Fiberglass cure question

[Rickam]

Hi all,
New guy in a quandary. I'm trying to lay up fiberglass with polyester resin over plywood. I put a coat of resin on the wood first, then mixed resin at the proper ratio, applied to cloth with temperature in the 70's. Came out today and it had dried but the cloth and the brush I used were still flexible and the cloth isn't adhered to the plywood. It's also not tacky at all. Any ideas what I did wrong? Thank you.

Rick A

 

[alldodge]

Yes, I think
Appears you did not use hardner in the first coat of resin applied. Resin needs hardner (MEKP) to harden. Just applying resin does nothing but make a mess on the plywood

 

[sphelps]

What alldoge said is probably correct. Also your hardener could be old or not the right amount or not stirred up good enough ..

 

[Rickam]

Thank you both. I used hardener in the first coat and mixed in IAW charts I found online- about 1.5 cc to 4 oz. resin. I stirred it for a couple of minutes. Would you think that's not enough for a small amount like that? Don't know if the hardener is old; just bought it from a California online supplier who has high ratings, FWIW.

I'd think it would still be tacky if it hadn't cured. Do you think applying heat may help?

Rick A

 

[chevymaher]

They sell hardener at auto zone and such. Get some there and mix a little see if that was it.

Yes higher temps help.

 

[Scott Danforth]

Thank you both. I used hardener in the first coat and mixed in IAW charts I found online- about 1.5 cc to 4 oz. resin. I stirred it for a couple of minutes. Would you think that's not enough for a small amount like that? Don't know if the hardener is old; just bought it from a California online supplier who has high ratings, FWIW.

I'd think it would still be tacky if it hadn't cured. Do you think applying heat may help?

Rick A

unfortunately, you will need to start over.

the wood now has un-mixed resin sitting on it. not sure you can clean it off.

I normally mix per the instructions on the container for about a 1% mix as I am usually glassing in high heat.

 

[alldodge]

Poly resin has a shelf life just like the hardner, but the resin is shorter. This is one of the reasons I try not to buy the stuff from a brick and mortar store, unless they sell a lot of the stuff. Can keep the MEKP in the freezer to make it last longer

 

[gm280]

Hi all,
New guy in a quandary. I'm trying to lay up fiberglass with polyester resin over plywood. I put a coat of resin on the wood first, then mixed resin at the proper ratio, applied to cloth with temperature in the 70's. Came out today and it had dried but the cloth and the brush I used were still flexible and the cloth isn't adhered to the plywood. It's also not tacky at all. Any ideas what I did wrong? Thank you.

Rick A

Post a few pictures of what you are dealing with and working on. There are so many reasons it didn't come out right.

It could be the hardener or the resin it self. However, when resin goes bad, it usually gets so thick you can't get it out of the container. At least that is how it does for me.

The MEKP should have a strong chemical smell and closer to a watery liquid and if it does, it probably is not that either. I can't see any reason your mixture didn't work. Even if you missed the proper ratio, it would still harden up eventually.

4 oz is a ~118.3 ml (cc) so 1.18 cc would be a 1% mixture. 1.5 cc is surely enough. And since you stated you mixed for a couple minutes, sounds like you did it correct. Pictures my offer a better reason. JMHO

 

[Rickam]

Thank you for your replies. Here's a pic of one corner. The resin is dry but I can peel the glass from the plywood and it's not rigid.

The resin is a little thicker than water but the hardener has what I'd say is a mild acidic smell, not strong as you suggest. Sounds like that may explain the problem.

Rick A

 

[alldodge]

Being able to peel it away is a good thing since it didn't setup. Remove it and try you stuff on a test sample. Also resin alone needs glass to be able to bond. If you find the resin will harden, then wetting the wood is good, but at the same time lay a layer of glass and then more resin to soak thru

 

[tpenfield]

Rickam was the plywood previously treated or coated with epoxy?

