To Double layer the bottom ?

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Jim Dodd
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To Double layer the bottom ?

Post by Jim Dodd » Sun Jan 31, 2016 10:27 pm

I have for years on my canoes, on the outside, double glass layered the bottoms of my canoes.

I was making up some test samples the other day with carbon fiber, and Kevlar, and epoxy.

Just for kicks, I did a sample of one layer of 6 oz E-glass, and one of two layers of the same. Saturated them with epoxy, and let them set for a week.

It's incredible how much stronger the double layer was compared to the single layer. Not to mention the extra abrasion resistance !

Anybody contemplating building a canoe, I highly recommend double layering the outside bottom !

Make up a sample as I did, and see for yourself !

Jim
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Cruiser
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Re: To Double layer the bottom ?

Post by Cruiser » Sun Jan 31, 2016 10:31 pm

Hi Jim,

I like the idea of it being tougher, but some of my portages stretch to a kilometer. Any idea of how much additional weight that will amount to?



Brian

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Jim Dodd
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Re: To Double layer the bottom ?

Post by Jim Dodd » Mon Feb 01, 2016 9:38 am

Hi Brian

Weight will be a guess. It will depend on how much of the bottom you want cover, and the weight of the cloth.

My last solo, that's 16' 4" long. I covered to the 4" waterline with 6 oz E-glass. I would guess that the cloth, and 18 oz of resin, would weigh in at about 5#. In reality, this was a little over kill for a solo.

I could have used 4 oz and reduced the coverage, which would reduce the resin. Guessing you could get it down to half of that.

Any hull that is wide, or maybe over sanded, would benefit greatly !

I'm always reminded of one of my best friends that had built the lightest canoes around, required duct tape to make it back out of the BWCA one Spring. His hull cracked right down the center.

Me, I tend to over build. Every builder should weigh the possibilities.

Jim

PS I put my extra layer on top of the main layer. After the resin has cured for 24 hrs, I come back with a scraper and feather the edge. After varnishing, I can hardly locate the extra layer line! I've found this procedure to be the best.
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Patricks Dad
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Re: To Double layer the bottom ?

Post by Patricks Dad » Sun Feb 07, 2016 9:49 pm

An extra layer on the outside is an abrasion benefit but not as effective for resistance to impacts on the outside. If you want to protect against impacts from rocks hitting the outside, you should put the extra layer on the inside.
Randy Pfeifer
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Jim Dodd
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Re: To Double layer the bottom ?

Post by Jim Dodd » Sun Feb 07, 2016 11:46 pm

I've heard, and read that Randy !

I worry more about abrasion than impact. So far it's worked pretty good ! Even when a canoe flies off the top of my truck, going down the highway at 60mph.

Jim
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Re: To Double layer the bottom ?

Post by Cruiser » Mon Feb 08, 2016 8:54 pm

I was digging through the forum last week and ran into a series of posts suggesting that it isn't good to beef up one side of the canoe, that it is better to keep the strength on both sides the same.

I will go looking and post the link if I find it.

Brian

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Patricks Dad
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Re: To Double layer the bottom ?

Post by Patricks Dad » Mon Feb 08, 2016 10:24 pm

Brian,

The link(s) you are referring to are likely discussing the same topic I raised about the damage done by external impacts is largely focused on the inside and hence the need to put glass on both sides. But if the goal is primarily for abrasion, adding a layer on the outside is fine.
Randy Pfeifer
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Randy.Pfeifer1@gmail.com

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Re: To Double layer the bottom ?

Post by Cruiser » Tue Feb 09, 2016 10:10 am

I think you are correct Jim, it was a discussion on the technical stuff and what adding layers does and does not do. Pretty much what you are saying but with more words and explanation.



Brian

RBAIRD
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Re: To Double layer the bottom ?

Post by RBAIRD » Tue Feb 16, 2016 12:43 pm

Jim
I was wondering when you do the double layer, when do you add it?
The same day you glass the first layer or do you wait?
I plan on doing both sides as may have over sanded making the pattern on my Nomad
Thanks for your help Randy

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Jim Dodd
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Re: To Double layer the bottom ?

Post by Jim Dodd » Tue Feb 16, 2016 8:34 pm

To me there is only one way to double layer the outside !

