Lance Campbell

Another quick question for any that might know..

My process today, was going to be the same that I've done several times before, which was shoot my PVA Friday morning, shoot Duratec mold primer in the evening, then layup my mold this weekend starting early Saturday morning. This has worked very well for me so far.

But... tonight I crack open my new gallon of mold primer, and find it has completely separated, and after a hour and a half of mixing with a power mixer, it is still unusable.

So.. I've currently got a 13 foot fuse plug and fence, ready to go, with a good, smooth coat of PVA on it, in my paint room, that can keep it clean and at a steady temperature.

How long can I leave it like that? I placed a new order for paint, but it won't ship untill Monday at the earliest. Ideally, I'd like the weekend to make the mold, so that means my next window of time to make it, is a full one week away. Will it still be ok to proceed shooting my primer over PVA that has been on the fuse/fence for a week?

Thanks for any thoughts,
Lance

Lance Campbell

By the way, here's the project, and how it currently looks under PVA. You'll see that jigging this thing up again, should it be necessary, and resealing the crack between the fence and the plug is no small amount of work, which is why the questions...

moldmaker

My Feedback: (5)

The PVA will stay on for a long time .You can leave it set till primer gets in with no problems .

TT2

My Feedback: (13)

Lock the room and wait until the Duratec arrives. The PVA should be OK provided it stays BONE DRY. How come you don't use a surfacing epoxy? Just curious. I would think that Duratec would be too delicate for a mold face...that is unless the 'mold' primer is different than the 'surfacing' primer (polyester-based) that I use on plugs.

Good luck on the project and keep us posted!

-Tom

Lance Campbell

Tom and anyone else curious,
You are correct, it's the Duratec Surfacing Primer. One thing I learned when trying to figure all this out, was that there was a ton of different ways to do things, and that many different ways all work well. This quote was from Fibreglast, about the primer: "Duratec Surfacing Primer is the best choice for coating your plug or reconditioning your mold." Marketing hype perhaps, but so far it has worked well for me. It seems to be a very hard, dense primer and seems to do a good job.

My process for mold layup, layer by layer, has been:

* Partall Waxed plug
* PVA sprayed
* Duratec sprayed
* West's epoxy, mixed with Colodia Sillica to help with runs, and West's Graphite powder 423. (this turns it really black, which has the side benefit of helping to see where you've put it down well, or not, and gives a nice background for the cloth laying. As the white cloth gets wetted out, and clears up, the black shows through. Pretty extreme color change, to help ensure it wet out properly. This layer is put on pretty thick, and left to cure out, fairly well, so the first layers of cloth won't 'print through' over time.
* West's epoxy, mixed heavily with cotton flock, to about peanut butter stage. I use this to fill all sharp corners, or edges to smooth out and help the cloth layup to follow.
* 4 layers of cloth / West's epoxy.
* One inch cubed balsa blocks glued on with thickend West's epoxy over the part, not the flange. (this make the mold very thick around the part, and gives it a ton of strength, with little weigh gain.
* 4 more layers of cloth/ West's epoxy.
* One last note, that between the main layers of coth, I put an extra layer on the flange, since there are no blocks out there. That make for a total of 14 layers on the flange, and is a nice thickness for my bolts used later to hold top and bottom together.

If you'd like to read the long winded build of the project, you're welcome to take a look.

[link=http://www.mmrca.org/lance/sledframe.html]http://www.mmrca.org/lance/sledframe.html[/link]

At this point, I think I'm going to take Wednesday off work and try to get the primer shot Tuesday night (4.5 days after the PVA was shot), and then layup at least to the balsa block stage Wednesday. I could then do the 4 layers on top of the blocks on Sunday.

Any other thoughts on PVA life? How long have you left stuff at the PVA level and been ok?

Thanks again for the input and advice.

Here's a couple shots of completed wing tip molds The texture you see on the flange, is actually from the Formica I used to make the flange around the original plug:

moldmaker

My Feedback: (5)

Lance i applied PVA to a mold then decided not to lay the part up .A year later the pva was still on the mold . PVA does not seem to go bad if not exposed to a lot of heat . Such as storeing mold in attic Or setting in sunlight for a long period of time .

boater

My Feedback: (2)

Lance, I had the same thing happen to me as Moldmaker, but my PVA started to seperate from the mold in small spots. I live in Sacramento, where it can be very hot and dry. It wasn't a big deal, I just hosed off the mold and reshot it. The seperation was very easily seen, since it turned whiteish. Man o man, that's heck of a project. Good luck with it. Thanks for the pics and reports of your exploits on your web page. You haven't had any problems mixing polyester primer as gelcoat and epoxy backing? Got to admit you seem to be doing just fine. Can see that you would like something to transfer all those time consuming etchings on your plug to the mold perfectly! Rudy

lilhachet

My Feedback: (2)

LOL, your asking for help here? You be asking for help from NASA,lol, if nobodys seen this man's project, the only thing I can say is WOW!!!! And I thought I was having problems with my mold. GREAT job. I would love to see this thing fly, seeing it's my all time favorite. Keep up the great job.Back to my GP 20 cub,sigh.......