brushes vs. spraying

[Hans Lassen]

just curious: would spray-painting a hull (many thin layers) produce an equally good coat as the application of paint with brushes? (I had major trouble avoiding "running drops" on the last job, that's why I'm asking)

Thanks
Hans

[NormMessinger]

I'd say it depend on if you have spray equipment already or not. One can get perfectly acceptible results with brush and/or roller. I sprayed Prairie Islander's hull because I had a spray outfit. Spraying System Three WRC (water reduced coating) is a lot different than spraying barn paint so I had a considerable learning curve but in the end I think the job was much better than I could have done with a brush.

[Bruce Hooke]

Without doubt, a good spray job can give you a very nice finish -- if done well it should be better than what you could do with a brush. HOWEVER, I would be hesitant about shifting to spray coating as a way to get around the problems you are having with brush coating. Unless you already have experience with spraying similar finishes I think you will find that spray coating is quite a bit harder to do well than brush coating.

What you might want to do is say a bit more about the problems you are having with brush coating, so that people here can offer suggestions on what to do differently the next time.

[Bill Perkins]

Norm is there anything specific to watch out for when spraying the system 3 ? A friend with equipment has offered to help me and I think I'll go that route above the waterline .Sprayed their clear too ?

[John Blazy]

Ditto Norm, on the learning curve with spraying, but I'd spray most large surfaces any day over brushing. Real key to that statement is experience, and equipment. You gotta know what and how much to reduce with, you gotta have much experience spraying with a spray gun to lay it dwn evenly - one sag or run, and it defeats the purpose of spraying. You need good lighting (shop fluorescents laying on the floor so you see the reflection) and a trained eye to see if wet-out is occurring.
I suggest spraying nowdays because HVLP units are lower cost, and they can blow clean, dry, warm air. If you heat the coating, and let the sprayer run for 15 min before coating (hot air will heat the gun), you'll get great atomization on thick varnishes from heat-thinning.
If you use air from a compressor, it will atomize well, but you'll lose more paint in overspray. Cut the pressure down, and wrap heat-tape around the gun and pot - just as good a result-less overspray.
Of course, brushing doesn't leave all your equipment, tools, and T-saw with a film of overspray either (I sprayed my boat IN the shop).
Spraying allows thicker film build only where you want it to, like on the foredeck below, but less on the edges. I had a few sag/runs, but wiped them off with my finger.
http://www.imagestation.com/picture/sraid79/p34b2e5d693f7d49d1d7bb051dae7a086/fb20e32b.jpg
I used a seven-stage turbine HVLP and I shortened the hose to get it to heat the gun faster. I had to wrap the handle in foam cuz it got too hot, but atomized very well.

[NormMessinger]

Bill, WRC really want to run and it does not cover very well so my tendency at first was to put too much on. Once I caught on to putting down very light coats and following with another as soon as it flashed off, I did okay. Use a same colored undercoat. Clear coat handles the same way. This is the fourth summer for the boat which set out doors year around. The paint still looks like new and the time or two I've accidentally hit it with a power sander suggests high abrasion resistance.

Beautiful job, John. Neigh! AWESOME job.

[JimConlin]

Will somebody please give the Army training film lecture about spraying LPU finishes!

Chemist?

[John Blazy]

Thanks, Norm. Mahogony makes any finish look good.
Jim, I copied this from another thread that Conrad S wrote, and sums this up well, from the voice of much experience:

"With thousands of hours behind all kinds of spray guns, I can tell you............ what Norm says in his first post.

The reality is you can't be taught through this forum. You can be successful though, if you're willing to practice/experiment some before taking on the actual project.

Successful spray painting requires you to strike the correct equilibrium between: the equipment you're using, the material, air pressure, amount of reducer, temperature sensitivity of the reducer, ambient temperature when spraying, air movement in the spray area, and application speed. Got it!? Practice, Think, Pray! (Sorry, Norm! )"

This is soooo true. I agree as a warning, because as a professional finisher myself, I still screw up sprayed finishes because of different coating properties and project shapes. Warning because I do not want to see someone have high hopes in the last eight hours spraying their boat that took 800 hrs to get to this stage, just to be disappointed by runs and sags - inevitable for beginners, even for pros that are out of practice.

