7.8.3 & 10 Riveted right leading edge and cut skin for pitot mast

Time Spent: 4 hrs 30 mins

It’s Sunday so I considerately waited until 10am before I fired up the compressor and rivet gun. I hope my neighbours appreciate it! I enjoyed riveting today, it’s great to see things going together after so much prep work.


The left leading edge assembly also houses the stall warner. This is not in the plans or instructions as the original Van’s aircraft didn’t have them. Instead it is supplied as an optional kit. Even though I’m having an AoA I decided to fit the stall warner any way. However as soon as I reached the point of riveting this I found the electronics get in the way of the bucking bar, doh! No big deal, I unscrewed the electronics and finished riveting.


Once all the riveting was done I adjusted the stall warner as per the instructions so that it triggered with minimal movement.


Next I reviewed the instructions and it was time to deal with the pitot. Van’s pitot is simply a piece of 1/4” tube bent to an L shape and fitted to the leading edge. I didn’t like that for a couple of reasons. One, it’s too fragile and, two, I want an AoA (Angle of Attack). As I’m fitting Garmin electronics, I decided to use their pitot/AoA but this device needs to be fitted to a mast. After some research I found the SafeAir to be the best for this job. All this research was done last year some time so all I needed to do was find the mast I’d bought. Luckily I’m a semi organised person and found it fairly quickly.

I read the instructions and researched build logs before making a start. To fit this part I need to cut a hole in the bottom wing skins just outboard of the last inspection panel. Scary! Finally I decided on a location for the pitot mast being one rivet away from the rib nearest the access panel. A friend of mine fitted his there too so it seemed logical to follow suite.


Next I drew the outline on the skin using the paper template and then drilled the skin with a uni bit.


Using my dremel and various files I opened up the hole to the same shape as the template. After careful drilling, filing and sanding I finally offered up the mast to see if it would fit. Nope! Not even close! What?! How could this be? I checked the template that came with the kit and it was obvious what was wrong. The template was a photocopy and had not been copied to scale!!! Well, at least it was smaller rather than larger. Enlarging the hole freehand was not a a good idea so I made another template using the mast as a guide and fitted it over the top of the hole i had already made. I then enlarged to that template. A couple of adjustments later and the mast finally fits.


I’m quite pleased with the result. I will probably fill the very small discrepancies with body filler if I think it needs it. It may not.

Next was to do a major tidy up of the workshop. I try and keep it tidy as I go but this week lots of tools didn’t get put back. Now that’s done both leading edges and both fuel tanks are ready for inspection when my inspector returns from his holiday.

7.8.10 Assembling the Leading Edges

Time Spent: 5hrs 10mins

Today I woke bright and early and couldn’t wait to start the weekend by assembling the leading edges.

The work started by first dimpling the nutplates and then covering them in JC5A jointing compound. Once that was done they were cleco’d to the tank attach jointing plate and riveted in place. As soon as I tried to set the first rivet I realised I needed a third hand to hold the work piece. I popped it in the vice and that did the job nicely. 10 minutes later all the nutplates were riveted in place.

Next was to JC5A the flanges of the first rib and then Cleko it to the top side of the l/e skin. I repeated this process until all the ribs were in place.


Once all the ribs were cleco’d every other hole to the top I then gently laid the assembly in the wooden frame that I built the fuel tanks in. Then I cleco’d every other hole starting from the aft holes and working forward. The assembly soon nestled in place nicely.

Once both leading edge assemblies were complete I riveted the stall warner access plate in place using the hand squeezer. I also disassembled the stall Warner and torqued any nuts there. I checked the operation then reassembled with JC5A compound and cleco’d it to the left skin.

I then set up the rivet gun and compressor. I went ahead and riveted all the rivets in the right leading edge. This was surprisingly tiring but I got it all done with only two rivets drilled out and replaced.

I didn’t have time or energy to do the left riveting so I called it a day. I couldn’t resist sitting it in place as I left the workshop though. Looks great riveted and no clecos holding it together.

