LumberJocks

How do I spray Poly??

  • Advertise with us

« back to Woodworking Skill Share forum

Forum topic by Rick posted 09-09-2010 02:55 PM 3291 views 0 times favorited 14 replies Add to Favorites Watch
View Rick's profile

Rick

354 posts in 1865 days


09-09-2010 02:55 PM

Last night I tried my best to spray poly for the first time. It was General Finishes water based Gloss Poly. I used a sprayer from Rockler that seems to have many many glowing reviews.
http://www.rockler.com/product.cfm?page=10469&filter=sprayer

I assumed that with spraying I would have a surface that was much smoother than brushing or wiping on. This wasn’t the case for me though. The fine mist settle on the surface as.. a mist and dried the same. It was not a nice layer of poly but a layer of mist. So it was not smooth.

I thinned the poly very little. Maybe 1/10 extra water. It seemed pretty thin already.

Since the mist was not creating a smooth surface I opened it up to let more product out. But that just created larger tiny mist puddles that I felt the need to quickly smooth over with a clean cloth.

I would sand after every spray application also.

What’s the deal here???


14 replies so far

View PurpLev's profile

PurpLev

8476 posts in 2303 days


#1 posted 09-09-2010 03:21 PM

spraying leaves a uniform thin coat, but that does not happen on it’s own – even with spraying there is a learning curve, and techniques that needs to be practiced.

from the sound of it – the finish either half dried before hitting your work, or there was not enough finish put on the work to begin with. sounds more like the later – not enough finish applied

how far do you position the sprayer from your workpiece? are you spraying too fast perhaps? don’t over speed up the spraying motion – let the finish cover your workpiece. do controlled motions slightly overlapping each pass.

After you are passing with the sprayer – you should have a nice full coat of spray on the workpiece -it actually will look like you have too much of it – but as long as you have an even coat, once dry, it’ll be just fine – there is no real need to sand between coats, unless you have some mistakes to fix.

As for thinning the finish – I used the very same finish, but did not see a need to thin it down with water – I sprayed it AS IT out of the can. if you have pictures of what your finish looks like – it may show some hints as to what is going on there.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View DaytonB's profile

DaytonB

154 posts in 2521 days


#2 posted 09-09-2010 03:28 PM

I haven’t tried water based poly before but it sounds like its “flashing” (drying before it hits the surface). Your humidity and/or temperature is not in an acceptable range. I’m not sure what you use to retard water poly but that’s what you need to do. See if there is a number on the can, call the manufacture and see if they can recommend anything.

If/when I spay a finish I use precat or sometimes catalyzed lacquer. it’s a mess and wouldn’t be good to shoot in a basement or living space because of the solvent but it does an awesome job and is very rugged and durable. You can also have it tinted like paint. I’ve shot Oil paint before but it is a terrible mess, never again.

View Rick's profile

Rick

354 posts in 1865 days


#3 posted 09-09-2010 03:28 PM

My movements were kind of fast.
My initial coat went on extremely heavy because I was allowing for waaay too much poly to be applied.
After that I was scared of putting too much on so I had the setting way down and applied it fast.

Most times I could touch my piece about 30 seconds after setting the sprayer down and it would be dry. I imagine this will shock you.

So I think I should open the sprayer up a tad more and apply with slower movement. right?

View PurpLev's profile

PurpLev

8476 posts in 2303 days


#4 posted 09-09-2010 03:36 PM

yup, go slower- you are better off over spraying then under spraying.

the only time that you will REALLY be overspraying is if you notice the coat starting to sag and run down. otherwise even if it seems heavy – it may not be.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View Rick's profile

Rick

354 posts in 1865 days


#5 posted 09-09-2010 03:46 PM

Thanks guys. I appreciate it.

View Rick's profile

Rick

354 posts in 1865 days


#6 posted 09-09-2010 04:07 PM

I’m not sure if the pressure was too high or not. I can’t adjust anything with my system except for how much product comes out. it’s the rockler sprayer that I linked above. It’s actually highly rated for such a low price.
Here’s the manual for the sprayer. not much there.
http://www.rockler.com/tech/RTD10000042AB.pdf

View Rick's profile

Rick

354 posts in 1865 days


#7 posted 09-09-2010 04:45 PM

I have no gauges on this setup nor can I attach them. The hose it uses is not even close to a standard air hose line. It was the first time I used the gun so I assumed it was clean. I took it apart and it looked clean as well.
I’m not sure what the humidity is here but it was just perfect weather outside lately. About 72 degrees last night when I sprayed.

