Grinding out tabbing... how far to go?

[Zach]

Hi guys.

I've got a few bulkheads, and partitions that need to come out. Got a sneaky suspicion that the tabbing currently there is all secondary bonds of polyester...

How far do you guys grind to get a good bond with the new tabbing? I'm not so fond of the idea of smoothing out the roving...

So... do you guys grind to a flat uniform surface? Knock off the loose flaky resin rich mat, and keep on going?

Thanks,

Zach - Trying to get over all the little nit picky things that I've been mulling over for to long, and get back to making progress!

[Zach]

Oh yeah...

Been meaning to ask, any of you guys find a lot of dry mat inside the decks? I was curious what the yellowish tinted resin was in a few spots, and ground out loose and flaky glass!

Been deciding if I want to reuse the skin after adding a little glass back to the underside or just laminate a new top skin.

Gosh darn it... I've derailed my own thread within 10 minutes of its birth. (Grin!)

Zach - Thinker of random thoughts, and asker of trivial questions. (Grin)

[Tim]

I've got a few bulkheads, and partitions that need to come out. Got a sneaky suspicion that the tabbing currently there is all secondary bonds of polyester...

No suspicion there; I am sure that's exactly how it is.

How far do you guys grind to get a good bond with the new tabbing? I'm not so fond of the idea of smoothing out the roving...

So... do you guys grind to a flat uniform surface? Knock off the loose flaky resin rich mat, and keep on going?

It depends on the situation, and what you're trying to accomplish. You don't have to eliminate every tiny divot in the old roving, but if the surface is particularly lumpy, either sand it more, or use a small amount of epoxy filler to help you along.

I have seen a wide variety of conditions existing in old Pearson tabbing, from dense, resin-rich, thick, and well-bonded saturations of mat and roving to incredibly brittle and dry weaklings that one can peel off with bare hands.

Get rid of anything loose, always--whether it's the entire bond, or just loose flaky dry areas in your work area. If other existing areas are sound, not resin-starved, and well bonded--that is, they don't peel or grind right off with moderate effort--then it should be OK to leave these areas as a basis for your new work. It's usually pretty clear what is OK and what is not--use your logical judgment.

Been meaning to ask, any of you guys find a lot of dry mat inside the decks?

All over the place with regularity, and not just in decks. But don't get too excited about it; remove the loose and flaky stuff as you go and strive to do better with your new work. Your boat is going to be full of less-than-ideal layups. It's the nature of the beast and one must accept it as part of the deal.

Been deciding if I want to reuse the skin after adding a little glass back to the underside or just laminate a new top skin.

Go with the new skin--easy and better. Oh yeah, it's also easy and better.

[Quetzalsailor]

I think I'm on the same page as Tim in this but... but I don't have any confidence about where enough is enough. If you grind an area of roving down to something perfectly clean then you've ground off every crossing of fiber in the top thickness of the roving. If you knock it off to, say, 50% of the area clean then you've still cut lots of fiber and you've got alot of lousy, dirty old surface. It might be a judgement call, but I don't feel that I've seen enough to make a useful judgement.

It's interesting to note that others have the same problems that I've found on the NE 38 and before that on the M 27. Neither mfr used mat to snuggle layers of roving together. Both had areas of poor bond in cold joints: bubbles, extra resin, no-lams, poor wetout of tabbing, resin starved areas. My approach, even with the above-mentioned clouds of doubt, is to remove all material down to the hull layup, but as little of the hull layup as possible. I remove all defects that seem reasonable - I've learned to recognise what they look or sound like - but I don't grind into the hull layup except to get the surface as clean as reasonable.

This is tougher on the NE 38 because so much of the internally visible glass was added in after the hull layup. The boat was laid up in halves and cold-bonded internally across the centerline and the in-keel structures were cold-bonded as well as the tank tops and maststep. Alot of this later stuff is not nearly so neatly done as the hull. (The Morgan 27 had a 3/4" deep puddle of neat polyester that had drained out of the engine bed tabbing. It had cracked for lack of fiber and engine oil had filled the cracks. I ground it all out, coated the clean area in epoxy and the boat no longer stank.)

[Hirilondë]

I think I'm on the same page as Tim in this but... but I don't have any confidence about where enough is enough.

A technique our painters use for sanding is to mist the surface to be sanded with a haze of paint. They aren't looking for a coat, just a speckling of the area, then sand until it is all gone. By doing this you know there is none of the original surface left and you haven't removed any more than necessary.

[Zach]

Thanks guys!

I've got a little more confidence in the bulkhead removal. (Grin)

[Summersdawn]

I trick I use sometimes with old roving is to get a good stainless steel (has to be stainless, not plain steel) wire brush, and scrub the surface with that initially, then grind it reasonably smooth. This way you are keying all the surfaces, even if it isn't ground all the way down. Don't use a regular wire brush, or you will get little rust spots all over the place.

[Ceasar Choppy]

Some of the tabbing on my Pearson was so resin starved, I used a puttyknife/scraper and a hammer to remove it. Much less dust that way... even when I went back to sand the area to be re-tabbed.