you.
From contributor A:
Thinner will vary the drying time because there is more stuff to evaporate, but it also depends (perhaps even more) on the type of thinner used. Standard lacquer thinner is a medium-speed drying thinner, but something like butyl acetate is a good bit slower without being brutally slow. Some thinners, like butyl cellosolve, will take until next week to dry. Don't be bashful about trying standard lacquer thinner, thinning your pre-cat 20-25% and spraying gently.
Always sand in between coats with 320, whether using sanding sealer or pre-cat only. I always sand the raw wood with 180.
When spraying pre-cat lacquer, sanding sealer is an option (not required at all for nearly any pre-cat). I personally do not bother (pre-cat, or post-cat). A good pre-cat looks great in 2 coats. If I have to use a sanding sealer, I end up doing 3 coats (one sealer, two topcoats) which is 33% more labor/time/material for producing roughly the same look and durability.
The fact that sanding sealer is cheaper is only true if you are able to use it in replacement of one of your pre-cat coats. If you only spray 2 coats, I suggest you skip the sealer and just spray 2 coats of pre-cat. You generally get a more durable product, and you definitely get a better finish (higher percentage lacquer solids in the pre-cat than in the sealer).
Sanding sealer is easier to sand, but pre-cat should sand fairly nicely anyhow if you give it an extra hour or so to cure.
From contributor A:
My "don't be bashful" comment, by the way, means that the 20-25% standard lacquer thinner should work just fine, give it a shot. I prefer something a bit slower, but that's just a preference.
From contributor E:
I agree with the others about keeping your finish wet as you spray. There could be several things causing the issue you have, spraying too little finish to get a wet coat, taking too long to spray the full coat, not fully cleaning the parts before spraying, all could cause problems.
I don't use any sanding sealers for my finishes. For drawer boxes I shoot 2 coats of post cat and get a very nice finish. Also I'd skip the sandpaper for drawer boxes. Use the extra fine sanding sponges which are quicker, and them give a quick scuff before you spray the second coat.
From contributor A:
I often sand raw wood drawer boxes with 220 grit sandpaper. You wouldn't want to do that on doors because of potential adhesion issues over time, but in a drawer box it won't make a hill of beans difference, except that your first coat of finish will sand a good bit easier. Those fine or super fine grit sanding sponges mentioned will work well for getting into your corners.
From contributor R:
No idea how much fluid you are moving, but also try opening it up to get a wetter coat. Move the gun faster of course when you open it up. How far is the gun from the surface? Maybe too far away. Also maybe too wide of a fan pattern. Spray a piece of paper or cardboard. I shoot smaller width pieces like that with a 6" to 8" pattern. You have some setting off. You should never see a cloud with an HVLP gun. As a side note, I don't spray solvent anything inside a drawer. Smell hangs in there too long. I either use a water base, or shellac.
From the original questioner:
I think I figured out some of the problems, just haven't been able to put it into practice.
1) Too much thinner - I was using about 25% and my supplier told me yesterday I should be at 5% (25 seconds).
2) My pattern was way off - it was misting the drawer and sending off a cloud of bounce off, so I reduced the size of the fan.
Gonna see how that works and if not, I need a slower drying lacquer.
From contributor A:
If you are only going to thin about 5%, and if you still have issues with overspray dingleberries in the box, use a very slow thinner. Even I, after spraying for the past 8 years, still prefer to thin my clear for drawer boxes at least 10-15% with butyl acetate (a fairly slow drying clear).
Most manufacturers think and speak in terms of ideal for proper film build and very, very few of them actually have any real amount of shop experience, so keep that in mind. Some of the worst practical advice I've ever had came from the reps who sold, and from the technical troubleshooters.
From contributor O:
That 25 seconds of viscosity means nothing unless the gun manufacturer is the one who is stating it. You also need to have the proper viscosity cup - there are a couple of different types with different flows.
You thin the material to what the gun manufacturer recommends, not the finish manufacturer. Of course you can go more or less to suit your needs. But you should also heed the manufacturer's maximum thinner rating. If you have to thin more than that, you may need to get a different gun to spray it.
From contributor A:
Contributor O, I was not aware of what you just said about viscosity. I will follow that from now on.
From contributor E:
From what I was told by the company that manufactures my spray gun, the finish suppliers will recommend using the least amount of thinner possible. Reason is the thinner is bumping up the finish VOC's? Not sure how true it is, but they told me to go ahead and thin the material until it flows well and lays down the way I need it to.
I spray MLC finishes through a turbine HVLP gun and have to thin at least 20%, and on some of the thicker finishes up to 30% to get it to lay out nicely.
From contributor A:
There are several reasons you want to use the least amount of thinner possible. You mentioned VOC's. Plus, it's just expensive if you thin so much that it requires multiple coats (especially labor costs). Plus, you may end up with too thin of a final dried mil finish, which obviously isn't good. Just remember that unusual situations (spraying the inside of a box) are outside the range of what most paint vendors understand. Thinning more is often what needs to be done, and because most of them seldom pick up a spray gun in a production environment, they just don't understand.
