I'm hoping that someone can shed some light on a problem that I'm having.

I'm currently trying to regelcoat the bottom of my Nacra 6.0 cat. The gelcoat had been completly worn down and the glass was exposed. As I was preping the hulls, I noticed that a previous owner had attempted to solve this problem using some sort of greyish paint. The prep work ended up taking much longer than I expected since I had to sand all of this stuff off.

I sprayed the gelcoat onto the hulls while the boat whas in my garage, and used a couple of electric space heaters to keep the area nice and warm while the gelcoat cured. I used 12 drops of hardener to 1 once of gelcoat, and thinned the mixture a bit using acetone so that it wouldn't clog the sprayer.

Here's my problem, I have an area on each hull, just forward of the daggerboards that never fully cured. It's still takey (sp?) and it's been almost a week since I sprayed it. I'm wondering what went wrong? I have two possible ideas.
1. I didn't get all of the paint off the hull there.
2. This would have been the point farthest away from each heater, so was too cold to cure.

How do I fix this problem?

Thanks in advance for any help, I'm pretty frustrated at this point.

Gel coat doesn't cure completely when exposed to air. After sraying it on, you should spray a light coating of PVA (poly vinyl alcohol - mold release agent) over it to seal it up while it cures. After the cure, the PVA can be washed off with water. There are also additives that you can mix with the gel that form a protective film while the gel is curing to allow for a complete cure.

For your particular problem, I'd spray another light coat of gel over the tacky section and use the PVA as described above to get it to cure completely.

There's a good article on re-gelcoating here.

I'm sure there are lots of experts out there, but I did a similar job to my Hobie 20. The gel coat won't cure unless protected from the air with a mold release (not the green fuzzy stuff, but what the boat came out of in the first place). The stuff I use is purple (I forget the name) and is available at West Marine. You spray it over the wet gel coat and that allows it to cure very quickly - 12 to 24 hours depending on the hardener mix. Without this buffer, you could be waiting weeks for it to cure. Once the gel coat is fully hardened, you just wash and buff off the mold release which has dried to a film coating.

What did I tell ya.

I forgot to mention that detail.

Yes I did apply a PVA release agent. I originally tried to apply it with a PreVal sprayer, but had problems with it clogging up the sprayer. I then used a cheap brush to apply the PVA. When I discovered the tacky areas yesterday I reapplied the release agent in hopes that the area would cure overnight, but I'm not sure if the hardener/gelcoat would set up any more or not.

I think it's weird that about 80% of the new gelcoat curred just fine, but that small area on each hull didn't.

Alec

Poor stirring of your gelcoat and/or catalyst getting old? Think about scraping it off and redo. I once had to scrape and redo a whole sticky Hobie 16 Hull. @$%^&#$%^&@#$&*

Alec,
the first thing I would do is use acetone to remove all the gelcoat that is not hardened. You may find that the whole gelcoat repair comes off with acetone. The areas that apear had may not be fully cured. If they aren't, on hot days the gelocoat will stick to whatever it comes in contact with, ie hull cradles or sand even. This is bad. I have had this happen several times, usualy with old gelcoat. I would note that the shelf life of the stuff is limited and the can should never be allowed to freeze. IF you bought it from west marine or similar it may have been on the shelves too long.

for small patches it is easier to brush it on with a foam tiped brush. Get the correct build up by adding multiple layers. I usualy add 2-3 coats of gelcoat, waiting just long enough for it to partialy tack between coats (20-30 min if it is warm0. I have had mixed results thinning gelcoat with acetone. To spray it, I think I use styrene instead. Add pva or i it is a small spot, cover with wax paper or plastic rap. Anything that prevents oxygen from getting to the gelcoat will work.

Good Luck

Eric Anderson

In the future put wax in the gel coat before using….You should be able to buy the wax additive where you bought the resin. If you can’t buy it ready made, find some plain gulf wax paraffin, shave up some of the wax and put it in a small glass jar…add just enough styrene to the wax to make it a liquid (you will have to stir it to help the paraffin completely dissolve). Add this wax/styrene mix to the resin after it is catalyzed (always put in any additive after catalyzing resin). I like to put in a bit more wax then recommended as it ensures a complete cure and easier sanding…many times the gel coat that has the wax added to it already, floats to the top of the can even when mixed well, when you use it... the first batch or two is alright, then the remaining resin is wax starved...Personaly I add a small amount of wax even to the products that claim to have it already added...I have had to deal with too many sticky finish coats.

