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Old 30-04-2016, 19:38   #1
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Quick Question - Time between fiberglass layers?

Quick question, as I've been getting contradicting information from several different sources on this.

I need to repair some impact damage on my keel, the keel is about 1/2 to 5/8 inch thick on the leading edge. There is no access to the back but I have ground out a 12:1 feathering around the hole and put in a backing layer.

How long do I have to wait between layers of fiberglass? I am using West System Epoxy with the 205 fast hardener. My plan is to use a layer of mat, then a layer of woven and continue until complete.

I've been told I had to wait an hour between layers, I've been told to let it mostly cure between layers and I have also been told not take a break between layers and just keep laying it all on until it is at the proper thickness.

Thoughts? I would appreciate any real world experience with this.
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Old 30-04-2016, 19:53   #2
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Re: Quick Question - Time between fiberglass layers?

You might to checkout using peel ply. It allows you let the layups dry without having to sand for the next layup. Here's a discussion Peel Ply?
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Old 30-04-2016, 20:08   #3
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Re: Quick Question - Time between fiberglass layers?

I'd look at all of the great guides on the West Systems site:

Applying Cloth & Tape

But, if you want the short version and are using epoxy then wet-on-wet is preferred, it gives you a chemical (rather than just a physical bond) between layers. Lay up as many layers as you can without worrying about it slumping/sliding. If it is going to get thick (>1/4"?) then you have to worry a bit about heat buildup as it cures, see what WEST has to say.

Once you get to a point where you have to stop (heat/slump/lunch) if you can dent it with a fingernail you can continue with a wet-on-wet application. If it gets much harder than that then you have to start looking at surface prep techniques between layers (peel ply, sanding, washing for amine blush).

Books could be written on this (and have), so spend a little time at the WEST site.
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Old 30-04-2016, 20:10   #4
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Re: Quick Question - Time between fiberglass layers?

Quote:
Originally Posted by ElCapt Drew View Post
Quick question, as I've been getting contradicting information from several different sources on this.

I need to repair some impact damage on my keel, the keel is about 1/2 to 5/8 inch thick on the leading edge. There is no access to the back but I have ground out a 12:1 feathering around the hole and put in a backing layer.

How long do I have to wait between layers of fiberglass? I am using West System Epoxy with the 205 fast hardener. My plan is to use a layer of mat, then a layer of woven and continue until complete.

I've been told I had to wait an hour between layers, I've been told to let it mostly cure between layers and I have also been told not take a break between layers and just keep laying it all on until it is at the proper thickness.

Thoughts? I would appreciate any real world experience with this.
===

I have always layed up multiple layers wet-on-wet. The risk is that it may start to sag at some point unless you can support it in some way. If you let it cure completely then you'll have to clean or sand off the amine blush before proceeding. I've never used peel ply but it sounds like a good suggestion. In any case you'll need to do a fair amount of grinding before the final fairing steps.
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Old 30-04-2016, 20:31   #5
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Re: Quick Question - Time between fiberglass layers?

Many thanks guys.

Much appreciate the information.
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Old 30-04-2016, 20:48   #6
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Re: Quick Question - Time between fiberglass layers?

Hi.

As stated above, wet in wet is far better than fully cured laminates on top of each other.
Wet means that the laminate is still very slightly tacky and not fully cured.

Use the peel ply only on top of the last layer. It creates a resin rich surface which can more easily be sanded. You will also take less glass away from the last layer this way.

If you use it in between layers, your laminate contains far to much resin.
Interlaminar shear strength is terrible in this case.
Peel ply in between is never a good idea. If one accidentally misses to peel it fully, you end up with an in built weak spot.

Never use mat with Epoxy.
Mat is usually made with a binder which is designed to break up by the Styrene inside Polyester Resin.
That will not happen if you use EP as it has no Styrene inside.

Additionally, and I am aware that the main reason for you to use epoxy for your specific lay-up might be it's better water resistance, the following applies.
Mat has a far higher level of crimp than woven materials or uni and bidirectional material.
Imagine it as if you pull on the fibers and they try to stretch before taking the load.
While doing that they loose some of the connection to the resin matrix.

Epoxy has a higher level of elasticity than Polyester and the fibers of woven or multiaxial cloths are already lying in load direction.

You want to use only woven or uni- and/or multidirectional materials with Epoxy. Only that way you fully use its superior properties fully.
Alter the fiber orientation in each layer.

Good luck with the project!

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Old 30-04-2016, 20:57   #7
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Re: Quick Question - Time between fiberglass layers?