7.8.2 Priming the Leading Edges

Time Spent: 2hrs 3mins

It’s been a long time since I last did any spray painting so I was a little apprehensive about this. So first I did a little refresher research. I found this very useful guide for making sure the spray gun was correctly set up…


Once the gun was set up and ready to go I setup a table and the hanger ready to hold the parts while I sprayed them.

Next i mixed 500ml of PR30B wash primer. Once it had sat long enough as per the instructions I poured it into the spray gun via a filter. I was ready to go so I donned my paper suite and face mask and sprayed the parts. I forgot how much wash primer runs. Not a problem but I’m sure I can do better next time.


While the wash primer was drying I mixed up some coffee and then some PR143 epoxy primer. It didn’t take long to prime the parts with the top coat primer and they were soon hanging up in the workshop drying (curing?). That’s it for today, nothing more can be done until these items are dry.

Skins are stood on some 2×4 blocks to let them dry.


Not a bad session, except that one of the skins fell into the other and the primer has rubbed off. No big deal I have some spray can primer that I can use when it’s dry if need be.

The Priming Experiment

There are so many different primers on the market that it is hard to choose which one is best.  So I decided to set up a little experiment (in addition to my article on priming).

I have primed (or not) various bits of scrap aluminium (from Vans Aircraft) to the same standard as I have on my aircraft build.  I screwed them to a block of wood so that the metal suffers maximum moisture exposure from the woods water retention and left the whole piece on the roof of my green house at the mercy of the elements.

Every 3 months I plan to take a photo so that I can track the progress of corrosion over a long period of time.

Experiment Start: 1st August 2015

The Vans Aircraft Priming Experiment

1st November 2015 (3 months later)

Vans Aircraft RV priming

Priming 101 (UK Edition)

Priming wars!  That’s how it is known in the Vans Aircraft RV builders fraternity and for very good reason.  Being a newbe, my first mistake was to assume that there was a single primer that did it all and all I had to do was find ‘the one’!  I was SO wrong and it wasn’t until I had finally overcome my preconception that I was able to move on and fully understand priming!

What I did learn, though, is that there are so MANY different ways to prime the pride and joy that it quickly sparks fierce debate if you ask any other builders opinions.  I am certain that everyone of us builders wants to do it the right way, but with so much choice it’s hard knowing which is the right way.

Vans Aircraft priming etch primer epoxy

To help other newbe builders and to clear my head, I am writing my musings on what I’ve learn’t during my time researching, building and, finally, priming my RV-7.

So first I needed to get the most fundamental question…  What is priming?

Priming is the act of covering metal to delay or prevent corrosion.  In other words, stopping rust destroying our precious metal aircraft and, hopefully, extended it’s life.  Understanding the priming process, well that’s an art!  To help me decide I broke it down in to a series of choices. These are choices I had to make before buying the equipment and primer.  If it helps, here are the questions I asked myself…

Choice Number 1:  To prime or not to prime, that is the question…

Bare metal is very susceptible to corrosion from such things as humidity, salt air, chemical spillage, fuel spillage and so on.  The best method of protection from corrosion is to cover the metal with some kind of barrier that will act as a sealant against these risks.

Do you want to protect your metal from these risks?

  • No?  You’re done, get building!
  • Yes? Go to choice number 2…

Choice Number 2: Is Alclad protection enough?

Most (but not all) Aluminium that Vans Aircraft use is Alclad.  Alclad is a very, very thin layer of pure Aluminium that is bonded to the aluminium alloy below and is supposed to prevent the air or other evil corrosion from reaching the previous metal.  I’ve heard a rumour that Vans Aircraft did an experiment and left a piece of Alclad Aluminium outside.  After 3 years the unprimed, Alclad only, piece of Aluminium showed signs of corrosion and pitting.

Do you think Alclad Aluminium is sufficient protection for your aircraft?

  • Yes? You’re almost done, get building but watch out for all the non-Alclad parts that need priming!
  • No? Go to choice number 3…

Choice Number 3: Surface preparation…

So you’ve decided to join the ranks of the primers, welcome aboard!  It wasn’t so difficult getting here was it? No doubt you’ve probably already got your spray gun out and ready to shoot some primer.  Well hold on there tiger and remember the 5 P’s… Proper Preparation Prevents Poor Priming!