Always use styrene to thin polyester resin not acetone. Wipe the old area with styrene in place of, or in addition to acetone... it tacks up the old material for a better bond.

Bob

Like all jobs well done, 90% of the job is in the preparation, and the rest is usually getting the basics right.
prepare the surface to be re gel coated by sanding it back to good clean original material, mask off the areas that you don't want to be covered with the new layer, wipe the area to be covered down with a rag wet with acetone ( this will clean the area of any dust, "oil", moisture, and actually "prepare" the old surface to best accept the new gel coat) It is often a good measure to apply a thin layer of "bog"over the area before you get to any gel coating, then fair it back with 240 grit dry paper this is to fill any pin holes, particularly if your back to actual exposed glass fibres. (always wipe with acetone before any layer is applied whether bog, resin, or gel coat) When it has been faired then masked and wiped down mix your gelcoat with a "small" amount of "wax in styrene" which it is best to purchase already mixed from a fibreglass supplier (or boat builder). It should be 5% wax in styrene, and a very small amount goes a long way. Better still, if you purchase, instead of just gel coat, "flo coat" which is already mixed for external (out of the mould) gel coating, this will leave your finished surface of the gel coat hard and non "sticky" when it has fully gel'd, and you can then fair it with sand paper and wet and dry with out the paper clogging up with every stroke. The MOST IMPOTANT THING ABOUT MIXING GEL COAT is that you NEVER NEVER add more than 2% catalyst to your gel coat/resin, as to increase the catalyst (incorectly called hardener) does several nasty things that you don't want. as a larger percentace of catalyst is added the chemical reaction becomes more violent, more heat is produced, the polymer chains formed are smaller and smaller to the extreme that the mix will smoke or the finished product is almost "chrystaline" but whatever the result the finish gel coat is appreciably weakened and at times, over catalysing will actually leave what appears to be "unset" areas of gel coat/resin. If you are working in cold temperatures, never increase the percentage of catalyst, but after applying the gel coat raise the temp[erature of the air around the job with heat lights,or blow heater etc. If you use the correct catalyst percentage mix, MIXED WELL with the gelcoat, ie stir for up to a minute or two, after aplying, when the temperature around the job is above about 20 degrees celcius, the gel coat will gel in 45 to 60 minutes, give it about another hour at that temperature and you can then fair it back and cut and polish it to finish.
Don't try to put it on "thin" as that is not how gel coat is meant to be used, and it is very poor practice to "thin" it with acetone, (if you have to thin it, thin it with "styrene monomer") it is not like "painting" you cannot finish "off the gun" you have to be prepared to shape and fair back by hand. If really thin layers of gel coat are applied they become more succeptable to irregular settings. The volume of gel coat is so small that the required chemical reaction will slow down dramitically and in some instances not apparently go off at all, or if the ventilation is poor the whole thing can "tripe". If the application is done correctly polyester is a very easy material to work with, and will not need any thing applied "on top" of it to cure it, in fact by applying PVA over wet gel coat you suffer the great risk of breaking down the catalyst in the gel coat by the intrusion of the "wet" PVA

Hello Mr Gelcoat,
Gelcoat and polyester resin are air inhibited. This means it will not go off on the surface in the presence of air. To spray gelcoat on the exterior of a shape/body, the gelcoat must have polystyrene wax added to it. The wax will rise to the surface and keep the air away from the gelcoat and it will cure to a hard finish.
Bill

Next time use paint.

Gelcoat, while it can be used as others have pointed out, is alot more work for nothing. Particularly on the bottoms.

I used to do glass repair and the only thing you did really wrong is the acetone. Styrene is the only way to go. I never used to use mold release and I was wet sanding within hours in summer and the next day in winter.

try awlgrip...amazing stuff. Expensive tho.

for the bottoms, I'd use rustoleum from a can. Flows great, dries rock hard and sands nice. CHEAP

Hi Darryl; thanks for the information. What is "bog"?

I was reading on the beachcats website that someone used Pledge instead of PVA to seal off the gel coat. Anyone have any thoughts on this?

Alec

Bog is OZ for filler mixed into polyester resin- Hopefully microballoons or (light) or silica gel (heavy) until it can be spread with a squeegee and won't run off. Note: When catalyzed will often go off FASTER than gelcoat.

Gelcoat is polyester resin with less silica gel in it, but with pigment too.

