Gelcoat shrinking/lifting over semi-perm?

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#1

For the second time, I’ve shot gelcoat for a mold, only to have it lift as it cures, from a concave area of the plug. Laid down approx 30 mils (wet), mixed around 2%. It “B” staged in an hour or so, then I followed up with tooling gel (MEKP @ 1%) a couple layers of veil and a layer of 3/4 ounce CSM to “stabilize” everything. At 10P last night all seemed well. Checked it again this morning (10 hours later) and, the last 12" or so (near the edge in that concave area), had lifted/bridged ever so slightly! Went ahead and pulled the piece off. Other that waviness in the area that pulled, it’s not too bad.
What I’m wondering is, best intentions aside, if I shot myself in the foot by using the WOLO on the pattern? I clayed the edges, and the problem SEEMS to be where the gelcoat is “pulling” between the clay and some higher spots on the pattern, and the WOLO is SO effective that there’s not enough surface tension to hold stuff in place as the resin cures?

So, what are my options? Cut the MEKP in half to kill the heat and slow it down? How far back can you safely cut back w/ tooling gel (US Composites/black)?I did a temp check during all this, and I appeared to be getting around 80-83 degrees in the lay-up, and a 1 - 1.5 ounce leftover sample in a cup was clocking around 180 degrees.

Anything?

#2

youre using a semi perm over your plug?

I dunno what to tell you but I wouldnt use anything like that when I really needed the tooling gel to sit still.

#3

Yeah… kinda what I’m thinking, too. Thought it was a good idea at the time because I was wanting to slip the mold off the plug (large hood with an OEM scoop) lengthwise, and capture the full detail, as opposed to filling the scoop and lifting the mold off the pattern vertically. I have the necessary draft to get away with it (and I HAVE pulled two successful practice pieces… didn’t stick, anyway), just can’t get the tooling gel to stay put for the real deal. Kind of a shame, too, because the plug is dead-nuts! LOL!! Oh, well… live-n-learn! Back to the drawin’ board…

#4

Semi-permanent mold release are made in different levels of “slipperiness.” Get a different one, or use wax. The industry solved this problem a long time ago, don’t kill yourself over it.

#5

Cleaned the pattern up and went over the whole thing thoroughly with Frekote cleaner. That may or may not have completely affected the WOLO that’s already on there, but at least tape does try to stick now. Next attempt will be wax only (TR104 Hi-Temp).

Also, just to try and be thorough through all of this, I did a gel test (2 ounce samples) this afternoon and timed it against the shop clock and measured resin temps with an infrared gun I have. Work area was 83* F. Tooling resin @ 1% kicked in 23 or 24 minutes after it crossed the 90* point, in the cup. Tooling gel @ 2% went about 12 - 13 minutes and also gelled around 90* in the cup. Would it hurt to back off the concentration on the gelcoat a bit to cool it off? It did seem to “B” stage fairly quick the other day.

In any event, gonna try it again tomorrow or Friday.

Never say die!

#6

Whenever you use a SP mold release such as WOLO, and you are going to make a mold from it. It is a good idea to make a blow off part. (Kind of what you did). By making a B.O.P. you remove the excess mold release. Typically your first part of a mold/plug (whatever you may have) WILL pre-release. For sure if the mold/plug is smooth. However your second will be spot on!

If your tooling gelcoat is Polyester based you will have a problem with “allergating” if you don’t wait long enough OR wait to long to do your second coat. Typically just keep going untill you reach you 20-30 mills.

If your tooling gelcoat is Vinyl-ester based you will not have any problem with the application. Just be warned that V.E.G. Is tougher but brittle, so you must make your mold stung enough that the mold will not flex after you make it. Additionally the surface is WAY harder to sand but will last just about forever. Also keep the percent catalyst at 2 percent, this way the gelcoat will cure properly and allow you to polish nicely.

#7

Thanks! That may explain a thing or two! I DID notice that the gloss of the area that had been laminated over had been knocked down to a satiny sheen. And the hood I’m using as the pattern is (for the most part) polished/shined to a fare-thee-well, and the problem area is slightly concaved,… so with the WOLO on top of that… well… like I said, “live and learn”. :rolleyes:

#8

Isnt spraying 30 mils at once a little thick?

#9

Possibly. Was shooting for 25-30 mils wet, total, for the tooling gelcoat. According to my gauge I had 15 mils +/- after the first cup (24 ounces) over the course of several minutes, let it sit while I catalyzed/mixed the second cup, and then finished it off. I had about three passes per cup, so I figure about 5 mils/pass over an area of about 12 sq/ft.

