Mold release failure

I built a female mold for daggerboard skins, but as you can see, I had a little trouble getting the first skin out of the mold after the vacuum bagging. The mold is a series of frames on a strongback, with a glued on surface of a couple of 1/8 inch hardboard. The top layer has a glossy white surface, sort of like the stuff on the walls of cheap hotdog stands.

I waxed the surface at least 5 times with Partall Paste #2. The can states: "It is designed for use on mold surfaces prior to application of Partall Film #10 or as a general purpose release agent/edge wax . . ." I didn't have the film, but I interpreted this as saying I could use it without the film. It was as if I had not used anything at all. In fact, the glossy white surface was more attached to the fiberglass than to the hardboard. After prying the entire mess off the mold, I wound up cleaning up the laminate with a sharp wood chisel for the hardboard, and MEK actually dissolved the glossy white surface!

The mold frame is still intact, but before I rebuild it, I need to know what I did wrong. Did I use the wrong wax or apply it incorrectly? Or will the wax not work on some surfaces, such as glossy hardboard. One clue: 2/3s of the way down the mold, there was a seam that I filled with epoxy. That is the black band you see on the layup, where the layup didn't stick at all.

So, I'm wondering if I can rebuild the mold surface with the hardboard and just give it a coating of epoxy before waxing it, or if I need to use some other material. Will the Partall Paste #2 work by itself, or do I need to use a different mold release?

Thanks,
Larry Forgy

 

I have used that white hardboard a lot for molds and never had any problems. But I used wax and pva, and never vacuum bagged or used epoxy. Vacuum bagging and/or epoxy can cause sticking problems even in well cured and broken in fiberglass (polyester) molds. You might try using glossy formica which would easily fit that frame. Or you could cover it with plastic sheeting.

Also it might depend on how you applied the first coat of resin or gelcoat.

 

Yup, me, too--tons of molds and only one ever stuck, and it was on the first part. I use Meguiar's Mold Release #8.

 

Along with the photo, Larry's 'I had a little trouble' made me laugh. A classic understatement. A little trouble to me using that stuff would be a few inches in a sharp corner.

Possibly, since the stuff is so cheap at $10-12 a 4x8 sheet, that the "quality" varies between manufacturers and Larry got something from China, who fairly often get rid of their hazardous waste by shipping it to us in the form of a finished product like pet food or Sheetrock.

I'm thinking though that the problem might be with vacuum bagging, epoxy or applying the first coat of resin with a wire brush or something like that.

BTW, is that 1 side of 1 daggerboard or enough skins for for 2?

 

SamSam and Tinhorn,
Thanks very much for the responses, but "worked for me" is not as helpful as I had hoped! This is indeed the cheap stuff (although I think it was >13$ at Lowes). At 1/8 inch thick, it seemed about the right stiffness/flexible to go on the mold. Two layers and I had a good solid 1/4 inch skin. I didn't see any other sheet material that looked like it would work.

All my previous foils were made by shaping a core and vacuum bagging the skins over it. Here, I want to build two 9 foot daggerboards with 18 inch chords. I would be fairing until I was cross-eyed, so I built my first mold that I could use four times to make the two boards. What you see in the photo is one side of one board.

After waxing the surface, I laid down a bog of epoxy, silica and graphite powder, and then laid the the first layer of cloth into that. I don't think that would have harmed the surface. Tomorrow I will do some test pieces with wax and with an epoxy coating and see what happens. Until you guys, I assumed that the problem was the hardboard, but now I think I need to test issues with the waxing.

Thanks,
Larry Forgy

 

I've also used heaps of melamine faced temporary tooling & also what here is called polyester board-ply with a matt or gloss finish, some will release with no wax or anything, I've had a stick up using pvc storm pipe whilst using gelcoat & polyester resin & cured that problem with multiple sprayed coats of PVA release agent to build a thick coat- PVA is like a "get out of jail free card" in monopoly, I'd try that in your testing. Regards from Jeff.

 

Epoxy has a lot more tendency to stick. I would recommend either to change the board to something else. (real melamine, premade polyester laminate, aluminium or steel sheet). In that case you can demould using a good wax.

