Bruce Barker
01-11-2009, 1:11 PM
I've learned a lot here, so I want to add something to the pile of knowledge. Hopefully this info will be helpful to someone...I paid dearly to learn this.
My wife and I needed to rehabilitate our kitchen cabinets before selling our home. They were made of out-of-fashion 1980s vintage ash, with unattractive grain. On the advice of experts, we decided to go with a "Java" or "Coffee" stain color (very dark brown but not quite black). Because of the heavy application, we needed a gel stain. It was almost like painting...most of the stain that was brushed on, was left on the surface. That's how much we needed to cover the wood.
We wanted to use a water-based urethane for health and ease-of-cleanup reasons, and ended up using satin Zar Ultra Max Polyurethane.
And there you have the basic plot...putting on water-based urethane over oil-based gel stain, and making it all look good. Fast forward, the final results were fantastic. I will post photos once we have put the kitchen back together. But getting from idea to result was ... traumatic. We had serious problems getting the urethane to lay down over the heavy stain.
So here are the shop notes I kept. The guy "Mauricio" who keeps popping up in the notes is the local HVLP spray-gun expert at an upscale paint store in Southern California. He was very helpful and set up my Porter Cable PSH-1 gun (twice in fact) and even sprayed a couple of doors for me. The shop notes also attempt to record the gun settings that worked. The "M" in the scales is where Mauricio set them.
Hope this helps someone!
-----------------------------------------
HVLP Porter Cable PSH-1 Setup for Zar Ultra Max Urethane over Gel Stain.
AV (Air Volume) at bottom of gun, 2-3/4 to close. The AV adjust is important. Factory setting: was all the way open. Mauricio sets it at 1-1/2 to 1-3/4.
Open / Down / Increase 0 - - - 1 - - M 2 - - - Closed / Up / Decrease
PA (Pattern Adjust) on left of gun, 2+ to close. Factory setting: all open. Mauricio 1-1/4, but says “adjust to taste.”
Open/CCW 0 - - - 1 M - - 2 + Closed/ClockW
FC (Fluid Control) at upper back, 9-3/4 from all out to all the way in. Factory setting: unk. Mauricio sets it 6-1/2 to 7-2/3 closed.
Open / Out /Increase 0 - - - 1 - - - 2 - - - 3 - - - 4 - - - 5 - - - 6 - - - M - - - 8 - - - 9 - - - Close/Decrease
Regulator on gun: 45 to 50.
Notes: For urethane use the 1.5 tip. 2 is too big. Run water through the gun before starting the day. Stir the urethane with “crazy 8” motions, lifting the solids off the bottom. Filtering is important! Should be a filter at the bottom of the cup; also filter when pouring into the cup through a FINE paper/mesh filter. Set the compressor’s regulator high (note 100 is max input according to the gun’s manual, but Maurico says ‘as high as the compressor goes.’ I went with 100, obviously) and let the regulator on the gun throttle it down to 40-45-50 for water base and 30-35 for oil base (Mauricio upped it from his initial setting of 45 to 50 to get the urethane to atomize better). BTW, this setting is the ‘static’ setting when you’re not spraying, not the ‘dynamic’ one while air is running through the system. (The dynamic pressure will drop maybe 15 psi below the static setting.)
