Bottom Problems - Need Advice

k9th · Post by **k9th** » Wed Dec 21, 2011 3:13 pm

I need some good advice from my friends here on the forum.

I had the bottom hull of our tri-cabin sand blasted a couple of months ago when I pulled the boat for the winter and it revealed that I have several pretty good size osmotic blisters and hundreds of tiny pinhole eruptions.

My mechanic is recommending that we repair the fiberglass as required, sand it all down, and then put a barrier coat of 40mil thickness followed by two coats of bottom paint.

Since I know absolutely nothing about this and it is going to cost quite a bit, is this the correct process in this circumstance and will it rectify the problem? What causes this condition to begin with?

koviak · Post by **koviak** » Wed Dec 21, 2011 5:57 pm

Yes this is the normal procedure for blister repairs. Sandblast bottom, repair all blister damage (after they are dried out),(2) coats of barrier paint and (2) coats of bottom paint. Instructions need to followed to the letter on each can for good results. If not the bottom paint won't stick to the barrier coat. Causes of blistering are from water getting into the layers of fiberglass (thin gel coat layer or type of resin used and wetting out completely during build). I have seen boats repaired over 15 years ago without blisters returning.

Big D · Post by **Big D** » Wed Dec 21, 2011 9:11 pm

To be done right, this is a labour intensive and thus costly job. The materials aren't cheap either. In simple terms:

- Blast
- Wait until moisture content is low enough (critical)
- Wet out and repair large blisters with thickened epoxy, let cure then sand
- Wet out a section with epoxy (I use West) and wait for it to kick off a bit (gets tacky)
- Apply a thin layer of an epoxy paste mixture 407 or 410 and Cabosil or Callodial Silica. If done right, the pinholes will be repaired. Should look like peanut butter. Work fast.
- repeat for next section
- let cure
- Sand bottom smooth
- Four coats Interlux barrier paint (follow instructions)
- 2 coats bottom paint

and never worry about your bottom again!

Are you doing this or is someone else?

k9th · Post by **k9th** » Wed Dec 21, 2011 10:36 pm

I am paying my mechanic to do it. His estimate of materials & labor is $7,000 and I trust him implicitly. His estimate pretty much outlined the same steps that you have detailed.

prowlersfish · Post by **prowlersfish** » Wed Dec 21, 2011 10:57 pm

surprised F boat rarely have blister issues .

Big D · Post by **Big D** » Wed Dec 21, 2011 10:59 pm

There are a few critical steps/proceedures along the way. If he's done this a few times before and has customers that you could talk to then go for it if feedback is positive. A substandard job will come back to haunt you. The only other red flag that comes to mind is that I would only proceed if it will be done in a controled temperature environment; in a building.

Paul, who knows what a previous owner did to the hull. I'm sure you've seen some things that have made you scratch your head once or twice! I know I have.

captainmaniac · Post by **captainmaniac** » Wed Dec 21, 2011 11:06 pm

Were the blisters evident before the blasting or only after? If someone is a bit too aggressive with the blasting they can rip open any weak spots or voids behind in the gel and the result may look like osmosis when it in fact wasn't... That's why you shouldn't just hire any guy who has a blaster - you should always stick with someone who has experience doing glass hulls as they know (better than others) how to do it with less or no damage to the substrate. It's certainly not the same as blasting steel plate or brick - you need a lighter touch.

Would be good to know if the hull really was (is) wet, or the blasting was just too harsh.

Either way, the method of repair is the same. And if it is wet, definitely giving it time to dry thoroughly before you begin is critical... if you try to repair before it is dry you are wasting your time (and money).

Big D · Post by **Big D** » Wed Dec 21, 2011 11:10 pm

Big D · Post by **Big D** » Wed Dec 21, 2011 11:10 pm

ooops

Big D · Post by **Big D** » Wed Dec 21, 2011 11:11 pm

What the?

Is there a way to delete a post you just submitted? I had a hickup.

prowlersfish · Post by **prowlersfish** » Wed Dec 21, 2011 11:14 pm

I have seen many blister jobs come back after a few years , In some cases the repair makes the problem able larger . sand blasting or any over aggressive blasting to solve a minor blister issue can cause a major issue later on . a barrier coat in NOT made to take the place of gel coat.

prowlersfish · Post by **prowlersfish** » Wed Dec 21, 2011 11:16 pm

Looks like 3 of us on the same thoughts at the same time .

Big D · Post by **Big D** » Wed Dec 21, 2011 11:17 pm

You're right Paul, a barrier coat alone will not do but the epoxy treatment noted above is better than gel.

prowlersfish · Post by **prowlersfish** » Wed Dec 21, 2011 11:18 pm

I agree as long as it is done right

k9th · Post by **k9th** » Thu Dec 22, 2011 5:25 am

He has done this many times and is going to repair the fiberglass before the barrier coat is applied. The blasting was not overly aggressive. He has a company from Chicago that specializes in marine hull repair come and do the blasting and then he and his team do the rest.

It is sitting now for the winter and no work will be done till spring when the temps warm to the right place.

Thanks for all the good advice and input. I appreciate it and you all have a great holiday!