Epoxied Mat over Polyester Hull

[rbk]

Originally Posted by expozen

The West literature specifically says to not use acetone after sanding and to just vacuum. I used a space heater to pre heat the area to eliminate any condensation. The epoxy is hard. It just won’t stick. I used a space heater to heat the work after completed. Even without the heater 2 days at 50 degrees should be more than enough time with the fast hardener. I’m also not sure the heater does much to heat the completed work since it’s below the waterline. And I’m stating 50 degrees because that’s about that the water temp is. The air temp without the heater is about 60. With the heater is about 70.

Acetone can be used to thin epoxy (wouldn’t recommend for structural), a wipe down definitely helps. I prefer methyl hydrate as it leaves zero residue. It is like trying to adhere epoxy and glass mat to a pile of sawdust. Overall temperature isn’t as big a deal as people make it out to be (I’ve set expose below freezing on cold hills without issue) but trying to bond two pieces with different temperatures can create issues but my monies on a wipe down before placing.

[rbk]

Originally Posted by expozen

You can’t. They are different sized openings in the container.

I’ve seen plenty of people put the preverbal square peg in the round hole through brute force and ignorance, never say impossible.

[rbk]

How did you apply the mat and resin? Brush with resin, place mat and saturate or place mat and try and saturate?

[jimbunyard]

Sounds like the only thing it could be is that the reinforcements you're using were for polyester resin. If the epoxy is hardening fully, it should stick regardless of whether you vacuumed the surfaces or wiped them with acetone.

The only other thing that seems to fit all your symptoms and descriptions would be that the reinforcements were damp when they were laid up, though if you hadn't said your two-cloth test also failed I'd have suggested that the polyester surface you're laminating onto has too high a moisture content.

[Island Time O25]

Asked my boatbuilder buddy about this. He said his first suspicion, if the lay up was done correctly, would be a stale hardener. As in past it's expiration date or not closed tightly enough from even very recent use.

When mentoring me on the ins and outs of epoxy work he used to impress on me not to stock up on hardeners and always buy them fresh in enough quantities to do a particular job. The resin itself if properly closed tight can last a few years or more. But the hardener, once opened, will not sustain its effectivenes for very long as it is almost impossible to keep it tightly closed for it to retain its efficiency.

Several times, on non structural jobs, I had used a year old or even older already opened hardeners. I did notice that it took much longer to cure but eventually there was no discernable difference. I would not try this on the structural components though.

Also, while West System is most go to epoxy, there are many as good or better systems in the industry. And for a fraction of the West prices. Another boat builder I know locally once recommended an industry used brand (can't recall the name) which he said is very forgiving of being off its 55/45 mix ratio. Said one can err as much as 10% either way without any loss of structural integrity. Kind of like epoxy for ratio challenged.

As I am too cheap for "West by gouging brothers" and their implements I use an electronic postal scale and 91% alcohol (192 proof i.e. 96% is even better) wiped deli containers (new) for mixing cups. Just make sure I get the ones with fully flat bottoms for better mixing. Also it is not just the temperature but the ambient humidity that screws up the cure time.

[Wotname]

Originally Posted by expozen

......... The hull surface was preped by removing paint with a wire brush on a drill, than cleaned with acetone, then brushed with a hand wire brush, then cleaned with acetone, then lightly hand sanded with 80 grid, then vacuumed. ..........

Was the 80 grit paper sharp or dull or in any way compromised with wax or other contamination?

I get better results aggressively sanding with new unused (i.e. clean and sharp) 60 grit.

All (or almost all) the adhesion is mechanical so the mechanical abrasion must be clean and sharp.

[Benz]

Mat is very difficult to get epoxy to soak into--it has binders that are meant to dissolve in polyester. Unless you wet the mat out on a table, squeegeed the resin thoroughly through it, and then flipped the piece and squeegeed resin on the other side, there's a very good chance your mat was dry where it was supposed to stick to the hull. Even with polyester it's a good practice to pre-wet the mat before applying it, if possible. It's a lot of work wetting it out in position. Wetting out mat, in position, with epoxy, is asking for trouble.

