My plan for infusing a canoe with vinyl ester resin

[ahender]

The company I purchased the resin said 25 minute working time. The directions on the can say 15 minutes. This has me a little concerned.

I will be infusing a 12 foot canoe mold. It will be an ultralight. Target weight with all trim and seat is 20 pounds. My goal is for everything to be composite. I have carbon, s-glass, and kevlar. The first canoe will be s-glass.

My thought is three 1/2" resin lines (3/8" hole diameter"). Center bow to stern (about 18" from each end) and one on each side half way up (three parallel resin lines). Each will have a 6" wide mesh under the feed line similar to Enkafusion. The furthest the resin will flow is 60". I do not want to put mesh over the entire hull. It will speed the infusion time but waste a lot of resin. I assume just after the resin passes each feed line, I then release the resin flow. Is this correct? Does air in the line prior to the resin flowing matter?

Does the resin bucket have to be below the resin inlet or can I place it higher up to reduce the length of tubing?

I'm thinking of heating my mold to about 80-85 degrees and chilling the resin to about 60 degrees to give me extra feed time. Is this a good strategy? The resin is supposed to have a viscosity of 200 mpas. I'm thinking lowering the resin temp 10 degrees will give me 30 minutes and heating the mold an extra 10 degrees will "theoretically" reduce the viscosity back to normal. I'm in the Southeast USA so mornings are about 70-75 degrees.

Step 1: Gel coat. One thin coat entire mold then an additional coat bow, stern, bottom. Both the gel coat and infusion resin will be colored. The directions which came with the "white" gel coat states "Colored gelcoats can require up to double the amount of hardener shown." White is a color. Bought this from US Composites. Should I call them for clarification? The instructions state 1/8 oz MEKP per pint.

Step 2: 9 oz s-glass over entire mold and an additional layer on the bottom and slightly up the side (impact areas). Additional reinforcement bow and stern. I estimate 50 oz of fiberglass per layer. I estimate 33 oz of resin will be needed for the fabric. 50 divided by 1.5 (60/40 ratio of fiberglass to resin.) The mesh and tubing will also be factored into total resin needed.

Step 3: The core. This one I am still experimenting with. I will lay down one or two layers of 6" drywall mesh. Two layers on the bottom, bow, and stern and one layer on the rest of the hull. With a spreader, press and skim coat the mesh with Gorilla glue. I have done test runs on a flat surface with the mesh and glue. It is extremely hard, light, flexible, and waterproof. It's going to be a booger to shape, sand, rasp. I have looked at all possible core options and none of them do anything for me. Either too expensive or low durability. I do not mind the extra labor. I'm embarrassed to say how many hours I have in this project. So what's a few extra hours? Okay, maybe more than a few… Tonight I will experiment with adding a little fumed silica to prevent the glue from running.

Step 4: I'll have to add a skim coat of thickened resin to level the foam core after it is shaped. Added weight but will be required.

Step 5: Repeat step 2.

Step 6: Paint or gel coat.

My biggest concern is how long the it will take to infuse each section. I will do a small test to get a better idea.

Thanks … Alan

 

[Chris Rogers]

Hi Alan,

Your drywall mesh has me both interested and concerned! Will you made a complete flat test panel of the whole laminate? It would be very helpful to test your process before laying up a full hull. You may find it easier and lighter to use a standard core material like Soric or thin contour-cut foam. Your two piles of 9oz glass should be about 3.5-4oz/square foot. Adding a core of 1/8" 5lb core should bring you up to 5-6.5 oz/square foot. Adding 2mm Soric would give you about 6-7.5 oz/sf - maybe a little less with Soric LRC. VE resin will infuse nicely but unless you use a core that is also a flow media you will probably want to use at least some surface flow. Try a test with no mesh and see if it goes the distance. Consider using a perforated release film between the peel ply and the flow mesh. It will throttle resin flow and make removing the mesh easier - especially from a single skin area only 0.03"-ish thick. Make sure to leave a good zone of a few inches free of flow media before the resin gets to the vacuum perimeter so the resin can catch up and even out without leaving dry spots.

You will do well heating the mold but deliberately cooling the resin is probably not necessary and will increase the viscosity in the tube. This is more applicable to epoxy than vinyl-ester because of the cure process - which is less abrupt. Within reason you can adjust the catalyst rate which will change the cure time. The resin jug - or better the manufacturers data sheet - should tell you a gel time at a temperature for a given catalyst percentage. They may specify a minimum catalyst percentage - like "no less than 1.5%" or something - so just don't go below that.

The issue with putting the resin bucket above the part is siphoning - and the risk of getting a pool of resin growing in your part faster than it can spread out. If you have the pot at roughly the same level as the part this should be fine. Below is good, way above is less ideal but if you watch it and have adequate flow media it should be ok. You may want to adjust the speed of resin flowing into you part by partially clamping the tubes.

Do you think you could skip the three steps and just use the drywall mesh between the two layers of glass in one infusion? There's a product I was playing with recently called powerRibs by Bcomp - its a flax mesh - like a big screen made of stitched rope. It adds a similar mico-grid structure for stiffening. It does use a lot of resin but the idea is sound.

I'm interested to see how your drywall mesh tests work!

 

[ahender]

Thank you very much for the feedback and suggestions. I did a very small test with drywall mesh, Gorilla glue, and fumed silica. I think it will work quite well. I used a very thin mesh, not what I will typically use. That roll of mesh has vanished (been misplaced) so I ordered more. I think adding a thickener will help with a more consistent expansion, as well as keeping it from running on a vertical surface. So far I have not added moisture. I will test adding a fine mist later today.

Alan

 

[ondarvr]

Canoes and other small craft like this do better without a core, and when using carbon and kevlar you're much better off going with epoxy.

The shape and contours of the hull are designed to enhance the stiffness if needed. But with epoxy and carbon it doesn't take much to do this.

Spraying gel coat thin can lead to problems, so try for at least 12 mils.
The reason they say colored gel coats may need more catalyst is because they tint them themselves, but don't adjust the gel time afterwards.

Adding pigments can slow the gel time, the more you add, the longer it may drift out. White is not a color in this aspect.

Don't cool the resin much, the viscosity increase will just slow the infusion down. You are better off getting the correct resin, or using a different catalyst that will extend the gel time like HDP75.

I'm assuming you got an infusion resin.

 

[ahender]

Thank you very much for replying. The first attempt I will be using fiberglass. I've decided to roll the gel coat. The pigment ratio is one ounce of pigment to 1 quart of gel coat.

Yes, using a vinyl ester infusion resin.

Alan