I just came from another thread where Minaret told us that every boat with balsa core
. He seems a bit disgusted with balsa cored boats but then again his current
boat doesn't have balsa core
and on CF we always claim that what we don't have is bad, bad, bad
But he might well be right because my high tech SCRIMP process layup
with vinylester resin did develop a soft spot on deck
which I was sure was core rot
This case was rather easy to deal with because it is a very small spot and there is good access from below. I'm also not impressed much by fiberglass
damage because I worked with it since building my first (Mirror) dinghy
First step was to take a drill with 4.5mm bit outside and drill holes all the way through around the perimeter of the soft spot. There were small but clear circular cracks around two areas, each baseball size and I drilled in the center of each too., clearly this is impact damage and water
got through these cracks into the core. Here is the first picture taken from underneath and after this drilling:
The discoloration already suggests that the damage goes a bit beyond the outline of the soft spot as can be expected. We have a 1" thick balsa core here.
I decided to tackle this from underneath in order to limit the repair work on deck
as much as possible. This makes it a bit tougher to do because gravity works against us, but I got used to that anyway
I got a 60mm holesaw from my collection and opened it up:
This immediately removed the worst of it plus it allowed to remove more around these holes. I later had to make two extra holes for a total of 4 in order to get to everything. After removing all soaked balsa it's time to dry everything out, for which I use a continuous fan and a heatgun every hour or so to blow it out with good hot air. Using a small flashlight You can easily see in between the fiberglass
layers if there is more rot or not.
I did find that the pieces of end-grain balsa were encapsulated by resin, but not so well as I thought it would be. It almost looks like the rot was able to pass through into the next balsa piece, dissolving these barriers. From now on I will state that water
damage will be limited to the damaged balsa pieces plus one circle of pieces around those for every 10 years it has been wet. The pictures still show very clearly a hard line for the extend of the damage and those are the resin-filled spaces around the pieces of balsa. Only with the SCRIMP process you get the encapsulation to this level so that damage is contained.
The next step is the hardest part and that is to make the upper skin water tight again. There are too many cracks to fix them from above, so I will laminate a single
layer of woven cloth from beneath , through these holes, to the underside of the upper layer of fiberglass. This is where gravity will be my enemy but it'll be okay. I have 12 ounce woven cloth and epoxy
, both from West System, that I'll use for this. When the upper skin is waterproof again, we'll have to fix up the core and then close the bottom. I will then likely re-drill some holes from the top and the bottom to use for injecting a slightly thickened resin to fill up the voids that I will have in the core. The deck is slanted pretty good here so I can do half or more of the injecting from below. I will still drill some holes from the top for that so that air can escape and I can see resin come out when the area lower is filled up. I'll add photo's.
I was very close to grabbing the Fein Multimaster and cut out a rectangle of the visible spot instead of just these holes. It looks like it will be easier and faster that way and that is surely true for fixing the upper layer of glass. But from there on it will be more difficult for putting on a new core and new lower fiberglass laminate restoring original strength or better.
Another option is to do it from above and this is the quickest way until it's time to do the finishing. These skins are very thin and I like to keep them intact as much as possible.
To be continued...