A greasy surface causes the primer to ‘miss’ areas of the metal as the grease acts as a sort of barrier.  You can see areas in this picture where the primer was prevented from working properly due to poor preparation.

Vans Aircraft RV Priming Grease

Grease is often invisible.  Honestly it is really, REALLY invisible and comes mostly from our grubby little fingers.  The only way to see this invisible grease is to paint some primer and watch it peel off or not adhere, there is your grease!

There are many ways to prepare the surface for priming such as:

  1. Scuffing the entire surface of the aluminium to a dull matt finish (excluding skins, they only need a light scratch).  I did this AFTER drilling & edging but BEFORE dimpling & fluting so that I got every mm of metal possible.
  2. Air blowing the aluminium dust off the metal
  3. Washing in Fairy Liquid (or Dawn Liquid for our US cousins)
  4. Degreasing with Paint Thinners & green scotch bright pad
  5. Degreasing with MEK (Methyl Ethyl Ketone) and a green scotch bright pad
  6. Degreasing with Deoxidine 624 (or Alumiprep, US brand) & green scotch bright pad

How can you tell you’ve cleaned properly?  Run water over the metal and if it ‘globs’ together like molten lead, it’s not clean, go back and scrub again.  If it runs of in a uniform flat flow (sheets off) then it is clean, nice job!  Make sure you have gloves on from now on to prevent the metal from getting greasy again.

FWIW I personally chose to only do options 1, 2, 3 and 4 above.

So, back to the choices: Do you want to clean the surface?

  • No? Good luck and send me some pictures of your invisible grease please!
  • Yes? Move on to choice number 4…

Choice Number 4: Adhesion layer…

This is where I found things MOST confusing.

This section is referred to by many as priming.  But the word ‘primer’ used here and again in the next section refers to two VERY different tasks.  So, for simplicity I refer to this section as ‘adhesion primer’.  Adhesion primer is designed to ensure that the next layer of primer has a really really good surface to bond with and there are 2 popular options…

Option A: Alocrom 1200 (UK name) or Alodine (US name).  This adhesion primer chemically converts the metal surface to add Chromate to the aluminium.  It is usually applied by brushing and leaving it on for a minute or two before rinsing with water (de-ionised if your really going for it).  It is also possible to dip the parts as well but I haven’t tried that yet.

Option B: Etch Primer (AKA: Wash Primer, Acid Etch or PR30B).  Usually the type of Etch Primer preferred is a Zinc Chromate Etch ‘Adhesion’ Primer.  Which, similar to Option A, adds a Chromate coating to the metal by using acid to etch the surface of the metal and bond the Zinc Chromate coating before the acid evaporates.

Never do Options A & B together, it is either one OR the other.

Almost all ‘Adhesion primers’ do NOT protect well against corrosion alone.  They are often porous to aid bonding and, if you read the technical documents, almost always require a sealing coat (see Choice Number 5 below).  So what’s the point?  Well if you want the next stage to stick like the proverbial to the metal then this layer is what’s needed.  Also being another layer, it will add another layer of protection which will help somewhat.

Do you want ultimate bonding of the next layer?

  • No? Skip this step and move on to choice number 5…
  • Yes? Wise choice, some say.  Read on…

Choice Number 5: Priming, at last!..

Finally after so many decisions, and probably much indecision, you have at last arrived!  This is what it has all been about, protecting your hard work from the evil of corrosion.

‘Primer 2’ is the top coat of primer and commonly referred to a sealer primer.  This is a layer that will seal your metal from the elements and protect it for years and years and years and years. Some say that ‘Adhesion Primer’ is all that’s needed and sure enough that layer WILL protect your aircraft for a long time because the corrosion will have to pass that layer before even reaching the metal.  But Sealer Primer will protect it for even longer.  Sealer Primer is usually an epoxy primer (or urethane primer) that dries to form an impenetrable barrier between the elements and the aluminium.

