Fiberglass work?

[Daddyo]

When laying new glass over old do you have to grind all the gelcoat away before laying the new glass? Do the seams in each layer have to overlap or is it sufficient to overlap the but joints with the following layers? Is the job stronger or weaker if you lay up all the layers at one time or let each layer set before wetting the next?

 

[Fotoman]

Yes you have to grind away the gelcoat. Not sure I understand your second question. Regarding the last one, the proper way to do it is by steps of 3 layers. This maximises the bond and the strenght. More layers will generate too much heat and this can cause your piece to melt or even catch on fire. You start with a mat then a wooven then a mat. Repeat as necessary to achieve desired thickness and strenght and voilà.

 

[Capn Chuck]

I have laid on eight layers of 40 oz. biaxial at one sitting with no ill affects and the hull is doing just fine six year later. Quite often we do 4 to 6 layers at a time. It actually makes a better bond then letting it dry, grinding and laying more layers. I do this for a living. We have never had heat build up or fires. Depending on what kind of repair you are doing, you start with a larger piece and make it progressively smaller by about 1/2 to 1 inch. You can start with the smaller and work to the larger or do the opposite.


-- Edited by Capn Chuck on Friday 9th of July 2010 06:21:49 PM

 

[FF]

"Secondary bonding" , and glassing after the initial hardening period requires that it be ground that 75% of the surface is glass for the new resin to bond to. (USCG sub T build rules).

This usually means any glassing after the first 24 hours , tho with uninspected work and Vynelester resin about 3 days does work.The Gellcoat and everything else in the way of the glass fibers has to go.


I would use epoxy for a structural repair as first choice (with appropriate glass) or Vynelester as second choice .


Use laminating resin (no wax) untill the last layer is inplace.

Rather than keep 2 styles of resin , we usually roll a top coat on an hour after the layup , and grind it off before painting.

Inital sanding can be a pleasure or a horror , we use a 2 inch $70 Bher Manning pad with a glued on sanding disc of #16 or 24 floor sanding paper.

Silicone carbide as the sanding material works better than aluminum oxide of most auto body discs, and its far easier to not wreck the surface with the big flat pad.

Wear a good dust mask and vaccume everything.

Talcum powder on yourself , is good for later glass dust removal.

Get a "steel roller" and learn how to use it when glassing , A MUST!!!

IF its a small job OZ marked plastic cups will work to measure the hardener, but the squeeze bottle with measuring cup built on top is faster and far easier , under $10.

-- Edited by FF on Saturday 10th of July 2010 04:38:05 AM

 

[Daddyo]

I'm going to lay two layers of cloth on the decks where I removed the teak.

 

[Capn Chuck]

Daddyo wrote:

I'm going to lay two layers of cloth on the decks where I removed the teak.

Your best bet is to do small sections at a time, overlapping where you start and stop. Lay down both layers at one time and be sure and sand or grind the areas that will overlap the next time. It is considerably more expensive but I highly recommend you use epoxy, look at MAS as opposed to West. You do need to run the new glass up th side of the cabin and bulworks for a professional looking job and to avoid possible leaks later should the deck flex. That means rounding the corners slightly with thickened material to allow the cloth to lay better. West System has lots of information you can download from their site. Also consider what matt you will use. Not quite waht you are doing, but might be helpful, http://www.soundingsonline.com/news/dispatches/392-jan-8/247752-clear-the-decks Good luck. Chuck

 

[Daddyo]

I much prefer MAS over the West System. Why the smaller areas? I was planning on two layers of 1708 cloth.

 

[Capn Chuck]

You work with what you are comfortable doing and you don't want to have the epoxy set up while you are still working. In addition, will you really want to walk through the wet epoxy as you are working. You will do a better job not trying to work with large pieces of mat and wet epoxy at the same time. If you decide to do large areas at a time, it will become apparent why.

 

[FF]

I'm going to lay two layers of cloth on the decks where I removed the teak.


Why? For what purpose ?What do you expect to gain from the cloth layers?

I am asking only because cloth is a really unusual choice.

 

[Daddyo]

I'd like some more stiffness.

 

[Capn Chuck]

Daddyo wrote:

I'd like some more stiffness.

Your choice of the 1708 will do just what you want. Chuck

 

[FF]

Stiffness is THICKNESS, we have used epoxy to glue down a core material , foam best , Nadia core , cheaper, and cheap boat resin or better vynelester on top.

Sandbags work for pressure to hold core to deck while the epoxy cures.

Thickness is the key BUT if using epoxy be sure the epoxy will dissolve the binder used on many mat and thick glass combinations.

Most epoxy does, given time , but some are better than others at wetting out glass materials.

Just for a bit of stiffness I would lay down Vynelester in 1 1/2 oz (cheapest ,most common) mat. Enough layers to get the thickness-stiffness desired.

For offshore where wave tops may get robust , a 1/2in core will do wonders for a springy deck.





-- Edited by FF on Monday 12th of July 2010 04:15:34 AM

 

[Daddyo]

I wonder if I should add a layer of marine plywood over the existing decks before adding the glass, or is this just overkill and not worth the extra weight? What is the thickness of two layers of 1708?

 

[Capn Chuck]

It is of course your decision, but I can't see any benefit to adding plywood and all of the extra work and weight this will add. The thickness of the cloth is not as much an issue as the type of cloth, its components and the correct amount of epoxy or resins that you use.

 

[Marin]

I've mentioned this in other posts, but a fellow on our dock with an Island Gypsy removed his teak deck a few years ago and installed a fiberglass deck. I don't know the materials that he used, but he applied four layers of fiberglass and then a non-skid finish on the top. It took him a summer and a half to accomplish this and to me, the job looks as good if not better than what a manufacturer would do.

Another fellow on our dock is a retired marine engineer. He helped the Island Gypsy owner with advice and suggestions, and later told me that, in his opinion, two layers of fiberglass would have been sufficient for this particular boat. Four, he felt, was overkill. But, he said, the Island Gypsy now has decks strong as a battleship. And he agreed that the job the owner did was as good as he'd ever seen.

The owner himself told me that, had he known what a task it would be to do it right, he never would have started. But he's very happy with the results. So it sounds like two layers of glass to replace a teak surface are minimal, and it may be that, depending on the stiffness of the boat's deck with the teak gone, even three or four layers may be beneficial.

 

[Fotoman]

Capn Chuck wrote:

I have laid on eight layers of 40 oz. biaxial at one sitting with no ill affects and the hull is doing just fine six year later. Quite often we do 4 to 6 layers at a time. It actually makes a better bond then letting it dry, grinding and laying more layers. I do this for a living.

-- Edited by Capn Chuck on Friday 9th of July 2010 06:21:49 PM

This goes against all the manuals on fiberglass I've seen and the course I took. But hey, if it works fine.

*

 

[FF]

"This goes against all the manuals on fiberglass I've seen and the course I took. But hey, if it works fine."

It really depends on the layup technique.

If the exotherm doesn't get out of hand there are no problems , 'cept a really long day and usually a higher resin content and lower glass ratio than "optimum" .

No big deal if the loading is as low (400%) safety factor on most boats .

And resin used to be .17C a pound so the money loss is small.