Proper way to clean foam panels

[pescaloco]

Hey guys,

I'm sure I'm not the first, anyway my situation is I have a large project that I can not work on all the time. Several years have gone by and some of my rigid PVC foam composite panels have had small amounts of moister and dirt/dust collect on them. And some have water marks (stains) meaning they got wet but are completely dry now

I vacuumed the panels and gave a light wipe with acetone (but the panels just don't seem to like the acetone) they get a whitish discoloration after wiping.
How do you properly clean a rigid foam panel and be comfortable they are clean and ready for lamination ?
If it helps they were previously pre-wetted primed, some the small voids (cell structure) should be at least partially filled with resin

Thank you for any advise/feed back

[elhix]

I've had a similar problem, no moisture but very dusty foam. I used a vacuum cleaner and then an air gun which seemed to get the sheets clean.

Given you've primed them with resin an issue is going to be the bond between that resin and the consequent lay-up. A light sand and comprehensive blow off with an air gun should do it?

[pescaloco]

Originally Posted by elhix

I've had a similar problem, no moisture but very dusty foam. I used a vacuum cleaner and then an air gun which seemed to get the sheets clean.

Given you've primed them with resin an issue is going to be the bond between that resin and the consequent lay-up. A light sand and comprehensive blow off with an air gun should do it?

Thanks for the reply, I was wondering if anybody was going to.

I am probably just paranoid, but I had a section I recently did which had a weak bondline even though the panel was cleaned, wet out very well and done in the flat (horizontal position) I ended up yanking the glass off and it pulled off with force but no core failure what so ever.

I looked at a vacuum baged from the factory (prepreg panel) and found the peel resistance of the glass sheathing was also very poor. I'm starting to think that it must be very difficult to make a PVC panel especially in a hand layup that will have such a good bond that the foam core will (fail) seperate with the mat glass attached, showing core attached to the glass.

Is weak peel resistance a normal condidtion with foam ?

Originally Posted by pescaloco

Is weak peel resistance a normal condidtion with foam ?

Yepp.
Foam belongs in a fridge! (inside the panels)

In a few cases a roof with a foam sandwich can be a sensible idea too, that was it!

[AndrewK]

When you peel the laminate from the core you should see foam on the laminate for both hand laminated and vacuum consolidated panels. If you are saying that the failure is occurring at the laminate secondary bond to the pre-primed foam then you are not getting a very good key to the primed surface. You need to do a more thorough and aggressive sanding. I assume you did not use peel ply when priming.

[pescaloco]

Originally Posted by AndrewK

When you peel the laminate from the core you should see foam on the laminate for both hand laminated and vacuum consolidated panels. If you are saying that the failure is occurring at the laminate secondary bond to the pre-primed foam then you are not getting a very good key to the primed surface. You need to do a more thorough and aggressive sanding. I assume you did not use peel ply when priming.

Andrew

Yes you are correct I did not give an agressive sanding to the primed panels, but attention/care was taken. A more agressive sanding is in order, the stuff is just so soft the primer coat is all but lost if I lightly grind with a
36G disc.

Very strange though to find a factory vacuum baged panel have the same peel and a stiple pattern (as my panel) from the released resin on back side of the peeled glass. Since I posted I have done a series of test panels with various meathods of primer and prep and found some to have a considerably higher stregenth bond.

In my case I think you hit the nail on the head, there has been a considerable time lapse since the panels were primed and then glassed, thus requiring an agressive sanding to achieve a sound secondary bond.

Thank you for you reply

[pescaloco]

Originally Posted by apex1

Yepp.
Foam belongs in a fridge! (inside the panels)

In a few cases a roof with a foam sandwich can be a sensible idea too, that was it!

I see your not a fan

I have to say it is not a good feeling to have doubts when putting so much time / money into a project. (for me anyway)
But aside from a couple miscues/mistakes (which I re-did) I have to say I am still happy with the results and so far all my cutouts seem to have have a good bond.

Originally Posted by pescaloco

I see your not a fan

That was the most polite way to express it, thanks!

But right on the spot!
Except for raceboats with a lifespan measured in hours (maybe several hundred), a foamcore is weakening the structure, means counterproductive.
And no matter what my NA´s or other specialists tell me (and their calculations have some logic), this remains to be my opinion until Hannibal brings the Elephants back!