Different epoxy primers have differing properties.  Some are great fillers, but they are thick and heavy.  Some are excellent at protecting against more than just moisture, they also protect against oil, fuel and other chemical spills but they are expensive.  What you choose here is entirely up to you and some common brands used by uk builders are PPG PR143 and Aerowave 2001.

Are you going to sealer primer?

  • No? Too heavy and a waste of time. Get back to building and stop time wasting!
  • Yes? Great, now to choice number 7…

Choice Number 6: Priming everything or not…

Some builders choose to be selective in their priming.  For example they will ‘Adhesion Primer’ everything structural (ribs, spars, stiffeners and inside of the skins) only.  That makes sense, if the horizontal stabilizer is a near sealed unit doesn’t that act as another layer in the same way as ‘Sealer Primer’?

However, on the visible parts (ie cockpit spars, seat backs & cabin area) priming with both adhesion and sealer primer is a good idea as these are most likely to suffer spills, scratches, wear and tear.

And then there’s the inside of the skins.  Some people don’t prime the inside of the skins because they rely on the Alclad to protect the skin.  I decided to prime the inside skins because I live in the UK and it’s wet here, very wet!  Another reason is that if I can’t afford hanger space for a short time then I would like to have the best protection while it sits outside.

Are you going to selectively prime?

  • Yes? Good on you, get building!
  • No? Priming everything? Woah way to go man!

Choice Number 7: Bluing – The blue vinyl that covers the metal…

The aluminium that comes shipped from Vans Aircraft is covered in blue vinyl.  Many builders leave the blue vinyl on as long as possible and on the outer skins often until they have finished building which could be many years later.

Vans Aircraft, however, recommend in the build manual to remove the blue plastic as soon after inventory as possible.

A very wise aircraft painter told me that he has seen many RV parts that have been in long term storage with the bluing left on suffering from corrosion because the bluing creates a moisture trap.

Other RV builder say that the bluing protects from scratches.  But the bluing isn’t very thick and any scratches that the blue vinyl can protect from can easily be buffed out with scotch bright.  Any scratch deep enough to tear the vinyl would have gone through it any way.  So in essence it’s not really protecting from much.

I decided to leave the bluing on my metal until I started building the part and then I removed it completely, even from the skins.   It gets more difficult with time to remove the blue vinyl so choosing the right time to remove it could save a lot of work.

To protect the skins from corrosion during storage I am priming the outside of the skins the same way I am priming everything else.

Removing all the blue vinyl?

  • Yes? Good on you, don’t forget the last step!
  • No? Read up on using a soldering iron to help remove the vinyl, it really works!

Choice Number 8: Jointing compound…

Now that everything is ready to be put together and has been adhesion and/or sealer primed (or not) the last important corrosion related question is jointing compound.

This compound sits between any two metals joins such as spar to rib and/or spar to skin.  The purpose of the jointing compound is to repel moisture from between the joints.  Moisture that sits between the joints could remain trapped allowing it more time to attack the surface.  Of course you could leave loose rivets which would allow the moisture to evaporate but that’s probably not a good idea.  Instead a jointing compound should protect the joints.

Where jointing compound is REQUIRED is between dissimilar metals.  It will stop the metals reacting and greatly reduce corrosion in those areas.  Some builders use jointing compound on every joint and even on primed parts.  My aircraft painter suggested that primed parts already had 2 layers of protection and that jointing compound was not necessary.  My inspector insisted that jointing compound IS absolutely necessary.  I love self building!

Are you going to use jointing compound?

  • Yes? Welcome to the world of budgie poo!  Let’s build!
  • No? Read on…

Conclusion

Remember that priming your aircraft is an intensely personal choice which is why it always invokes such fierce debate.  There is no right or wrong here, only YOUR choice (actually I think the LAA insist that aircraft built in the UK are primed).  All of these steps are optional and results will vary depending on your ability, the chemicals, temperature, tools, the environment, weather and so on.  It is even possible with some primers to simply spray epoxy primers (primer 2) directly onto the bare metal skipping all the other steps!  It’s your choice.

