Filling holes

[Stemar]

I have a 4" hole in the bottom of my hull where I'be removed the skin fitting for an old log. I've ground it out to taper the edges and now have to fill it up. It's a foot from the nearest keel, so not in an especially highly stressed area and the hull (not counting gelcoat) is about 3/4" thick.

The plan is to epoxy one layer of cloth on the inside so I've got something for the first layer from underneath to stick to, then while that's still a bit tacky, build up to full thickness of the layup from the outside.

Logic suggests that I should start with a small piece and make each layer bigger to fill the taper, but I've a vague memory of having read that it should be done the other way round, so the first layer has plenty of area to stick to, and the subsequent layers simply build up the thickness and fill the hole.

Is this memory correct, or a merely symptom of advancing age? (what little hair I've got left being blond may not be helping!)

I'm thinking of fairing the outside with a polyester filler (Halfords or similar) 'cos it's a lot cheaper than epoxy. Is this a no-no below the waterline?

 

[Swagman]

Suggest you'll find it easier to work by filling from the inside. Cut a bung 5mm thick and covering the internal faces of it with waxed paper, insert from outside so its 2mm proud.
Then fill down from inside onto the bung.
It will help to avoid any voids in the filler - and better on your neck / back!
Don't use a cheapo filler. Go slap some water hard and you'll get an idea of the pressure than water can apply to a flat surface area when pounded- you don't want the plug being pushed upward once underway.
So suggest you grind off surrounding area inside before you start and finish off inside with woven cloth / resin laid over the plug onto the ajoining hull area. It will help tie your plug in solidly.
Remove bung once filler is near off, and finish from outside building to gelcoat. Hopefully you will then have a permanent fix that will stand the test of time.
Good luck
JOHN

 

[Aja]

Steve

The way I was told to do it and it worked for me was:

Position a piece of formica or similar on the outside of the hull. Prop on place if necessary.
Cut circular pieces of cloth to slightly overlap hole. You'll need quite a few.
Working from the inside, wet the cloth into position, layer by layer until hole has been filled.
Finish of - on the inside with increasingly bigger pieces of cloth to cover the hole. These will need to be quite big - maybe at least 6"x6" and then 10"x10".

Remember to remove any previous gelcoat on the inside of the hull and ensure everything is scrupuilusly clean.

When the resin has gone off, you can remove the formica from the outside. This should leave minimal if any filling required.

Hope this helps.

Donald

 

[tangomoon]

I have an old transducer hole in mine and take the cap off in winter to allow throughflow of air from the bottom up so to speak. I think it is this that keeps the boat free of smell and mildew. Just remember to replace come spring. Wessex resins would be able to give you advice on that if you are using their products http://www.wessex-resins.com/

 

[oldsaltoz]

G'day Steve,

I have to agree with Donald on this one, working from inside is cleaner and faster and you will get a much better than overhead work.

Start by grinding the outer edge of the hole at around 12 degrees, this should leave a clean area about 1 1/2 inch all around the hole.
Now go inside and grind at about 15 degrees to start with, then as you get further out reduce the angle to form a ring about 10 inches round, make sure ALL old coatings are removed.

You should now have thin sharp edge about a 1/4 inch up from the outside of the hull and a gentle slope from 10 inches back to the top edge of the outer cone finish,
I wish we could place drawing on here.

Get hold of some plastic like Formica Laminate and wax the side facing up. secure it with some tape then add solid props to close any small gaps, the smoother you get this, the less sanding later.

Mix a small batch of resin and hardener (About 2 table spoons will do) and add some 'closed cell' balloons, spread this all around the bottom about 1/8th of an inch thick but not more. Let this go tacky then add one layer of thin roving's, this will help to ensure no end fibres get thu the filler and cause wicking later. You can mix your next batch leaving any left over cells in the mix as you won't have much left over.

Have most of the glass patches pre-cut and start with the largest and work down till you get to the top of the first wedge (The smallest part of the hole).

Then small patch first and working up the the largest that will cover the whole area ground off, top this with another layer of roving's.

You should end up with a patch that will be invisible after fairing on both sides.
Don't forget to add at least 3 layers of resin on the finished glass, this will reduce the risk of water ingress later.

Tips:
Use an epoxy resin and cloth designed for use with an epoxy. Do Not use chopped strand mat (CSM) because the voids in the weave are too large and the finish will not only use a lot more resin, but be weaker than if the correct the cloth was used.

Don't rush, you are laying up a thick layer with a small surface and heat build up may be a problem, so take you time and let the heat dissipate.

Roll out the resin, epoxy and cloth should be close to a one to one ration by weight, standard resins with CSM are closer to 3 resin to one mat by weight. Leaving too muck epoxy between strands will weaken the structure and make it more brittle and prone to cracking. The small aluminium threaded roller is best.

Mix small batches 50 to 100 cc to start with in wide shallow containers, this will give you a larger surface area and reduce heat build up in the resin.

Latex examination gloves are cheap with 100 to a box - get some.

Avoid overuse of chemicals like Acetone by cleaning off tools with white vinegar then finish off cleaning with Acetone, used Acetone can be placed in an air tight container and stood overnight, the particles will settle to the bottom and you can use it again and again.

Always wipe the ground areas with Acetone 3 to 5 minutes before starting to apply resin and let it dry out, only use white cotton wipes and plenty of them, this will avoid contamination.

Flowcoat (a mixture of resin and colour pigment) will be fine on the inside
Outside should have the extra layers of resin, than 2 coats of epoxy primer followed by what ever you normally apply.

Hope this helps.

Avagoodweekend......

 

[andy_wilson]

Polyester will not adhere to the epoxy. Traditional wisdom is to use all epoxy for below the waterline, as this sticks like 5h1t to cured polyester.

One method would be to attach a sheet of laminate to the outside to follow the curve, apply a release agent and start (from the inside) with a finishing layer of thickened epoxy. Then apply layers of a suitable glass reinforcement with epoxy, overlapping the hole for strength. If appearance and thickness is not an issue from the inside, overlap generously for your own piece of mind. If he finished thickness is crucial you should have a generous taper (12:1 I think) to keep the finished thickness within the original spec., Also taper the outside, but somewhat less.

Once cured, remove outer 'template', fair / fill / fair / prime / AF.

 

[srp]

PBO June 2006 did an article on this. They suggest (after the usual cleaning up and tapering etc) covering the hole on the outside (polythene sheet taped to a bit of thin ply, stuck to the hull with gaffer tape). First on is a thickish epoxy mix as oldsaltoz suggests.
Then lay up about 4 or 5 layers of biaxial glass cloth on a bit of polythene on the bench, starting with LARGE circle first, and getting progressively smaller so the last circle is about the same size as the hole. By the time you've laid this up the very first coat you've already done will be starting to cure. Lift the whole lay-up off the bench on the polythene sheet and apply it to the hole, using the poly sheet as an applicator - use a squeegee or roller to squeeze it all down, removing air bubbles and ensuring close contact. After an hour or so you should be able to remove the poly sheet and apply a floating coat of resin over the whole lot.
Then you can sort out the outside.

Yes, they really do say stick the largest circle first, the reasoning being that you will get the maximum area of adhesion with the GRP. The subsequent circle don't have a sticking problem as they are being applied wet-on-wet. Not sure I really go along with this thinking myself, but the article was prepared with the help of Wessex Resins.