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PostPosted: Sat May 29, 2010 1:29 pm 
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First let me thank everyone on this forum and esp Jeremy from Surf City for help with this project, I couldnt have got this far without all the great info!

I have an 18 ft Sol Cat (very similar to a 18 Hobie, but faster ;-) j/k

I've sanded the entire boat taking off the old paint that someone had pained over the original, badly worn gelcoat. I have also done a complete bottom job adding 2 layers of glass tape strips along the bottom and fairing with Marinepoxy. Now Im ready to spray!

1. First problem: Was going to start with the dagger boards and mixed a small batch of gel coat plus Duratec additive (40%) and thinned aprox 5-10% with Laquer Thinner. BUT the spray comes out in BURSTS of gel about every 1/2 second and does not flow smoothly like it should. I've done plenty of repairs around the home with rattle cans, but i'm new to the whole HVLP world so I dont know if my HVLP settings need tweeking or... Is the gel coat STILL too thick?

WHAT AM I DOING WRONG??

Here's my set up: a 5 HP Craftman air compressor that will give 7- 9 CFM, and a new HVLP gun from TCP Global (ebay :) (filter in the air line to catch moisture etc), and changed the 1.8 mm tip to a 2.5 mm tip for gel coat.

2. If I do get the spary to work correctly, do I spray 4-5 coats with a few minutes between coats? Or let completely dry before the next coat? I read on one of the forums to go with 10 coats... can that be right?! Im trying to go for about 20 mils ... but honestly i have no idea how many coats that will take??

3. I did purchase wax additive... do i really need that if i have Duratec in the gel coat and spary PVA to harden?? Does the wax help/hurt with the duratec??

Thanks in advance for all the help!

Gordon


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PostPosted: Sun May 30, 2010 7:51 am 
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Location: Boston Ma / Newport RI
I did a bunch of HVLP spraying for work on cabinets and the problems I had getting the sprayer to work well came from the compressor being undersized. How many gallons of air does your tank hold? Most guns need at least 10 gallons, 15-20 being better if I remember right.

Definitely spray the gel with the PVA, it's what makes the gel cure hard, otherwise it will stay gummy for a long time.

Good luck!

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PostPosted: Mon May 31, 2010 12:36 pm 
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Thanks for the reply Blair. My compressor is 25 gal, its a 5 hp and pumps 7-9 cfm.
Ive been playing around with the mixture and thinned the gelcoat and duratec with about 20% Lacquer Thinner (as per Jeremy at Surf City Catamarans). That has helped, it still doesnt spray quite like i would like, but then again it may just be the nature of gel coat.

Next question would be how long is the minimum to wait before sanding? It seems to dry fairly quickly (w/in couple hours) but not sure how soon I should attempt the sanding process.

Im also using Duratec, which has a hardening property, wax additive, AND PVA .... is this overkill? Does anyone see any problems using all three? Harder is better right?

Thanks again for the help!


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PostPosted: Thu Jun 10, 2010 4:24 pm 
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Location: New Port Richey Fl.
I resprayed my 18. First coat 100% gel, second 25% duratec 75% gel, third 50% gel 50% duratec with sanding aid added, better than coating with PVA. Don't use sanding aid if spraying more than one coat unti final coat. Follow one coat after another just after first coat begins to kick. Use MEK for hardner 15% straight gel, 20% with duretec Thin with styrene enough to get a good flow, forget about percent. Use several coats to get coverage desired because of thinning. I waited 24hrs before sanding.

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Last edited by HOBIE 911 on Thu Aug 09, 2012 11:10 am, edited 1 time in total.

