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Boat Restoration Project - Fairing

When we first viewed Du Bleiz we knew that we wanted to fix the many ripples in the hull by fairing it. Most of the plate ripple would have been caused by welding distortion during the original fabrication, but there were also some impact dents typical in a 45 year old yacht.  What we didn’t realise was just how time consuming this would be. We had stripped the hull back to bare metal and repaired some sections of the toe rail and given it a coat of Muki EPS holding primer. We also applied a couple of coats of SML 2 pack surface  tolerant epoxy primer below the waterline. It’s accepted practice to fair over an epoxy painted surface, rather than fair direct to the substrate, provided that the paint is either not fully cured or has been given a mechanical key with 180 grit sand paper prior to fairing.  Painting the surface before fairing enables you to work the paint into  (and give protection to) pitted areas.

The DIY nature of the project meant we did not want to employ  a professional fairing company,  but we thought that getting a local plasterer in to help might speed things up  – we were wrong! We hired two plasterers who had done some good work on Malcolm’s house. The product we gave them to use was Jotun Megafiller Multi, packed in a 10L Comp A + a 10L Comp B.  Although expensive, it’s an excellent product. To mix Megafiller you simply add equal parts of each of the two components, so each pack will make a total of 20 litres.  It sounds a lot, but if your average thickness is 5mm, then a 20L pack will only cover 4m². It starts off thick but as you mix it becomes more smooth and runnier. I would say that the final consistency was not unlike smooth peanut butter – it’s sticky! It can be applied at thicknesses of up to 30mm per application and has a typical “pot-life” once mixed of 45 minutes at 23?C (considerably less at higher temperatures).  Click here for the data sheet. The plasterers claimed that it was more difficult to spread than plaster, and fairing requires a completely different technique to plastering,  but after five days the two of them had basically made a diabolical mess!  It appeared to us that they were just daubing the stuff on and then taking ages to sand it all off again. They were also wasting large amounts as they were overestimating how much they could do before it went off.

We had no choice but to let them go and attempt it ourselves. It occurred to us that how this should have been started was to identify all the low points and fill those first. Once the general shape was ok then skim the whole hull to make it uniform. The plasterers didn’t appear to have done this so the first thing we did was to locate all the high points by sanding back the filler they had slopped on! We then marked the low areas with a marker pen by eye and built up the filler in those areas. The major difference is that we were applying the filler smoothly so there was little need for sanding between layers. After each application we would leave it a couple of days to fully harden and just sand the edges and any trowel/float marks, review, mark and apply more filler. In the images below we used lines to indicate high areas and circles to indicate low areas.

Sanding
We sanded general areas with a Makita orbital sander and then used hand finishing sanders to insure we were getting an area as flat as possible. We tried sanding using an electric and also an air powered long sander, but they were very difficult to control on a vertical surface and quiet heavy.

I think we went through the process of sanding and filling, sanding and filling the whole hull about 15 times. On the last four times a sanding board was made out of 9mm ply, 1800mm long by 115mm wide.  Using double sided tape we stuck a length of 80 grit cloth-backed sandpaper (it’s 115mm wide) to one side of the ply and fixed 4 wooden door handles to the other side, so that the board could be used by two people together, sanding in broad sweeps over the surface.  Note the slots cut in the sandpaper and the ply;  this allows it to bend to the shape of the hull at the same time as keeping the paper stuck to the board.  It’s good exercise but tiring and very dusty as we couldn’t figure a way of extracting the dust!

Towards the end of the process we painted the hull with a coat of holding primer.  This is a very thin coat that sands off easily; as we sanded low areas are indicated by remaining paint. For more localised sanding of high spots we found the hand long-sander worked well.  It has a Velcro back and you can buy sandpaper on a roll to fit. 

In the end we reckon we had spent  approximately 250 man hours to fair an area of 30m². We used 100 litres of Megafiller and about 50 8” sanding disks.  It’s all about compromise – we probably could have achieved 90% of the result in half the time.  The final irony is that although it’s not perfect, the small imperfections that were visible when it was in the yard up in its cradle aren’t noticeable at all now that Du Bleiz is back in the water!

PART 1 -  Introduction
PART 2 -  The viewing, purchase and survey
PART 3 -  Preparing the deck and hull
PART 4 -  Finding corrosion
PART 5 -  The Bilge
PART 6 -  Fairing
PART 7 -  Painting - Primer

 

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