Our big issue was water-based urethane over a heavy coat of oil-based gel stain. Mauricio says if urethane is put over oil-based or gel stain, wait a minimum of 72 hours before spraying urethane. Smell the stain to see if it’s dry. If not dry, you’ll get an alligator-skin effect where the urethane beads up and doesn’t flow (which we got consistently on this job). Since we went on with a very heavy coat of gel stain to cover the ugly underlying wood, we got alligatoring even after a week of drying. What Mauricio recommended to combat “alligator skin” is lay on very light dusty coats of urethane, maybe three of them. Then put on the final coat heavy enough to “overwhelm” and flow over any nonadhesive areas. The idea is that the little bit of urethane that sticks during the first thin coats, provide areas for the final flood coat to adhere to. This must be what Mauricio meant when he said: “If difficult adhesion, put on very thin coats and sand 220 between them. Before the last coat sand with 600.” But this requires a lot of urethane for that flooding coat as the surface is now quite rough due to the multiple thin dusty coats. Also it is risky (may not have enough light coats down and still get the alligator effect, only now with lots of urethane on the piece), and the flooding coat only works on horizontal surfaces. The other route, and the one I eventually switched to, is: if the alligator effect happens after putting on a medium coat, wait for it to dry just a little to the consistency of honey (a few minutes), then brush it out with a foam brush. The little bit of drying before brushing makes it stickier and likey to bond over the nonbonding areas. Wait too long to brush and you’ll get brushmarks b/c the urethane is too dry to flow. Let it dry and lightly hand sand with 220—the risk is you’ll sand thru to the bare wood and then you’ll have to stain again. Do this, and the next spray coat will adhere pretty well, and most of the brush marks will disappear when the next coat levels. Sand again and spray again; by now the spray will be laying down perfectly. Mauricio says urethane often needs 4 coats, and the pro’s do 2 of sanding sealer and 2 of urethane, because sanding sealer is cheaper and easier to sand. I ended up using the sanding sealer and it was a good call. The final result was excellent, and far superior to the original finish on the cabinets.
Wipe the surface with a water moistened rag before spraying. Don’t use a tack rag, can have some oil in it. Use a damp microfiber cloth to clean before spraying. Wait 1-2 hours between coats, but you can pretty much see and feel when a coat is dry. If holding the gun too close you’ll get orange peel (looks like the finish was sneezed into place). Hold it maybe 15 to 18 inches away. Atomizes better, if further away. Can add Flotrol or a little water (1-2 t per gun’s cup) if not atomizing well. Tried this and I highly recommend adding water when doing horizontal surfaces. Do the first spray pattern left to right, overlapping spray patterns by 40 or 50% … wait a minute … then second spray pattern in an up to down pattern. (The result is a weave).
Urethane can sit in the gun for maybe 2 hours before solidifying. Clean with soapy water then compressed air. Other solvents not necessary for water-base urethane. Mineral oil is recommended to lubricate the gun but I am shy of it, and would only use this during gun storage.
-------------------------------------------
My wife and I needed to rehabilitate our kitchen cabinets before selling our home. They were made of out-of-fashion 1980s vintage ash, with unattractive grain. On the advice of experts, we decided to go with a "Java" or "Coffee" stain color (very dark brown but not quite black). Because of the heavy application, we needed a gel stain. It was almost like painting...most of the stain that was brushed on, was left on the surface. That's how much we needed to cover the wood.
We wanted to use a water-based urethane for health and ease-of-cleanup reasons, and ended up using satin Zar Ultra Max Polyurethane.
And there you have the basic plot...putting on water-based urethane over oil-based gel stain, and making it all look good. Fast forward, the final results were fantastic. I will post photos once we have put the kitchen back together. But getting from idea to result was ... traumatic. We had serious problems getting the urethane to lay down over the heavy stain.
So here are the shop notes I kept. The guy "Mauricio" who keeps popping up in the notes is the local HVLP spray-gun expert at an upscale paint store in Southern California. He was very helpful and set up my Porter Cable PSH-1 gun (twice in fact) and even sprayed a couple of doors for me. The shop notes also attempt to record the gun settings that worked. The "M" in the scales is where Mauricio set them.
Hope this helps someone!
-----------------------------------------
HVLP Porter Cable PSH-1 Setup for Zar Ultra Max Urethane over Gel Stain.
AV (Air Volume) at bottom of gun, 2-3/4 to close. The AV adjust is important. Factory setting: was all the way open. Mauricio sets it at 1-1/2 to 1-3/4.
Open / Down / Increase 0 - - - 1 - - M 2 - - - Closed / Up / Decrease
PA (Pattern Adjust) on left of gun, 2+ to close. Factory setting: all open. Mauricio 1-1/4, but says “adjust to taste.”
Open/CCW 0 - - - 1 M - - 2 + Closed/ClockW
FC (Fluid Control) at upper back, 9-3/4 from all out to all the way in. Factory setting: unk. Mauricio sets it 6-1/2 to 7-2/3 closed.
