Stringers AARGGHHH!

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blueflood
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Re: Stringers AARGGHHH!

Post by blueflood » 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 ?

Marc



fallguy1000
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Re: Stringers AARGGHHH!

Post by fallguy1000 » Fri Jan 24, 2020 9:11 am

OneWayTraffic wrote:
Fri Jan 24, 2020 4:54 am
I 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.

C9DCDEC7-1E4F-4014-9FC6-F755D894CB61.jpeg

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.
AE901D4D-D348-48F3-8A5F-3A523775FF3D.jpeg
Photo clamping board with glue.

Then put one over the other and weigh down.
4BD99848-333D-4137-9333-21C08620D0C6.jpeg
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?
3E58DFB1-F7E4-4133-8B61-4B56F2342B48.jpeg
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.
Okay, I have some advice.

1. That is NOT cabosil. The white stuff looks like qcel or balloons which is used as fairing compound and does not have the same properties as cabosil or aerosil which is never white when applied. The balloons are ez to sand and don't have the same mechhanical properties. Take a picture of the bag. I have never seen white cabosil.

2. The thickened mixture is too runny. It should be like peanut butter. When you clamp; a good job should have minimal squeezeout. Balloons are a bit like marshmallows and they never firm up.

3. Both sides of the boards must be troweled out with a trowel for consistency. You can use a 1/16th" u trowel. A bigger trowel will require LOTS more glue. If you only have a 1/8 trowel; trowel on side out perfectly.

4. After prewetting the plywood; you wait until gel time. Otherwise troweling the thixo is impossible. The wood will be really sticky. That is a good thing. Do not mix the resin until the thing is tacky because troweling takes time to do right. Troweling over wet epoxy is a no-no here.

5. It takes quite a bit of epoxy, more than what it looks like you used, but less if you mix it a bit thicker.

6. This work is finicky, but not too hard. Ask a lot of questions; there is a lot of experience on the forum and people are glad to help.

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.

8. If you continue to use the wrong glue; the entire boat will have weak glue joins. So, please make sure and review this issue. It looks like you are using a fairing filler. By the way, I did the same thing on one of my bottom to hull joins and used ballons. Fortunately, I stopped doing that. The possibility exists that the material is cabosil, but it really looks like marshmallowy balloons.
My boat build is here -------->

viewtopic.php?f=12&t=62495

fallguy1000
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Re: Stringers AARGGHHH!

Post by fallguy1000 » Fri Jan 24, 2020 9:16 am

ps. Once you stick two sides together with 1/16th trowel each side and the proper glue; they will almost not be able to be pulled apart wet. They will slide, so consider spot screws. Things like to slide after you pour a beer amd are not looking.

Don't stand on them.

If you put weights on them; place the weights on a couple of 2x4s to balance the loading below.

Again, glue squeeze must be minimal when done right.

Another way to do this job is to put a piece of 1708 fiberglass in between the stringers instead of glue. The wetted 1708 is about the ideal size for a glue joint. About 40 mil Or one millimeter is a good joint. The 1708 method is done if you want to use mechanical fastenings and thus avoid squeezing the glues. I don't prefer the method here unless you screw things together.

Feel free to pm me any more questions as I check the forum daily, but don't read all the posts.

Sorry if I wasn't clear enough before.
My boat build is here -------->

viewtopic.php?f=12&t=62495

fallguy1000
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Re: Stringers AARGGHHH!

Post by fallguy1000 » Fri Jan 24, 2020 9:41 am

Also, consider this failure a win if we identified a filler error now. If I am wrong; I would be surprised.
My boat build is here -------->

viewtopic.php?f=12&t=62495

piperdown
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Re: Stringers AARGGHHH!

Post by piperdown » Fri Jan 24, 2020 10:21 am

Also, 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.
Eric (aka, piperdown)

"Give an Irishman lager for a month and he's a dead man. An Irishman's stomach is lined with copper, and the beer corrodes it. But whiskey polishes the copper and is the saving of him." --> Mark Twain

OneWayTraffic
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Re: Stringers AARGGHHH!

Post by OneWayTraffic » Fri Jan 24, 2020 12:05 pm

fallguy1000 wrote:
Fri Jan 24, 2020 9:41 am
Also, consider this failure a win if we identified a filler error now. If I am wrong; I would be surprised.
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.
It’s recommended for everything except fairing.
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OneWayTraffic
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Re: Stringers AARGGHHH!

Post by OneWayTraffic » Fri Jan 24, 2020 12:13 pm

blueflood wrote:
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 ?

Marc
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.

OneWayTraffic
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Re: Stringers AARGGHHH!

Post by OneWayTraffic » Fri Jan 24, 2020 12:22 pm

piperdown wrote:
Fri Jan 24, 2020 10:21 am
Also, 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.
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.

OneWayTraffic
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Re: Stringers AARGGHHH!

Post by OneWayTraffic » Fri Jan 24, 2020 12:30 pm

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.
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.

fallguy1000
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Re: Stringers AARGGHHH!

Post by fallguy1000 » Fri Jan 24, 2020 12:31 pm

OneWayTraffic wrote:
Fri Jan 24, 2020 12:05 pm
fallguy1000 wrote:
Fri Jan 24, 2020 9:41 am
Also, consider this failure a win if we identified a filler error now. If I am wrong; I would be surprised.
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.
It’s recommended for everything except fairing.
All good. Just too loose then.
My boat build is here -------->

viewtopic.php?f=12&t=62495

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