Correx: cheap, light, useful. Choose any three

Synopsis : From quick fixes to permanent solutions, Correx – extruded, twinwall, fluted polypropylene – has multiple uses in beekeeping. If you learn how to fold, stick and shape it you can save time, money and space. Here are just a few of the things I use it for.

Introduction

The Spring honey is almost ready to harvest. Supers went from ”filling nicely” to ”Woah! Damn that’s heavy” in the space of a week. They’re now fast approaching ”No more than two at a time” territory which means; a) they’re full, and/or b) I’m less strong than I used to be 1.

The corpulent supers prompted me to rummage through a teetering stack of equipment to try and find sufficient clearer boards to use before removing the honey supers for extracting.

Clearer boards are effectively one-way ‘valves’ that funnel the bees down into the brood box 2.

Quick fix clearer board – hive side

These are two and bit times a season pieces of kit … the Spring and Summer honey harvests and irregular usage to empty the odd brood box when compressing colonies prior to the winter. The rest of the time they sit, unused, unwanted and – not infrequently – in the way.

And, for convenience, you need more than one.

I like to have one for every hive in the apiary, particularly when taking the summer honey off. That way you can strip all the hives simultaneously, so avoiding problems with robbing. None of my apiaries are particularly big, but it still means I’ve needed up to a dozen clearer boards at a time.

That’s a lot of wood and limited-use kit to sit around unused. I therefore build lots of them from Correx.

Clearer boards – one wood and six made from ekes and Correx

This post isn’t about clearer boards. I’ve described those before.

Instead it’s about Correx and the myriad of uses that it can be put to.

If you don’t use it you’re probably missing out.

If you do, you probably have some additional uses to add to the list below.

Correx

Correx is a registered trademark owned by DS Smith. Other trademarks (by other companies) include Cartonplast, Polyflute, Coroplast, FlutePlast, IntePro, Proplex, Twinplast, Corriflute or Corflute … and there are probably some I’ve missed.

It’s all very similar stuff, variously described as corrugated plastic or corriboard, and perhaps more accurately described as an extruded, twinwall, fluted polypropylene.

If you don’t know what I’m talking about then you’re probably familiar with the material they make For Sale signs from … that’s Correx 3.

Under offer ...

For sale …

Correx is lightweight, impervious to most oils, solvents and water, relatively UV resistant and recyclable. These characteristics make Correx ideal for a range of beekeeping applications.

It is easy to cut and can be folded, with or across the ‘grain’ if you know the tricks of the trade.

Correx is available in a range of thicknesses – typically 1-8 mm. Two millimetre Correx is often used as a protective floor covering in new buildings. However, it’s rather thin and flimsy.

Almost everything I use is 4 mm and so, unless I state otherwise, assume that’s what I’m referring to in the text below.

Almost certainly the stuff I use is not Correx, but I’ll call it Correx for convenience 4.

Before discussing 5 applications I’ll make a few comments on sourcing Correx and cutting, gluing and folding it.

Free Correx

For Sale signs belong to the estate agent selling the house. However, they’re often not collected after the house sale completes and are dumped in a nearby ditch, stuffed down the side of the garage or otherwise discarded. Many still have the 2.4 m wooden post attached.

If they really are unwanted it’s often a case of ’ask and ye shall receive’ … and, if the sign is in a ditch, you don’t probably even need to ask.

When I lived in a semi-urban area I used to carry a handsaw in the car to help my repurposing of these sorts of signs.

Elections are another good source, particularly if the candidate in your ward a) loses ignominiously, and b) immediately retires. It’s unlikely the political party will find another Archibald Tristan Cholmondeley-Warner to stand for them, so the electioneering signs are – like the politician – surplus to requirements.

As always, never walk past a part-filled skip without having a good look at the contents 😉

Never!