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PostPosted: Thu Jun 10, 2010 4:28 pm 
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Tried to edit previous post. use sanding aid mixed with gel/duretec final coat. Better then coating with PVA

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PostPosted: Fri Jun 11, 2010 9:03 pm 
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i'm in the process of wet sanding after spraying several coats of gel on my 16 hulls. i used an hvlp gun from harbor freight with a 2.2 nozzle. i used styrene to thin at a 5:1 ratio (plastic mixing cups from your local automotive paint supply store work well) and then added 10cc of MEKP catalyst per 16oz of non thinned gel. 16oz of gel when thinned will fill the 20 oz cup on the gun and covered almost one hull. i went through a gallon of gel and got about three heavy coats. i recommend using PVA , figure 1 qt per hull. you don't want to run short of PVA or you'll be singing the blues. you may even need more for an 18, but it's cheap enough so don't skimp. i had access to a spray booth and was able to spray 2 cups (40 oz) before cleaning the gun. used acetone for that. the sprayed gel was already kicking when i was ready to apply the next coat and after the final coat, i cleaned my gun once again and put the "stock" nozzle (1.4mm) back in, then sprayed all surfaces with the PVA. i was running about 60psi at the gun which created a lot of orange peel, but i had consistent flow at that pressure. it was very hard to see the "wet" coat i was spraying as i was using white gel on a white hull. i also waited overnight to begin sanding. one nice aspect of PVA is that it washes off with water and a little agitation, what's left is all your hard work. probably more info than you need , but maybe others will benefit.


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PostPosted: Sat Jun 12, 2010 10:22 pm 
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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!!!! ] :D

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).

Happy Sailing!


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PostPosted: Sat Jun 12, 2010 11:26 pm 
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PostPosted: Sun Jun 13, 2010 7:00 am 
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Can you elaborate on the prep work involved before you spray? I will be giving this a try with my H16 soon. How much have you invested so far?


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PostPosted: Tue Jun 15, 2010 8:30 am 
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I have been also reluctant to spray gelcoat as reading all the horror stories. While sailing in 25mph winds January 2nd, we were putting the main down in big waves and on the fricken rocky shores of Lake Washington and popped a compression and created a 1/2"x1" impact on the bottom of the hull of my 21SE. I figured this would be easy to repair and while at it I would complete a bottom job. It was very easy to glass the few impact areas on the hull and to fair out the bottom with a 24"x2" air sanding board.

Now I needed to wait for a sunny weekend +60 degree day to spray the gelcoat and this only took 6 weeks!!!!

I sprayed the gelcoat on Sunday and this was so easy I wondered why I did not do the whole boat!!! Of course the new gelcoat is bright white compared with the older gelcoat. All I need to do now is light sand and buff! Should be on the water this weekend.

I used Fiberlay fiberglass products and Harbor Freight $18 HVLP sprayer. I did not need to thin the gelcoat and it also had wax in it, so no other sealing required. Way Way easy :mrgreen: I wiped down the boat with Acetone and sprayed. Not much overspray.

I will complete the whole boat maybe next winter as now it is way past time to be on the water!!!! Let me know if you have any questions and I will be glad to answer, but I am definitley no Pro. J is the man for professional help.


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PostPosted: Tue Jun 15, 2010 11:40 am 
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How much do you think it would cost to respray the whole boat if you did the work yourself? How do you sand inbetween of the non skid?


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PostPosted: Tue Jun 15, 2010 12:22 pm 
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I would not mess with the top deck. I would only gelcoat from the deck down.

I think a gallon would adequately cover both hulls of of my 21 SE. The cost of the resin would be about $100 with some MEK and other supplies, ie sandpaper, gloves, respirator cartridge replacements, Buffing compound, etc. The whole job should be less than $200 in supplies if you have the tools.

Other more experienced people can definitely correct my estimate as I could be missing something.....


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PostPosted: Tue Jun 15, 2010 3:47 pm 
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Dude!! Hat's off to you. That is a monumental task!

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PostPosted: Sun Aug 01, 2010 5:31 pm 
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sORRY FOR THE TYPO. 1% STRAIGHT GEL, 2% WITH DURETEC ADDED. I LIVE IN FLORIDA WHERE IT IS HOT AND HUMID, % MEK MAY NEED A LITTLE TWEEKING BASED ON AIR TEMP/HUMIDITY FACTORS

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PostPosted: Tue Aug 09, 2011 4:23 am 
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What would a shop charge to spray an h18?

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