Fiberglassing over wood

[coopec43]

I can't find the thread now but someone suggested using epoxy resin instead of polyester resin when fiber-glassing over wood as it adheres to wood better.

I find polyester/CSM much easier to use than epoxy so I sand the wood then "paint" it with a thinned down polyester. Thinning down the polyester with 10% acetone allows the resin to soak into the wood, I then proceed normally with the lay-up. (That tip was passed on to me by someone "in the game" many years ago)


WOW! I just did a google and found!

When used on porous materials like wood, the resin will not penetrate the wood and form a strong bond unless it's thinned out. Polyester resin also is used for gel coat, which is fiberglass paint that has to be thinned for spray application. Polyester resin can be thinned out using no more than 10 percent acetone.

https://itstillruns.com/thin-polyest...e-5869845.html

[Spot]

Hi Coopec43,
You may want to look into some 'Styrene versus Acetone' debates for your application.

https://forums.ybw.com/index.php?thr...-resin.322768/

I don't have a dog in this fight. I use epoxy and avoid acetone as it has been linked to epoxy allergies. I do know that styrene+wax is what is added to regular laminating resin to make it a 'sandable' gloss or hot coat.

[coopec43]

Originally Posted by Spot

Hi Coopec43,
You may want to look into some 'Styrene versus Acetone' debates for your application.

https://forums.ybw.com/index.php?thr...-resin.322768/

I don't have a dog in this fight. I use epoxy and avoid acetone as it has been linked to epoxy allergies. I do know that styrene+wax is what is added to regular laminating resin to make it a 'sandable' gloss or hot coat.

I'll have a look at that but the guys posting on the thread you gave a link to seems to be suggesting you add the acetone to the resin used for the lay-up. Of course that would be wrong. The thinned resin would be only used on the wood to provide a key.

I don't think the thread is relevant and the guy does not know what he is doing. But thanks.

NOTE
I just read James Bell's comment #11 and he confirms exactly what I am saying.

"In the link I provided, it talks about thinning resin when applying to wood, so it soaks into the wood better but for general laminating, ie: fibreglass onto fibreglass, I would not thin the resin'

[coopec43]

As far as acetone causing allergies I have real doubts as our bodies produce acetone.

Your body normally contains some acetone because it's made during the breakdown of fat. Your body will make more acetone from body fat if you are on a low-fat diet. ... Blood carries acetone to all body organs, but it does not stay there very long. The liver breaks down acetone to chemicals that are not harmful.Ja

AND

The bloodstream absorbs acetone rapidly and completely from the lungs and stomach. The bloodstream can also absorb acetone from the skin, but less rapidly than from the lungs and stomach. ... The liver breaks down acetone to chemicals that are not harmful.


As far as styrene is concerned that is a different matter -you have to be careful and should wear gloves when fiber glassing

[Benz]

People often thin gelcoat with acetone when spraying. And yes, polyester will bond to wood, especially if the surface is sanded up nice and rough. But the question is (since this is a boating forum), why would you use glassed wood on a boat? If the wood is meant for a coring, then water intrusion (which is likely) will destroy it. And it seems that Epoxy is far better at keeping water out than polyester or even vinylester. I do a lot of work with both epoxies and polyesters, and am unwilling to incorporate wood into any structure, unless the wood is not part of a laminate (like trim or a post, but not glassed).

[coopec43]

"avoid acetone acetone as it has been linked to epoxy allergies"

I don't follow that (The epoxy hardener can burn)

[coopec43]

Originally Posted by Benz

. But the question is (since this is a boating forum), why would you use glassed wood on a boat? .

Really!!

I used polyester today on wood! The distance between two bulkheads is 5 ft 10 inches which is not really long enough for a bed. So I am making a box for my feet which will be fitted into a hole in the aft bulkhead. Five bits of ply held together by polyester/CSM. (I'll sand it and paint it tomorrow)

I used polyester over ply to make a platform for my toilet. Polyester over ply for the chain locker.

All my bulkheads are polyester/glassed into the hull and that is standard practice

Most fiberglass boats are built with plywood bulkheads laminated to the hull for strength. Typical construction (called "tabbing") involves bonding bulkheads to the hull with strips of fiberglass cloth wetted with polyester resin. ...

I could go on......

Epoxy would be an overkill. But I make up my epoxy glue (using epoxy/talc) for gluing timber to timber.

[slug]

Originally Posted by coopec43

I can't find the thread now but someone suggested using epoxy resin instead of polyester resin when fiber-glassing over wood as it adheres to wood better.

I find polyester/CSM much easier to use than epoxy so I sand the wood then "paint" it with a thinned down polyester. Thinning down the polyester with 10% acetone allows the resin to soak into the wood, I then proceed normally with the lay-up. (That tip was passed on to me by someone "in the game" many years ago)


WOW! I just did a google and found!

