1973 222 Project started

[slippery73]

Got to work on the boat some more today. Got the rest of the transom faired in and got the skin coat of glass over it. Turned out really nice, less of a pain than I figured. With the cooler weather and overcast skies it didn't gel to quick like when its hot out and i got the entire thing done all in one batch. I was rolling it out like mad expecting it to kick and it didn't until I was done.

[LilRichard]

Slippery - is that glass laid over the gelcoat?

[slippery73]

Yes, its laid over the gel coat.

[LilRichard]

Typically glass over gelcoat is a no-no - it does not adhere as well to gelcoat.  What was the purpose of that extra layer?  Strength, or were you trying to level for fairing?

[slippery73]

The layer of cloth across the transom is meant to prevent cracking in the gelcoat where the I/O drive was patched and filled. Any time major holes are filled it is a good idea to lay a thin mat over the area and feather it into the rest of the boat. Sometimes you need a hot coat to smooth it out after the initial batch is set but I got mine pretty smooth the first go around. Prep work is key when you do this step, I could have ground all the gelcoat off and faired more but then I would have been glassing over fairing compound. Which wouldnt be any better than glassing over the gelcoat. If you notice in my pics before I layed mat I ground all the edges where the mat would end so I have good glass to glass adhesion. This prevents the mat from having a starting point for it to delaminate. With it prepped like this there wont be any problems down the road. You can see a little better in my pics on how I did it, it shows the edges feathered in.

[slippery73]

[fabuck71]

Looks great, and makes tons of sense.  Do you rough up the gel-coat first?  May I ask, what is a "Hot Coat"?  Thank you.

[slippery73]

Yes, transom was sanded before mat was applied. Sanded with the straight line sander at 36 grit, then to the DA at 60 grit, leaves plenty of "tooth" for the glass to bite. Also, cleaned very well, two washdowns of acetone. A hot coat is a heavier catalyzed coat (meant to gel quick) of resin applied over the mat to smooth over any spots that still have texture to them. Generally not done in boat building, they do it on surfboards to give that ultra smooth coat without sanding into the actual fiberglass fibers and weakening the structure.

[fabuck71]

Cool, thank you for your response.  Looks good.

[LilRichard]

So my question still remains - why would you glass anything over gelcoat if the bond is not as strong as to glass?  

If you have low spots after grinding, I would use a light coat of structural putty to kill the voids (resin, fibers, cabosil) then add mat.  Better yet, add a layer of 1808 under the mat.  I would just be very leery of putting glass over gelcoat.  

I also never use a DA before glass - it is not NEARLY as rough as using a traditional rotary.  A DA erases a lot of its own scratches - that's why you can use coarser mediums with a DA then with hand block sanding for finish work.  Anytime I am laying cloth or mat I grind with a 24 or 36 grit (Max) - you will never see those scratches once you lay cloth over it anyway.

I can not remember the exact metric - but a gelcoat bond is something like 50% of the strength of a fiberglass bond.  In fact, I recall another gentleman on the classicmako site doing exactly what you have, and then he ground it all off on account of his concern over the bond strength (once it was called to his attention).  

Not suggesting you do that - but I would not want to mislead folks that laying glass over gelcoat is a commonly accepted practice.

[71flatback]

I've seen a lot of fishermen around here lay glass over gel coat just as a quick fix and usually it peels off within 6 months. I think if i'm gonna take the time to glass i might as well do it right. I also agree with LIlrichard about not using th DA before glassing, it always seams to be too smooth to stick real well, but it does stick. I'm not trying to tell you you're wrong because it's your boat. Just my two cents

[slippery73]

Im going to have to disagree on this one, if properly prepped the adhesion quality will be more than adequate for this type of repair. This is a non structural repair remember, it is done to keep any crazing in the gelcoat from popping up from extensive fairing work. The edges have been ground and feathered in, giving the mat no starting point for it to delaminate. As far as the adhesion strengths go, this type of repair is still far stronger than  any glass to wood bond will be as long as its done properly. I would not recommend laying glass over unproperly prepped gel coat, In my case it was a viable option without all the unnecessary grinding of the transom.

[fabuck71]

OK then ...... my question is, if I'm laying new gel-coat over old gel-coat on the floor and properly repaired all the spider cracks, can't I just rough up the old gel-coat with 24 grit and paint on the new gelcoat?

[slippery73]

Painting or spraying gelcoat over old gelcoat is not an issue, if you did have crazing or spider cracks you will want to figure out what there were from before you regelcoat or they may reappear in your new coat. If they were stress cracks you will need to lay new mat over your deck or reinforce your deck from below somehow. Sometimes you will get crazing or spider cracks in gelcoat from the gelcoat being applied to thick, gelcoat is always shrinking so after 15+ yrs you will see what looks like stress cracks, a good way to tell the difference between the crazing and stress fractures is by examining the actual cracks itself. Crazing from shrinkage is identified by its complete random pattern, cracks go every which way, usually are very short and they dont start at any one point (think dried up lake bed). Stress cracks are usually long, they may have one point that is an impact point or weak point in deck and cracks may radiate from there, should be easy to identify. If your deck had light crazing from shrinkage go ahead and scuff sand good and reapply your gel coat. If you go this route I recommend duratec high gloss additive 1904, this will allow you to mix 50/50 gelcoat to duratec and spray with a conventional or hvlp gun with a 2.0 tip. It really thins the gelcoat out and makes it flow nice out of the gun, reduces orange peel, and cuts down on wetsanding. Also allows the gelcoat to catalyze and cure without the use of wax in the gelcoat. This is the way im going with my boat and it is super easy, you will want to get a mil gauge also as you will need to spray or roll it to 20-26 mils finished thickness. You will want to make sure boat deck, sides etc. are extremely clean for this step. I would do a wash with TSP of entire area, water rinse two to three times, then acetone entire area, biggest mistake made be people at this step is inadequate prep work. Old gelcoat absorbs, oils, contaminates etc. that will come out after its recoated, skip the correct prep work and you will have issues later on.

[fabuck71]

Thank you, I am going to roll it on because I don't have the facilities to spray.  So basically make sure it's sanded...... clean, clean & cleaner before rolling on.  Then thin it down some?  Do I get gel-coat w/ or without wax?