Regards
Richard

[Herman]

There you go...

I do like foam. When well used it produces nice and durable products.

But then again most foam I see is in one-off or "artisanale" production, where workers know what they are doing, and care about the product they make.

[tunnels]

Originally Posted by pescaloco

Thanks for the reply, I was wondering if anybody was going to.

I am probably just paranoid, but I had a section I recently did which had a weak bondline even though the panel was cleaned, wet out very well and done in the flat (horizontal position) I ended up yanking the glass off and it pulled off with force but no core failure what so ever.

I looked at a vacuum baged from the factory (prepreg panel) and found the peel resistance of the glass sheathing was also very poor. I'm starting to think that it must be very difficult to make a PVC panel especially in a hand layup that will have such a good bond that the foam core will (fail) seperate with the mat glass attached, showing core attached to the glass.

Is weak peel resistance a normal condidtion with foam ?

If you want to increase the peel resistance use a higher density foam , the lower the density the easyer the peel , The lower the density the easyer the shear as well another point to remember with foams ALWAYS use a higher density than you think you should ,OR what is specified . CORE SHEAR IS A MAJOR PROBLEM WHEN USING FOAMS READ ABOUT IT ITS A FRIGHTENING SUBJECT

[pescaloco]

Thanks Tunnels

I have been using mostly 5 and 8 lb density cores

I have a friend that did destructive tests on dozens of foam core composite panels. Once started, they delamned like unzipping a parka. The razor-cut ones and denser ones did much better. I would look at foam use in terms of "areas", i.e., if one needs a panel stiffened put a piece of foam in there but bring it back to solid glass.
An example; a new boat construction, Airex cored throughout, new shifting mechanism wasn't well attached, boat bumped rock at low speed in harbor and sheared foam core in one hull. I think they injected epoxy in there but I feel that the boat was a total loss before it was launched! Use this stuff for non-structural panels or race-boats.
One final thot, you hear people talk about using closed-cell foams so that water doesn't migrate. From my observations, ALL foam is open cell with moisture and a few freeze/thaw cycles. Lots of mushy foam up north here...

[tunnels]

This is a general rule of thumb to foams !!
Foam in the top sides has never been a problem as long as it is well stuck and stuck well . The bottoms of yacht hulls need a higher density than the topsides and again well stuck .
Power boats ,foam in the topsides ok but from the chine down Balsa needs to be the only core to use !! yes i have made launchs that had foam IN THE BOTTOMS but they were slow boats not high speed and the bottoms were more rounded , faster boats have flatter panels and get a lot more pounding . Its the pounding and flexing of the panels thats the problem .Foams dont like flex and shear and next you have a whole bottom come loose . I have never seen Balsa shear ! not even in test conditions !!
Yes it comes come apart from the surface its stuck to because the way it was stuck down or the system it was stuck with !! but it did not shear!!.
Shear is when the core breaks apart with in its self, NOT when it comes loose off the adhesive its stuck with . TWO DIFFERANT THINGS !! dont be confused between SHEAR and DELAMINATION !!they are not the same !!

Those tests I talked about left one layer of bubbles on the epoxy skin.
I don't care much for a bottom done in balsa but for a different reason - I feel one wants solid here to take a hit. That being said, I have a friend with a 35 year old balsa bottom that is dry, stiff and sound. He ran aground once and drove both rudders completely through the hull... and maybe a cup of water came into the boat, a repair was made and everything fine.
On this boat, 30 years ago, http://www.lulubelletours.com/ one could see the rudders In the lazarette!

[tunnels]

I hear what you are saying ! There are boats that have foam bottoms that are still perfectly ok . When there is a sail drive or skin fitting to be installed i always make sure theres a 100mm wide perimeter around that has no foam and is solid glass with no core at all . Sound a little exstreme but prevention during the build process id better than the exspensive cure later on .
I was bought up in the days before foams hit our markets as the be all to end all and followed closely on its heels were a bunch of problems we had never heard of or exsperianced before .
I shudder to think back on some of the boats we made in the begining and how the cores got installed , but in saying that they never came back for any reason , must have done something right !!