First fascia panel powder coated

Having got a scrap of aluminium coated with primer, a couple of weeks ago, we took several leaps forwards, using one of the fascia panels for the courtyard side of the east wing. The approach is fairly low-risk: Once nailed into place, it will be a good 3m above ground level, so any minor imperfections would be hard to spot.

Preparation
I drilled 3mm holes 1cm in from the top edge to let us wire the panel to our supporting frame. We got a bowl of water with washing up liquid and used a scouring pad to get loose crud off the panel. This gave it a scrubbed look in places and we got quite a bit of oxide off. We did notice a bit of pitting, otherwise a good smooth surface. Once dry, we scrubbed it down with acetone using a J-cloth. We moved the oven from our bothy/shed onto the floor immediately opposite the spray booth, so it was straightforward to gingerly lift the whole assemblage round and lower it in.

Trial & error
I experimented with the compressor and spray gun set up. I set the outlet air pressure to less than one bar and used an adjuster screw on the gun to fine tune the powder flow. After a couple of fits and starts where I got clumps of powder blowing out, I managed an even flow. The electrical side of the sprayer was easy, I fixed the grounding wire via a crocodile clip to the very top of the panel, which will be out of sight. I powered up the high voltage until and used the foot control to switch it on/off. I practice it was easier and more comfortable to use the foot control in one hand than on the floor by foot.

Coating the primer
So, I got going, covering the panel, 30cm x 250cm, with what I hoped was an even coat of primer. If I could see hints of aluminium below the powder coating, I re-coated it until it was an even, dull finish. I took care to get the back lip covered, that fits over the bottom of the fascia board.

Curing the primer
A niggle is that the oven is barely wider than the panels, it was a challenge not to tap/scrape the bottom corners of the panel as it went in. Then it was lid on, lid closed down (with six small woodworking clamps), then switch the power on. The electronics on the oven are smart and remember the target temperature between runs, so there was nothing else to do but watch the temperature climb to 180c, around 20 minutes. The controller does seem to learn as it is used, it manged the last few degrees more quickly that the first few times and never went over-temperature by more than 0.4c. As the oven got to 180c, I started my phone timer and, after 10 minutes turned the power off, then left the oven to cool down to 80c or so before we took the lid off. As an aside, I noticed the extension lead and kettle leads got distinctly warm and I make a mental note to fully unwind the extension lead for future runs.

The result was really quite impressively good, with a couple of small patches of over-thick coating. I smoothed these down with 180 sandpaper under a small piece of wood, the recleaned it with acetone. There were a few pits that had not quite filled. I had also used slightly too-long piece of wire at one end, which meant one corner was just touching the bottom of the oven, it came out with the aluminium showing.

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Prepping the top coat
We broke open our 25kg back of RAL 6004 blue-green powder and put an inch or two in our second powder bottle. I used our test scrap of aluminium to practice on and was a bit disappointed at the uneven coating I got, but I went ahead and cooked it. The result was OK, the powder had melted to cover most of the imperfections. I suppose given the rough surface, I should not really have expected better.

The top coat
So I got going on the primed panel. This coated better than the test piece, I put what seemed like a quite heavy coat on, until all signs of primer were obliterated and the panel had a dull but very even appearance. I put it as carefully as I could into the oven, but brushed both bottom corners on the insulation, partly wiping it off. This is clearly going to be an ongoing challenge.

So we cooked the panel and waited with some trepidation for the oven to cool down, then lifted the panel out. And lo & behold, it was good! It had a beautiful even matt-ish (slight sheen) finish,with just three imperfections: The two bottom corners were showing primer, as expected and there was a 3cm scratch on the front surface that had gone down to the aluminium. The pits all appear to have filled.

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I ordered a small bottle of touch-up paint and will see if that is good enough. Otherwise we were very pleased with the finish and we both like the colour. The next steps will be to see if we can process two panels or more at a time and to finish folding the remaining panels.

The Powder Coating Oven works!

As Jill was folding the first batch of fascia cladding, Ric built a booth to house the equipment we will use to spray the powder on to the aluminium. It was wider than 2.5m, so it could take full-length sections of cladding. He had a shelf underneath to hold the compressor and the electronics for the spray gun. He got it set up to his satisfaction, then we broke into one of our 25kg bags of powder. This happened to be the grey epoxy primer. We put a couple of cm into one of our two spray canisters, he set the pressure at 1 bar, pressed the foot pedal to get the static charge and tested it out on a manky, rough piece of waste aluminium. He got us along to spray the other side. My first pass was too light, with aluminium still showing through, the next pass finished the job.