When used on porous materials like wood, the resin will not penetrate the wood and form a strong bond unless it's thinned out. Polyester resin also is used for gel coat, which is fiberglass paint that has to be thinned for spray application. Polyester resin can be thinned out using no more than 10 percent acetone.

https://itstillruns.com/thin-polyest...e-5869845.html

Wood doesn’t “absorb “ ,

coatings are surface protection

Epoxy has superior mechanical properties and is the best surface protection

Don’t thin epoxy or you will degrade its mechanical properties

To achieve full penetration of any coating, heat the substrate
Once heated , coat the surface during its cooling cycle . Wood out-gasses when the temp rises , wood in gasses when the temp falls . The cooling cycle assures max surface penetration

Epoxy comes in various viscosities

A popular low viscosity epoxy resin is made by international ...https://www.international-yachtpaint.com/en/au/boat-paint-products/fillers-and-epoxy/epiglass-ht9000-standard

[Spot]

Polyester resins are polyester solids dissolved in Styrene Monomer.
So why are people using acetone as a thinner for polyester? Because it's there and cheaper and has worked for most in the past.

Keep in mind that I wish you all the best on the project. Too cold here to work on the boat so the keyboard is getting a workout.

As to the body naturally containing acetone, great. With my figure and metabolism I am a powder keg waiting to go off. Some foods have styrene in them too like my beloved coffee but it is not a license to expose myself to any more of it industrially.

I don't have epoxy allergies...yet. From firsthand accounts it is a cumulative exposure that one day results in a severe adverse reaction. Acetone breaks epoxy molecules down from too big to absorb to small enough for absorption through the skin. Better to use other cleaners like vinegar, isopropyl alcohol, or citrus soap before the epoxy cures.

But it is even better to wear gloves as you mentioned, the amine hardeners are not so gentle either. The less exposure to dust, fumes, chemicals, etc. from all of this boat work the better.

The real point is don't settle for the first answer you get on Google, poke around and take in some counter points. The first person found on Google may have only done it once and was lucky, another person might have 30 years in the industry and can say more about it. Or you meet a clown like me and have to suffer though whatever he says about it...

And again, all the best on your project. Looking forward to hearing about your success.

PS for me, epoxy over wood is not as effective as epoxy+cloth over wood, especially on wood that sees weather.

[slug]

Water barrier effectiveness is s function of epoxy coating film thickness

When you epoxy impregnate fabric over wood you create the correct film thickness in one shot

A good technique for many applications

[valhalla360]

A big question is where will the wood be?

I you are doing the exterior of the hull, I would go epoxy with cloth.
- Polyester is actually very slightly porous, even more so if you thin it out, so I wouldn't trust it to keep the wood dry long term.
- Cloth does two things. To fully wet it out, requires a minimum film thickness, so no thin spots. Also as the wood grain works, it stops that movement from opening up
cracking the film.

Interior (not in the bilge): Far less critical and you can get away with many options.

[Benz]

Originally Posted by coopec43

Really!!

I used polyester today on wood! The distance between two bulkheads is 5 ft 10 inches which is not really long enough for a bed. So I am making a box for my feet which will be fitted into a hole in the aft bulkhead. Five bits of ply held together by polyester/CSM. (I'll sand it and paint it tomorrow)

I used polyester over ply to make a platform for my toilet. Polyester over ply for the chain locker.

All my bulkheads are polyester/glassed into the hull and that is standard practice

Most fiberglass boats are built with plywood bulkheads laminated to the hull for strength. Typical construction (called "tabbing") involves bonding bulkheads to the hull with strips of fiberglass cloth wetted with polyester resin. ...

I could go on......

Epoxy would be an overkill. But I make up my epoxy glue (using epoxy/talc) for gluing timber to timber.

That most boats have plywood bulkheads tabbed in does not make it good practice: it is simply cheap practice. Look how many threads there are about bulkheads rotting where the chainplate let water in. Then look at how many threads there are about wet wood-cored decks.
You may do as you wish, but be assured that mixing wood and polyester in a structural application is a recipe for a repair sometime down the road. I don't even like wood-epoxy boats, though I realize that some which were done right have endured for many years. How long till someone adds a through hull and doesn't prep the hole correctly? But I digress. This thread is about polyester, and the dangers of trusting it both to bond strongly enough to wood and keep water out. It does neither well enough for me.

[coopec43]

There's plenty of 50 year old polyester yachts with marine grade ply bulkheads still sailing.

What production epoxy/glass boats are there? I am not aware of any but that is not to say there aren't any.

"That most boats have plywood bulkheads tabbed in does not make it good practice: it is simply cheap practice."

What is the alternative used in production boats? (Maybe they use a product called G10? What is the cost of that? I shudder!)

"How long till someone adds a through hull and doesn't prep the hole correctly?"

If someone is stupid/careless enough to do that then damage may result but it doesn't matter whether polyester or epoxy gas been used.

[HankOnthewater]

Hi Coopec, seems you asked a loaded question.
I understand you are using polyester resin on timber (?likely plywood), on an interior application (lengthening a berth). In all likelihood that plywood will never see water anyway.
By all means add some acetone to the resin for the first coat, I have done it, by could not tell if it really worked or not, but the story that is draws resin into the timber is a plausible one. Never seen any negatives from using acetone for that reason. But if the timber is new and dry, polyester resin will stick very well to it. Made a few fuel and water tanks like that... but used vinylester resins for that.
As far as I know none of the tanks have failed.

[er9]

thinning polyester with styrene at max 10% is better because the styrene mixes with the resin and cures with it. acetone doesnt cure with the resin and must evaporate through the resin which causes fisheyes and voids in the curing resin. 10% styrene to resin makes it very thin. you wont even need that much.

only concern with using stryrene is not to use more than 10% because it will start to slow down and affect the cure the more you add. more than 10% can prevent the polyester from curing.