Re: Stringers AARGGHHH!
Posted: Fri Jan 24, 2020 8:41 am
..and confirm; your pieces have been pre-wetted ? i.e. coat of epoxy on both pieces prior to spreading the glue ?
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Okay, I have some advice.OneWayTraffic wrote: ↑Fri Jan 24, 2020 4:54 amI just needed to get that out. This is fustrating.
Boat is a C17 and I have a build thread C17 in New Zealand.
Photos will follow when I edit this post on my iPhone.
I spend 4 hours last night laminating two layers of my transom (12mm x2) and stringers. This is my second attempt at stringers.
First I thought I would show my method in case there is something I am missing.
I dispense epoxy into a cup (WEST with slow hardener, using pumps this time, and I checked the first few batches on a digital scale to confirm the pumps are on ratio.)
Then I mix for about 1 minute, maybe 2, scraping sides and stick etc.
The cup is paper lined with a 'bio plastic' called Ingeo, it is not waxed.
Then pour into a bigger plastic mixing container.
I then brush this on with a chip brush wetting the entire surface.
I then get some more epoxy thickened with Cabosil (Wood flour is not available commericially in NZ.)
Brush that on one surface until it looks like this.
Photo clamping board with glue.
Then put one over the other and weigh down.
I followed this exact same procedure for my stringers, and one of them (call this bad stringer) has a good half metre near the front where there is daylight between the layers! I drilled small holes visible here and in the end I could get a saw blade through! I then got my holesaw and took some plugs out of both stringers.
The plugs on here from my 'bad stringer' show delamination between the layers of plywood. This is the same stringer with the daylight near the front. I could pull these apart by hand.The epoxy on the left plug shows no sign of being in contact, it was smooth.2F765C77-934B-488F-9F85-3670B19D32C0.jpeg
The plugs on the right from my 'good stringer' show a nice solid bond, but who is to say that there isn't voids in that stringer somewhere?
My options at this point are
A) to attempt a repair, cutting out the whole front of the bad stringer and regluing, taking several plugs out of both stringers checking and epoxying back etc, then when I finally put this in the boat wrapping the whole stringer with so much biaxial that it won't matter what it is made of.
B) Buy some more plywood and try again, but if I do this I really need to rethink my lamination. How does one ensure that the stringers are bonded everywhere? And if not, how close to everywhere do I need to be? Obviously rocks every half metre or so isn't cutting it.
If it makes a difference, I have far more glass than I need (it was economic to buy a 100m roll of double bias) but am curently out of plywood, except scraps.
I am glad that at least that is not the problem. I'm using a 20L bag of WEST 406. I used it without issue on my dinghy.
Laid on thick with a chip brush. The wood is very dry, but I did wait for a while before adding the glue. I didn't get to the stringers until I had glued the transom.
WEST recommends ketchup for bonding large flat surfaces and mayo or pb for general bonding or uneven surfaces. I was working within those guidelines, or so I thought.piperdown wrote: ↑Fri Jan 24, 2020 10:21 amAlso, to keep them from sliding apart you can use wooden dowels to keep them lined up.
After cutting and shaping, clamp them together and drill some holes for dowels. Precoat the wood ( I also don't think you used enough nor thick enough) let gel, mix up some more epoxy and thicken it appropriately, spread, then insert the dowels in the first piece and then put the second on top lining up the dowels.
I used screws to clamp some items together along with weights spread out.
Have you gone around to any commercial woodshops and requested their sawdust? From there if you have a sieve you can use it to get the fine particles. Can't recall who it was on here but that's what they did. From a 5 gallon bucket of sawdust they got about 2 lbs of woodflour.
Thanks Fallguy this is exactly what I needed to hear. I've had a whole 5 hours sleep, and for now I'm going to do nothing but drill a few plugs in my transom. If the bond is good I'll accept it, if there are issues I'll rebuild that as well.7. I worked with a guy years ago who told me to do it right or don't bother. Sometimes, it is better to fail twice and teach yourself to be careful than mush on with errors. At the beginning of my build we struggled for a couple months learning to vac bag. I build a couple of large 33 foot long panels that cost about $1500 each that I rejected. I recommend you suck it up, accept the error, and make new stringers. They are the backbone of the boat and you will always be glad you did them right.
All good. Just too loose then.OneWayTraffic wrote: ↑Fri Jan 24, 2020 12:05 pmI am glad that at least that is not the problem. I'm using a 20L bag of WEST 406. I used it without issue on my dinghy.
It’s recommended for everything except fairing.