Finishing Rooms and Techniques

[laserguy]

Hello all,

I searched this subject here and didn't find much.

I just built a smallish finishing room and was wondering what techniques people used to move air and fumes out of the room while filtering the air for particulate matter. My room is only 8' x 7' and about 10' tall. It has two windows in it that I normally leave closed to keep dust and such from entering the room. I need to keep it as clean as possible.

Also, I have been looking for good guides on finishing techniques and the plusses and minuses of certain stains and finishing coats (conversion varnish vs conventional urethane etc. )

I was hoping that the wealth of knowledge contained within this forum would possibly have some good ideas/links for me look at.

Many Thanks!

Mark

[jeffreymcgrew]

First off, only spray water-based product in your finishing room. With the water-based finishes available today you have no excuse. We use Target Coatings, but there are several others out there. Anything non water-based can kill you without the right setup, either via fumes or via explosion!

Second, we just put a high-CFM ceiling fan running into a sealed duct that goes up and out the roof of our finishing room. We had a duct in the roof we could take over for this, but you could just use a window. Water-based product just makes a mildly irritating 'fog' that dissipates very quickly anyways, so it's more just getting it out of the room quickly than anything else.

Third, as for intake, we simply just let the air that filters around the cracks of the doors into the room, and then we mop and keep the room clean. Water-based finishes dry quick enough that we haven't had a huge problem with getting dust in them.

Fourth, get yourself a HVLP spray setup. It's a much finer mist that you can control, and it drys a lot quicker with much less overspray. Working in a small room it's vital. And they aren't too much, we use a Wagner conversion gun and get pretty good results.

[Gary Campbell]

Mark...
We use a 15,000 CFM exhaust fan in a 14 by 40 room. Filtered out and tacky filters in.

The only time we had a problem was with waterbourne finishes, they plugged the filter and sucked it into the fan. And the slow drying material adhered to a few boats that were owned by persons with no sense of humor! No more waterbase for us. Post cat lacquers with low or no VOC and instant dry.
Gary

[jeffreymcgrew]

Gary brings up a good point. If you're setup with filters and fans for non-waterbourne, you got to stick with that. We've had a hard time finding any finisher locally who's setup to do water-based stuff due to this.

So I guess you've got to choose more what sorts of finishing work & at what volume you're going to do, and then plan your room around that instead of the other way round.

[thewoodcrafter]

Required air movement in this state is 100FPM.
That means the air must move into the opening of the booth (10ft x 8ft)80ft2 at 100FPM. That will require 8000CFM. Depth of the booth doesn't matter.
If you make the back wall a plenum with a filter bank at least 1 ft away from the existing wall the filters will last for several months with daily spraying.
One of the best fans to use is a vaneaxle (sp).
Grainger has many to choose from. With these fan the motor is out of the air stream and does not need to be explosion proof.

[laserguy]

Thanks so much for the responses so far.

Adding a couple of more questions.

Jeffrey, I have wanted to use only waterbased for many reasons but as I look at the systems there are seemingly many drawbacks (lack of stain colors, long dry times, inconsistancies, etc.) Do you have a preference in HVLP equipment? I only really need a gravity feed system as my volume is not large.

Gary, "Post cat lacquers with low or no VOC and instant dry." do you have a prefered vendor? That sounds great!

Roger, under what conditions do you need that much airflow, I am not going to be finishing in volume but just need the room to remain clean dust wise.

Thanks again for all the help and knowledge!

Mark

[Gary Campbell]

Mark...
We have switched to M.L.Campbell products. There should be a supplier near you. We get ours from Specialty supplies. We tried the waterbourne, but our 85%+ humidity kills the drying time, added to warping and grain raise, and we were forced elsewhere.

Note: That IS how much air movement is required for a spray room. Our room is 10x14 =140 sqft x 100 =14,000CFM. IF you have any of the regulatory people checking on you.... you know the rest.

