Divinycel question

[fallguy]

I want to bond the 80 weight Div foam to my hullsides 2 part poly paint with 5200 for bond strength and open time.

The only question is whether I ought to precoat the foam with epoxy to make a more uniform surface.

@rxcomposite Do you know?

… or anyone else know if best to bond the 5200 to the rougher surface or to epoxy?

I did some hole fill and minor repairs with epoxy/cab mix.

The surface gets harder with epoxy is all. So, it seems like it would be a bit tougher even in handling before the work.

thanks

Dan

 

[rxcomposite]

5200 is a very good adhesive. We used to bond our hardware with 5200 to a gel coated fiberglass and it is almost impossible to separate. The adhesive will bond to wood, glass, metal, ceramic, or anything that has a good substrate.

Coating the foam with epoxy is a good idea. Better if you add fiberglass.

 

[fallguy]

I think I’ll try to glass the backside, just to make the 20’ long part more resilient to damage prior to application.

I am going to get the boat on the hard as soon as the pieces are done.

 

[rxcomposite]

Is that the chine strip core you are bonding?

 

[fallguy]

Yes. Spray rail.

I glassed one side of one of the 4 pieces today.

 

[wet feet]

I do hope you have built in some curvature to those parts as bending glassed Divinycell won't be a trivial task and it gets a lot more interesting if you need to persuade them to a particular location.

 

[fallguy]

I do hope you have built in some curvature to those parts as bending glassed Divinycell won't be a trivial task and it gets a lot more interesting if you need to persuade them to a particular location.

it is all dev panel; the only question is whether I can get them to compound a bit

I am using 6 oz glass only, so that ought to help as well.

 

[fallguy]

@rxcomposite

or anyone else on the board with great wisdom

What exactly is the rationale for adding epoxy and or epoxy and glass to the back of the splash rails?

They are made with H80 Divinycel.

I also need to know if I ought to sand the substrate which is glossy 2 part polyurethane.

My question lies in one simple fact.

The polyurethane paint is a consistent bond. If I sand it; some of it may be less bonded than the rest. Ditto glass. If the glass on the back starts to shear from the core; it is over and that surface will have less bond area than Divcel.

 

[rxcomposite]

We may have a different approach. We added spray rails on our chined boat because it was throwing too much spray.

We bond our shaped foam core using our base poly resin thickened with microbaloons. The resin is bumped up to a fast cure so that we can hold it in place while it cures. The micro balloons forms a slurry compatible with the foam. It fills up the hollows and the rough surface to form a good bond.

YES, microbaloons can be added to added to any resin you are using, even VE resin to thicken it. Slurry to just even up the surface, paste to form like clay to any shape that we can sand after. It offers something that when cured can easily be sanded. We are not looking for strength, just something to bond and any excess that can be sanded off.

For aero space application we use the commercially available “Bondo”, a microsphere laden bonding putty or Syntactic foam, a microbaloon laden foam that can be easily sanded off to any shape we want.

After bonding and curing, we give it a coat of glass to strengthen it. Sometimes three layers. We sand off the gel coated surface to get a 100% good bond. Gelcoat is weak. Gelcoat is ISO resin with some solid colored pigments added. Anything that you add to the resin (including acetone) makes it weak.

The spray rail needs to have rounded edges to glass it over. To keep it “as sharp as possible”. We apply a putty of resin + fumed silica, or milled fiber afterward. Hard to sand but we do get a good sharp edge. And strong.

 

[tropostudio]

@rxcomposite - fumed silica (such as 'Cabosil') works as a thixotropic agent in polyester resin just as it does in epoxy? It would make sense if it does. Also, when doing admixtures into poly or vinylester, do you mix those in before adding the catalyst?
Curious because all of my boatbuilding projects have been with epoxy resin systems. Thanks.

 

[ondarvr]

@rxcomposite - fumed silica (such as 'Cabosil') works as a thixotropic agent in polyester resin just as it does in epoxy? It would make sense if it does. Also, when doing admixtures into poly or vinylester, do you mix those in before adding the catalyst?
Curious because all of my boatbuilding projects have been with epoxy resin systems. Thanks.

It works much better in polyester and VE than it does in epoxy. And it works a bit better in polyester than VE.

When you add catalyst depends on a few different factors. Some fillers will start to affect the gel time and extend it, that takes a while though. So if you make large batches ahead of time you need to know this. If you use it soon it doesn’t matter.

In the industry the vast majority of putty is made in advance in large amounts, then smaller amounts are catalyzed as needed. You can mix it when needed if you want, you can do it either way, its not going to make much of a difference.

 

[tropostudio]

Thanks for the info! Good to know how it works with poly and VE systems.

 

[fallguy]

I would think adding catalyst after thickening runs the risk of incomplete mixing.

In the case of epoxy at least, you’d never mix fillers into resin before adding hardener for fear of making chewing gum..maybe if they were colorized?

It would make more sense if both parts had fillers and color change, etc. But I’m not the guy to answer and definitely defer to @ondarvr . He knows the business best.

 

[fallguy]

by the way, I am now sharpening back the rounded edges .. I did not glass the back, but I did overcoat it with resin and then sand and then fill with fairing compound .. I was not able to appreciate glassing the back

As I approach the day to glue them on, I am getting more nervous about having trouble and a bit worried I need a mechanical fastening and that tape may not cut it for holding…

Maybe the ends and every four feet or so. Maybe some 316 oval head stainless on fancy washers…predrilled so they don’t move the final location..

I did have a build error. So used to wet bagging, I skipped using thickened epoxy on the end seams at 4 foot or 2 foot intervals and if I pick them up wrong; I heard one make a loud crack. But once things are glued on; that concern goes away; the outer edge has skins both sides.

 

[wet feet]

If you drill holes for mechanical fastenings you are introducing stress raisers and potential leak paths.If you have sufficient time when doing the job,and you ought to try hard to arrange it,gently attempt to wrap the first part around the hull in the correct location.If they are causing concern already it might be best to cut an extra length to learn with and see how that goes.First you need to mark the location on all the relevant surfaces and then use the trial piece to see if it can readily conform to the shape and can be persuaded to sit where it is needed.If it breaks at the joints you will have the opportunity to think up a way to use the shorter sections in such a manner that the joints are fair and not obvious.With thick foam it isn't always practical to use a heat gun to make the foam conform as it is such a good insulator and at worst you may have to make a bending former away from the boat to create sections that are shaped to suit and which will immediately sit in the correct location when taken to the boat.Once the mating face is bonded into place and the foam glassed over,you should be ready for refinishing and launching.Once on the boat,be prepared for local damage but losing the whole piece shouldn't happen as you are hardly likely to hit a piece of debris that has the precise shape to make even contact with the whole surface at the same instant,but small pieces of flotsam may leave individual dings for later filling.With an already watertight surface beneath the foam,it shouldn't matter,screw holes or bolt holes make the situation worse.With two or three plies of glass over the foam the total bonding strength is huge and need not extend too far over the original surface.A light cloth as an outer laminate will make the cosmetic part easier.