Sanding heat causes delamination?

[moonie5961]

I found this post in a thread discussing the removal of a barrier coat in another forum, has anyone here ever heard of this, or is it another example of chicken little mentality?

"Sanding an older boat to the extent necessary to remove the barrier coat is a really bad idea. That kind of sanding produces a lot of heat which can trigger a break down of the resins deeper in the laminate. This provides a mechanism for deeper blisters and delamination to occur. Barrier coats provide not assistance in preventing this kind of blistering."

[Rachel]

Boy, I sure hope not. If so, wouldn't that mean that when we grind our hulls (say, when removing a through hull and patching the hole), we were wrecking them?

I can't see how sanding to remove a barrier coat would be any different than sanding to remove any other bottom paint, gelcoat, and/or to prep for a patch.

Will be interested to hear others' thoughts.

Rachel

[moonie5961]

This is the only time that I have ever heard such a thing, I don't think that its true- if nothing else, just because its' the first and only time I've ever heard anything like it. The idea just kept floating around head as I felt the heat buildup while sanding the failed barrier coat off of my hull. I thought I'd see if anyone else had ever heard it. The guy who posted it seems very knowledgeable-but I'm reluctant to say who it is, my momma always said not to talk 'bout people, ya know.

[moonie5961]

I just dredged the old thread on the other site, which can be found here.

It strikes me as I write this that I am making a habit of posting some ridiculously novice questions, I apologize for lowering the collective IQ of this board. :)

[preserved_killick]

I think this is total bunk. Personally I've sanded/ground big holes in the hull and while doing so stopped to brush away dust with a latex gloved hand and the surface just is not that hot. I've experienced way hotter fiberglass on a deck in full sun.

For what it is worth, after trying a few methods I had the best luck removing my barrier coat using a scraper. The carbide scraper is a little work, but then so is holding a sander at odd angles, and the scraper is quiet so you can listen to music/podcast ect. And no dust. Step 1. Put on some music of choice, I used some old Rolling Stones. Step 2. Sit on a milk crate under the boat. Step 3. Reach up, pull down scraper. Repeat step 3 as often as necessary.

[Triton 185]

I think this is total bunk.

I agree, just because it is written on the Net - it does not mean it's true. It is important to "consider the source".

[Rachel]

... just because it is written on the Net - it does not mean it's true. It is important to "consider the source".

I hear you, but on the other hand, I think I can see where moonie is coming from, because the person who posted the info (in the linked thread, elsewhere) is someone who is very knowledgeable about boats and boating in general, it seems.

(I'm not saying I agree with the actual information; just that I can see where one would think "Huh, if this person says it, maybe I shouldn't just toss it off without a second thought" and then would check in with the gang here.)

[Triton 185]

(I'm not saying I agree with the actual information; just that I can see where one would think "Huh, if this person says it, maybe I shouldn't just toss it off without a second thought" and then would check in with the gang here.)

Rachel, you are good with pointing out the obvious.

Moonie, I believe that when one is learning there are no questions that can not be asked. I can tell you from personal experience that this Forum is a great place to learn. We should all keep asking questions.

[preserved_killick]

(I'm not saying I agree with the actual information; just that I can see where one would think "Huh, if this person says it, maybe I shouldn't just toss it off without a second thought" and then would check in with the gang here.)

I don't know much about lots of stuff, but there's a couple of subjects I consider myself very knowledgeable (sailing is not one of them), having had experience that's difficult to acquire. I've noticed that often those who speak the most on a subject are not necessarily experts in the field.

Having said that, I'm usually grateful for any opinions that others offer, even if it makes me stop to think for just a second before moving on.

-jeff

[Maine Sail]

IMHO it's bunk, if a sander is used by anyone other than a total dunce. I suppose, if you held a high RPM rotary sander in one spot for a long while you could heat the substrate to a dangerous temp that may afffect some pockets of uncured resin, but anyone with half a wit knows not to do this. A dark colored hull will reach a far higher temp in hot sun than a properly used sander will. Also nearly every boat manufacturer suggests a sanding with 80 grit and a de-waxing when commissioning the hull.

To my way of thinking, if sanding is exposing moisture penetration, or uncured resin issues the problem is not the sanding but the underlying issue that you have moisture in the laminate or a badly laid up hull to the point that even the low temps of sanding are causing the blisters to expand.

Having stripped a fair number of hulls in my day I have never seen nor felt temps approach anything more than warm to the touch. Go to the Carib and try and walk on a gelcoat deck in the direct sun or put your hand on a flag blue hull.. OUCH!! Walk around a boat yard up North on a sunny day and put your hand on a red, blue or black bottom..hot..

We know warmer waters are more prone to cause blistering but sanding is a different process that occurs out of the water with a moving sander than will not be in one spot for more than a few seconds at a time. If any of this heat theory is correct one must assume that boats on the hard that see direct sun with dark colored bottoms would see massive blistering problems. My 31 year old hull bottom is black, has been stripped, sanded and barrier coated twice in it's lifetime and has zero blisters.

I do recall from working in the hydronics industry that polyester resin based fiberglass pipe can take constant working temps, 24/7, up to 200F. This pipe has the same physical properties as a polyester resin built glass boat has though the lay up is different. If your hull is getting anywhere near 200F you'd know it. I suspect the temp range is much wider for other uses other than the multitude of chemicals and fluids that can run through fiberglass pipe. Also keep in mind that marine exhaust elbows, water lift mufflers and fittings are often made of ....fiberglass. Vernatube exhaust fittings can run at temps up to 250 degrees with no damage..

Heck one can sand latex paint without developing enough heat to even bubble it and varnish too.... I would not get worked up over sanding the bottom of a vessel as nearly every boat out there has had this done..

[moonie5961]

Thank you for weighing in! The original poster elaborated on his post-it can be found on the link below, if anyone is interested and has not seen it yet.