Preparing Sumara – Stripping the Mast

These three tools stripped 99% of the varnish with the help of a heat gun

These three tools stripped 99% of the varnish with the help of a heat gun

You can see just how thick the varnish was

You can see just how thick the varnish was

26th December 2013 South Dock Rotherhithe

Sumara’s mast is now 23 years old and the varnish has never been stripped off. Despite a trip to the Caribbean and various trips to colder places the varnish actually looks pretty good. However each year there are two or three blisters which need repairing. When I prepare the blisters for primer coats it is obvious that the bond between the thick varnish and the timber is giving way. It would be possible to slide a scraper blade under the varnish and lift a much bigger area. Although I could leave major work on the mast for a few more years it seemed wise to tackle this job while the boat is next to home in South Dock before leaving on the Russian Expedition. There is very little evidence of water penetration so the timber all looks clear of staining. The mast is made from Douglas Fir as a hollow box glued with resorcinol resin and solid by way of the spreaders and winches.

I decided to take off only the necessary fittings but to leave the track and fittings around the spreaders in place. Using an AEG heat gun with two speeds and six heat settings I softened the varnish and lifted it off with an 30 mm wide Hamilton scraper – slightly blunted to avoid scratching. The thick varnish lifted off easily in sheets. I then scrape over the area again without heat using the brilliant Bahco Ergo Scrapers. It was interesting that the newly applied varnish (in the repaired blisters) was really hard to get off because it had better grip on the timber and less thickness.

For the most part the stripping was pretty trouble free but some areas lifted patches of the grain. This was hard to prevent even by scraping gently across the grain but it is limited to a couple of areas about three inches long. I’ll need to see what it looks like once the mast is sanded but I suspect it won’t be worth trying to fill or scarph in a grafting piece. It is possible that the grain lifted due to the timber being very slightly damp. All the more reason to get the old varnish off. I didn’t quite finish all the scraping on Boxing Day due to it getting dark but the process would be complete after eight hours work (the mast is 36 ft long).

That said, I think I need to spend another two full days to remove the fiddly bits and to sand the mast prior to varnishing. I am debating the idea of giving it a coat of preservative first. It will eventually be varnished with Epifanes Gloss Varnish.

I have invested in the Festool Linear sander which I hope will make the sanding process very fast (I need to sand between each coat of varnish too so that is nine x 36 foot!). I have to make up a profiled block for the linear machine which only sands with a back and forwards motion. The profile will match the curved corners of the mast perfectly. I hope to be able to sand the mast in two hours using this and other machines.

I’ll post some photos later and update as I go.

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