Sunday, April 12, 2015

More Detail on the Micro Repair

My recent post http://rosslillistonewoodenboat.blogspot.com.au/2015/04/micro-repair.html about repairs to a Phil Bolger Micro generated quite a bit of interest, and the following comment from Dave is an example:-

Thanks for the blog post, Ross, but you left out the details on the very parts I'd be most interested in seeing!

So if you do a future post on the nitty gritty details of truing up and patching the damage, I'd be most interested in that. 


Well, after taking initial photos of the damage, I didn’t many more during the repair process, simply because of time pressure – but here is a brief look at some aspects of the job: -


Initial job was to do a rough paint removal around all of the damaged areas to get a clearer idea of the extent of the damage, and to remove components/timber which had been destroyed. It also allowed ventilation and thorough drying.
Initial job was to do a rough paint removal around all of the damaged areas to get a clearer idea of the extent of the damage, and to remove components/timber which had been destroyed. It also allowed ventilation and thorough drying.

A small puncture wound on the forward/starboard topsides on the outside, and

....the corresponding spot on the inside

Brutal removal of paint, damaged timber, and broken epoxy fillets 

Brutal removal of paint, damaged timber, and broken epoxy fillets

Paint removal from around the forward bulkhead on the interior of the cabin, where the floorboards had punched through.
Most of the work shown above was done using a heat-gun and a variety of sharp scrapers. The paint was all two-part epoxy primer/undercoat and two-part polyurethane topcoat (I know, because I built this particular boat myself fourteen years ago!) and removal was not ever going to be easy. However, the heat-gun and scraper combination is a good choice as long as you are very careful about never overheating the material and damaging epoxy adhesive and paint in locations which are not part of the repair. Other primary tools include chisels, 4" angle grinders, drills, sandpaper - and elbow grease!

Next stage was to carry out a more gentle sanding  using (in this case) a 5" random orbit sander, going down through the grits to about 120 or 180. On the internal areas, the job is more difficult to achieve, and I made heavy use of a Fein Multi-master detail sander and plain, simple sandpaper on a sanding block, or folded triple. Hard work!
See above comments

See above comments
I don't have many photos of the next stage, but it mainly involved pulling usable components back into position using a variety of improvised tools such as lengths of purpose-cut steel angle-iron with holes drilled at strategic locations, and also temporary through-bolts and backing pads. This work can be very satisfying if done properly, and with attention to detail. The key is to have an open mind, and to be prepared to be bold with your surgery.

Once I was happy that my bracing would all work, and that all interfering debris was removed from joints, I opened the whole lot up again, and even spread damaged components further apart (using wedges and chisels etc). With the components held apart, it was relatively easy to treat all surfaces with un-thickened epoxy resin and hardener in order to prime the mating and damaged joints using disposable bristle brushes. This is a very important step if you expect to achieve a good structural repair. With the work area well primed, it was then a matter of applying a rich mix of epoxy/hardener combined with the recommended structural glue/filleting powder additive.

With the structural epoxy  mix worked into all joining areas, I screwed, bolted, or clamped the repaired sections together, which is why the previous work dry-fitting the bracing and jigging was such an important step. Where appropriate, I applied structural epoxy fillets at the same time.


The above two photos show steel angle braces screwed into position over the epoxied repair. In the case of Micro I had the luxury of using straight sections of steel to hold things in place, but on more conventionally shaped boats the same thing can be done using shaped and bent timber splints. I'll show an example of this in an up-coming post on a Whitehall repair.
Interior shot of the repaired bow transom, topside planking, and forward bottom planking. This was taken while the initial epoxy work was still wet and ugly. This work was followed by additional cosmetic epoxy filling.
Exterior shot of the starboard, forward topsides repair taking place. The actual puncture damage is quite a small spot underneath the centre of the plywood pad.
Matching plywood pad on the inner surface of the topside panel. As you can see from the exterior shot above this one, I placed twelve screws through the hull and into the internal plywood pad and pulled them in tightly over the epoxied repair. Note that both pads have been covered in a film of plastic to prevent them being glued to the hull permanently. All of those screw holes had to be repaired later, but the repair turned out well. The plywood pads were large enough to take up the curve of the topside planking when screwed together.
Structural work complete, glass applied where required, fill and cosmetic work done, and the two-part epoxy primer/undercoat applied (the white paint - three or four coats)
Topcoat (two-part polyurethane) applied, with just some minor black line work to be done between the green topsides paint and the off-white bottom paint (that is my little step ladder relected in the paint by the way).
Because of a lack of photos, time and space, this has been a very brief overview of the job, but it may give you some inspiration. Unfortunately, I have no photos of the way I repaired the forward watertight bulkhead of the cabin - a job involving more steel angle bracing and numbers of temporary through-bolts, nuts and fender washers.  In a post in the not too distant future, I'll show the repair of a glued-lapstrake Whitehall tender which suffered very serious damage to her hull in an accident. Most people considered her a write-off, but we were able to give her a new life.

Just a word about repairing screw and bolt holes. Many people simply fill the holes with thickened epoxy and sand the surface smooth after curing. I do not do this because the "cylinder" of hard epoxy in the screw hole intersects the surface of the repair at 90 degrees, and is sure to result in a circular crack in the paint after cycles of expansion and contraction due to temperature changes over time.


My approach is to heavily chamfer the hole on the inside and outside surfaces using a wide countersink or by dishing-out the surface using a sander. Then I fill the hole and the chamfered areas - this gives much less of a stress-riser where the epoxy fill intersects with the surface. However, if the repaired holes are going to be covered with a layer of fabric set in epoxy, this step is not necessary.

2 comments:

  1. Thanks, Ross - nice writeup, and good-looking repair! That's just the kind of information I was hoping for. That epoxy is good stuff, isn't it? -- Dave

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  2. Thanks, Dave. The Whitehall repair I mentioned is much more interesting - I just need extra hours in each day so that I have time to write!

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