With all that said and having ranted on for hours about priming I am about to contradict myself enormously…

Many aircraft manufacturers don’t prime at all!  

WHAT?!  That’s right, I’ve looked.  Next time you go flying have a look inside the aircraft your renting.  Likelihood is it won’t have been primed but yet it’s not rotten.  How can that be?

One reason is because owners regularly spray ACF 50.  ACF 50 is essentially a grease that creates a barrier of protection instead of all this priming nonsense.  Another reason many aircraft survive decades without primer is because they are well maintained.  They are kept in well ventilated hangers, have never even heard of IFR, and are loved more than the family pet!

Of the aircraft that I have seen with corrosion it is usually on the outer skins and caused by scratches, stone chips or acidic bird droppings that are left.  Sometimes even a poorly painted aircraft will suffer corrosion if the paint does not bond correctly causing a moisture trap between it and the metal.  But what often amazes me is the spars and ribs show no sign of corrosion whatsoever.

So it seems that corrosion may not be the evil nemesis after all. It might be the way we treat our aircraft AFTER we’re done building it.  So the final and MOST IMPORTANT question should be…

Choice number 9: How do you plan to treat your aircraft after it’s built?


*Disclaimer: This article is written to the best of my (little) knowledge(!) and likely to contain many errors and offend many people.  Please feel free to comment, correct me, flame me and insult me as appropriate after all we're RV friends!

Horizontal Stabilizer: Rear Spar Assembly

RV7-HSTotal Time: 4 hrs 05 mins

Tuesday 15/06/15 Section 6.1.1 to 6.1.5:

I was off to a slower start than I was expecting today mainly because I am still getting used to the tools and equipment.  Also I’m finding reading the plans challenging as the wording takes some getting used to.   2hrs 40 mins

The obligatory before and after of the very first part.

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After

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And the first assembly…

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Wednesday 17/06/15 Section 6.1.6 to 6.1.8:

The next part to prepare & assemble is the rear hinge brackets HS-411 assembly.  The bearing needs priming so I will have to move on to the front spar assembly while I wait for it to dry after priming.  Don’t worry, I spotted the bracket was on the wrong side just after I took this photo!  55 mins.

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Saturday 20/06/15 Section 6.1.9 to 6.1.11:

Now the bearing has dried I just need put the assembly back together, clamp it and set my first rivets.  That’s the rear spar assembly all complete.  30 mins.

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The Training Project

I thought it would be a good idea to ‘prime’ all the new tools before using them in earnest on the actual aeroplane.  Some months ago I purchased the training project along with the preview plans / builders manual and now seems like the perfect time to get started.

Vans Aircraft Training Kit

On Tuesday I spent 2 hours making a start on the kit.  Most of that time was spent working out how to use the new tools and learning to read the plans.  I’d done pretty well on the whole, or so I thought.  Once I started back-riveting it all went wrong.  My back riveting was terrible and I couldn’t understand why.  At first I thought I hadn’t set the rivet gun properly or that I had faulty tools.  In the end I called it a night.  2hrs

On Thursday evening I ventured back up to the workshop and had a think about things.  I had read somewhere that the rivet gun may need a high pressure setting so I whacked it up to 90 PSI but still the rivets were not setting.  They would go to about half way and that’s it.  After 20 mins I decided to leave it alone.  20 mins

On Friday morning I had a visitor, Richard, who is an experienced builder having completed his RV build last year and won the LAA best home built 2014.  We chatted about everything from priming to dimpling.  When it came time to dimpling I tried to show him what was wrong but, would you believe it, it blooming worked this time.  So well in fact we had to turn the pressure down to 40PSI!  Richard thinks that I perhaps didn’t have the gun seated on the rivet properly due to the angle of the metal.  I probably agree.  2hrs

Once Richard left I cracked on with the training project.  I found a new lease of confidence following his visit and couldn’t wait to get through the project.  I could only manage another 2 hours before I needed to go out.  2hrs

On Saturday I was determined to finish the training project.  In hindsight I wish I hadn’t set a time limit as I am sure I could have done a better job.  Maybe that’s lesson 1 right there?

