I am making some infused fiberglass parts and using infusable poly resin with them. These laminates are 6 layers thick and i need to thin the resin. I ran out of styrene and wont get shipment till tomorrow but I need to manufacture today. Is it terrible to thin with acetone for the time being? I need to add about 15% thinner the rest resin.
um, id say yes(its bad). but i dont know 100%
free bump for you though
You need to thin the resin because there are 6 plies of 'glass? If it’s infusion resin, there shouldn’t be a problem even with 30 plies.
Don’t add acetone!
i have infused of these already and both stopped about half way even with 3 layers of flow media. I usually thin with styrene but my shipment will not come in time for me to have a finished test fitment piece
do not add acetone
Are you pulling a full vacuum? Something is definitely wrong with your process or setup.
no full vacuum but they are just rather large parts and it is around 85 degrees in my shop so everything kicks rather quickly. I have thinned this size of part before with same amount of layers and had no problems. I just contacted the customer and we are going to make when the styrene comes in. i also am almost 6ft elevation so my vacuum if I am lucky is 25hg.
you need to achieve full vacuum before infusing. are you doing a leak-off test before infusing to insure there are definantly no leaks? You have all the time in the world when doing RTM/infusion to setup, so do it properly. once infusion starts there is no stopping and any errors/shortcuts you made earlier will become apparent.
Thinning the resin wont slow its cure time, just increase its Viscosity (to my knowledge). you can get promoters/inhibitors for polyester to decrease/increase gel time. That is the only way to prevent resin kicking before a full infusion is achieved.
Insure the resin your using is Unpromoted - this allows you to add inhibitor to slow the curing process. My supplier has 2 poly RTM resins available, one is prepromoted for MEKP cure and the other is unpromoted which is what you’d use inhibitor with.
To my knowledge you can change the geltime from 10-15mins up to something like 90mins.
i have perfect vacuum with no leaks. This is also 6 layers of 32oz fabric so it is a very thick piece. I got my styrene in and infused it perfectly with no problems. Thanks for all the info. I literally have several thousand infusions under my belt and quite seasoned to it for my applications. I just needed a quick fix and never thinned with acetone and I google searched it and in wikpedia it said acetone was made also to thin resin so that is why I asked. Problem is fixed now, test part was perfect now for production. woohoo
It’s made to thin resins (usually gelcoats) in open molding. The acetone evaporates.
With infusion, you’re trapping it in the closed system. I’d recommend against it if I saw a company doing that. But if you’re satisfied with the results…
thats a good explanation. I didnt use it, I only had to wait a day for the styrene to come in so i waited
I one asked a similar question (thinning with styrene) of an industry expert and he was very opposed to thinning using this type of method. The issue is that it turns long chain molecules into short chain molecules and changes the mechanical properties of the product. Should you run into issues with the infusion the product supplier will be of little help to you as they cannot make any reliable recomendations about an unknown product. His final words on the subject was to use the appropriate resin for the job and dont mess with it.
are you talking thinning with acetone or styrene? If I am infusing with with per for fiberglass or some small cosmetic parts I always thin my resin per application. It is just what works for me
I guess there’s not really an issue thinning with either Styrene or Acetone in a hobby composites shop, or even in a general composites shop assuming the customers are not requiring optimum performance (i.e. strength, robustness etc.)from the finished part. The gentlemen who told me that it should not be done were speaking in a context of large production parts in a factory setting. If resin in a part like a boat hull were to be thinned like this then there is a slim possibility the infusion may go badly but a very substantial risk that the structure may begin to fail years later. That is bad for the boat owner and bad and expensive for the boat manufacturer in terms of waranty claim and reputation damage.
If thinning like that suits your application then go for it.
Cheers
Splint
I used to make cab tops for buses before I did this. The molds were over 20ft long and we thinned everything with styrene. It was just what we were made to do lol. Never had any problems with it. So I stuck with what worked 
Guy i work with uses styrene or acetone to thin resin for parts.
He does a lot of unconventional stuff though… some of it works well, other times it’s like watching a bloody horror movie.
I honestly don’t know the right way to thin PER or VER.
I do know you can buy infusion specific VER, not sure if anyone makes an infusion polyester resin? I prefer VER or epoxy myself.
anyone thin their epoxy?
Use High Gloss Additive to thin VER and IVEX-400 is a great infusion resin.
Cooks composites has a RTM poly resin and that is what I am using on some of my fiberglass stuff. I still thin it past that about 15%. I have never had a problem thinning with styrene. I did thin a little bit of clear gel coat that thickened some and when I popped the part I had a lot of pin holes in the gel that I have never had the problem with before so I am assuming it was the acetone that made it happen.
High gloss additive is not a structural resin. Hopefully the parts aren’t expected to bear any important loads and your customers know what they’re getting.
At my former composites and plastics job training classroom, we use to PER Gel coats and lamination resins thin with acetone.
But what I like to do on hand lay ups was to gel coat, let it “B” stage, dry lay in the pre-cut (was cut with templates while gel coat was “B” staging) reinforcements (rookies need the extra work time) and it may be 2 - 3x layers!
Then thin the lamination PER around 10% (1/4" float in a 44 oz cup) with acetone, throughly stir / mix BEFORE adding the MEKP.
NEVER MIX ACETONE & MEKP unless you want a fire or explosion!
Then pour, stiple, roller, brush the resin thru all the layers of reinforcements (rarely lifting a layer to wet the bottom layer out) keeping an eye out for trapped air pockets…
Again for open mold lay ups…
The secret was to througly stiring / mixing the resin and thinning agent before catylazing the resin.
Rookie: try mixing the resin more or pouring the resin (without hardener) in a long thin stream from 1 cup to another to pop any bubbles…