Proper use Polyvinyl Alcohol PVA ? weird reaction

General Composites Discussions Composites Talk
#1

[b][i]I have been using this stuff for a while, but I think I must be doing something wrong…

I apply meguiars mold release wax a couple times before applying the PVA.

I consistently get these “lines” in th surface of the finished part and also in my mold. I know the lines are from me brushing on the pva-

however, if I do not use the meguiars mold release wax before the PVA, I dont get the imperfection lines.

Is the rule to not use the mold release wax, or any other compound or polish with the PVA?

I was reading about this Rexco “part all paste #2” that is said to be used before the pva- will that solve my problem? [/i][/b]

#2

Sorry, I don’t use PVA because of that I use Chem Trend Chemlease One FS Semi-Permanent Release and Meguiar’s Universal Mold Release Wax #88.

I think PVA works better when you spray it.

#3

^

is the Chem Trend One FS semi-permanent release in a paste form? Also, is that applied in combination with the mold release wax?

#4

I’d highly recommend spraying it. I used to brush it on and didnt like the streaks. I stopped and then used lint free cloths to wipe it on. It worked very well, but not nearly as well as spraying it. Yes spraying takes more time, but you get an even coat that way. It won’t cost you much either. Harbor freight spray gun = $25 bucks. I’d recommend using a mini or touch up gun. Its cheaper too.

Then a small air compressor will run you $100 if that depending on where you go. Try craigs list, harbor freight, lowes (great place for cheap tools) or pawn shops.

I use meguires paste wax from autozone. The gold tin. Not meant for molds, but its a good carnuba wax. I then use partal PVA.

#5

^thanks for the advice, I appreciate it alot.

alright I will go out and buy a spray gun setup- I guess I have been putting it off for too long to have one set up.

I was thinking of wiping it on with some lint free cloths- I figured that wouldn’t give the streaks?

#6

Chem Trend One FS semi-permanent release is a liquid.

http://www.chemtrend.com/

http://meguiarsmoldrelease.com.hk/index.php?_room=2&_action=detail&_page=5

http://meguiarsmoldrelease.com.hk/index.php?_room=2&_action=detail&_page=6

#7

Wax properly and avoid PVA entirely.

#8

^
I would like to try casting a part without pva. I am worried about the percentage chance of the part sticking to the mold.

I found this good article talking all about this problem:

http://winshipmodels.tripod.com/pva_mold_release.htm

It says that if you apply pva twice (cast 2 parts) to the finished tooling mold, the 3rd time you go to cast, the pva is no longer needed because the percentage is around %1 percent of the change of sticking.

has anyone had a mold stick on them w/o using pva?

#9

Very good find! That sure did help me out.

I’ve been using a regular meguires carnuba wax from my local auto supply store. It works great. Its not a cheap wax, its about 13 bucks a tin so I figured it would work. Its never failed so far and has worked just as well as any paste wax I’d purchase online from composite distributors / sellers.

My question is, if you have a mold with a textured surface, (meaning a non perfect smooth polished surface) do the basic rules still apply? Or should PVA then be used in order to help prevent sticking?

I’d like to get away from PVA since I have problems with the PVA ripping while placing the first layer of twill carbon fiber down into the mold with an adhesive spray. I’d much rather skip the gel coat, make a quick production run of several parts in a few days, then spray duratec gel coat over all the pulled and trimmed pieces at once.

With out thread jacking… The information I read about the PVA Mold Release sounds pretty good. As a guy who has had a part stick and destroy a brand new mold (first layup with wax and no PVA) I am very scared to destroy another mold. Even though its been over a year since that has happened. I will give it a try on one of my simple super glossy flat molds. I will post the results after with pictures and explanation of how I did it and succeeded or failed. I made the first part today on that new mold using wax and PVA, I’ll make another tomorrow, and then Thursday I’ll try with out PVA.

I’m already scared just thinking about it :-/. However if it works, then I’d be glad to have my problem of PVA tearing solved. I hate having to slow production time down by adding gel coat first then the fabric in order to prevent PVA tearing.

Thanks again for the helpful information! I’ll post back in a few days.

#10

I use PTM&W 0828 when I need the best. They ship fast & this stuff rocks
(I never had to bake it)

http://www.ptm-w.com/dynamicdata/data/docs/pa0828%20bulletin.pdf