a couple fiberglass questions

[Mikeopsycho]

How long can you wait between layers of new fiberglass (no wax) without having to grind and clean with acetone?

Also, how long after grinding old fiberglass can you wait to lay up new glass before you should grind again?

Thanks folks. Mike

 

[81 Checkmate]

Epoxy or poly?

No expert.......only have used poly.....I have waited weeks in - between layers of glass. I just wiped down with a clean rag then went back with a wipe of acetone then started glassing again. Ya know things come up that need to be done instead of the boat.


It's best to do all the layers at one time.

 

[Mikeopsycho]

Thanks 81 Checkmate, I'm using Poly.

 

[81 Checkmate]

Like i said before...this was my first restore project and that was my experience........So far so good.

Im sure the experts will chime in...

 

[GT1000000]

Howdy Mike,
Yeah, the way I have always done it is if the stuff you laid down becomes sticky/tacky after a wipe down with acetone, you should still get a fairly good bond...if it doesn't get sticky/tacky I would give it a quick ruff-n-scuff...
GT1M

 

[Mikeopsycho]

Great info, thanks guys!

 

[Rickmerrill]

These are good questions. I thought this would start a big debate but so far no. I read someone here that said the navy uses 16 hours as their max. Then I was reading article today, because of your question I was researching, and he said 16 hours too! But I don't like that answer and I hate gummy sanding so until I find out otherwise I'm going with the "if it still gets tacky with acetone" advise of GT. Funny no one took the second question so here's an opinion. You can wait a long long time as long as nothing contaminates it. I'm not sure what, if anything, happens if you leave it exposed to the elements.

 

[Georgesalmon]

Current thinking advises that to get a primary bond you can't wait longer than 16 hours between layers. After that its called a secondary bond and you should abrade the surface, but not wipe with acetone. Just sand it and vacuum up the dust. Probably won't matter that much in our little boat projects but if you sent a piece for testing interlaminar strength it would be less with a secondary bond than a primary one.

 

[Woodonglass]

This ^^^ is the recommended layup schedule!!! Contamination IS the culprit and it comes from humidity, sunlight, air and other variables. After 2 days, it's always best to scuff it and clean it. I too, like to wipe with acetone but as GS says it's not absolutely a must. For sure the factory boys don't !!!

 

[Mikeopsycho]

Thanks for the informative answers. Although I do like GT1M and Checkmates answers, I'm gonna err on the side of safety and follow the 16 hr rule of thumb that Rickmerrill, Georgesalmon, and WOG suggest.

Hmmmmm, ok, so it looks like I wasted a lot of time by grinding, scuffing everything at once, I should have just waited till I was ready to work on each area, at least as far as tying into the original glass on the boat goes. My reasons for grinding all at once were to get it all over with, and to avoid multiple clean ups. Oh well, live and learn. At least scuffing what has already been grinded (ground?) should be easier, just a light touch up I guess. And I will wipe everything down with acetone after vacuuming, I gotta think removing the fine dust is a good thing.

This brings me to another question.........how long should you let the acetone dry before laying up fiberglass? Does it even matter?

 

[Rickmerrill]

Wood can we get a clarification? When you say after 2 days scuff and clean does that apply to recently ground original fiberglass? I wasn't clear but thought you were talking about new glass. Mike, the thought occured to me that since we are all doing repairs we're all going to be starting out with secondary (mechanical) bonds so maybe it's not that big a deal wether we get good primary or secondary bonds as long as they are good bonds. Weakest link and all that. Love the question about acetone, keep digging man!

 

[Daniel1947]

OK, so if I have this all correct.... I finished grinding and sanding the interior of the hull after removing all the old wood over a week ago, and then I gave it all a good wash down and flush with clean water. I now have most of the new wood cut for transom and stringers, making trial fits and adjustments as I go. I will need to scuff all the areas I am planning on attaching the transom and stringers again? And also scuff all the areas I plan on just laying some 1708 for additional support? I know I need to wipe these areas down with Acetone prior to applying resin and cloth.

 

[Rickmerrill]

Yep that's the question Daniel. George if you see this just wondering why/where you got the "not wipe with acetone". Not a challenge just wondering if someone somewhere has evidence that there is an issue with acetone wipe before laminating.

 

[Woodonglass]

Ok, the 2 days is for New Glass layups only. For Old Glass that has been ground down to fresh layers all that's required is to ensure no contamination has occured over the delayed time period. If it's gotten greasy or dirty then fresh grinding and cleaning should occur. IMHO cleaning with a good chemical wipe down is good insurance against any kind of contamination and does not affect the glass in a negative way. Acetone has a High and Fast flash point so 5 -10 minutes is usually ample time allowance before applying fresh resin unless you really soaked the area and that's really never necessary.

Hope this clarifies things a bit.

 

[Rickmerrill]

Thank you, sir.

 

[Mikeopsycho]

Thanks WOG, that clarified things a lot!

Good point re "weakest link" Rickmerrill.

 

[Mikeopsycho]

Sorry guys, another question popped into my head while I was supposed to be sleeping, applying gelcoat.

Does it matter how long after glassing an area, say a boat sole, before rolling on gelcoat? Would the 16 hr rule of thumb apply? What kind of time is optimum between multiple gelcoat layers, ie- 1st coat un-waxed then top coat with waxed?

 

[Rickmerrill]

Yep 16 hour rule gelcoat is polyester based. Got to go look up the other question. BRB!

 

[Woodonglass]

Spraying Gelcoat is NOT like spraying paint. The final coat should be as thick as a Penney. 20 mils approximately and then you sand and polish away the orange peel. You'll end up with 15 mils or a bit thicker.You should try to apply 4 coats each aprroximately 5 mils thick and you apply them one after the other just as soon as the previous one tacks up. Just like the poly resin when applying glass. It big issue is the equipment You MUST stay on top of it and NOT allow the gel to Kick Off in the gun or it will be ruined. Acetone flush IS essential prior to the gel starting to kick. It takes some planning and coordination but the DIY'r can do it if planned and coordinated properly. You can wax the last coat or shoot PVA over the entire hull just as it starts to set up.

 

[Rickmerrill]

Hey wood he was going to roll it on. Mike have you taken a look at the videos at Boatworkstoday.com? He did three or four good ones on gelcoat but he was simulating a hull repair not just rolling some in a ski locker but you might get a few useful tips. He was using a brush and just said wait for it to start to flash. Hum, wonder how you'd know. Because conditions can change curing time once it has set up enough that the roller doesn't lift up the first layer you're good. Maybe 20 minutes to an hour depending.