The best in HVLP that we have seen is from C.A.T. Their guns are not cheap, but can be configured for virtually any finish. We use the CAT SLP series.
Gary

[porscheman]

Mark,

Jeff Jewitt, of Homestead Finishing, has a good book entitled "Great Wood Finishes" with a section on building a portable spray finishing booth. Though it can be moved, my booth (which is modeled on Jeff's basic design) has been stationary for several years and it has worked extremely well.

Here's a photo of the inside of the booth:


8442

The back wall has an explosion-proof fan mounted in it and the wings/sidewalls are made from rigid foam insulation for lighter weight. An open framework in front of the fan holds a set of doubled-up fiberglass furnace filters - I've never had to purchase high-end expensive media filters for this setup.

The photo below shows the exhaust path from the booth, which is channeled via a lightweight "tunnel" through an outside window.


8443

Several points made by other posters are worth remembering:

1) The booth fan must be an explosion proof design, either via a direct drive explosion proof motor, or via a belt driven fan with the motor outside the booth airflow. Further, all switches, light fixtures, and other electrical items must be sealed or placed outside the booth airflow - sparks from these electrical devices can create an explosion hazard.

2) I have not found the need to filter incoming air to the booth, which in my case is drawn from an open window behind/beside the booth. I'm not pulling air from within the shop, so there's no chance of dust-laden air from that environment coming through the booth. The only time ambient dust is an issue is for a 2 week period in late March when tree pollen is very heavy in the outside air and can cause problems.

3) The angled side walls of the portable both create a modest venturi effect, which when combined with the powerful exhaust fan (sorry, don't remember the CFM) easily pull the overspray air from the booth. I've stored a motorcycle and several other valuable items immediately adjacent to my booth and have never had any overspray problems. In addition, the solvent based finishes that I spray flash rapidly, so any of the material in the exhaust air dries tremendously fast and is simply dust by the time it gets outside. Thus, I've never had wet overspray impact anything on the exerior of my shop.

4) I've tried both water-based and solvent-based finishing systems from 4 or 5 manufacturers and have come to the following conclusions. First, solvent based finishes are much more applicable to the low volume of finishing work that I do (maybe 5 to 8 gallons per month). Given that volume, the amount of VOC I'm releasing is very minimal. Second, these solvent finishes flash much quicker, are less sensitive to ambient humidity, and can be catalyzed or retarded to alter drying time and finish flow-out. That's much harder to do with water-based finishes. And finally, most of the solvent-based finishes tend to be slightly less expensive and more time-tested than many of the newer water-based formulations.

As Gary mentions, Campbell makes an excellent line of solvent-based finishes that have been my preferred material for the past 3 years. In particular, their Krystal conversion varnish (both clear and pigmented varieties) is exceptional. It has very high solids (I can finish in two coats, three on high-wear surfaces), sands beautifully, and has amazing moisture and abrasion resistance.

Finally, you can make a nice, low cost drying rack for component parts - I spray most of my work unassembled, so there are lots of parts to store while they dry. Keeping the wet surfaces horizontal while drying eliminates runs/sagging and promotes much better flow-out. Here's the drying rack, made from 2x4s with holes drilled to accept 16" lengths of 1/2" EMT conduit. The conduit rods can be pulled out of the holes to create taller openings for things like assembled drawer boxes (note the closer vertical spacing on the right side of the rack - spare rods are laying in the bottom of the left side).


8444

I hope some of these ideas help. Regards.

John

[thewoodcrafter]

Mark,
You need that volume to keep overspray off your previously finished items.

[laserguy]

This has got to be one of the best, most friendly message boards ever. Thanks ever so much for all of the information.

I went to the IWF last week and frankly I came away more confused then when I went in as far as how I should set up my finishing system. These posts have helped a ton in both general and specific advice.

