Foam Friendly CA or ePoxy ?

[Delta Whiskey]

I have a large foam core wing that has a crack in it, as I have lots of ePoxy and very litte CA, would it do the job or should I get some more CA?

Edited By Delta Whiskey on 26/09/2012 09:29:32

[ken anderson.]

epoxy and a couple of carbon braces and then a little light filler......also white PVA will work with foam...

ken anderson ne..1. repairs dept...

[Delta Whiskey]

Cheers, repair dept........that I have !

[Steve Hargreaves - Moderator]

Yep PVA works very well......also PU glues (aka Gorilla Glue). What sort of foam is it Doug?? By the way check your CA first as not all CAs are foam friendly.....a lot dissolve it!!!

[Delta Whiskey]

Not sure on the foam type, seems to be blue / grey centre core, white foam in the actual wings, but crack is where the scapel tips are, it's about time I got around to repairing it, and plan to do so in a bit. Going for epoxy and some carbon rods. Then resheeting and covering. From my other thread really but wanted to check I could use epoxy.

[Greybeard]

Doesn't pva just dry on the outside but remain tackey on the inside when used on foam?

[Delta Whiskey]

Posted by Greybeard on 26/09/2012 10:22:40:

Doesn't pva just dry on the outside but remain tackey on the inside when used on foam?

Anyone know the answer to this, as this maybe the best option for my repair as the crack is quite narrow and I will need something that can flow freely down into it rather than epoxy might just stay near the surface?

Never done any repairs like this before, so posting a few pics as a learning curve and advice along the way !

 

Edited By Delta Whiskey on 26/09/2012 11:23:28

[Delta Whiskey]

Will epoxy carbon rods in, but will need something more flowing to seal hairline crack. Will try a small area with the little thin ca I have or the wood glue if you think it'll hold?

[Delta Whiskey]

Used the wood / pva glue as the foam had a slight reaction to the CA, letting set, then will epoxy rods in. Also beefed up the area round the central square for the flap servo.

The tool box added some weight to push the foam together after I got as much as I could in the crack.

It does'nt look like this will be anywhere near strong enough, but until I get the rods set and it resheeted, I guess I won't be able to tell, I still have a bandage to fall back on, but hoping not to use that!

[Delta Whiskey]

oh No !

Two issues - one big !

First the small one - seems Greybeard maybe right the PVA (wood glue) is still very soft and tacky, will leave overnight and see if it sets. Now the major problem, I sucessfuly used epoxy securing one carbon rod in, and then onto the 2nd rod with a different make of epoxy a cheap one from the bargin shop (blue hardner & pink epoxy) which I thought was a bit strange, anyway just been back to check on it and I now have a big void below the carbon rod !

Seems the cheap epoxy has eaten my foam ! Question is now, can I just fill it with some epo foam I have left of even that squirty foam builders often used to fill gaps and use decent epoxy this time or is my wing not useless ?

Rod on rhs removed showing eaten foam right thru to the top sheeting!

[sticky fingers]

WD DO NOT USE CA on white foam unless as stated earlier, epoxy will always be the best option if there is any doubt .A little tip is to warm up slow setting epoxy on a radiator to temporarily thin it, this l wil aid flow quite well into the crack. PVA relies on evaporation of the solvent and can be a bit unreliable when sticking foams

Dave

[sticky fingers]

could have been polyester you used , deadly on polystyrene foam.

Dave

[Pat (rActive) Harbord]

Yes sounds like polyester (usually has red hardener - and is often sold in halfords for bodging up car body repairs) or I guess you could repair your glass fibre canoe. I think you are lucky to have any wing left.

Carefully dig out any polyester/foam gunge fron the wing and see what you have left. You will then have to make a call on what to do next.

all good fun, you could consider trialling unknown glues and materials in small non critical areas. Also keep an eye on the additional repair weight.

[Pat (rActive) Harbord]

Oh, and a hair drier blown over decent epoxy will have it running into small gaps just fine

[Delta Whiskey]

I did not know any epoxy would do this ! Can I use the squirty foam that is sometimes used by builders to fill gaps?

Also known as expanding foam ....

Edited By Delta Whiskey on 27/09/2012 11:04:26

[Delta Whiskey]

Thought it sounded familer - I posted a question on this 2 years ago ! So I guess as a gap filler expanding form with the carbon rod in the middle and sheeting top and bottom would be fine !

At least I have an option now to move forward and get this big wing repaired !