Buying Correx

Correx is relatively inexpensive when bought in multiples of 2.4 x 1.2 metre sheets 6. I’ve paid about £10 a sheet delivered for 5 or more, purchased from eBay, but can’t find anything quite that price when I had a quick look this week.

You might not think you need 14 square metres of Correx but you’d be surprised at the things it can be used for. It’s also easy to store behind a bookcase or in the shed.

Correx sheet

Correx sheet …

It’s also worth asking at local plastics and printing companies that may have offcuts or failed print runs. It doesn’t matter what’s printed on the Correx 7. There’s a beekeeper in Northern Ireland that crafted a nuc box out of election propaganda bearing a photo of the candidate. The nuc entrance was arranged to be the politicians mouth.

Be creative.

Finally, Correx is often used to make guinea pig cages or runs, so befriend a cavie-keeper and you might locate the mother lode 8 😉

Correx engineering

Thin Correx (4 mm) is easy to work with. It can be cut with a Stanley knife. All you need is a good straightedge, a steady hand 9 and a sharp blade. Marking up the sheets is easiest in pencil as many pens don’t work on the smooth impervious surface 10. Pencil works equally well on black or white sheets.

I’d recommend you don’t use scissors as they tend to crush the sheet. It’s also difficult to cut large sheets with a small pair of scissors.

Folding Correx

Correx has a ‘grain’ created by the vertical internal ribs that connect the upper and lower faces of the sheet. If you need to fold the sheet you’re working with, the method used depends whether you are folding across or with the grain.

To fold across the grain you need to crush the ribs without cutting through the upper face of the sheet. To achieve this use a pizza cutter and a straightedge. A pizza cutter is usually sufficiently blunt that the sheet isn’t cut. The crushed side of the sheet becomes the inner angle of the fold.

Pizza cutter

Pizza cutter … take care scoring the Correx

Making folded corners requires a little ingenuity but is obvious once you realise how the sheet folds 11.

Corner detail

Corner detail …

To fold with the grain requires a small amount of surgery. First cut on either side of a rib, then fold the sides back leaving a T-shaped piece – formed by the rib and a small piece of the upper face of the sheet – protruding. Then, with a steady hand and a sharp knife, cut the leg of the T away.

Folding Correx with the grain – cut one of the ribs away

The sheet then folds easily with the uncut face forming the outer angle of the corner.

Gluing Correx

This is tricky. I’ve tried every glue in my workshop and none of them work. The surface of Correx has some sort of treatment that means that glues do not adhere. There are tricks that involve flaming the surface to remove the treatment, but – at least in my experience – they are hit and miss.

Usually miss 🙁

There are commercial hotmelt adhesives 12 that can be used – like the ones the estate agents use to stick two signs back-to-back – but they are quite expensive.

Whatever the surface treatment is, it also prevents many sticky tapes adhering properly or permanently.

But there’s one exception … Unibond Power Tape Plus. It’s available in silver and black. Critically for beekeeping it’s both waterproof and temperature resistant. This tape is about a fiver a roll and this represents excellent value for money.

Sticky stuff ...

Sticky stuff …

I’ve got some Correx hive roofs held together with Unibond Power Tape that have been in constant use since 2014, outdoors (obviously) in temperatures ranging from sub-zero to 30°C or more 13.

Highly recommended.

To help the tape stick even better it’s worth gently abrading the surfaces to be taped together using wet and dry sandpaper and then cleaning with a solvent like acetone. Press the tape down firmly and check it in about a decade or so.

Uses

I’m going to concentrate on the uses I make of Correx, because those are the things I have experience of.

There are lots of other things you could use it for … for example, I’ve not built nuc boxes from Correx, but I know you can. They are increasingly used by the bulk commercial nuc suppliers. If you don’t want to build your own you can purchase these boxes for £9 to £12 each 14, flat-packed, in National or Langstroth formats. These boxes tend to use interlocking tabs to hold them together, rather than tape or glue. They might be suitable for short term, summer usage, but not for overwintering a nuc colony.