Could I have done that more effectively?

#10

If your spraying a mold then I wouldnt spray more than 5 mils on the intial cup of gel. That will help bring any air that was trapped up to the surface and prevent your tool from having a porous surface.

Ive done it both ways. Spraying a thin layer and letting it sit results in a night and day quality tool surface.

On such a large part I can see why it would lift. 30 mils all shrinking at the same time can produce a lot of pull.

#11

So, on a part this size (and the issues of semi-perm release agent aside), you’re laying down the first 5-6 mils and letting it flash off for a few minutes and repeat that twice more for 15-18 mils (wet)? Then letting the first 15 mils “B” stage before repeating the process for the next 15 mils (wet)? Or are your wet passes and intervals different from that?

I’ve had no issues with porosity or alligatoring (I’m not in a race when I make my passes), but I have to get past this issue of lifting. I don’t mind that it may take multiple tries to get it right, just that I want to HAVE it as right as I can get it before I commit to the whole thing.

#12

OK… trying again. Went over the plug with Frekote cleaner the other day and waxed it with Meguir’s, this time and buffed the snot out of it. Seems to be less dust residue than with TR Hi-Temp, also, which I like. Laid down 20-25 mils (over the course of 10-15 minutes) and pulled out some of the heat this time, too (just over 1 1/2% MEKP). It’s been an hour, now, and it’s “B” staging nicely. Going to cover it with a layer of veil and then a layer of 1 1/2 ounce mat… maybe two. Then we’ll see if it lifts, again… :rolleyes:

#13

Well hope it turns out. Im curious too as to what your lifting problem is.

#14

I have a great Gel coat problems trouble shooting guide and I have sent many copies out for a member or former Mod. to re-type it as it is old (but none of them did so, but enjyed them…:mad:).

I’ll be trying to scan it and work with that maybe tomorrow during all the big auto races on TV…and uploading it to the PPV section.

#15

FWIW, all appears to be well this time, as far as the lifting is concerned. It may be that the combination of thinner, cooler gelcoat along with the veil and two layers of 1.5oz mat did the trick. It’s been through its’ peak exotherm and cooled, and when tapped on, has no “hollow” areas. I’ll know when/if I pop it off tomorrow. As long as I have no warping or ripples (or stuck it to the plug :rolleyes: ), I’ll be satisfied with this part of the learning curve.

I did get some alligatoring this time, though, inside of the scoop nostrils (they’re about 2" deep). That would be the trade-off for the success with the thinner gelcoat that I’ll have to accept and deal with. As it is, in order to try and get gelcoat in there I have to lay the gun down almost parallel with the hood to spray back inside. It’s just no good trying to spray from such an oblique angle unless you want to lay it on heavy, and, well… you know. I’ve been considering that if I fill the scoop in an inch or so it would go a long way to alleviate the issue and also ease fabrication. It wouldn’t be totally true to the OEM feature, but there’ll be enough of it left to still look appropriate.

If all goes well, I’d like to (hopefully) lay it up one last time, with the altered scoop, just to be certain I have the details right before I move on to do the whole hood. I’d rather go through THIS process a few more times, if necessary, than on a much larger piece. Knowhatimean?

#16

Finally… popped the piece this morning. No lifting or porosity, no distortion to speak of and nice clean details. :smiley: Save for for a little alligatoring (my fault), I’m quite pleased.

Looking back, I would say that the majority of this experience had more to do with “operator error” than anything. From letting the gelcoat sit too long before laminating, gelcoat too thick without sufficient backing to hold it in place, too hot of a mix for the conditions… all on top of the fact that it’s been quite a while since I’ve done any of this and I’ve gotten rusty. The semi-perm system definitely sealed the surface of the plug and it COULD have been a factor in some of this early on, but for the most part,… it was mostly ME. :rolleyes:

As for the semi-perm release… I have to say it worked quite well. And while using the whole system on a plug may be overkill for most folks, if you have a plug that represents a substantial investment of time and money, using the cleaner and sealer (followed by wax, instead of the final semi-perm release barrier) could possibly be an effective insurance policy for a good release, without the worries of a pre-release of the gelcoat. At least that will be my approach on the next plug.

Thanks for all the help, guys!

#17

Congrats!! Nice to see someone who learns from there mistakes AND admits it. I had some co-workers that have never heard of that concept.

I know a couple shop owners down here that build boat molds…large boat molds.

They sealed a 34 foot mold, then put semi perm on it, and then followed by 8 coats of wax…the gel pre-released and they didnt know untill they pulled the completed part. I can only imagine the money lost.