[Chotu]

I'm guessing dry mat, like the last poster, or surface contamination. Sweat? Sunscreen?

If you could peel the epoxy off the polyester, that's about all it could be.

If the epoxy hardened, it was good.

[Jdeuel]

Did the leftover epoxy set up and harden in the cup?

[singlespeed]

Space heater? What kind? Using petroleum products fired space heaters in proximity with epoxy is know to cause problems, due to the release of hydrocarbons.

This type of repair really calls for vacuum bagging. Thorough and even saturation of the matt will be guaranteed. It is inexpensive and very easy to do, as any number of YouTube videos show.

[Happydrv]

Originally Posted by Simi 60

Mat?
Like chopped strand mat?

Pretty sure it doesn't work with epoxy.

Works well. Just need to wet it out properly.

[Cheechako]

It's just hard to say, but if I'm doing that I want to grind aggressively to bare glass, not wire brushing. Coat the bare glass with epoxy, then laminate immediately. But epoxy bond has never seemed like a chemical bond to me, more of a mechanical bond. Is it really a chemical bond?

Also, you say "Both the risen and hardener were preheated in the sun" ... if I did that with fast hardener it would be smoking hot and unuseable within a minute (if you are mixing a small mini cup or anything larger). How much were you mixing? Did it not get real warm when spreading? That might indicate that your mix was not proper.

[Clivevon]

Chopped strand mat (CSM) not bonding to polyester resin hull using West epoxy: I have had the same experience but on a much bigger & much more serious scale (big osmosis job done by professional boatyard in Mallorca - I thought they knew what they were doing.......Silly me). My understanding since then is that EPOXY RESIN IS NOT SUITABLE FOR USE WITH NORMAL CSM.
If your hull is polyester, why are you using epoxy?

My understanding is that the powders used within the CSM to bond the mat together are intended to be soluble in POLYESTER resin, not Epoxy resin. They do not dissolve in Epoxy resin, so you do not get a proper bond.
In my case the layers of CSM (covered by glass cloth) held together for 12 years but when the blisters returned, i found i could literally scrape that CSM off my underwater hull in sheets by hand using nothing more than a wood chisel. In places it was easier than stripping wallpaper.... As you might imagine, it was quite a chilling experience given the thousands of sea miles since the "repair"...
The mat came off so cleanly down to the level of the previously peeled hull, you could still plainly see the old pencil marked grid lines where they had measured the moisture levels.
The second set of repairs were done under close surveyor supervision using a mix of layers of CSM & glass cloth but all done with VINYLESTER resin (which is a superior form of polyester resin, apparently). Epoxy was only used as the top coat.
I have since heard that they do now make a special CSM designed specifically for use with epoxy, as well as the normal CSM, but the normal CSM should only be used with polyester or vinylester resin.
I think you may just be using incompatible materials.

[rbk]

Using polyester over cured polyester does not give a proper bond. Only epoxy should be used over any cured resin. CSM should also never be used on the outside of the hull (that should have the first giveaway Cliveron about that yard). OP said mat but has he confirmed? Maybe he meant cloth? Chances are csm though.

[Cheechako]

Originally Posted by rbk

Using polyester over cured polyester does not give a proper bond. Only epoxy should be used over any cured resin. CSM should also never be used on the outside of the hull (that should have the first giveaway Cliveron about that yard). OP said mat but has he confirmed? Maybe he meant cloth? Chances are csm though.

Poly Laminating Resin has been used for many decades over poly laminated resin. It's more common than epoxy actually. In fact that's how fiberglass boats are built. Sometimes the hulls sit for weeks or months before more components were laminated into them. Repairs are commonly done that way also. No idea where you got that from.