The other option is to use PVA, and in combination with the board you use now, it might be the more simple option.

a third option is to vacuum a flexible vacuum film into the mould, (PVA film, Airtech SL200) and laminate on top of that.

 

I have had little experience of this and not a good person to listen to on fibre glass use but I have had some experience of making flat sheet with a pane of glass. I used furniture wax and did not buff to a shine but left a visable coat of wax.

It popped off like water off a ducks back and multiple sheets were made with the one wax application.

I used furniture wax because of advise off this forum and not least the 10th of the price of so called professional release agent.

I have never been one to accepted that you get what you pay for.

 

a similar thing happened to me the other day, i made a temporary mold and had it stick up so bad i had to destroy the mold to get the part out.... All i used was about 3 sprayed coats of PVA onto the 3mm foamed PVC board... was like i used nothing at all. I had a thought that it might have been caused by rolling and brushing the first coat of resin on the mold surface and this mechanical action ruined the PVA barrier?

Who knows, but from now on i will use wax AND PVA, as ive not yet had a problem when using both together...

 

Okay, now I am really confused. I made up some test panels to see what would stick and what would not.

I made up six panels using three surfaces: the hardboard with glossy white coating, plain brown hardboard, and aluminum roof flashing (which I am considering as an alternative). For each surface, I coated one sample with epoxy, and left the other bare. I waxed all six samples and then epoxied a small piece of 1708 fiberglass to each and vacuum bagged the whole thing.

To my surprise, the glass came cleanly off all 6 samples, including the one that was identical to the mold surface!

The one thing I changed was my waxing technique. The Partall can says "Cover 3 to4 square foot sections at a time. Excess should be wiped away with a clean dry rag. Begin buffing when moderately dry, approximately one minute after application (wax may become difficult to buff out if left on longer)."

I followed those directions, but after reading some remarks on forums, I think I might have been repeatedly putting wax on and then immediately taking it off. So, this time I put two coats on and left them alone for 15 minutes. I then put on a final coat and quickly buffed it to a shine.

So, is it possible I just screwed up on the waxing? Because I had not done this before, I tried to follow the directions exactly. Do people with experience just ignore the directions on the can?

Larry Forgy

 

Difficult to say. Common technique is to apply wax (as thin as possible), after a minute or so, when things went hazy, break the surface, then wait for 10-15 minutes, and buff (all with clean cloth). This 10-15 minutes depends totally on the evaporation of the solvents, but in my opinion 1 or 2 minutes is always too short.
But be careful! wait too long and buffing becomes a pain.

In general 2 coats of wax should do, but most apply more, to account for forgotten spots. However, putting 8 coats on is overkill.

 

dont tell any one , sssshhhh!!!

Do people with experience just ignore the directions on the can?
sssssshhh dont tell any one , yes most laminaters cant read !!!ssssshhhh!!
And even what they can read they just go blah blah blah seen it all before and do there own thing !!!.
Like herman said wax on wax off and thin coats with at least 5 to 10 minutes between on and off and polish !!. one thin well rubbed coat left for a while and then polished is far better than lots of heavy coats that non really ever add anything to the layer below just still only one coat .

 

Yeah, I see your point.

I'm thinking Yes. Not that you messed up, but perhaps that Partall paste isn't the ideal mold release when used by itself.

I can't remember ever having a part stick when I used Meguiar's #8 (gold can). Two to four applications depending upon how scary the situation looks--wax on, remove the bulk of it right away, polish after a few minutes, wait at least 15 minutes before repeating the process.

There are directions on the can? What'll they think of next?!

 

I think I may have found the culprit. Someone thought the glossy white surface might not be able to stand the heat from the layup. Today I took a piece and applied a heat gun to it. In less than 20 seconds the white coating would easily peel off with the slight touch of a putty knife.

I was using a very slow epoxy, but the form had at least 5 layers everywhere, with up to 16 layers in the hull exit area. Even the very slow epoxy must build up a fair amount of heat in that layup. Time to use an alternative surface.

Larry

 

You already have a wealth of information of what to use and how to do so is your choice to select from the lottery of things and go do it .
you now know what dosent work so make you selection and get on with it .