Gary/John, I was also thinking of Campbell products. They impressed me at the show. I did like Valspar also. Especially the powder glazes they had for antique/recess shadowing. Would the C.A.T. Techline-1.7mm Gravity HVLP Spray Gun located at this site
http://www.finishsystems.com/cathvlpsprayguns.html
Be about what I was looking for? I am staining by hand but will want to do clear conversion varnish with spray.

John, thank you for the pics, they are worth a thousand words, I can clearly see how to set this up from them. Love your drying rack I was thinking of something very similar except with dowells, but your idea with the conduit is much better. I think I'll pick up that book today, thanks for the tip. On the bottom photo (of the rack) you have filters behind the part rack, is that hooked to the same fan? it also looks portable, is it self contained with an exhaust you can run outside? Very nice looking setup!

Roger, I'll be sure to get a fan that is both explosive proof and has the required volume. To be honest I wasn't really thinking about overspray, but that is definately something to keep in mind, thanks.

[porscheman]

Mark,

I too have found the Bot forums to be amazingly informative, which is why I'm glad to add my thoughts to questions that I feel qualified to answer...

Regarding Campbell vs Valspar and the ability to do glazing, Campbell has a product called Amazing Glaze (I've mentioned it previously on these forums), which is sprayed on - you can use a low budget HVLP gravity feed gun from Harbor Freight for this task since film thickness and pattern accuracy isn't mission critical. This stuff flashes from a liquid to powdery film in about 60 seconds, at which point you can begin to wipe/brush it off to accentuate the details. The glaze can also be left on for several hours, if needed - the open time compared to oil-based glazes is huge.

On the drying rack, the galvanized EMT conduit works great to minimize any possibility of sticking to a new finish. It's also easy to clean with solvent if it does get finish on it.

Regarding the "thing" sitting behind the drying rack in the photo, it's actually a vacuum veneering frame-press table which can be tilted down when not in use. The white grid that you see (which DOES look strongly like a filter bank....) is the grooved platten on the frame press table. So as I said, I'm not filtering any air coming into the booth - I just screen the airflow in front of the exhaust to catch as much overspray as possible. My drying racks sit just outside the booth opening, so that fresh air moving into the booth passes through them to facilitate faster drying. In that position, it's impossible for any overspray from within the booth to degrade the finish on the previously sprayed items. But as Roger/Gary point out, you do want to be mindful of CFM. I think I paid about $500 for my booth fan, but it's not an investment you want to cut corners on.

Regards.

John

[Gary Campbell]

Mark...
I am running pressure feed on all our guns. We use a 2.5 gal with air stir & 25' hose for stain (.8mm), the same without the stirrer for clears(1.0mm), and a 2 qt with 5' hose (1.1mm) for colors. I cant tell you if the 1.7 is sized correctly for gravity, but the tech guys at CAT are great and can set you up correctly, I am sure. Depending on if or how much you reduce or retard the material, you may have to go up or down a tip size or 2.

Ditto on the amazing Glaze. Its great and easy to use.
Gary

[bill_lumley]

John , I have built a similar booth based on Jeff Jewitts article but my results are not as good as you report . I think I need to redesign based on the input here . I have a single 20" box fan and a single 20" square fiberglass filter in front of it . Jeff never specified air flow reguirments that I recall . My problem is that I exhaust inside in the winter and I get a lot of dried overspray (dust) coming out of the unit . I am not sure if this is just escaping my small filter or if the lack of air flow allows the overspray to be drawn around the exterior booth and then picked up by my fan which has better air flow outside the booth than in front of the filter ......

