Vinylester layup over H80 core 2 sides at once

First- I am a backyard hack. I am playing with this stuff for pleasure craft.

I am replacing old, degraded plywood bulkheads with sandwich core panels of Divinycel H80. 3/4" or 19mm core. I have a raptor fiberglass staplegun. The staples are fiberglass and can be sanded. I was wondering if for the first layer adjacent to the core- it will be 1.5 oz CSM- can I staple it down on both sides, then wet the whole panel out with vinylester, then peel ply, flip it over and wet out the opposite side? The reasoning being to reduce the chance for it curling up during cure and shrink.

I was advised to put a layer of CSM next to the core. Then it will get two layers of 1708 each side after that.

I wasn't sure if I could wet out the core enough by soaking thru the CSM? Anyone ever done this? Obviously, I don't want to risk dry core that doesn't adhere to the CSM.

I already have the H80 and vinylester and fabric. I am just considering how to do my order of operations.

 

When I was researching the process with those products, they recommended using a product called Divilette .
Its a thickened Vinyelester, and you buy it by the tub.
http://www.matweb.com/search/datasheettext.aspx?matguid=686ac9cab4bc44fc93529e282bce24e6


This is because wetting out CSM, and getting it to adhere properly to the foam.

This conversation on a forum provides an alternative method
"
"Divilette is a polyester resin based syntactic foam product. It is intended for use with polyester or vinyl ester laminates. Most builders using epoxy follow a method similar to what you propose; a thickened epoxy paste in lieu of Divilette. "

http://www.freeforum101.com/woodsde...cdb889c62514317992939def8&mforum=woodsdesigns

 

I was under the impression that Divilette was for scored/cut and scrim backed or perforated foam cores, not solid.

The little literature I found online from them seems to imply this but isn't explicit. My local supplier mentioned the wet CSM trick.

The reference I did find was here:

http://classxboats.com/htdocs/Engineering_Research/Foams_and_Coring_Materials/DIAB/Divilette_Application_Guide.pdf

The previous flat panel I laid up this way seemed to work well. It is resin rich, but still light with the H80 core. I used 1.5 oz/ sq yard CSM and medium viscosity AOC vinylester. No thickeners. I did wet the panel prior to laying down the CSM, (to penetrate the open cells) then added resin and rolled it in, and put 1708 over that. (This was a hatch cover.)

 

I suppose I can thicken some vinylester with cabosil and milled fibers or glass balloons, but I don't see the point in a thicker unreinforced bond line. And the divilette literature even warns against this.

 

Don't think you need 1.5 oz mat for this,( it adds unwanted weight) from memory I used only half-ounce mat as the initial laminate on Divinycell, which from a little testing seems to give a good bond to the foam, superior to the bond with the next layer of unidirectional, IIRC. And I think you are right about the syntactic foam being intended for the scrim-backed foam squares, as a light-weight fill for the gaps, to help prevent water migrating far from areas of damage.

 

It certainly is designed for 'block' filling.

When you think about all the hassle you have to go through to mix the correct stuff for just plain foam, the ready mixed product makes sense.

The " thicker unreinforced bond line" is a bit of a red herring- as your foam is about the thickest unenforced bond line on the boat.

The main aim of the intermediate layer, is as Mr E mentioned - is to prevent moisture migration more than adhesion . The best rate of adhesion you can get on foam is pretty small, due to the non re-inforced makeup of the material. You can easily rip the first layer off of foam with a big set of pliers, on the very best adhesion.

The forces that keep laminates and foam together are the ones created from effective layup design - eg laminate that don't flex away from the foam, and the ones that are strong enough to resist impact.

Thats why chines are mostly solid glass, because foam is only good in compression. For sheer and tension, it has to rely on the laminates.

However, Divilette is expensive, and you have to buy a big lot of it in one go, and if time is not critical ( eg paying someones wages ) I would be prepared to mix up a custom goo - and as long as it is resin rich, non slump and void filling it should work as well.