Roofs

I’ve made lots of Correx roofs and they are still in everyday use, either on hives or on stacks of spare boxes. I’ve described how to build them in detail, together with their pros and cons.

Correx in the frost ...

Correx in the frost …

Everything I wrote 7 years ago is still valid, so I won’t repeat it here.

A single 2.4 x 1.2 sheet of Correx is big enough to produce 8 roofs. Even if you can’t find Correx cheaper than £13 a sheet that’s still less than £1.75 a roof including the cost of the tape holding it together 15.

I routinely successfully overwinter colonies with Correx roofs covering a 50 mm thick block of Kingspan insulation.

Semi-permanent division boards e.g for vertical splits

In my experience these are one of the few things 16 that cannot be satisfactorily made from 4 mm Correx.

These types of boards might be separating brood boxes for a month or more while one half of a vertical split requeens. During this time the board tends to warp. The bee space increases on one side and is destroyed on the other. Consequently the bees build unwanted brace comb above and below the frames.

Split board ...

Correx split board …

I now only use my 4 mm Correx split boards in extremis. I know that some of the commercial beekeepers use 6 mm or 8 mm Correx split boards. The additional rigidity of the thicker Correx presumably withstands warping sufficiently.

If When I run out of equipment I’ve been known to use split boards as crownboards. For the same reasons – warping – I try and avoid using horizontal sheets of Correx in the hive for extended periods.

Temporary division boards e.g. Cloake and clearer boards

In contrast, Correx is ideal when used for limited periods in the hive. One obvious application is the removable slide in a Cloake board for queen rearing.

Cloake board ...

Cloake board …

Mine was built from a For Sale sign rescued from a skip in Newcastle. It’s one of the thicker pieces of Correx I’ve used (6 or 8 mm) and is significantly more rigid than the standard 4 mm sheets. However, I’m sure that 4 mm would do as the slide is only in place for about 24 hours to induce the emergency response and initiate queen cell production.

As I wrote in the introduction, the majority of my clearer boards are built from Correx. I now zip tie the escapes to the underside of the board 17 and then pair them with a simple eke when I need to use them for clearing supers.

Zip tied escape on a Correx clearer board

These work fast and efficiently, they don’t warp and they can be separated from the eke and stored separately (where they take up little space) if/when the eke is being used for something else (like a spacer to provide an upper entrance, or whilst vaporising from above the brood box).

Floors

The only floors I’ve built with Correx are those for bait hives when paired with two stacked supers. These work really well.

Inside ...

Bait hive floor

Bait hives should have solid floors, so if I want to use an open mesh floor on a bait hive I simply lay a small sheet of Correx on the mesh and remove it once the hive is occupied.

Varroa trays

Most, or at least many, commercial Varroa trays are made of Correx 18. To make counting mites easier it helps to draw a grid on the tray.

Varroa tray gridded to make counting mite drop easier

Of course, to make counting mites really easy it helps if there are few of them. Use miticides properly and at the right time. In that way your Varroa levels will never get too high and you’ll never run out of fingers when counting the mite drop 😉

OK, perhaps a slight exaggeration, but it’s certainly easier to count low numbers of mites rather than thousands. I’ve seen post-treatment mite drops so heavy you could trace patterns through the mite corpses with your finger, and the easiest way to count them was with a digital lab balance.

Ewww!

Landing boards

Almost all of my hives have Correx landing boards. Some are integral to the kewl floors I use …

Correx kewl floor landing board

… while others are attached to the outside of my bee shed.

Laden foragers returning ...

Laden foragers returning …

You can paint Correx with a variety of different types of paint. Radiator enamel or car spray paint works well. Using different colours and/or decorating the landing board with distinctive shapes helps bees orientate to the hive entrance and reduces drifting.

For vertical surfaces, try sprinkling sand onto the semi-dry paint before over-spraying to provide laden foragers better grip when entering the hive.