I did some spraying today in a booth with a large Devilbiss fan and boy did that thing move the overspray . I could see the excess spray move horizontally toward that fan . I don't have the room for such a large fan but I am wondering if I significicantly increase air flow and filter area will I keep all my overspray confined to the booth and filters . I found an article today here that confirmes that might be what is required but I am looking for input here also .

www.highlandwoodworking.com/index.asp?PageAction=Custom&ID=88 (http://www.highlandwoodworking.com/index.asp?PageAction=Custom&ID=88)

Thanks Bill

[woodworx]

I have been using a lot of different waterbased products. I have refinished over 700 tables for a restaurant chain in Cali. I have had a lot of success as far as durability with 2 products. Home Depot has a Varathane waterbased floor finish, and Zar's waterborne oil finish. The Zar is great, and is nice to shoot with my HVLP, but expensive. I seal EVERYTHING I stain with Bullseye Seal coat or some other Shellac sealer. It Seals the oil/solvent off from the waterbased finish, thus gets rid of any fish eyes. Plus, if you spray the sealer on, you only have to wait about an hour between stain and sealer. Also the shellac gives the wood a nice deep rich tone, especially with multiple coats.

[porscheman]

Bill,

I can say without hesitation that a box fan with a single furnace filter is probably inadequate for spraying anything but the smallest of woodworking projects, and inherently dangerous if you are spryaing anything flammable. While I don't know the CFM that the box fan creates (I use large banks of these box fans in my wood drying kiln), I'm guessing that its probably 20 to 50 times lower than what I have in my booth. As other posters have mentioned, you want to move SERIOUS amounts of air through a booth for safety and spraying quality purposes. As you noticed in the booth with the big Devilbiss fan, you should be able to clearly see the overspray mist pulled strongly towards the exhaust end of the booth.

Beyond the airflow requirements, here are some other important thoughts and considerations:

1) Unless you have an industrial-strength booth with expensive full-wall media filters (not plain furnace filters), you need to aim the exhaust air from the booth outside the shop/building. This also means that you have to provide an equivalent air replenishment source - either fresh air from an open window or very heavily filtered booth exhaust air (again, that's an expensive solution to engineer). If these measures are not taken, you will develop an increasingly larger accumulation of recirculated overspray with all the evaporated solvents and VOCs, etc. That poses a safety risk (explosion/fire), a health risk (even with a respirator, VOCs and solvents can be absorbed through the skin, eyes, etc.), and plenty of chances for affecting the finish quality of your project. Bottom line is you need to vent outside and replenish from outside unless you have a big dollar booth.

2) I didn't mention it previously, but the principal reason for the furnace filters in front of my exhaust fan is simply to reduce the amount of overspray accumulation on the blades of the fan. Simple fiberglass filters (and even the fancier pocket-style media filters) are not going to capture the evaporating solvents and other extremely small particulate. Even with the 4 sets of double filters in my booth, I have to scrape overspray accumulation off my fan blades about once every three months (roughly every 15 or 20 gallons of material). One of the nice things I've found about spraying Campbell's Krystal conversion varnish is that after it has dried overnight, the vast majority of that dried overspray on the filter elements can be eliminated with a high pressure air nozzle. This has really cut down on the frequency with which I have to replace the filters. Lowe's has been my best source of good quality, inexpensive filters - only $0.60 each for a 20x25x1 filter.