**LINK**

[Delta Whiskey]

I guess the easiest fix is just to cut some foam out to fill the gap, cut it in half and sandwich the carbon rod between it, and use decent model epoxy to secure it, as I've just read some horror stories about using expanding foam in models. Mind you they do a low expansion foam spray now too !

[Steve Hargreaves - Moderator]

I've never heard of epoxy melting foam...as the guys said might it have been polyester resin? That would destroy your foam. Smell both....epoxy isn't a very nice smell but polyester is quite nice.....certainly if they smell vastly different then you have two very different resins!!!

Personally I think I would now cut out the damaged/melted foam & replace it with soft balsa block. Gorilla glue or similar might be my glue of choice from now on...including fixing the carbon rods.....it will foam up & fill the gaps but watch out....when it foams it will push things around so you do need to clamp everything in place.

I wouldn't use one those expanding foams either DW...I don't know & stand to be corrected but I have a gut feeling they might be deadly for your foam.....plus the foam produced isn't particularly strong either.....

Good luck....

[TinPot Pilot]

I'm sure most of you will have heard this warning before:-

On the Subject of the Expanding Foam

A friend of mine once built a canoe. He spent a long time
on it and it was a work of art.Almost the final phase was to fill both ends with polyurethane
expanding foam.He duly ordered the bits from Mr Glasplies (an excellent
purveyor of all things fibreglass) and it arrived in two
packs covered with appropriately dire warnings about expansion
ratios and some very good notes on how to use it.Unfortunately he had a degree, worse still two of them. One was in Chemistry, so the instructions got thrown away and the
other in something mathematical because in a few minutes he
was merrily calculating the volume of his craft to many
decimal places and the guidelines got binned as well.He propped the canoe up on one end, got a huge tin,
carefully measured the calculated amounts of glop, mixed
them and quickly poured the mixture in the end of the canoe
(The two pack expands very rapidly). I arrived as he was completing this and I looked in to
see the end chamber over half full of something Cawdors
Witches would have been proud of. Two thing occurred to me,
one was the label which said in big letters:
"Caution - expansion ration 50:1" (or something similar)
and the other that the now empty tins said "approximately
enough for 20 small craft"Any comment was drowned out by a sea of yellow brown foam
suddenly pouring out of the middle of the canoe and the
end of the canoe bursting open. My friend screamed and
leapt at his pride and joy which was knocked to the ground
as he started trying to bale handfuls of this stuff out
with his hands.Knocking the craft over allowed the still liquid and not
yet fully expanded foam to flow to the other end of the
canoe where it expanded and shattered that end as well.A few seconds later and we had a canoe with two exploded
ends, a mountain of solid foam about 4ft high growing out
of the middle, and a chemist firmly embedded up to his
armpits in it.At this stage he discovered the reaction was exothermic
and his hands and arms were getting very hot indeed.
Running about in small circles in a confined space while
glued to the remains of a fairly large canoe proved
ineffective so he resorted to screaming a bit instead.Fortunately a Kukri was to hand so I attacked the foam around his hands with some enthusiasm. The process was
hindered by the noise he was making and the fact he was trying to escape while still attached to the canoe

.Eventually I managed to hack out a lump of foam still
including most of his arms and hands. Unfortunately my
tears of laughter were not helping as they accelerated
the foam setting.Seeking medical help was obviously out of the question,
the embarrassment of having to explain his occupation
(Chief Research Chemist at a major petrochemical
organisation) would simply never have been lived down.
Several hours and much acrimony later we had removed
sufficient foam (and much hair) to allow him to move
again.

[TinPot Pilot]

continued

However he still looked something like a failed
audition for Quasimodo with red burns on his arms and
expanded blobs of foam sticking everywhere. My comment
that the scalding simple made the hairs the foam was
sticking to come out easier was not met with the
enthusiasm I felt it deserved.I forgot to add that in retrospect rather unwisely he had
set out to do this deed in the hallway of his house (the
only place he later explained with sufficient headroom
for the canoe - achieved by poking it up the stairwell.Having extricated him we now were faced with the problem
of a canoe construction kit embedded in a still gurgling
block of foam which was now irrevocably bonded to the hall
and stairs carpet as well as several banister rails and
quite a lot of wallpaper.At this point his wife and her mother came back from
shopping......Oh yes - and he had been wearing the pullover Mum in law
had knitted him for his birthday the week before.

Be warned!

[Delta Whiskey]

Yep thanks both, will be avoiding that, blasa block or more foam as it will be sandwiched between sheeting should solve it. Need to get some proper epoxy now !