I wet out the main layer of cloth, on the hull. I let it cure PAST the tacky stage. Lay on my second layer and wet it out and at the same time apply the first fill coat to the side. Wait an hour or two, and while the resin is still tacky, apply the second fill coat. I stick with this routine of applying fill coats while the previous coat is still tacky. Until I've completely filled my weave.

Some will put the extra layer underneath the main layer. The only trouble, is when it comes to sanding the hull, you will sand into the weave of your main layer, trying to smooth the hull. Thus creating a weak line all along the edge of the second layer. In my book that's just wrong !

On the inside. If you want to double layer the inside, and you don't sand the inside. You can put the second layer underneath. I still don't !

In glassing the extra layer on the outside, I come back in about 12-24 hrs, and feather that edge with a scraper. It's easy while the resin is still soft.

A pic.
Image
You can see in the photo, that I've applied at least two bias strips on the ends. I do these the same time I wet out the extra layer. I do the wide bias strip first, and then the narrow one. When done and varnished, it takes a real sharp eye to find the seams !

Good luck !

Jim
Last edited by Jim Dodd on Tue Mar 15, 2016 7:23 pm, edited 1 time in total.
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RBAIRD
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Re: To Double layer the bottom ?

Post by RBAIRD » Tue Mar 15, 2016 1:35 pm

Jim thank you, you have been a great help
Probably not the last question but I hope it is
I'm getting ready to order my epoxy I'm going with west and I'm getting 2 gallons, I am going to double layer inside and out with 6oz. Cloth is 2 gallons enough? Or to save on shipping should I order an extra gallon?
thanks again

sedges
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consider 4 ounce double and a caution

Post by sedges » Tue Mar 15, 2016 3:54 pm

I think that 6 ounce double layer inside and out is overkill unless you are really going bash this canoe around a lot. I went from 6 ounce inside and out to 4 ounce overlapped below the waterline inside and out. This has proved to be a durable lay-up for canoes that get used hard in rough places. You will save a lot of weight going to 4 ounce. It is also a very easy cloth to work with.

My current lay-up is 4 ounce overlapped to the waterline inside and 4 ounce overlapping at the keel and a layer of 2 ounce to the waterline outside. This is lighter still and still plenty strong.

The caution. When doubling layers both inside and out make sure your waterline layers do NOT match inside and out. A laminate that makes an abrupt change in strength ( 4 layers of cloth to 2) tends to break at that edge when stressed. I would make the inside extra layer 2 inches higher than the outside.

Two gallons should do it for any of the lay-ups discussed.

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Jim Dodd
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Re: To Double layer the bottom ?

Post by Jim Dodd » Tue Mar 15, 2016 7:15 pm

I agree with Sedges, double layering inside and out is a little much for a 1/4" thick stripper.

Just finished glassing the outside of my son's canoe. It's a little 14' solo.
We opted for a 6 oz main layer, and 6 oz extra layer to about the 4" waterline.
4 oz cloth was the same price as 6 oz cloth, so we use 6 oz. I agree the 4 oz double layer would be fine.

We will do the inside with a single layer 6 oz. I've built NEARLY everything this way.

I will agree this maybe overkill to some, and that's OK ! I want a bottom that doesn't oil can, and this works for me.
As for resin use, it will depend on several things. How big is the canoe ? Cloth thickness, Amount of fill coats (most people don't put enough on). How many if any extra fill coats on the inside? Many just go with one wet out coat on the inside. I like to fill the weave on the inside. So much easier to clean.
Flotation chambers, and if you glue your gunnels on. All these contribute to how much epoxy is needed.

Does West make a two gallon kit, resin and hardener ?

Good luck ! And Questions are always good. Sometimes we get different answers and that's good too !

Jim
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Jim Dodd
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Re: To Double layer the bottom ?

Post by Jim Dodd » Tue Mar 15, 2016 7:29 pm

Here is a pic of a hull with two bias strips and a double layer on the outside.
Image

Jim
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RBAIRD
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Re: To Double layer the bottom ?

Post by RBAIRD » Wed Mar 16, 2016 9:30 am

Thanks for the answers Jim west doesn't make a 2 gallon kit but I was looking to pick up 2 gallons worth
I am planning on using it for the rest of my glue ups
I'm building the 17' nomad
I'm not sure of the cloth thickness I'm going with the extra 6oz as it is less than 4oz and I do not want the oil can effect as my hull has 2' wide flat bottom
Thanks

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