You can mix your own "bog" with many things added to resin or gel coat. If I was re gelcoating the bottoms of a cat ( of which over the last 45 years I have done several thousand) I would mix industrial talc powder vith gel coat until I have a "non slump" viscosity This makes it easy to apply (my prefered way is to put it on with a stainless steel paint scraper, as it is easiest to "sculpt" the bog (filler) to where it is needed) I would use talc with gel coat because the main "thickening" ingredient in the original gel coat is talc (the three prime components are resin, talc, and pigment, these form the greatest volume) so by using talc, the relative mass of material that I am putting onto the hulls is some what close to the original gel coat that has been worn away. I use gel coat instead of resin with the talc because after I have faired this "bog" filler back and then applied the finished coat(s) of gel coat, it is very much easier to finish off with out showing "darker" resin/glass colour through any spots in the gel coat where it has been faired to the original surface or where you have wet rubbed a little to enthusiastic and made the gel coat transperently thing in the odd spot.

"bog" filler will never "go off" faster than gel coat. the resin content in the "bog" reacts at exactly the same rate as the resin content in the gel coat. Why "bog", at times gels faster than the same equivilent volume/weight of gel coat is for just that reason, ie the same volume of "mixed" bog to the same volume of gel coat. When you calculate the volume of catalyst for filler, you must realise that there is a much smaller percentage of resin in the filler than in the same volume of gel coat, so that the catalyst should be calculate for the volume/weight of actual resin in the mix and not for the entire mass.

“"bog" filler will never "go off" faster than gel coat. the resin content in the "bog" reacts at exactly the same rate as the resin content in the gel coat. Why "bog", at times gels faster than the same equivilent volume/weight of gel coat is for just that reason, ie the same volume of "mixed" bog to the same volume of gel coat. When you calculate the volume of catalyst for filler, you must realise that there is a much smaller percentage of resin in the filler than in the same volume of gel coat, so that the catalyst should be calculate for the volume/weight of actual resin in the mix and not for the entire mass.”

If that was the case then Epoxy “bog” would not kick off faster than an equal amount of resin since the proportions of resin to hardener are at fixed ratios for epoxy resins…but it does…the added fillers probably keep the resin from losing heat as quickly when it exotherms during the curing process. Which in turn, cases the reaction to be accelerated.

Bob

Who's talking about epoxy?? what I understood was that we were discussing gel coating of a "polyester" FRP catamaran, nothing to do with epoxy, vynalester, or phenolic resins, acrylics, eurathanes, propolins, ethylines or any other of the vast array of so called "plastics" Mind you if you want to get really technical and "stuff up" some one who asked for simple advice for a non "professional" on the way to repair his cat by diverging, then yes. certain substances mixed with resin or gel coat DO have an effect on their gel times over straight resin and or gel cvoat, ie if aluminum tri hydrate is added, as a filler, or as a fire retardent then the effect on gel times is radically different, also if you add a product called "sealite" (a trade name) which is actually powdered "marble", (used for pour moulded vanity tops etc,) to have a finished effect undetectable by the general public from actual marble when done well, also changes the gel time ratios. But that is not relevent to any thing that was wanted on this original posting, simply why did his attempts at repair to the bottoms of his hulls fail and help in how to rectify the problem, Not a complete discourse on the FRP industry.

My take on the matter is, yes…we want to answer the original question…basically… a batch of gel-coat is on the boat and it’s not setting up…where does one go from here…?

But just as important is how to avoid the problem again in the future…such as making sure there is wax additive in the resin, mixing the two parts thoroughly (not just a couple quick stokes around the bucked with the stir stick), mixing in one bucket and pouring it into/working out of another bucket, doing a small test batch if you are unsure of the correct resin/catalyst ratios for the temperature you are working in, avoid working in direct sunlight if at all possible, adding any fillers or thinners to the resin only after the resin and catalyst have been thoroughly mixed, and being aware of the fact that there are many types of fillers, if you put a filler in the mix which is easy to sand, it is also not going to stay on the bottom of your boat as long as one which is difficult to sand.

Bob

Hi,

I've only had 100% success when I started buying ALL the necessary stuff from MiniCraft in Florida. They sell gelcoat that can be sprayed with a normal sprayer and cures in air in 30 minutes. NEVER use acetone to thin. Minicraft sells a spray reducer that works perfectly. See: http://www.minicraft.com. Call them and they will set you up with everything. Unfortunately it sounds like your prior work will have to be removed. If it didn't kick by now, it's not going to.

P.S. They also sell tints that can get you an exact color match. I did 9 large areas on a 31 foot boat and now I can't even find where they were.