How to fill a hole in the bottom of the boat.

[chewi]

No offence, but if you had to do it again, you didn't do it properly in the first place. Polyester will bond perfectly well to cured polyester if it's properly prepared.

well I thought I did it properly, no worse than others might do, and no different to what I did with epoxy afterwards.
Epoxy worked, polyester didn't .

Several others told me about that afterwards.

I won't be trying again with polyester.

 

[eilerts]

Yes, it is possible to do everything right and still get a unacceptable bond with polyester, but polyester can sometimes bond better than epoxy. It is the randomness that makes it tricky. For a larger hull repair I always test the bond on the actual hull.
I really don't know why polyester sometimes fail to bond to some cured polyesters. It could be the type of polyester used for the hull, the moisture level of the hull, the temperature, or other factors.
What worries me with epoxy is that some beginners have read so much about the superiority of epoxy that they think doing it correct is optional.

In this case, I would recommend the OP to use epoxy. It is easy to use, more reliable, and what is left over has a much longer shelf life.

 

[Tammany]

12:1 bevel on both sides as mentioned. Did 6 on mine altogether. Epoxy resin only, polyester doesn't chemically bond with cured GRP. I used to work in the grp manufacturing business as a developer and spent days testing various glues, resins, cloths etc etc. Stress tests, fire testing, freezing etc. The west system guide is perfect instructions. You can see a repair in this pic on mine. This one covered the galley seacock. 3/4" thru hull their originally. A small hole does become a big patch but it will never ever fail.

 

[PaulRainbow]

12:1 bevel on both sides as mentioned.

So, for a 10mm hole you'd suggest grinding away 120mm each side of the perfectly sound hull ?

Epoxy resin only, polyester doesn't chemically bond with cured GRP.

Neither does Epoxy.

 

[Lon nan Gruagach]

So, for a 10mm hole you'd suggest grinding away 120mm each side of the perfectly sound hull ?



Neither does Epoxy.

For a 12:1 bevel (inside and out) on a 10mm dia hole, wouldnt the widest part be 10mm +12 * thickness of hull?

 

[Tammany]

For a 12:1 bevel (inside and out) on a 10mm dia hole, wouldnt the widest part be 10mm +12 * thickness of hull?

No, the 12:1 bevel is based on the thickness of the hull not the width of the hole being filled. If it's a big hole then you can make a puck as a temporary support but you are better off doing both sides at the same time so you get a full bonded cure where they meet.

 

[Lon nan Gruagach]

No, the 12:1 bevel is based on the thickness of the hull not the width of the hole being filled. If it's a big hole then you can make a puck as a temporary support but you are better off doing both sides at the same time so you get a full bonded cure where they meet.

That is what I thought I wrote:
10mm (diameter of the puck) plus 12 times the thickness of the hull. (its 12 times since we are talking diameter and the 12:1 is on both sides of the hole with a bevel inside and out only needs to bevel half the thickness....)

 

[lw395]

don't use polyester as a fix Andy!
I had to to do mine again (same problem) in epoxy after realising ( the hard way) that polyester does not bond well to old polyester.
Grind the hole both sides so you can fill it with a plug then glass over it both sides with epoxy so the plug cannot be pushed though.

If you can't make polyester stick to polyester, give up and get a tradesman in.

 

[VicS]

So, for a 10mm hole you'd suggest grinding away 120mm each side of the perfectly sound hull ?

The chamfer is 12 times the thickness not 12 times the size of the hole but if you chamfer both sides you only chamfer 12 times half the thickness. Id agree not necessary anyway for a small hole. Bevel from each side, fill and and glass over as I suggested in #4

Neither does Epoxy.

But epoxy is a better adhesive by far.

I suspect one of the problems with "plug" repairs with polyester is that it cures more quickly than expoxy. therefore tends to heat up and expand as it cures. Then when the cured plug cools it contracts again breaking the "bond" with the surrounding laminate If this is so reducing the proportion of catalyst should help by reducing the curing rate.

 

[eilerts]

If you patch from both sides you only need 1:12 of the depth you grind. Anyway, the fundament of the rule is to make the area of adhesion scale with the thickness of the laminate. If the specific part of the boat is designed to withstand a heavy load, then the laminate is made thick. Hence, when you repair this spot you need a large adhesion area to make a strong enough bond. The 1:12 rule is taking care of this.