View Rick's profile

Rick

354 posts in 1865 days


#8 posted 09-09-2010 05:05 PM

It seemed pretty thin as is, but I’ll put some more water in and give it a try.
I wonder why it would be for use with only solvent based?

View mnguy's profile

mnguy

161 posts in 2053 days


#9 posted 09-09-2010 05:31 PM

Low pressure HVLP’s like the Rockler are ‘recommended’ for solvent based products because solvent based products are generally lower viscosity than water based, and therefore atomize better at the low pressures generated by these 1 and 2 stage turbines. Typically, the chemistry of water based polys needs to be tailored for viscosity of either brushing or spraying; they don’t thin well, unlike many solvent based products. Thinning water based poly even small amounts is not generally recommended. Therefore, you should select water based product designed for spraying (General makes both spray and brush products).

Based on my experience with a higher pressure HVLP, I think PurpLev’s advice on technique is sound. It does sound like the Rockler gun is atomizing your finish, so it’s probably more application rate and technique. If you are still struggling, try some General Enduro Extender, which will increase the open time of your finish and give it a chance to level out before it dries. If your conditions are hot and/or dry, you can get flashing of the water carrier before the finish hits the wood. Also, remember that the turbine is heating the air as it compresses it, and this exacerbates the problem.

Good luck!

View Rick's profile

Rick

354 posts in 1865 days


#10 posted 09-09-2010 06:18 PM

Thanks guys. I suppose the finish needs to be thinned more than I thought.
Any suggestions on viscosity for water based poly at 4psi? It sure shoots out like it’s more than 4 psi, but I guess that’s what the book says it is.

View mnguy's profile

mnguy

161 posts in 2053 days


#11 posted 09-09-2010 09:00 PM

I can second Barry’s recommendation on ML Campbell’s Agualente. I have sprayed it in both clear satin and in pigmented versions. It sprays really nicely right out of the can and produces a much better finish in clear than Minwax water based poly (I’ve sprayed that on shop cabinets).

Rick, if your General product is designed for spraying, I don’t think you’ll need to thin it. If it is a 2-way product (brush or spray), I think you’ll need to thin it the appropriate thinner (not water) to work with your relatively low powered turbine. If it a brush-only product, I suspect you won’t be able to spray it at all.

View Rick's profile

Rick

354 posts in 1865 days


#12 posted 09-09-2010 10:36 PM

I called the guys at General Finish and he said I should spray it as is right out of the can.

View PurpLev's profile

PurpLev

8476 posts in 2303 days


#13 posted 09-09-2010 10:53 PM

I keep hearing about people thinking you need a 4 stage system to spray waterbased finishes. I got very good results spraying General Finishes Water Base Polyacrylic – as is , out of the can, no thinning, with my 2 stage system – using the FINE needle (and I have a larger one too, but did not find the need for it). Like Rick, I just had to learn how to spray:

http://lumberjocks.com/PurpLev/blog/series/2911

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View Ger21's profile (online now)

Ger21

648 posts in 1786 days


#14 posted 09-18-2010 03:06 AM

I use an old $100 Wagner sprayer that looks very similar to the Rockler, and I’ve sprayed about 30 gallons of Minwax water based poly through it.

As was mentioned, do NOT thin it. You don’t need to.

You need to spray it on so you have a nice “wet” coat. Depending on temperature, it should stay wet for a few minutes before starting to dry. In cold weather it can take 15 minutes or more to”dry”, but shouldn’t be handled for at least an hour or more. At 80°, it can start to dry in less than 5 minutes.

If you have a lot of overspray in the air, it’ll settle on your work and leave a rough finish.

I spray in my garage, and open the doors immediately after spraying to let any overspray out, then close the doors while still wet to keep out dust.

I get very good results with 2 coats. One heavy coat, or a few lither coats 10-15 minutes apart. Let dry 1 or two days, and sand with ros (220 grit) until perfectly smooth (remove all shiny areas). Then one more coat. It must be totally wet, but no heavier than that. Should give you a very nice smooth surface, provided there’s no dust in the air, or particles in your finish.

One other thing to watch for. Vertical surfaces can be tricky, because water based poly drips very easily. It’s tough to get the surface wet without dripping. If I do get drips, I let them dry and remove them with a scraper. Then lightly sand everywhere, and spray again.

Sounds like you just need some practice. Good Luck.

-- Gerry, http://home.comcast.net/~cncwoodworker/CNC_Woodworker.html

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com

Latest Projects | Latest Blog Entries | Latest Forum Topics

GardenTenders.com :: gardening showcase