My white Correx landing boards are starting to exhibit UV damage after 4-5 years of use. Either avoid white, paint them or put up with having to infrequently (and inexpensively) replace them.

Miscellaneous

Most of my nucs are red 19 or blue. When I’m making up lots of nucs for queen mating I pin Correx shapes above the entrance to help the bees – and particularly the queens – distinguish between the hives. Again this reduces problems with drifting.

Correx signage on poly nucs

Almost all my nuc boxes are Thorne’s Everynucs. These are well designed except for the cavernous entrance. Again, Correx can be used to fix the situation; I use it to block the entrance entirely for travel, or to provide a much reduced entrance that is easier for the small colony to defend.

Correx, the beekeepers friend ...

Correx, the beekeepers friend …

I’m currently busy rearing my first queens of the season. The method I’m using involves sealing the standard hive entrance and redirecting the bees to an upper entrance 20. This process is really speeded up by leaning a sheet of Correx against the front of the hive, directing the returning foragers to the upper entrance.

Correx sheet redirecting returning foragers

Doing this stops the bees milling around the original entrance and is particularly helpful in borderline weather conditions e.g. low temperatures and intermittent showers 21, when it prevents bees getting chilled.

Correx and tape were used to build these ‘fat dummies’

Fat dummies for queen rearing? Correx to the rescue.

I could go on … but I won’t.

You’ve got the general idea by now.

If you’ve found additional uses for Correx then please add a comment below.


 

Footnotes

  1. Probably both.
  2. All mine are of a single design – blatantly copied from Polyhive on the BeekeepingForum.
  3. At least in the UK … I’ve no idea what estate agents realtors use in the US.
  4. It’s the best known trademark, the easiest to say and saves me typing the 34 additional characters needed for extruded, twinwall, fluted polypropylene.
  5. Or at least presenting, I don’t want to get close to the 3000 words exceeded by the last three posts.
  6. It’s should be delivered rolled or unfolded.
  7. Like Vote Cholmondeley-Warner.
  8. Or perhaps share the costs … and potentially even broaden your diet.
  9. Or spare fingers.
  10. Posca queen marking pens do though for inveterate ’notes on the roof’ beekeepers.
  11. See here for more details.
  12. Tecbond 261 for example.
  13. And, since 2015, in the notoriously arid Scottish environment.
  14. I’m not going to recommend any particular suppliers as I’ve no experience of any of them.
  15. For comparison, and serving the same purpose, a flat-pack National hive roof in cedar is about £55.
  16. For beekeeping that is … but you can build lots of other things, like boats and planes from Correx.
  17. Standard duck or gaffer tape does not work – the escapes fall off within 24 hours in the warm, humid atmosphere. Unibond Power Tape does work, but zip ties are easier to remove.
  18. As an aside, polystyrene Varroa trays discolour very quickly and this makes counting mite drop a frustrating exercise.
  19. Which of course appears black to the bees
  20. On which, more in a later post.
  21. Typical queen rearing conditions here in Scotland.

12 thoughts on “Correx: cheap, light, useful. Choose any three

  1. Frazer

    Thanks again David.
    I’m ,as you know, a convert to correx, and I used your idea of having only one wooden roof as a work platform in the apiary…
    The major benefit for me has been missed out by you though. It is…..
    The thought that if a bstd thieves my hives again, they will be more easily traceable and much less saleable!
    I did think of attaching a plug to the base of my hives so if some ‘unauthorised’ person lifted my hives and made off with them they wouldn’t know where the clouds of bees were coming from 😁😁😁
    Sorry to hear about the brood box incident. Been there, done that too😏

    Reply
    1. David Post author

      Hello Frazer

      Thanks for the reminder for the ‘one real roof’ in the apiary. I knew when I wrote the footnote about the Thorne’s cedar roof that they are not truly equivalent, but also knew that I was galloping towards another 3000 word article. There are only so many caveats I can include in every statement! To balance thing up it’s worth remembering – another caveat – that Correx roofs make ideal trays to carry home dripping supers.

