Patching

[stownsend]

Evening all

Whats the best way to patch the hull of a GRP boat following the removal of through hull fittings. I've just removed several fittings that are not needed (they would have had to have been replaced if I did need them). I was going to fibre glass from the inside and then fill from the outside. Any better ideas ?

Thanks in advance.

Cheers

Stu

 

[jfm]

Erk this is tricky cos you need the patch to adhere very well to the hull, if it's a big boat/big hole/hole under water/moored in the water. Most yards would use epoxy resins rather than polyester for these jobs becuase it sticks better to older hulls, and obv you need good preparation etc. If this is a big job specialist advce would be good idea.

Also many yards would deeply/widely countersink the outside hull aound the hole, so the patch/plug becomes an hourglass shape and is mechanically locked in, if you get my drift. That would be much better than the patch and filler that you describe

 

[orizaba]

i would agree with jfm ,had an amount of large holes on my boat to fill,4 2inch skin fitting and one 6 ,inch exaust.
i cleaned /sanded back an area of at least 6 inchs around all the holes inside and out,assuming you are going through solid fibreglass as i was i then chamfered the edges then taped over the hole on the outside and fibreglassed over the hole from the inside,when it had gone of i filled the holes on the outside and faired to the hull,then 2 layers of fibreglass over that and then fine finishing mat to blend it all in,all mine were underwater fittings so a bit of a raised area was not visible,
not sure about whether to use epoxy or polyester,i used poly as it more user friendly and you don,t have to worry about bloom/wax/humidity,saying that after the hull was finished she was coated in epoxy,make sure all is clean dry and no paint wax residues ,hope this is of some help goodluck

 

[stownsend]

I'm going to use the west coast system of resins and have started to edge the holes, the biggest is 2 inch wide so quite small.

Cheers

Stu

 

[BrendanS]

oldsaltoz is your man for this. He's a professional, and gives out advice on PBO forum, and doesn't look in here, so I'll send him a pm to take a look at this thread.

 

[oldsaltoz]

G'day stownsend, I got a PM from BredanS, I only read the reader to reader page at the moment, not enough time and too much to do, oh well.

Pretty simple project just a few points to look out for are:

You need to grind both sides of the holes to be filled, go for about 15 degrees, this will mean a 2 inch hole will be close to 6 inches wide when grinding has completed.

You can reduce the dust inside by using a dremel or other tool rather than a grinder.

It is important to avoid any contamination so you need to grind from top down and starting on the left side working to the right. you must have clean glass, no paint, sealant or other material left inside the repair area.

After grinding wash down with Acetone (also good to clean up later and clean your tools).

You can now block the hole on one side, use a plastic container lid, ice cream container lids are good, or a smaller round bit of ply or other material wrapped in plastic sheeting or cling wrap. hold this in place with a prop and tape or self tapping screws. I normally start on the inside.

Have your glass ready cut, if using Epoxy resin (and I would) you must use cloth designed for epoxy resins and not CSM (Chopped Strand Mat). The first patch should be cut to finish half an inch inside the ground area, the next patch about an inch inside that and so on down to the smallest about the size of a 2 bob bit. Start with the large patch first and work down to the smallest, at this point you can bend a plastic ruler over the layers to highlight any high or low areas. Note you will need a small threaded roller to squeeze-roll out most of the resin as you go, epoxy resin should be at a ratio of one resin to one cloth by volume. Standard poly resin and CSM is closer to 3 resin to 1 mat.

Mixing resin, must be done with a high degree of accuracy and conditions must be right, temperature above 16*c and humidity below 73%. This means start after 0930 hrs and apply your last coat before 1430 hrs or risk doing it all again. Always use wide shallow containers when mixing resin to maintain a larger surface area, this reduces self heating in the resin, another good job for a plastic ice cream container.

Apply a coat of resin to the area you are glassing before placing any cloth, wet out with an 80 mm wide roller and roll out any excess with your threaded roller, place the next patch, apply resin and roll out, repeat this till you have filled the area. In the inside, when the area has been filled I place one more patch to just overlaps the prepared area, the small overlap is ground off the next day to leave a tidy finish then a two coats of resin is added to seal any exposed strand ends.

The outside is filled much the same as the inside after grinding a little of the new glass to give a good key, also grind off any runs of resin, the finish should be a couple of mm below the bent plastic ruler, let this cure overnight and wash it in the morning with a running water hose and rub with a green plastic kitchen scourer till the water no longer forms beads (You don't have to use chemicals all the time). dry this off and sand it to just remove the high glass with a 120 to 200 grit paper, Mix a small amount of resin (2 egg cups) and first paint on a layer of resin, with the remaining resin add some closed cell balloons or spheres, or 'Q' Cells, they all look like dust but are made with resin and are very tiny bubbles, Mix to a bit thicker than toothpaste and apply to the area being filled, level it using a bent plastic ruler or the back edge of and old straight backed hand saw, that's what I use all the time, not much sanding to do when finished this way. Let it cure overnight and wash as above to remove any residue by the curing process, then sand and fill any remaining lows, let this cure and wash as above then sand flush and apply 3 coats of epoxy resin, you can avoid further sanding by applying wet over tacky coats, or wash and sand to remove only the gloss between coats.

After the last coat of resin has been applied and cured, wash and sand to remove gloss them coat with an epoxy primer paint, let it cure and give it a light sand before applying your choice of antifouling.

Hope this helps.

Avagoodweekend.

 

[MaltaBob]

What a bl66dy good explanation - TOP Man - well done!

 

[stownsend]

Excellent, thanks for the instructions - I'm off on leave for 21 days so praying we have some better weather then we've had recently to get the boat water tight ready for re-fitting.

Thanks again

Cheers

Stu

 

[longjohnsilver]

Thanks, one of the very few posts I've saved. Excellent stuff.

 

[BrendanS]

he's the business, and only accepts praise humbly, but has been providing advice on anything to do with fixing or making epoxy type things for years, here, or at least on pbo. He deserves an award from the forum for some of his advice