Polytunnel Part 8 - Protective Tape and Covering
Good day to you! If you've followed me this far, then you must be dedicated! These are my allotment diaries and recently, I have been putting together a series of posts looking specifically at the polytunnel build process. This is the latest in the series and looks at the steps taken to prepare the frame for covering, and then moves onto fitting the polythene cover. So let's get stuck in!
The polytunnel kit comes with foam heat protection tape, and some gaffa/cloth tape. These are used on the metal frame in locations where the polythene will come into contact with the metal framework. The thinking behind the foam protective tape is that during periods of sunshine, the metal framework can get very hot and if the polythene cover comes into contact with that hot metal, then it can degrade quicker. Also, despite being stretched drum tight, there will always be a little bit of movement, especially when windy, so having the foam tape in place stops the polythene rubbing directly onto the metal. Finally, the gaffa tape is used to wrap around the ends of the ridge pole where the ends can be sharp.
Once all the framework is taped over, the instructions also advise to tape over the cut edges of the rebate battens around the base rail. This helps prevent snagging the polythene as it is stretched over the base rail.
The next steps are definitely two person jobs. There's A LOT of pulling and pushing to get the polythene cover into place. In fact, it would be of a better help if both people also had 3 hands and arms! The polythene cover, although pre-cut to measure for your particular polytunnel size, it still quite generous, so there is ample to go around. However, making sure it's draped square and equal before anything is nailed into place is worth doing.
We started work on the middle of the door frames first, attaching a batten across the top of one door frame, but only using a couple of nails in the centre of it. We then moved to the opposite door frame and were able to put our full body weight behind the polythene to pull it tight across the ridge pole length of the tunnel, fixing it into place with another batten across the top of the door frame. Time for a coffee break and a think...
The next stage of securing the cover starts down one side of the tunnel, in the centre. At this point, we weren't trying to put any significant stretch or tension into the cover. Just enough to take wrinkles out, and for it to be held in place along the length of the tunnel.
Through a combination of pulling, stepping on, kneeling on and hammering, we then worked on the opposite side of the tunnel. This time, the aim was to get as much tension into the cover as we could, but above all, making sure there were no wrinkles or folds introduced or left in the cover. This took a lot of effort, but we got there in the end.
After everything was as tight as we could make it along the length of the tunnel, it was time to turn attentions to the door frames. This again is where the instructions and especially the instructional video were invaluable. Just being able to watch someone else pull the pleats into place, and how they achieve good tension in the cover is invaluable. First we worked along the rest of the top batten across the lintel of the door frame, before starting to use more strips of batten down the left and right of the door frame.
I found that as well as pulling diagonally down on the cover to add the right pleats and add more tension to the end of the tunnel, I also need to pull upwards a reasonable amount too. This was to make sure that the ends of the tunnel off the curve of the hoops, was also flat and tight. After doing this, all the cover was tight, but not what you would refer to as 'drum tight'. Back in part 7, I wrote about how the whole base rail frame was lifted by around 6cm temporarily. Now the cover had been secured into place, to add the final tension into the cover, we once again loosened off the bolts holding the base rail into place, and were able to carefully stand and put our body weight down onto the base rail, stretching the cover as we did so. Starting in one corner, we pushed the base rail back down the 6cm it had been lifted, and then bolted it back into place. By the time we did this all the way around the tunnel, the cover was then really tight and looked really good. When the weather warms up and the polythene becomes more supple, we could probably loosen the bolts off again and get it even tighter. For now though, it's as tight we as can possible get it.
Once the base rail had been pushed back down to it's original level (and after much huffing and grunting), we trimmed off the excess polythene from around the door frames and then added the final pieces of batten across the bottom base rail between the door frame and the corner of the hoop frame. Finally, the doors were added into the frames, and because they had already been fitted once back when the timber door frames were being built, they went in very easily.
To round off this epic and long shift on the plot, I finished off by adding the door hasps onto each door so when the doors were closed, they could be held securely in place.
Though the tunnel is looking almost finished, there are still a few things I want to do before I can call it 'job done' on the construction front. You will notice in the picture above that we have a lot of excess cover around the tunnel edges. I will be trenching some of this in around the perimeter of the tunnel, before removing any excess but that will be left for the final part in this series. I'll need to get that part done in the next day or so as we are forecasted 50 - 60 mph winds in the coming days, so everything needs to be secured down as much as possible before then!
Until next time, thanks for reading 😁