I've been doing fiberglass work of many years. I had a marine business that built and repaired mostly commercial boats. I'm retired now, but still use it for waterproofing my own decks and cabin tops. West Systems is my favorite epoxy. I don't use poly resin for anything.
When repairing hulls, I feather the patch area as far out as possible. After the sanding (I use 40 grit) I brush paint the area with straight epoxy. When it gets a little tacky, I coat again with epoxy + high density filler. HD filler has additional adhesive properties that makes a really strong bond. When that is just getting tacky I start with 2.0 rsm (because I always have a roll around for decks and cabin tops).
Each time the previous layer gets tacky, I do another layer. Watch the temperature. The thicker the resin the quicker the cure. You may need slow hardener on a warm day or need to switch to slow in later laminations. I'm in a cool climate and can use fast hardener on all but the hottest days. If the laminations get too hot, bubbles will form, some will pop leaving little holes the next layer needs to fill.
The purpose of painting with unaltered epoxy is to let existing exposed fiberglass fibers draw it in. The epoxy with HD filler is thick enough to fill imperfections and improved bonding. You want to start with a smooth surface. Otherwise divots give you trouble thru the other laminations.
Use good epoxy rollers, lots of disposable gloves and wear clothes you can throw away. I wet the cloth back so you're not trying to push all the epoxy thru the cloth. Sometimes for small repairs, I use a tray with epoxy and lay the cloth on the surface. Then lift it into place. If you're doing vertical or overhead, some kind of squirt bottle is handy for getting epoxy to thin spots. To repeat, good rollers make the job of wetting out much easier. And you must know that the cloth/mat turns clear when fully saturated.
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Old 30-04-2016, 21:21   #8
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Re: Quick Question - Time between fiberglass layers?

Btw.

Slapping all layers on without waiting at all in between might not be a good idea in warmer climates as there might be to much built up of exothermic heat in the process.
If you are in a colder area this might on the other hand be beneficial.

Usually partially curing after few layers works best.

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Old 30-04-2016, 22:23   #9
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Re: Quick Question - Time between fiberglass layers?

Most of the above is great information, & it sounds like you have things pretty well in hand. That said, if you want some visual references on repairs, plus some quality information, there's this thread Keel sump repair
And there's more in the way of technical references (some of them already mentioned) here Keel Meets Shelf
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Old 01-05-2016, 00:20   #10
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Re: Quick Question - Time between fiberglass layers?

QUOTE=Franziska;2110134]Hi.

As stated above, wet in wet is far better than fully cured laminates on top of each other.
Wet means that the laminate is still very slightly tacky and not fully cured.

Use the peel ply only on top of the last layer. It creates a resin rich surface which can more easily be sanded. You will also take less glass away from the last layer this way.

If you use it in between layers, your laminate contains far to much resin.
Interlaminar shear strength is terrible in this case.
Peel ply in between is never a good idea. If one accidentally misses to peel it fully, you end up with an in built weak spot.
][/QUOTE]

Peel ply sucks out extra resin leaving the layout less resin rich, as I understand it.Peel-Ply & Release Film Tips | Page 1 of 1
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Old 01-05-2016, 01:05   #11
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Re: Quick Question - Time between fiberglass layers?

That's correct in terms that it draws some resin out of the stack laminate , still directly underneath it you have a this resin rich area.

If you would vacuum bag (whole different subject!), it's used to separate the breather cloth from the laminate.
The breather helps to distribute the vacuum and draws up some more resin once the vacuum is mostly established.

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Old 01-05-2016, 08:56   #12
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Re: Quick Question - Time between fiberglass layers?

Don't use regular mat with epoxy. The binder needs the styrene in polyester resin to disolve.

You can use powder bound mat, specifically made for use with epoxy resin.
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Old 01-05-2016, 09:33   #13
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Re: Quick Question - Time between fiberglass layers?

Wet on wet is fine as long as shape holds. Don't wait too long or the resin will blush and require sanding or etc.
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Old 01-05-2016, 10:26   #14
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Re: Quick Question - Time between fiberglass layers?

Boat works today on YouTube is a professional with West Systems videos .
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Old 01-05-2016, 12:01   #15
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Re: Quick Question - Time between fiberglass layers?

For a repair 5/8 inch thick you would be well advised to spread the job over 3 days.

Definitely a good idea to use peel ply between each day's lay-up. Theoretically you don't need to sand between lay-ups when using peel ply, however, you will need to smooth any imperfections that remain when you peel it off the next day. Just give the surface a rub with 40 grit, either by hand or orbital sander to remove any lumps or shiney bits that the peel ply missed. Be aware that epoxy dust is very toxic when only 24 hours old. Use a good respirator and protective clothes.
Don't bother with chop strand Matt unless the supplier tells you it has the epoxy compatible binder. In that case it is good to assist the bond to any cured surface. Multiple layers of woven cloth is fine, just keep it about 1/4 inch thick and you should be okay with heat build up. Slow hardener is best in warm climates.
I built a Farrier 31 with West System products and used this method to build up heavily re-inforced areas like chain plate positions on bulkheads. I love West now and always use it. It is much easier and healthier to use than polyester or vinylester, as long as you avoid the dust. After a week it has completely cured and is not toxic.
Enjoy. Dave
PS. Essential items for your kit, yellow West Roller covers and a plastic squeegee. Use lots of disposable gloves too.
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