 

So back to the original question. Might it be possible to do what I was suggesting? Wet the foam thru stapled down 1.5 oz CSM?

Although at this point I might just wet the foam, slap on the CSM, staple it down, slather on resin, then flip, then repeat on the 2nd side and let it all kick.

 

Stapling the csm is entirely unnecessary.
Does your fabric have a csm backing ?
I would;
Lay up first side of laminate on a flat table finishing with a light csm, whilst wet roll resin into foam surface and place on laminate.
apply vacuum bag or use weights to hold foam down. A few holes to allow resin and air to escape will help.
When the heats gone out of it do the top layer, allow to cure and then release off the sheet.

 

I think the effort in trying to do it in one shot would be problematic.

If you are trying to save on by labour mixing and laying as much as possible in one 'session', just buy four sheets of flat melamine coated mdf, and do one side of four panels at a time.

Trying to flip a sheet of bendy foam, with wetted out csm on one side doesnt sound easy without a dedicated 'flipping machine'.

I would be very surprised to see the panel warp by letting it cure on one side first, especially since you are using 19mm foam. You could always weight the panel on top if you were worried.

Also, the biggest hassle is getting a smooth, uniform surface. Even with peelply as the top layer on CSM, it wont be a good surface.

Laying it flat on a smooth surface is going to get you a much better result.

 

So the stapling worked great. Other than I didn't clean the stapler well in a bucket of acetone, so I need to break it down.

The 19mm Divinycel did curl, though. I was a little agressive with the hardener, given the temperature. Probably a touch over 1% MEKP It is an unheated building, so tuning the MEKP % against the anticipated night time temperature drop is always a guess.


I had some 1708 DBM (with mat backing) for laminating the next bulkhead, so I skipped the 1.5 oz CSM. I laid that up in one go, 2 layers a side. Peel ply, then polyelthylene sheet and a flip over, then laminate the 2nd side. The stapler was jammed, so I didn't use it. I hope that works out. It looks great so far, but it still gelling. It doesn't seem to be curling. I am aiming for 0.7% MEKP in AOC vinylester mix. Not quite the slowest concentration, which would be 0.5%. But it is a bit cool up here to run that little MEKP. I expect it will harden overnight. Tomorrow or the next day, it will sit in the sun for some UV and thermal postcure. I hope that rate will result in a nice flat panel.

I am a bit over the scantling minimum (22 oz/yd) so even if it isn't perfect, it should be plenty strong at 34 ounces/ square yard each side in vinylester.

 

To get maximum benefit from VE you should use 1.5% SR Catalyst. (SR=slow rate)

 

I am following the manufacturers specs. 5, 10 and 15cc per quart (liter, as far as we are concerned) for slow, medium and fast gel times. I don't recall the brand of MEKP. With this stuff, 15cc/quart has a 10 minute gel time. Fine for hacking, but too fast for laminating. I have occasionally tuned it with 10% styrene monomer to thin it and slow it down by diluting the cobalt to work with CSM better. But I didn't this time.

 

I've been using 20cc per 32 oz of vinyl ester resin with good results laying up nidacore joists.

 

Where are you getting your resin? I got mine from Merton's in Springfield. He noted that the stuff is very active. It will UV cure without MEKP if you aren't careful. So 0.5-1.0% catalyst seems ok to me. And/ or up to 10% styrene added. 0.5% MEKP + 10% styrene + low ambient temps makes for a very slow cure, though.

This stuff seems to like to postcure in the noonday sun.

 

The VE resin was purchased from Hamilton Marine in Portland Maine.

I had NO issues with fast gel time/heat etc. with 20cc of MEK to 32 oz of resin.

Temp was 65F, ran a fan after applying.....within 3 hours I was able to flip the board and cover the other side.

Yesterday I did the same layup with polyester resin....20cc MEK to 32 oz resin.
The poly cured about an hour "quicker" than the VE resin. Same outcome....no issues.