Spraying on Spar Urethane with a HVLP Sprayer
Posted: Sun Jun 08, 2014 1:38 pmEvery few years I re-coat the woody sides of my teardrop with Minwax Helmsman Spar Urethane so the UV inhibitors in it will protect the wood from fading. I just did it so I thought I'd take and share some pictures in case it helps anyone else thinking of doing this.
I am by no means an expert at this. The first time I used an HVLP sprayer was when I built my teardrop and was unhappy with the finish on the sides from brushing. The second time was when I painted the aluminum on the roof as documented in my refurb journal (in my signature below). I've found with a little care and practicing on scrap wood or cardboard I got great results. You probably can too...
I bought the absolute cheapest HVLP (high velociy, low pressure) sprayer from Harbor Freight http://www.harborfreight.com/20-oz-8-cfm-gravity-feed-spray-gun-67181.html that happens currently to be on sale for $9.99. NOTE that it's coated with oil to protect it from rust so you have to clean it before first use with some mineral spirits, which is good practice for cleaning it after each use.
One thing about this model sprayer is it does not come with a wrench for removing the interior nozzle for cleaning and HF doesn't sell one even though the instructions that come with the sprayer says they do. I just used a large channel pliers to grip the outside of the nozzle to loosen it enough to unscrew it. I chewed up the outside of it a little bit but that won't affect it's performance and it will be hand tight and loosen-able going forward.
I recommend also purchasing a set of cleaning brushes http://www.harborfreight.com/5-piece-airbrush-cleaning-brushes-68155.html, a moisture filter http://www.harborfreight.com/disposable-inline-moisture-filter-68224.html, and a regulator http://www.harborfreight.com/160-psi-hvlp-air-regulator-68222.html. As you see you can get all of this for around $20 on sale.
I'd say that 50% of the stuff I buy at Harbor Freight turns out to be defective and I have to return it. The regulator turned out to be missing an O ring (I guess) so it never tighted up when attached to the sprayer and leaked air at the joint. Luckily I just removed it and was able to continue working as my compressor had a regulator. One thing I learned the hard way with Harbor Freight stuff is to always test your sprayer setup on the compressor before mixing up and filling it with material. Another good idea is to open and check out what you're buying in the store, as best you can...
The only big ticket item you'll need is an air compressor, but you should be able to borrow or rent one.
The actual spraying goes fairly quickly. The prep work takes me 1-2 days: wash the whole trailer, sanding (palm sander and by hand where it won't reach), wipe it all down twice to get up the sawdust (and pollen this time of year), and then masking all things I don't want sprayed.
Some tips:
Now onto some pictures:
All masked and ready to be sprayed:
Me suited up and well protected:
Checking sprayer adjustments on a piece of test cardboard:
And finally spraying
In case you were wondering, I put 8oz (1 cup) of spar urethane in the sprayer cup and that was enough to spray each side twice (one coat). I'm waiting for the first coat to dry before applying another one. I'll try to take some picture of the final result, but from past experience it will be smooth and evenly coated without any brush marks or thick spots.
I am by no means an expert at this. The first time I used an HVLP sprayer was when I built my teardrop and was unhappy with the finish on the sides from brushing. The second time was when I painted the aluminum on the roof as documented in my refurb journal (in my signature below). I've found with a little care and practicing on scrap wood or cardboard I got great results. You probably can too...
I bought the absolute cheapest HVLP (high velociy, low pressure) sprayer from Harbor Freight http://www.harborfreight.com/20-oz-8-cfm-gravity-feed-spray-gun-67181.html that happens currently to be on sale for $9.99. NOTE that it's coated with oil to protect it from rust so you have to clean it before first use with some mineral spirits, which is good practice for cleaning it after each use.
One thing about this model sprayer is it does not come with a wrench for removing the interior nozzle for cleaning and HF doesn't sell one even though the instructions that come with the sprayer says they do. I just used a large channel pliers to grip the outside of the nozzle to loosen it enough to unscrew it. I chewed up the outside of it a little bit but that won't affect it's performance and it will be hand tight and loosen-able going forward.
I recommend also purchasing a set of cleaning brushes http://www.harborfreight.com/5-piece-airbrush-cleaning-brushes-68155.html, a moisture filter http://www.harborfreight.com/disposable-inline-moisture-filter-68224.html, and a regulator http://www.harborfreight.com/160-psi-hvlp-air-regulator-68222.html. As you see you can get all of this for around $20 on sale.
I'd say that 50% of the stuff I buy at Harbor Freight turns out to be defective and I have to return it. The regulator turned out to be missing an O ring (I guess) so it never tighted up when attached to the sprayer and leaked air at the joint. Luckily I just removed it and was able to continue working as my compressor had a regulator. One thing I learned the hard way with Harbor Freight stuff is to always test your sprayer setup on the compressor before mixing up and filling it with material. Another good idea is to open and check out what you're buying in the store, as best you can...
The only big ticket item you'll need is an air compressor, but you should be able to borrow or rent one.
The actual spraying goes fairly quickly. The prep work takes me 1-2 days: wash the whole trailer, sanding (palm sander and by hand where it won't reach), wipe it all down twice to get up the sawdust (and pollen this time of year), and then masking all things I don't want sprayed.
Some tips:
- don't use the HDX masking tape - it doesn't stick well and tends to peel off if you look at it
- masking tape wont stick to any surface with silicon caulk on it. Cleaning any aluminum trim with Cameo aluminum and stainless steel cleaner remedies this
- On a warm 80 degree plus day you wont need to thin your spar urethane at all. If cooler you might want to thin it just a little (like no more than 10%) with mineral spirits
- Protect yourself, your clothing, eyeglasses and lungs with proper equipment. Most is pretty inexpensive but do get a good breathing mask suitable for working with chemicals
- Make sure your car, dog, etc is not downwind...
- Clean your gun immediately after each coat and/or use. Empty any leftover material from the cup and run a small amount of mineral spirits through the sprayer before dissembling it and cleaning all the parts and internals with mineral spirirts
Now onto some pictures:
All masked and ready to be sprayed:
Me suited up and well protected:
Checking sprayer adjustments on a piece of test cardboard:
And finally spraying
In case you were wondering, I put 8oz (1 cup) of spar urethane in the sprayer cup and that was enough to spray each side twice (one coat). I'm waiting for the first coat to dry before applying another one. I'll try to take some picture of the final result, but from past experience it will be smooth and evenly coated without any brush marks or thick spots.
