Iron Man Mk VII - Plastic coated foam: delamination advice?

[aerospaceguy]

Howdy folks,

I've been lurking here for quite a while, first joined to get information when making my first Iron Man suit at Halloween last fall. I've since moved on to my second suit, and having done the fiberglass method, (more or less, only the top half of that suit got finished in time) I realized that the hard shell was very difficult to move around in in and decided to make a semi-rigid foam suit.

I've seen great results from the plastic coated foam method and I've especially liked the results that Shelfside was getting. Anyway, I've got a large portion of the foam work done on the suit, as shown in the picture below. I'd done a few tests of the plastic coating a couple months back, before I got fully into the suit. On those tests, I didn't see any delamination. One test piece was PVA sealed foam with 2 coats of epoxy resin over top, similar to XRobots' method). The other is 2 coats of epoxy applied directly to the foam. Having sanded and painted both pieces (not to perfection, but at least with enough vigor to test them) I was satisfied with the results of both and they seemed quite durable.

Now, to the present problem at hand; I've started coating and sanding some of my pieces using PVA to seal them, and the delamination is catastrophic to say the least. The epoxy is peeling off the PVA as if it's barely bonded to it. I thought, "well this didn't happen with the test pieces!" but upon going back to my test pieces and beating them up a bunch, I found that the PVA sealed part was actually prone to delamination as well.

My question now for the community is whether or not anyone else has seen this using this method? This was 3 coats of 1:1 diluted PVA and one coat of pure PVA, followed by 2 coats of epoxy resin 24hours apart.

I've attached pictures of the test pieces: the PVA piece clearly shows the PVA layer delaminating, and the epoxy layer peeling off of that. The Pure epoxy test shows where I could peel the paint off, but this was due to the fact that the bottom of this piece had the foam exposed during sanding, so the primer didn't take to the exposed foam. My assumption was that this would have made this location a prime spot for peeling if it were to happen, but I could not separate the epoxy from the foam on this piece. Finally, I've posted a picture showing the most recent peeling on the spine area, as you can see it's quite extensive. At the moment my plan is to just coat the rest with epoxy, no PVA, but I'm confused why my delamination is so extensive, while others on this site have had such great results when still using PVA.

Thanks for hanging in for the long first post, any comments, critiques or suggestions would be greatly appreciated.

Regards,
Steve

 

[samcrow]

could it have something to do with the type of epoxy resin?

xrobots uses a resin that forms a plastic coating, not just a standard epoxy resin.

 

[texxxan]

Did you primer before pva....or pva before primer?...picture looks like pva first. You using the same glue as in the test? Doesnt sound like a plastic coating problem. Sounds like pva is not bonding to foam. I would try switching glue and making sure the surface of the foam is clean.

 

[aerospaceguy]

Re: Iron Man Mk VII - Plastic coated foam: progress!

Hi Guys,

Thanks for the replies.

Samcrow: I realized shortly after posting this that that was the difference. The smooth-on is a polyurethane, not an epoxy. Somehow I totally missed that little tidbit. Did some research, PVA is actually used as a mould release agent for epoxy... go figure!

Texxxan: Primer is after PVA and after body filler and sanding, glue was the same and the foam was quite clean.

I've been coating the foam in straight epoxy, then finishing with body filler and putty and the results have been great. I've included a few pictures. Been away on business and quite busy lately so I haven't had much time to get many parts finished.

Steve

 

[fallimar]

I'm hoping to use this method, so I'd love to know how to avoid delamination too. I'll have to trial a few different resins (I can't get smoothcast stuff locally as far as I'm aware) but yeah - it'd be great to see some troubleshooting ideas. I'll certainly contribute if I have any revelations when I start resin-coating.

 

[samcrow]

its looking good, I have finally started cutting all my pieces. Any I have figured, while foam is faster overall, its not speed deamon with all those angle cuts and takes time lol. I like the arms you have done. Cant wait to see more.

 

[fallimar]

I went and talked to a local supplier of all sorts of moulding and casting materials yesterday and he gave me some great advice. Apparently the cause of delamination in layering of polyurethane resins is that once cured, it forms an oily layer that causes subsequent layers to not adhere properly. The obvious fix for this is to apply layers before the underlayer has cured entirely, but this has to be done carefully as it's possible to get all sort of lumps, bumps and bubbles as the new product is dragged over the stuff already laid down. That's with the PVA/polyurethane resin technique.

He suggested the epoxy resins as a better alternative. The work and cure times are much longer than the PU resins and this causes potential problems with the layers being really thin and drippy. To fix this, he suggested mixing in talc as a filler. It bulks out and thickens the epoxy, gives a more opaque finish and gives you something to sand into. Sounds good, might cut down on the need for body filler/putty as well.

It's really good to know that sealing with PVA for epoxy resin application won't work. I've already sealed up one of my armour pieces with PVA so I'll use it as a trial for my polyurethane resin, using the method of applying before the underlayer has cured completely. I want to see what kind of results both materials give over a foam base.
Hope to have some results soon.

 

[aerospaceguy]

I'm interested to see how the talc filler works. What is the pot life on your epoxy? I'm using stuff with a 20 minute pot life which is okay when the epoxy spreads out and moves easily, so adding filler might be a problem since there's so little time to spread a thicker mixture. Although I guess I could just make a smaller batch.

I've found that the pure epoxy definitely has a tendency to run and create ripples in the surface, necessitating some amount of sanding and filling. The other thing is that the first, and sometimes second coats will have spots where the epoxy has run off and it hasn't covered the surface, instead it's just seeped into the foam. Not a big deal just generally requires another coat which usually means that there are more ripples in the surface to sand and fill.

I'll be interested to know if you have any problems with sharp edges. I've found it's difficult to get even coverage over edge areas if they are greater than about 70degrees, and inside edges get quite rounded out, although I suspect there's not much that can be done about this.

 

[fallimar]

The pot life is about 30 minutes according to the label. I've only just ordered some talc so I'll have to wait to try it out, and as I've never used anything like this before it might take me a while to get my head around it! Still, I've done my research

I'm hoping the edges and angles will be helped a lot by the talc filler, thicker product will help it cling to surfaces a bit better, and keeping it moving for a while whilst it gels might also stop it slumping into hollows. That's the theory anyway. I'll make sure to report on how it goes.