How long between layups with fiberglass?

szicree · #1 08-07-2007, 10:12 PM

I've always added additional layers of glass cloth when the previous layer is nearly set, but still tacky like masking tape, but am wondering how long I can wait. I mean, if I come back the next day, do I have to sand before additional plies are laid on?

Mike S · #2 08-07-2007, 10:27 PM

Get some peel ply, put it on the wet layup, and roll or squeegee it on.

You can come back in a day or ten years, remove the peel ply, and do the next layup. The surface will be ready by just removing the peel ply, sand any shiny spots.

The above is for epoxy-------------for most polyesters, things are a bit different, as they contain a wax and you really need to sand the surface before doing a new layup--------or just do all the layups wet, dont let the resin set up between layers.

Good luck,

Deems Davis · #3 08-07-2007, 10:29 PM

Think of it this way, the strength in fiberglass is in the fiber and not in the epoxy. If you do a layup on top of a cured section, then you will want to sand/roughen the section up until you just barely expose some of the fiber so that the epoxy will bond to the fibers in the underlying section. Careful, as you don't want to weaken the underlying section by sanding too much away

AlexPeterson · #4 08-08-2007, 06:39 AM

Quote:

Originally Posted by Mike S

Get some peel ply, put it on the wet layup, and roll or squeegee it on.

You can come back in a day or ten years, remove the peel ply, and do the next layup. The surface will be ready by just removing the peel ply, sand any shiny spots.

The above is for epoxy-------------for most polyesters, things are a bit different, as they contain a wax and you really need to sand the surface before doing a new layup--------or just do all the layups wet, dont let the resin set up between layers.

Good luck,

Mike, I believe you have this reversed - epoxies blush an amine of some sort to varying degrees depending on the epoxy. This is a wax like stuff that is easily washed off with soap and water, but will reduce the bonding between layers. The time between epoxy layers will probably vary depending on many variables, probably best to talk with the manufacturer.

See:
http://www.epoxyproducts.com/blush4u.html for more info.

cytoxin · #5 08-08-2007, 07:36 AM

i would sand it with 80 grit to roughen the surface wipe it down with mek and lay up more glass.
when i did my canopy i was having some bonding issues. i was cleaning with acetone. i switched to mek and man what a difference. '
i also tried metal prep, prep sol and mineral spirits. nothing bonded well untill i used mek.
data point :: i was using west 105 with the slow hardener.

jcoloccia · #6 08-08-2007, 08:26 AM

Polyester layups must be done while the underlying layer is still "green". Polyester has horrible mechnical bonding qualities and must depend on chemically linking with the underlying layer. If you wait until it's cured you're basically stuck and will have to use epoxy for additional layers or repairs, unless your piece isn't structural and you don't care about realizing maximum strength. By the way: the only reason to use polyester is if you're building a large boat, it's a lot cheaper than epoxy. It's inferior in every way to epoxy, except cost.

With epoxy, it's still best to add additional layers sometime after the mixture is gelled but before it's fully cured and rock hard. This allows the epoxy to chemically link with the underlying layer. If you do let it get rock hard, though, you must clean the surface with water to get rid of the "blush" (it's not wax but feels like it) and then sand the shinny spots (I usually lightly rough up the whole surface). This allows a mechanical bond to take place. The chemical bond is better AND less work!

Also, try to keep solvents off if you can. Water works fine. If you MUST use a solvent, holy cow you'd best be sure every last molecule is gone before you apply glue.

gpiney · #7 08-08-2007, 09:28 AM

If you are doing a layup over cured epoxy, just sand with 80 or lower grit (I use 40) and clean it up with Acetone. Acetone will wick off before you can get a layup ready.

Mike S · #8 08-08-2007, 10:32 AM

Quote:

Originally Posted by AlexPeterson

Mike, I believe you have this reversed - epoxies blush an amine of some sort to varying degrees depending on the epoxy. This is a wax like stuff that is easily washed off with soap and water, but will reduce the bonding between layers. The time between epoxy layers will probably vary depending on many variables, probably best to talk with the manufacturer.

See:
http://www.epoxyproducts.com/blush4u.html for more info.

Alex, no, I dont have it reversed. There is a wax used in polyester resin, helps it to set up by forming a top layer to block out the air. This is in a lot of polyester, specially if it is for finishing. Laminating resin usually doesnt have the wax. Problem is, a lot of folks dont know to buy laminating specific resin.

The epoxy blush is what the peel ply takes care of. Also, a big problem that many folks have is using too much resin, this only makes parts heavier and causes the blush problem to be worse.

jcoloccia · #9 08-08-2007, 12:26 PM

Mike's right. The epoxy film isn't wax, it just kinda' looks and feels like it.

You have to have some sort of top coating on the polyester or it will never cure. The top layer will forever be gummy and totally unsandable. The wax forms a protective layer that keeps the atmosphere out and allows it to finally cure. I've heard that some people use laminating resin (the stuff without the wax) even on the top layer and then put plastic or something on top to allow it to cure hard but I've never done that myself.

The easiest thing to do is just not use polyester at all and use epoxy instead.

az_gila · #10 08-08-2007, 12:51 PM

Quote:

Originally Posted by jcoloccia

You have to have some sort of top coating on the polyester or it will never cure. The top layer will forever be gummy and totally unsandable. The wax forms a protective layer that keeps the atmosphere out and allows it to finally cure. I've heard that some people use laminating resin (the stuff without the wax) even on the top layer and then put plastic or something on top to allow it to cure hard but I've never done that myself.

The easiest thing to do is just not use polyester at all and use epoxy instead.

As John says, I find it's easier just to use epoxy (especially the WEST products)

But, if you must use polyester resins, you can buy the laminating resin (with no wax) and just add the wax to the mix for the final layer that you will sand.

It's called Surface Agent...

http://www.fiberglasssupply.com/pdf/.../SurfAgent.pdf

I've used it, and it does work - it allows you to only keep one container of resin in the shop....

If you live near an applicable coast, the surfboard shops are a great supply source. They like their surface finish just as smooth (or better) as our aircraft parts...

gil in Tucson