      Supers in transit

      I’m not sure that thieves even keep the hardware when they steal a colony. Too many chances for hidden postcodes in the bottom corner of the brood box or whatever. I bet they just shift the bees (and/or split them into nucs) into another box and then use them or flog them. I don’t disagree with your view of their parentage. Only someone with an understanding of beekeeping would do such a thing, though they certainly aren’t “beekeepers”.

      I’ve heard of the ‘plug at the base of the hive’ trick, but never seen anyone actually do it. I wonder if it really works? I can think of other ways of achieving the same thing which might be even less detectable (and compatible with OMF’s). Perhaps a project for the winter?

      Cheers
      David

      PS Your email name always confuses me … apologies for calling you Neil earlier 😉

      Reply
  2. FRAZER

    No apologies required!
    I’ve decided, on a whim, that in the context of beekeeping I use ‘Frazer’ (but answer to anything. You learn to do that in the Police). I’ve learned Frazers speech of ‘The Auld Empty Barn off by heart. Always makes me laugh…
    Yes, thanks for the reminder of the use as a tray. Forgot about that one and its fast coming round to that time of year 🙂
    Bless you Sir,
    Frazer

    PS universalsitesupplies.co.uk are advertising 4mm correx in black only for £7.45 each for 10 off, plus vat and carriage .. total is £107.40
    Im going to invest in this as prices are going to rocket….

    Reply
    1. David Post author

      Hi Frazer

      I took the liberty of adding the link. Note that the page states that the sheets may be delivered folded in half lengthways … that might be OK, depending upon what you’re intending to build.

      I’ve also looked again at eBay. I think the best I can find is 3 sheets for £41 or 10 sheets for £130 though both state that the sheets will be sent not folded (or ‘flat’ as they say 😉 ).

      Fortunately I bought a lot a few years ago and have been moving it from house to house. The office I’m writing this in has 5 sheets of white Correx tucked behind the shelving units and the shed has at least the same amount of black Correx underneath the workbench. I cut the sheets into four to make them a little easier to hide store.

      Cheers
      David

      Reply
  3. Frank Lindsay

    I have used corflute here in NZ for years, all for free from real estate offices. Made lots of nucs but your ideas will add to it’s uses – thanks.

    My nuc boxes are a copy of and Auckland Beekeeper’s design, however I have wooden ends for stability and to hold the frames. Slightly deeper rabbits to allow bee space over the top of the frames, (the coreflute wraps totally around the ends) and ends are 25 mm deeper to allow for extra bees to accumulate under the frames to prevent early swarming when bees fill the nuc. (Idea from CC Miller).

    I cut half way through the corflute using a saw bench, folded it then lay it flat and ran a heat gun quickly backwards and forward along the cut until the edge just started to crinkle slightly then folded the corflute and hold it in place for a minute. The plastic bonds again into a strong joint. Yes, needs practice.

    For roofs I did the same thing but added a few staples to the fold over ends as they get a lot of use. Use the hot air gun to shape the sides in a bit at the bottom so you have to force the roof on to the nuc. This stops it blowing away in the wind.

    Only thing with corflute nucs is they require extra ventilation at the bottom (and one end) to allow any condensation to get away. A couple of saw cuts along the bottom seems to work.

    I enjoy reading your articles. Still learning after 50 years of beekeeping.
    Frank Lindsay
    NZ

    Reply
    1. David Post author

      Hi Frank

      Very interesting … and a whole lot more advanced than the stuff I botch together with Correx. I’ve not tried using a hot air gun on the sheets – either for joints or shaping them. I have tried flaming the coated surface to help glues adhere but it was tricky to heat it enough without melting it.