Anyhow, I did finish the training projects (there are 3 in the pack) and I am moderately pleased with the outcome.  While the finished product is not as good as I had hoped it would be I am now more aware of what can go wrong.  Some of the gotchas that caught me out on the training project are:

  1. Rivet gun pressure too high: Gun hops around the skin like mad creasing it as it goes, grrr!
  2. Unclamped work: Don’t, just don’t!  Go find some clamps or a friend and get that work locked down.  This is especially true when riveting.
  3. Drilling: USE DRILL STOPS!  That drill shoots out the other side no matter how much you think it won’t.
  4. Drilling 2: Be careful not to scratch the metal with the drill tip both before and during drilling.
  5. Bucking Bar: I should have covered it in masking tape, even the tungsten bar scratches up that metal good.
  6. SLOW DOWN:  This is by far the best lesson that I learnt.  Mixing up an AN3-3 rivet with an AN3-3.5 is not an issue on the training project but on the real deal it’s going to be expensive!

So the trainign project is/are complete.

Finished Vans RV Training Kit

Am I satisfied with it? No.  Have I learn’t from it? Without a doubt.

Would I recommend it?  Hell yeah, if you are a first time builder and need to ‘prime’ your new tools I think this kit should be compulsory.

Flooring

The workshop needs some sort of flooring.  I had planned on painting the bare concrete floor but I have been told by the cement people that an Anhydrite floor is not compatible with floor paint!  Doh!  Oh well I decided to go with cheap vinyl instead as I just need something that will make sweeping and mopping easier.  Dad helped lay the vinyl floor and overall I think we are both pretty pleased with it…

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We were both a bit gutted that the colour was different but I was half expecting that to happen as it’s common when using both 3m and 4m width rolls in the same floor space.  I just didn’t expect that big a difference, oh well who cares really?!  After the floor was laid Dad ran away and left me to install the skirting ‘All by myself’ (a song that I’ve frequently sung on this project)!

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and then…

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Just one last job reserved for a special person…

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And the workshop is FINISHED!!!!  Hooray!

Just 7 months from mowing the grass…

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to this…

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Thank you, thank you, thank you to everyone who’s been involved.  Especially thank you to every one on the team at Alcom Computing who kept things running while I was dealing with deliveries, builders and crisis after crisis.  A massive thank you to my Dad who was always there for me when I really needed a hand.  Thank you to my two wonderful kids for being so well behaved around dangerous equipment and for being so understanding about Daddy destroying their garden.

But most of all, thank you to my long suffering and infinitely supportive wife, Karma, who has been truly amazing throughout.

What project could possibly top this, I wonder?

Plumbing

I’m really keen to get the workshop finished so I’m pestering my brother, Jason of Union Plumbing and Heating, to come over and plumb in the bits and bogs!  So we started by running the waste pipe…

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Again, I surface mounted the waste pipe so that I had maximum flexibility in the future.  The tricky part was all the bends and angles while maintaining a downhill slope of the right gradient.  But we did it!  Jason then tiles the floor and installed the toilet…

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And bathroom sink…

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Next he plumbed in the kitchenette…

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And the hot water heater…

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That’s the plumbing sorted, thanks bruv!

Electrics

I decided pretty early on that I wanted to surface mount all the electrics for two reasons; firstly, I’m not 100% sure where I want the sockets yet and secondly after the aircraft is built I may want to reuse the building for something else and so it would be a waste fitting the electrics in the walls.

But before any electrical work can be started I need to get the fuse box (consumer unit) replaced in the main house as I think it’s older than I am!  All this has to go…

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And be replaced with a single, shiny new system which has been fully tested and certificated by Fowler Electrical who were brilliant.

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Before the electricians can connect the workshop to the main house I need to install the conduit, wiring, lighting and sockets in the workshop…

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That’s it for me, now I need the electricians to install the Workshop Consumer Unit and connect up to the incoming supply…

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We are ‘live’.  Sockets, lights and other bits all wired in.  Yay!