3) When you constantly pull fresh air through the booth, you quickly find yourself at the mercy of Mother Nature - in particular cold air or very humid air. Until several years ago, I had to pay very strict attention to ambient conditions (I keep a digital thermometer/hygrometer on the wall of the booth) so I could predict how my finishes would react during spraying and during drying. While I still monitor this info, I've learned one trick that has done more to improve my finish quality in the last few years than anything else. It came from an article in Woodshop News several years ago by Bob Flexner and was entitled "The Best Kept Secret in Finishing" - the title was well selected!! Basically, what you want to do is heat the finish before you spray it - this works for nearly every type of solvent-based finish - shellacs, lacquers, conversion varnishes, etc. I haven't tried it with polys or water-based finishes since I rarely use them. Heating the finish accomplishes several important things. First, it significantly reduces the viscosity, which is very helpful if you are spraying on a cold day (I've sprayed on days with temps in the mid-30s with excellent results). Lowering the viscosity also helps with finish flow out after it has been sprayed. On high-viscosity materials like heavily-pigmented conversion varnishes, I'll heat the finish even during the summer just to get the benefits of improved flow out. Second, heating the finish causes the solvents to flash much quicker, which is expecially important to help minimize blushing in high-humidity conditions. The "open time" of the finish is so short that the moist air doesn't have time to get trapped in the film surface. I've spraying several times while it was raining outside, bringing 95% humid air through the booth and drying room. The only thing to be VERY careful about is how you heat the finish - as usual, flammable liquids and heating sources are not compatible. Flexner describes using hot water to heat the liquid finish container, which works great. I bought an "electric teapot" from Walmart, which will heat a quart of water to near boiling in about 5 minutes. Before it starts to boil, I pour the hot water into a large plastic container, in which I submerge the 1 quart pressure cup (still attached to my spray gun). Because the pressure cup is tightly sealed, the water can't contaminate the finish and the aluminum container transfers heat to the finish in a quick, uniform fashion. I'll swirl the liquid in the cup every minute or so. After 4 or 5 minutes, the cup and the finish are warm to the touch and you are ready to spray. It works amazingly well....

Finally, in terms of "future directions" for my booth and spraying strategy, I've read several times about shops which have converted metal cargo containers into excellent spray booths. Obviously the all-metal construction is inherently fireproof and the size of the shorter containers is very similar to the $6K to $20K booths we've all seen at the trade shows. I live in Atlanta and used cargo containers from the sea port in Savannah can be purchased for just under $1000. Once I find some space to locate it (so it's not an eyesore), that's my next step. I'll use the fan in my current booth, along with a duplicate, to further boost my airflow.

I hope these ideas help, and sorry for the overly long response....

John

[Gary Campbell]

Guys...
Be careful of your use of the "foam sheets" They are dangerous at best when left exposed in a non volatile environment. Putting them near flammable vapors is asking for trouble. All building codes that I am aware of require that the foam sheets be covered by at least a 1/2 hour rated material. The gasses given off, should they be exposed to flame will kill you in seconds. In addition, they will melt, and may collapse when contacted by solvents.
Gary

[curtiss]

You might check with some HVAC people and try to find an old blower out of a gas furnace.

They are pretty quiet and move a LOT of air. Of course, any warm air goes right out with it.

[thewoodcrafter]

Any blower from a furnace will only move at max 2000CFM.
Spitting on a forest fire.

[wberminio]

I have a sheetrock and sealed finishing room 14x10.The doors are double sliding doors with industrial brush seals.The doors have a furnace filters for intake air(keeps the dust out) and a Grainger fan with shutters-http://www.grainger.com/Grainger/categories/hvacr/exhaust-fans/shutter-mount-exhaust-fans. THis is sufficient to eliminate the over spray.I use Apollo HVLP Guns, NOTE:THIS FAN WILL ONLY WORK WITH WATERBOURNE FINSHES/They are not Explosion Proof!
I ONLY SPRAY WATERBASE lacquer.Gemini Titanium.It drys quickly and is can be staked in one hour.The finish color is similar to solvent lacquer.No fumes/no insurance issues/no neighbor issues/fire department loves it.This has worked very well for me many years.



Erminio

[gerryv]

Makes a fella wonder if it's practical to powder coat wood, especially if your shop will need heating this winter.

[yobot]

Hi, Erminio.

The only Gemini brand I could find was gemini-coatings.com, and I didn't find any coatings that weren't flammable, even the water-borne products.

Would you mind sharing a link to the Gemini Titanium? I would really like to have a look at it.

Thanks,
David

[wberminio]

David

Gemini-coatings is the website.The waterborne products are Not flamable.Give them a call.I get mine from a local rep.Beleive me not all waterborne are created equal.I've spent years finding a high quality product.this is one of the best I've found so far.

Erminio