      My Correx roofs all splay out over time and – as you say – they have a tendency to blow away on a windy day. I just strap them all down. Frankly I’m amazed they have lasted so well. The black stuff seems remarkably UV resistant. It’s still flexible and semi-rigid (if that’s not contradictory) after 7 years in all sorts of weather.

      Delighted you enjoy the posts. I think one of the great things about beekeeping is that there’s always more to learn.

      Cheers
      David

      Reply
  4. Jonathan Court

    Hi David,
    I like a deep lid on my hives and cut my correx sheets so that I get three 74cm squares for the roof leaving five 46cm squares for numerous other uses, to cover moving supers, temporary crown boards etc. I made a bait hive out of an IKEA bedside table carcass and pinned a correx travel screen with mesh taped over a sizeable hole for the crown board, with a removable correx roof over the top so I could just lift it off for transport.
    I use Gorilla black tape which has not failed me outside the hive. Inside the hive it’s ok for a while but too long and sometimes the bees start to chew it.
    I expanded my hive numbers considerably this year and am using correx roofs over a 25mm insulation board square edged with silver tape, and a hive strap. I am still working on making an eke from 50mm insulation board with a space for fondant. Crown boards will be plywood. Certainly a lot cheaper than buying everything but time consuming. And much more fun.
    Would single sheets of 4mm correx work as dummy boards or would they need doubling to stop them warping?
    Thanks for all the tips and thought provoking info, always a joy to see your post updates in my inbox.
    Jonathan

    Reply
    1. David Post author

      Hi Jonathan

      Thanks for the tip about the Gorilla black tape. I see that regularly in the ‘Middle of Lidl’ (or was it Aldi?) and will give it a try.

      Perhaps try just a square of thick plastic – clear ideally – as a crownboard. I’ve got this on several hives at the moment and use it on all my bait hives:

      Bait hive, plastic crownboard

      I’ve been wondering whether two 4 mm sheets of Correx back-to-back and with the ‘grain’ running at 90° might stop of the warping. However, I think for a split board of some type you’d need to glue them together across the face of the sheet as each would otherwise warp, and separate. In contrast, two sheets, back-to-back and taped around the edge, might well work well as a dummy board. You’d still need to think of a constructive way to attach a top bar.

      Something to dabble with this winter as several of my ply dummy boards are busy delaminating this season (or have been for years, but are now too splayed to use).

      Cheers
      David

      Reply
  5. martin booth

    You might be able to pick up cheap or free Corex from your local football club, Corex is mostly used for pitchside perimeter advertising boards (if LEDS not used) . if companies don’t renew advertising then there’s 3ft x 7ft of Corex that is ready for the bin!

    Reply
    1. David Post author

      Thanks Martin

      Good idea. The advertising probably changes more frequently than political parties (perhaps annually?) so that’s definitely worth checking.

      Cheers
      David

      Reply
  6. Ivan Marples

    Hi David

    I am trying out Correx thanks to your previous posts on its use. Using Gorilla Exterior Wood glue (the cream coloured glue, not the clear glue that expands) and 24hr of clamping I bonded the corners of a roof, left outside on a bait hive for six weeks without any sign of dehiscence

    My experience is limited to n=1 (or n = 4 if you count the corners). Should I expect this bond to fail some time soon?

    Reply
    1. David Post author

      Hello Ivan

      I’ve not tried that glue, so can’t predict what will happen I’m afraid. All the glues I did try eventually failed, and I don’t think any got through a winter. However, in fairness, I didn’t try a huge range (just what was in the workshop) and I relatively quickly realised the specific gaffer tape I name (above) worked … the rest, as they say, is history.

      I’ve been using these roofs today to transport supers back from the apiary. I noticed that one has an early “2014” date on the underside, and is now over 8 years old and still going strong. Not bad for about £1.50 back then!

      If your glue joint lasts come back to this thread and add an update. I think comments stay open on posts for 24 months.

      Cheers
      David

      Reply

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