Open / Out /Increase 0 - - - 1 - - - 2 - - - 3 - - - 4 - - - 5 - - - 6 - - - M - - - 8 - - - 9 - - - Close/Decrease
Regulator on gun: 45 to 50.
Notes: For urethane use the 1.5 tip. 2 is too big. Run water through the gun before starting the day. Stir the urethane with “crazy 8” motions, lifting the solids off the bottom. Filtering is important! Should be a filter at the bottom of the cup; also filter when pouring into the cup through a FINE paper/mesh filter. Set the compressor’s regulator high (note 100 is max input according to the gun’s manual, but Maurico says ‘as high as the compressor goes.’ I went with 100, obviously) and let the regulator on the gun throttle it down to 40-45-50 for water base and 30-35 for oil base (Mauricio upped it from his initial setting of 45 to 50 to get the urethane to atomize better). BTW, this setting is the ‘static’ setting when you’re not spraying, not the ‘dynamic’ one while air is running through the system. (The dynamic pressure will drop maybe 15 psi below the static setting.)
Our big issue was water-based urethane over a heavy coat of oil-based gel stain. Mauricio says if urethane is put over oil-based or gel stain, wait a minimum of 72 hours before spraying urethane. Smell the stain to see if it’s dry. If not dry, you’ll get an alligator-skin effect where the urethane beads up and doesn’t flow (which we got consistently on this job). Since we went on with a very heavy coat of gel stain to cover the ugly underlying wood, we got alligatoring even after a week of drying. What Mauricio recommended to combat “alligator skin” is lay on very light dusty coats of urethane, maybe three of them. Then put on the final coat heavy enough to “overwhelm” and flow over any nonadhesive areas. The idea is that the little bit of urethane that sticks during the first thin coats, provide areas for the final flood coat to adhere to. This must be what Mauricio meant when he said: “If difficult adhesion, put on very thin coats and sand 220 between them. Before the last coat sand with 600.” But this requires a lot of urethane for that flooding coat as the surface is now quite rough due to the multiple thin dusty coats. Also it is risky (may not have enough light coats down and still get the alligator effect, only now with lots of urethane on the piece), and the flooding coat only works on horizontal surfaces. The other route, and the one I eventually switched to, is: if the alligator effect happens after putting on a medium coat, wait for it to dry just a little to the consistency of honey (a few minutes), then brush it out with a foam brush. The little bit of drying before brushing makes it stickier and likey to bond over the nonbonding areas. Wait too long to brush and you’ll get brushmarks b/c the urethane is too dry to flow. Let it dry and lightly hand sand with 220—the risk is you’ll sand thru to the bare wood and then you’ll have to stain again. Do this, and the next spray coat will adhere pretty well, and most of the brush marks will disappear when the next coat levels. Sand again and spray again; by now the spray will be laying down perfectly. Mauricio says urethane often needs 4 coats, and the pro’s do 2 of sanding sealer and 2 of urethane, because sanding sealer is cheaper and easier to sand. I ended up using the sanding sealer and it was a good call. The final result was excellent, and far superior to the original finish on the cabinets.
Wipe the surface with a water moistened rag before spraying. Don’t use a tack rag, can have some oil in it. Use a damp microfiber cloth to clean before spraying. Wait 1-2 hours between coats, but you can pretty much see and feel when a coat is dry. If holding the gun too close you’ll get orange peel (looks like the finish was sneezed into place). Hold it maybe 15 to 18 inches away. Atomizes better, if further away. Can add Flotrol or a little water (1-2 t per gun’s cup) if not atomizing well. Tried this and I highly recommend adding water when doing horizontal surfaces. Do the first spray pattern left to right, overlapping spray patterns by 40 or 50% … wait a minute … then second spray pattern in an up to down pattern. (The result is a weave).
Urethane can sit in the gun for maybe 2 hours before solidifying. Clean with soapy water then compressed air. Other solvents not necessary for water-base urethane. Mineral oil is recommended to lubricate the gun but I am shy of it, and would only use this during gun storage.
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