The best way to have a high chance of success, even if your first spray job, is to follow at least these two steps:
Choke the gun, and spray a practice quart.
All spray guns have two knobs - top for air, bottom for paint. Usually if you turn them clockwise in, they shut. With the air on high, a practice quart of paint in the cup, and a sheet of ply or cardboard vertical, open up the air knob, and then close the material knob all the way. Then, while pulling the trigger loosely, slowly open up the material knob til you see some paint on the cardboard - not flooding the surface. Then spray the whole panel for at least 15 min - will take a while at this "choked" setting, but will allow time to practice moving your hand at the speed of wet-out . I emboldened that because THAT is the golden key to knowing how to spray a finish well, without runs yet not too thin and dry. Open up the material valve when you're confident.

Another good tip is to mask off parts of the boat that are too much to spray at one time to eliminate overspray, like spraying only the starboard side of hull, then port, then the transom. You don't want to start spraying at the aft end of the port side, then work to the bow, then around towards aft again, hitting the transom, then end up getting overspray on the aft port side where you started.

Someone else can add here. Oh how addicting is a glass - smooth sprayed finish.
Rubbing out is also addicting, yet very frustrating if done wrong. Don't use less than 1000 grit paper to begin sanding dust/bug specks off (800 is as coarse as I go). Lots of water, and don't rub too long on one area of paper - if it loads up, the load will scratch the surface.
Next, use automotive finish rubbing compound (I use 3M Perfect It®) on a foam pad in a drill along with a water bottle to keep from burning the surface, but I stress very highly to use the next stage of buffing - the final glaze, or 'swirl mark remover' (always on a separate pad). You may think that rubbing compound leaves a glossy enough surface - Think again grasshopper!

[Hans Lassen]

Whew - thanks a bunch, fellows... this was truly enlightening. Really: I had always thought that the 'real' thing was to use brushes, you know ;) ? OTOH, I of course don't have access to some of the sophisticated equipment you mentioned. It's just that when I work on my own projects, I have all the time in the world (until supper, that is), and I can afford to work carefully, putting up layer after layer of paint or, preferably, oil, or varnish. But when I work with my students, time is limited, and as I rather have them do the actual work (how should they learn otherwise?), the results sometimes are not as spectacular as I would have liked them to be. This is when they get those 'runs and sags' on the side planks. It mars the finished product, especially when they have been working very carefully with the wood; and so I asked myself whether we shouldn't try those cheap spray guns propelled (?) with Butane gas. Will not contemplate that further, thanks to your input.
Please keep your fingers crossed, I will learn tomorrow whether we can show our boat on the Hamburg Boat Show next month. That would be the day smile.gif !
Greetings from the Baltic
Hans

[Bill Perkins]

Hans a Middle Path would be to have the students roll on a thin layer with foam rollers , while a helper comes right behind lightly brushing with a foam brush to smooth the surface and reach where the roller can't . This might be one way to control how thick a film they apply .

[John Blazy]

Good idea Bill.

[Ted Ford]

John;
Great post on spraying. I have used a Devilbiss Fineline HVLP with success in the past, but am having trouble with getting varnish and Brightside enamel to flow out after spraying. It dries to an orange peel finish. Increased fluid tip size, carefully adjusted viscosity, following recommended air, paint and fan width adjustments, but still have problems. If I spray a thin coat it does not flow level, a coat thick enough to flow, sags. Any ideas?

Ted

[John Blazy]

Hi Ted,
Thanks for the compliments. You've definitely described a common situation - flood on enough to levelout the orange peel, but get sentenced to sags. Too little and you get serious orange peel.
Go back to the fine tip. Small fluid nozzle and needle. The only way I've ever achieved fine atomization to get flat-flowing wetout is either add more solvent, or my favorite - add heat. When I sprayed 100% solids UV coatings, I wrapped heat tape around the cup (one coil only) and continued wrapping it up around the fluid head and air cap like a scarf on a cold day. Then wrapped hi-temp fiber reinforced tape over this. This really worked well - simulated spraying through a recirculating heated system.
The heat caused wet-out at lower film builds and the atomization was so fine that orange peel was reduced significantly - almost flat, no sags.
I simulate this now be running my HVLP to heat my gun as I descibed above. Adding heat tape would really help too - I ordered it from McMaster Carr and set it to low temp setting.
The drawback to letting the HVLP heat up the gun, is that you're pulling cold paint up into a heated gun which helps, but is nothing like pulling hot paint into a hot gun. A lower cost alternative to using heat tape, is to pre-heat the cup of paint, but be careful, and watch your timing if its post catylized. Will only work with a heated gun though, trust me from experience - hot paint will be cooled by cold fluid passages and especially the air. That's why HVLP is superior for this type of hot spraying.

[Ted Ford]

John-
Thanks for the ideas - will give them a try when I next paint - probably next Spring since I have to paint outside.

Ted