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At this point we decided we may as well fire up the oven and see if it really worked. We had acquired an oven thermometer that we stuck through the lid and into the top of the oven, to measure oven temperature rather than thermocouple temperature i.e. the temperature of the air being blown out from the fan. We hung the aluminium on a piece of wire, clamped the lid on and turned the power on. It was still set at 200c from our last trial run, Ric got it back to 180c and we watched it as it heated up. The oven thermometer reacted surprisingly (to me) quickly to the increasing temperature indicated by the thermocouple, but soon started to diverge by a few degrees. The question was, was this because there was thermal lag i.e. it was taking a long time for the heat to raise the temperature in the oven, or was it because the thermometer was rubbish? The difference increased right up to 22c at 180c, with the thermometer indicating 158c, at which point it stopped rising. It stayed like this for the 10 minutes we ran it at temperature.

We turned the whole thing off and after another 10 minutes lifted the lid off. The powder had fused and had left a not-bad finish, except that Ric had not cleaned the aluminium, so there were corrosion pits and bits of sawdust faithfully trapped in the primer. It answered the question about the thermometer – it is rubbish and the oven does in fact work as advertised! The heating cycle was about 40 minutes total.

When we have an area dry enough to have the oven on the floor next to the spray booth, we will get going on the cladding panels. At present we plan to scrub the outer surfaces down with scouring pads and soapy water, clean them with acetone and hang the panels in the spray booth on a rack one at a time for spraying the primer on, then lift the rack en-masse into the oven for 10 minutes at 180c. Then back on the rack in the spray booth for the final coat and back into the oven for another 10 minutes at 180c.

Powder coating – Oven

The first use of the metal folder was to make a powder-coating oven, using three sheets of 0.7mm aluminium. Ric folded a sheet to form the long sides and bottom, with false bottom below that. This housed a 2.5kw cooker element and a fan that drew air down from the middle of the oven, through the heating element and along the false bottom. He ducted the heated air into the oven at each end and folded a lid to go completely along the top. He used a digital controller and thermocouple to control the heating element. The electrics worked first time and we got the thing up to 50c for a sustained period. Ric wrapped it all with 100mm loft insulation wired on to the outside and, at the second firing, just got up to a sustainable 200c. It leaked a lot of heat out around the lid, so we bought a set of clamps to close up gaps. We await our electrostatic spray gun so that we can try it out for real. We have bought 25kg of primer and 25kg of our chosen RAL 6004 powder.

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Powder Coating

Having decided on timber windows with powder-coated aluminium exteriors, it was not a big leap to then think about powder-coated
fascia boards. We even have a RAL colour. We drew up shortlists, took the ones that we both agreed on and haggled down to – 6004 blue green. As an aside, do not look for RAL colours online. What with different rendering between devices and poor translation from RAL to RGB/CMYK, it is inconsistent & misleading. We bought a physical RAL K7 Classic colour swatch and were aghast at the difference.

We need to be able to handle chunky lengths of aluminium around 2m long. Ric has specced out a design for a) an oven that will cook them at 180c and b) a bending machine . We will start ordering stuff as soon as we get on site in April. For the oven, we need…

• 0.7mm aluminium sheets 1250 x 2500 to form the oven casing
• 100mm loft insulation to insulate the oven
• strapping to hold the insulation in place
• a 2kW heater and a fan, to heat the oven & spread the heat
• a PID temperature controller and associated bits, to regulate the temperature
• a thermometer, to go at the other end of the oven from the controller, to show when the whole oven is at temperature
• a ‘D’ format kettle lead and connector
• cables, screws etc. to construct the oven and wire in the electrics
• fencing wire, to suspend the aluminium inside the oven as it cooks

The folding machine has a fixed part that the sheet of aluminium is held on and a moving part that pivots round 90 degrees, to bend the aluminium round a sharp angle. It is a fairly standard bit of workshop kit, but ours will be larger than average. We need…

• a 2.7m length of 127x76x13 I beam (UB) for the piece that pivots up
• a 2.7m length of 203x102x23 I beam (UB) for the piece that holds the sheet in place
• a 2.7m length of 75x75x8mm angle to fold the sheet around
• 4 lengths of scaffolding tube to use as legs
• weld-on hinges to attach the two lengths of I beam together i.e. to create the pivot point
• bolts to hold it together

We will probably use 0.5mm aluminium sheeting for the fascia and 0.7mm for the windows. The primer and powder coating both come in handy 20kg packs – we might just get away with one of each. We will doubtless have to improvise a bit to get the whole thing working.

Whilst on aluminium sheet, we have changed our minds on heating the up-stairs areas of the steading. The building warrant expects us to use radiators, we now want under-floor heating. The only practical way to do this without using up room height is to use aluminium spreader plates under the floor boards, with 50mm PIR insulation under the plates. However, commercially-manufactured plates are not designed for using heat pumps (35c water, requiring 100mm pipe spacing) on floors with joists at 600mm centres. We reckon we can make our own, more cheaply than getting someone else to make them up for us as a ‘special’. We are not sure whether we will need a separate folding machine.