That's what I should have titled this thread
Well THANK YOU to all who have posted and I hope this will help others out down the road too. Hobie911 - MEK at 15%?! Do you mean MEKP? My gelcoat says to catalyze at 2%, and 1% for the Duratec, 15% seems really high. Maybe different type of gel coat.
Clewless – sounds similar to what I ended up doing. I know what you mean about spraying white on white! That was by far the hardest part of spaying, once I got the mixture to flow.
I think I've taken a little something from just about every post I've read and also I ended up doing a lot of test batches on my 4 dagger boards. This is what I found works the best for me:
[First let me preface this for those who, like me, have never sprayed gel coat or worked much with this sort of thing... there are a TON of variables involved in the whole process and this, I believe, is one reason you'll find many different opinions. For example, I read everything from 'never spray if the temps above 80 degrees' to 'its ok to spray in 90-100 degrees', and 'only 3 coats are needed' to 'go with 10 coats'. Then there was the 'dont thin with anything else but styrene', to 'Lacquer Thinner is best' to 'use acetone to thin'. And then there's the wax vs PVA question. And most of these were from what I would call reputable sources. Honestly, if I had to do it all over again, I would take my rig to gelcoat/fiberglass repair shops and get quotes. This project has cost about 3 times more than I had planned and taken 4 times longer. I guess the cost in materials doesn't bother me as much as the cost in time - I have a young family and my time is VERY valuable to me.
SOOOOO - consider this fair warning - it can be expensive and EXTREMELY time consuming. BUT if you have the dough and the time... then GO FOR IT!!!! ]
Here’s what I did:
Materials: Ordered all from UScomposites.com (fast shipping, could be other sites that are cheaper or better quality products, don’t know -only one ive tried)
3 ½ gallons of gel coat (comes with MEKP at 2% ratio)
1 ¼ gallon Duratec (comes with MEKP at 1% ratio)
1 gallon PVA
1 quart Wax additive (I think some call this sanding aid?)
Gallons of Acetone for cleaning (gun, equipment, mixing tools etc).
Taking into consideration:
Temperature – I sprayed at temps ranging 65-85 degrees. The 65 was much more fun , and I didn’t feel the pressure of spaying as fast as I could so the batch didn’t kick in the gun like I did at 85 degrees. I also adjusted my MEKP depending on the temp … slightly less during the warmer temps.
Brand of Gel coat – Ive only used this brand, but I had a guy tell me from another outfit that their gelcoat could be sprayed out of their HVLP guns (with 2.5 mm tip) with very little to NO thinning. Well, I don’t know what he was smoking, but there’s no way the gel coat I was spraying could do that. This stuff is thick!
HVLP equipment – here again could be a large range of preference. I bought an inexpensive but decent gun on ebay (about $40), and a 2.5 mm tip… however, I don’t know if it’s the gun, the tip or my lack-O-skills, but I couldn’t get the gel coat to spray very well out of the larger tip, so I used the “primer” tip (1.8 mm) that came with the gun, and that seems to work better though I do add a lot of thinner. I imagine for my brand of gel-coat a 2.0 mm may be perfect. Anyway the gun says 29-51psi, and I found 39 psi to be the sweet spot. (Also use a filter in your air-line to keep moisture out of your gelcoat, it does work).
1. Started spaying the sides of the hulls w/ around 12 oz of gel coat. I mixed in around 25-30% Duratec (you could do less for the first few coats…that junk’s not cheap!!). Then added 15% Lacquer Thinner (its worked fine with no problems so far. The gel coat seems pretty thick out of the can and my first few coats didn’t spray well. I increased my thinner to about 20% and it flowed really nice but this seemed to make my coats too thin so I backed off to about 14 - 15% thinner). Mix this really well then add the MEKP catalyst at 2%, (I dropped it down to about 1.5% when the temp started climbing to allow a little more working time).
2. I sprayed 5 coats total. The first 3 were like I described above, but because I felt like the coats were too thin and I’d end up having to spray 8-coats (it’s the stopping and breaking down the gun and cleaning every 20 min that I’m really sick of >:-S ) I mixed the 4th coat with 16 oz of gelcoat and slowed down my spaying so I made sure to get a nice solid coat on. If I did it again I’d go with 14 or 16 oz batches all the way through making sure the coats were thorough.
3. Last coat was a 16 oz’er with 45% Duratec added. Then I mixed in ¼ oz of the wax additive to help in curing (aprox 10-15 drops per ounce of gel coat). After spraying this coat, I sprayed the PVA (using a different hvlp gun with a smaller tip). The trick, I read, was to spray the PVA when the last coat was starting to set up: you could touch it and leave a finger print but it didn’t come off on your finger. I know the pva AND wax was probably overkill – but it seemed like added insurance just in case one didn’t do what it was suppose to. Plus both are fairly inexpensive.
I think it looks pretty good so far, and next comes the sanding! I can hardly wait to get this baby in the water!
I’ll try to post some pics (if i can figure that out).