In your case, the hull is not significantly weakened by the present hole, so you should not be worried about restoring the strength, just be sure that the filling does not pop out, ever.
Below the waterline I would, as a rule, always grind a bevel and make a patch, 3-4 layers of CSM, or cloth with epoxy. Be sure to remove antifouling in a area wider than you plan to grind, as dust of antifouling may interfere with the curing process.
There is no point in making the patch smaller than 5cm, as this only makes the work more fiddly.

 

[eilerts]

If you can't make polyester stick to polyester, give up and get a tradesman in.

I would be pretty mad if that tradesman show up with epoxy.
Any advice for me?

 

[PaulRainbow]

The chamfer is 12 times the thickness not 12 times the size of the hole but if you chamfer both sides you only chamfer 12 times half the thickness. Id agree not necessary anyway for a small hole. Bevel from each side, fill and and glass over as I suggested in #4

So, a 10mm diameter hole in a 10mm thicck hull requires a chamfer of 12 * 5mm. Isn't that a total diameter of 130mm, inside and out ?

Rather than grind away that much good hull layup, it'd be better to stick a 10mm button head machine screw through, with a couple of big washers and some Sikaflex

At least we agree with a sensible minimum of grinding.

 

[scottie]

I thought this was going to be about the one that the £50 pound notes disappeared through!

Other value notes also accepted

 

[lw395]

I would be pretty mad if that tradesman show up with epoxy.
Any advice for me?

Abrade the old GRP shortly before laying up new resin on it. Not hours or days before so that the surface oxidises or whatever. You want freshly broken polymer bonds on the surface.
Use good quality resin, and measure the catalyst.
Avoid damp days or very cold days.
If in doubt, do a little test piece and see how strong it really is.
Understand how strong your repair needs to be.

Something that's inadequately done in polyester won't be a good job just because it's in epoxy.
Use epoxy when it gives a real advantage, like bonding to epoxy-coated wood, metal etc. Or when the repair demands a high local strength. Or when the whole boat is epoxy to start with.

 

[Snowgoose-1]

And then this happens :

Thank you for youtube video. What great pair of sailors to have dealt with this.

 

[oldmanofthehills]

I have moved hull fittings on 3 boats, and filled in the old holes; all still safe and sound. I used fibreglass impregnated paste with chamfer on outside and inside of hole but also great big blob of fibreglass paste on the inside with 4 inch wide plywood backing plate after roughing up the surface, then glassed around the lot. Probable over cautious, but I dont want any more alarms and excursions than trying to pick up my trots and no one can see it under the lockers so little need to be flush

 

[Andrew_Trayfoot]

These are the holes:
4 x 4mm straight though the hull
1 x 8mm at 45 degrees through the hull

Plywood backing pads are probably a bit over kill!

 

[VicS]

These are the holes:
4 x 4mm straight though the hull
1 x 8mm at 45 degrees through the hull

Plywood backing pads are probably a bit over kill!

As was said right at te beginning of the thread. Bevel the holes a little from each side ( ie make them taper in from each side) and fill with an epoxy filler .. The Plastic Padding epoxy filler you mentioned in #20 should be just .
the job.

Just glass over the inside of the large one in particular as i think that maybe a little on the large side to just fill but not big enough to justify the full chamfering process I dont think.
The epoxy should adhere to the GRP better than an ordinary polyester car body filler and the tapering of the holes will mean that the plugs of cured material are locked in so that they cannot be pushed out even if they are not adhering well.

Wedge someting covered with some polythene over the large hole and fil it from one side. Fill the smaller ones from both sides probably

 

[Andrew_Trayfoot]

As was said right at te beginning of the thread. Bevel the holes a little from each side ( ie make them taper in from each side) and fill with an epoxy filler .. The Plastic Padding epoxy filler you mentioned in #20 should be just .
the job.

Just glass over the inside of the large one in particular as i think that maybe a little on the large side to just fill but not big enough to justify the full chamfering process I dont think.
The epoxy should adhere to the GRP better than an ordinary polyester car body filler and the tapering of the holes will mean that the plugs of cured material are locked in so that they cannot be pushed out even if they are not adhering well.

Wedge someting covered with some polythene over the large hole and fil it from one side. Fill the smaller ones from both sides probably

Thanks, for all the contributions.

I now have a plan.

 

[joyfull]

These are the holes:
4 x 4mm straight though the hull
1 x 8mm at 45 degrees through the hull

Plywood backing pads are probably a bit over kill!

Is the photo the holes after removing the VDO Sumlog?

I have the same on a Centaur. Not working with a short length of wire hanging out. Debating whether I have time and will to remove it this year or leave as is (no leaks)