What type of foam board works with Poly?

[ondarvr]

Re: What type of foam board works with Poly?

Test a sample to see if it holds up, foam designed to be used as a core comes in many different qualities and denstities and not all of them would be suitable for this type of application. To find a product that's not designed for this use and have it work at such a low cost would be amazing.

 

[KnottyBuoyz]

Re: What type of foam board works with Poly?

Test a sample to see if it holds up, foam designed to be used as a core comes in many different qualities and denstities and not all of them would be suitable for this type of application. To find a product that's not designed for this use and have it work at such a low cost would amazing.

Sort of like the "Holy Grail" of boatbuilding. I've scanned the internet, ordered samples of just about everything going and there's no magic and "cheap" foam that'll work in any structural core application.

That R-Max looks too light, 2lb/cu ft. That's about the same as plain styrofoam. I wouldn't use it in a structural area. probably fine for insulation in a cooler or ice box area. Again, as said, test first.

 

[Mark42]

Re: What type of foam board works with Poly?

My intent is not to use the foam as a structural component to the extent that foam in a transom is high density and must be structural.

The hard top I'm making (I believe) will get its strength from the FRP that covers the foam pannels. I would be using the foam as a form to lay the glass over, not a structural piece to be protected by FRP. Some pieces like the windshield frame will probably be 3/4" wood, with some wood strips in critical areas. The remainder, the roof and side pannels will be foam core.

As long as the FRP sticks to the foam I believe I should end up with a top that is fairly light weight, easy to sand and finish, and should hold up to moderate storm gusts if its moored overnight.

All windows will be 1/4" Lexan or plexy for weight savings. Also, the existing glass windshield and side pannels will be removed, and that should save a few pounds also.

So, if you think the foam is not going to give me my expected results, please say so!

Thanks,

Mark

 

[KnottyBuoyz]

Re: What type of foam board works with Poly?

I'm just concerned it might not hold up over time. If you don't walk on it or place weight on it and drill it full of holes it would probably be fine.

The test pieces I made are "incredibly" strong but as you saw in the pics I posted the core failed when I put the jig saw to it.

If the hard top gets a lot of movement such as you'd get by walking on it or if you put stuff up there and it bounces around, over time, the foam will fail. This in effect destroys the web of the I-beam and you've got only a small fraction of the strength of the sandwich panel left.

It's true what you said the piece gets its strength from the glass layers but it's equally important that the core keep them the right distance apart. If the core fails the whole part fails even though you still have two intact layers of glass.

Don't get me wrong. I'm not against using foam. In fact I like the stuff but as discussed there's no "holy grail" of cheap foam core. If risking a few hundred bucks wasn't an issue I'd try cheap foam. If risking a few hundred bucks is a big issue then I'd use ply.

 

[kalla man]

Re: What type of foam board works with Poly?

Mark, just to give you an idea of the stresses that my application is under. the live wells hold 7 gal. of water, which gets bounced around at 50 mph. they have also been full of beer and ice...no problem. I think it would do just fine as your hard top.. but like you said it would be a good idea to reinforce some areas with wood strips, maybe places you are planning to drill into with fasteners etc... oh and i saw on the R-max website that there were a few different products...I used the "R-Matte plus 3". I think you will be pleased with your result and the process..so easy to work with. just cut with a razor blade.. and i actually used toothpicks to hold pieces together as i was glassing them.

 

[Mark42]

Re: What type of foam board works with Poly?

Kalla Man, that is impressive performance. I am concerned about delaminating with stress, like what KnottyBuoyz experienced with his epoxy test. But if yours is holding up, I am very encouraged.

I'm going to do some tests and see how easy or hard it is to peel off some poly and glass from the R-Matte plus 3 (hope they stock it in the stores around me) after scuffing or scratching the surface to give more texture and holding ability.

To help prevent delaminating, I got an idea of making plugs in the foam. Maybe one every square foot or so. Just punch/drill out a 1/2" hole and then fill with a poly/filler mix. Then when glassed over, it will have a physical poly bond to the other side. It will add time to the project, but it could also add areas where stress cracks could occur, which would be a bad thing .

You guys have been a big help.

 

[KnottyBuoyz]

Re: What type of foam board works with Poly?

Post some pics as you go Mark. Looking forward to seeing how it works out.

 

[redfury]

Re: What type of foam board works with Poly?

I would imagine it would primarily depend on the ability or in this case, inability for someone to separate the foam from the foam ( being able to claw away at the foam with your finger and disengage the foam from itself...that's where I would suspect the strength would lie within the foam. Obviously denser foams will be harder to claw a finger through, and if the resin bonds to it, would create a stronger piece.

However, I was looking at building a livewell into my boat, and it would seem that this would be a great alternative to using a wood that could rot, if this is a closed cell foam....plus the insulating properties are going to be much more desirable.

 

[CalicoKid]

Re: What type of foam board works with Poly?

I was going to suggest looking at a polyisocyanurate foam before I got down towards the end of this thread. I belive Celotex is the same type of foam. There are others with kraft facing and no facing. THis type of foam is used everywhere, roofs, walls, refridgeration, etc. You could perforate it to get a good grip through the foam with your resin. If you can find thinner stock you may be able to bend it into a desireable curve before bonding which may add appreciable strength.
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[Mark42]

Re: What type of foam board works with Poly?

Hey CalicoKid - long time no see. Glad to have your comments. Thanks!

 

[CalicoKid]

Re: What type of foam board works with Poly?

Yea Mark, I've been out of the loop lately. I believe some of that foam board has glass strands in it too, I know some of it is itchy as hell if you cut into it and rub it accidentally.
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[Mark42]

Re: What type of foam board works with Poly?

I went to Home Depot today and looked at the R-Max polyisocyanurate foam boards in 1" thickness. Well, it is very light weight, it is covered with foil that comes off fairly easy, but there is one very big problem: The foam boards are far, far, far from being flat and uniform. The thickness varies as much as 1/4", every board I inspected was curved, and when I looked down its length, there were big noticable waves in the surface. I am afraid this stuff will look like crap when covered with glass.

After being very disgusted with the uniform quality of the R-Max boards, I went to the 1/4" Luan ply boards. Most were warped, but had a much smoother surface. I picked up a piece and it is not very heavy at all. Maybe 15-20 lbs tops, by my guess. Working with the plywood will require making a frame out of 1"x1" fir and glueing on the plywood, and the windshield frame would be made out of 1" fir. Just the roof and sides would be ply. Should still be fairly light. And I will not have the rippled pannel problems that the foam pannels have.

So, either use the plywood, or figure out how to work with the foam and get a nice smooth side and top out of that rippled foam board. Lots of sanding I guess.

Any suggestions on how to smooth the foam?

 

[KnottyBuoyz]

Re: What type of foam board works with Poly?

Any suggestions on how to smooth the foam?

Hey Mark

Foam panels are often done in or on molds specifically made for the part. Smoothness comes from how well the mold is made really. Making a mold for a one-off part doesn't make a whole lotta sense though. Think we discussed that before. I'll show you two methods that I've seen done.

Here's a mold being made for a roof being done in foam and resin infusion.

This is the panel being infused.

This one was done differently. Weights were hung from the panel which was laid across two saw horses. Care was taken to ensure the proper curvature before laying on the glass and epoxy. It works!

Unless you're very talented at making these types of panels I don't think you'll get a perfectly smooth part the first time. It takes time and a lot of effort. Look up "Fairing" on the web you'll find plenty of links to good info on how to get your part looking good. Be careful of the luan if you put a big curve into it, the grain will want to lift (check) on you. Precoating with a thin epoxy may help prevent that.

Good luck.

Rick