1972 hydroswift hull

hello, i've been reading on this site for a while now and decided to finally join.

i have a 72 hydroswift 21' that i would like to redo the bottom of the hull. it does have blister and shallow gauges. recently purchased from a yard that it was sitting for about 3-4 years. i've read a few post but couldn't find one that answers my particular question.
i want to remove the gel coat from waterline and under and repaint it, not with gel coat. i have previous auto body experience but none on boats. can i sand the gel coat off and add a few layers of barrier coat or epoxy then paint the bottom? whats the correct way to do the bottom.
i want to avoid the gel coat because i heard its a pain to finish it. the boat will probably not sit in the water for more than 2 days. its for pleasure day trips with the family.
from what i can see there is not fiberglass damage but gouges and blisters.
thanks!

 

Where the gelcoat is sound, leave it alone, and only fill and repair those parts that are unsound, before proceeding with painting with a 2-pack Polyurethane system. And being the bottom of the boat only, you could do it by brush even !(using a brushing thinner, of course) No-one will notice any minor blemishes under there, and you won't have to mask off. But if the bottom is bright and shiny and new, will it embarrass the topsides ?

 

i would say about 10%-15% of the bottom has blisters, gouges or the crescent shaped blister. im better off filling the gouges? then sand the crescent shaped blisters and fill that in? then just sand the gel coat and paint over it with a 2 part polyurethane paint?
i was thinking of using epoxy primer followed by an epoxy based paint, just to make a bit more waterproof because of all the imperfections to bottom...

 

Some PU 2-pack systems use epoxy primer, and that is a good idea imo. Epoxy fillers are a good idea as well. Epoxy has poor UV resistance and is not generally used as a vehicle in top coats. Do some research into what those blisters are, e.g. if possibly caused by osmosis, and how best to repair that kind of thing, though there are plenty here who will have had experience with that.

 

Press the blisters by hand to see if they exude water - if so you have some local Osmosis. Check very carefully that there are not pinhole sized blisters in the surface. If most seems sound, then Mr Efficiency's advice is perfectly sound. One thing I like to do on Osmosis infected parts is dry it thoroughly, sand back and reseal with one or two coats of resin prior to either re gelling or painting, 2K epoxy primers are good. Flicking off the gelcoat with a chisel will usually reveal if the water is in the layup or just trapped by the gelcoat. sanding does not usually show this as it abrades the layup surface enough to hide quality of the resin clarity/integrity.

I have seen blisters any size from 50mm to pinhead size, so examine closely. Mostly more recent boats are better, though I noticed one (modern) boat recently where you could see the blisters in the lines of the brush strokes of the gelcoat when the boat was moulded! Basically I would surmise, the builder probably had condensation in the mould but did not notice so applied gelcoat without drying the mould properly

 

Blister repair can be a bit of a gamble unless you just do a complete blister repair job.
The issue you run into is the blisters you can see are only the more mature ones, there are many thousands of potential sites just waiting to erupt, and as time passes they may. When the repair method only targets the mature blisters and leaves the rest of the water compromised laminate in place you never know when new blisters will show up, and they normally do at some point.

Some people think blisters are a gel coat issue, and while at times there are blisters in the gel coat itself, the normal location is in the laminate. Tiny blisters tend to be in the gel coat or at least close to the surface, the larger they are the deeper they tend to be. Small is 1/8 of an inch or so, larger than this typically means deeper. These small blisters frequently break open and leave a dark stain on the surface, the deeper they are the less likely they are to break open on their own. This is just a simple and general explanation, it can vary a great deal depending on the exact reason for the blisters.

The typical full blister repair would be to remove the gel coat and any affected laminate to whatever depth is needed to find good glass. Then, if needed, re-glass the surface to build it back up to where it was before. This would be done with either epoxy or VE resin, I’d use epoxy if the boat was going to be in the water all the time, but both can work. The remaining glass on the hull should be as dry as possible before any of the new coating (could be many things) is applied. Epoxy barrier coats can be used as further protection.

The boat owner needs to decide how the boat will be used in the future and how serious they are about getting rid of the blisters, plus balance the cost of repairs to the value of the boat, and how they will feel about the possibility of new blisters showing up in the future.

Since most blisters on this size of boat are more of a cosmetic issue than a structural one, there is no right or wrong answer, you can do nothing, or go to the other extreme and do a complete repair.

By removing the gel coat it becomes a much bigger job, the gel coat removal process tends to leave a rather uneven surface, and to make it look right again takes time, money, and good deal of arm and/or back straining work. Its not fun spending days on end laying on your back while filling and sanding under a hull that size.

 

Won't tell if it's from osmosis, boats been out of the water for a few years. I got some formula 27 from my local marine store and I'm going to fill in the gouges and sand the crescent shaped ones down to the glass and pit on 2 layers of epoxy primer then follow with epoxy paint.
Sounds good? I was going to sand a bit of the entire gel coat to see if can find more blisters to open up before epoxy. Should I fill the gouges then sand or sand the entire hull and fill as needed?

 

sand to the glass?

can these be epoxied over or do i have to sand to the glass?

 

A coin in the pic would help to get an idea of the size of the blisters.

The surface would need to be sanded down to remove all the blister, and it looks like the glass showing in the chipped out blisters is white, or has white strands of glass. This means it has been compromised and in a complete repair would be removed, but could be left in place if you wanted to take a chance.

The white strands indicate water has penetrated the laminate and has started to breakdown the bond between resin and glass. These voids can become larger over time and eventually turn into visible blisters. That's why earlier I said for a complete and reliable repair all the compromised glass needs to be removed. Many boats are repaired by simply grinding out the visible blisters and coating the hull with a barrier coat of some type, this leaves all the small voids (not visible on the surface) untouched and they frequently appear at a later time. The less amount of time the boat is kept in the water can extend the timeframe of seeing future blister

Since the blisters are close together, broken open and appear to be shallow, the gel coat in these areas should be removed or whatever you put over the surface would most likely fail rather soon.

 

Thanks. Those blisters are about a dime size. The fiberglass isn't showing just looks like the resin above the glass. So I guess I have to sand down to the resin then barrier coat from there.

 

I'm with ondarvr on this one. Remember that water travels down the glass strands into the laminate, or has started to in the past. Best to sand/grind off the gelcoat and get to sound laminate then seal, even if it means an extra thin layer of roving or CSM. Minimum would be two coats of resin to seal the ends of the fibres (ensure they are fully dry) to stop future water penetration, and then gelcoat or paint.

 

Not a pretty sight ! You wonder if it is worth the bother. You really need expert advice from someone who, on examination, would be able to judge what the root cause is. And whether it is a practical proposition to repair it. The condition of the rest of the boat should be taken into consideration when making those decisions, as well.