If so, Google 'amine blush'

 

[Rickam]

I bought some new hardener and am trying it. I noticed on the label it suggested 10 drops per oz resin, which sounds like a lot higher ratio than I used. I mixed it at 1% near as I could figure, which seems to be what all the charts recommend. Maybe I'm not mixing it strong enough. Last time I dabbled in fiberglass was so long ago I can't remember details (actually can't remember details from yesterday!)

The plywood is new, not previously coated.

Rick A

 

[Scott Danforth]

did you clean the old resin off of the wood you are trying to cover?

that has to come off

you will need to use lots of acetone, or simply start over with the wood.

 

[gm280]

I have been thinking about this one.

You know you don't have to have exactly 1% mixture. More is okay as long as you don't go way overboard with the MEKP, AND you can finish the coating before it kicks in. When you use more MEKP, the kick time reduces.

So if the weather is cool or cold in your area and you are working is a cool or cold shop, you can get away with more MEKP and still have enough time to get it applied before it kicks. I wouldn't go to a 10% mixture, but 2% 3% or so isn't going to hurt anything.

Second thing is, are you applying the mixed polyester too thin? You typically cover until the fiberglass material starts to disappear. If you are merely covering the fiberglass with only a little poly mixture, it isn't adhering to the wood. It will get hard, but may not be attached to the wood. Just a few other ideas here... JMHO

 

[tpenfield]

I am also wondering if there is anything particular about the plywood. The symptoms described point to something on the plywood inhibiting the curing process of the poly resin. Epoxy (amine) certainly does that, but perhaps there is something about the plywood that has a similar effect.

If you have a spare piece of the plywood, you could always run a test to see if a 2% (or 3%) activation of poly resin will cure on and adhere to the plywood.

FWIW - I tend to use 'older' (expired) resin for various things and small projects. Never had a problem with the resin not kicking. I certainly would not recommend doing it, but have yet to see it as a hardening fail.

 

[Scott Danforth]

I am also wondering if there is anything particular about the plywood. The symptoms described point to something on the plywood inhibiting the curing process of the poly resin.

Ted, OP stated in post 1 he coated the wood with un-mixed resin, then put the cloth over it and used a questionable resin and MEKP

so if the old resin was un-mixed, it has to be removed from the wood prior to anything sticking to it. Hence my comment on starting over.

 

[tpenfield]

Ted, OP stated in post 1 he coated the wood with un-mixed resin, then put the cloth over it and used a questionable resin and MEKP

so if the old resin was un-mixed, it has to be removed from the wood prior to anything sticking to it. Hence my comment on starting over.

In post #1 he indicated that he mixed in the catalyst after the first coat. When questioned about that, he indicated in post #4 that he used catalyst in the first coat as well, which is either contradictory to or clarifying of his #1 post.

That is about all we have to go by, else he would quickly have realized his error and know what he now needs to do. I'm not sure that is the case . . he seems to still be searching for answers.

 

[Woodonglass]

IF, in fact the first coat of resin DID have resin and hardener in it and you are able to peel it off...Then the chemical curing process did NOT occur for whatever reason. It's a Moot point now. It will ALL need to be removed and start over. I'd highly recommend doing a test run on the next one to ensure the mix WILL kick and harden. Don't forget that Poly resin REQUIRES the use of CSM prior to applying any glass fabric.

 

[Rickam]

I'm grateful for all the suggestions. The plywood is new and has no known coating on it. I covered it with a coat of resin mixed with hardener 1%, after it had dried I applied the cloth with the same mixture of resin. That was Sunday, IIRC, and today I peeled off the cloth. It was dry on the surface and somewhat sticky and tacky underneath- the side facing the wood. It's still flexible. I contacted the seller who gets it direct from a supplier and said it's fresh. I also tried some samples with higher ratios of hardener- to over 2%- and they dried but are still soft and flexible. My limited experience with fiberglass was long ago but I don't remember having a situation like this.

Rick A

 

[Scott Danforth]

I would get resin and supplies from a different source.