How To: Masking up: Best practice when working with marine epoxy
You’ve got your masking tape to hand and the waterline is ready to be marked up against the boot-top. But when it comes to the crunch, sometimes you just need an expert hand. David Johnson, Technical Operations Manager at West System International, explains how to mask up correctly and what, exactly, it has to do with marine epoxy.
I was walking through my local dinghy park recently and passed an unfortunate soul masking his waterline ready for antifouling. He was unrolling the tape about 300mm at a time and his waterline looked wavy to say the least. What’s more, his wife was standing back giving instructions as to the trueness of the line – no doubt she would be blamed for the finished result. It was too painful to watch!
I turned back and said, “Forgive me, would you like me to show you how to do this?”
I did this type of work three to four times a day when I was a lot younger and working in a boat yard but the art came back to me as though I had done it yesterday.
This boat was about 10m long, so I attached the masking tape securely at the stern and unravelled about 5m of tape, standing well away from the hull. Sighting down the strip of tape I could easily see a fair, true waterline as I followed my eye and the curve of the hull and laid the masking tape in a perfect curve. They said, “Please can you do the other side?”
What has this got to do with epoxy you might ask?
This is the same masking technique I have taught to many boat yard workers and individuals conducting an epoxy osmosis treatment to achieve a true and fair waterline.
There are two key points to consider:
- Choose the best quality masking tape money can buy
Due to the wicking nature of marine epoxy, it will defeat cheap masking tape and leave an indistinct ‘fuzzy’ line. 3M™ blue masking tape is my preferred choice.
- Double mask for an osmosis treatment
This tip applies to any scenario where you might require multiple coats. It gives you the option to remove a layer of tape after, say, three coats and still be masked up for the subsequent coats.
If you think about it, by the time you are applying the sixth coat you will have plenty of cured epoxy on your masking tape that will require a knife and straight edge to cut off. In fact, bringing your top layer of tape down by about 3mm will give a less distinct ‘step’ to the edge of the waterline.
Best practice masking up is all about work planning and choosing the correct materials and tools. As with many things to do with epoxy, it makes a lot of sense to think about things in advance.
Some time ago, for example, I was coating some locker lids for a sailing cruiser and could only coat one side at a time. On the underside edge I double masked the bare wood and removed the top tape after two coats. The underlying tape was removed after I had finished, thus removing all the large drips that had formed without the arduous task of sanding them away.
If you’ve got a boat-related technical question you’d like David to blog about, get in touch.