saltiest1 said..
Hi all. I'm finally hauling out in June and have some pretty big work to do on a solid lead keel. One of the jobs is epoxy repairs on the lead keel as previously it hasn't been done correctly so chunks of epoxy have fallen off. I need to heat the keel to about 25 deg in what's probably cool weather in order to get at least 2 layers set within 24 hrs Just seeing if anyone has had experience with this and if wrapping the keel in electric blankets would be a success.

I would enclose it and run fan heaters. What are you repairing fairing bog?

I use these for heating jobs in winter. They are pretty fierce and you should be able to leave them about 30cm away from the keel for an hour and it should be good and toasty. Keep checking.

www.bunnings.com.au/arlec-1000w-halogen-worklight-with-tripod_p7070522
Also get the epoxy a little warm to get it to mix well and go off. Move the lamps away a bit after the epoxy goes on the keel. You just want it warm - 25 degrees is nice for mixing and you can heat it some more for setting. Never heat it strongly - don't get it above 50 or 60 - so keep touching the area and make sure it is not too warm to touch. Heating epoxy after it sets is called post curing and it helps make the epoxy even stronger. But heating epoxy too much is how you remove it - it goes rubbery and you have a few minutes to remove a bolt or filler patch.

captainyanti said..
I'm sure you can get an additive to accelerate the curing time in cooler weather

Yes I have that. The problem is that the keel holds cold for too long for a quick set epoxy. It doesn't like much under 20 degrees c and nights are cool. 25 is ideal and I can't leave it on the dock for a week.

Be careful of "additives" for epoxy. Epoxy is a two part plastic. The hardener cannot be changed in ratio - I use 5 :1 resin as it is pretty nice and cheapest. You can change the hardener if needed. West used the have a hardener called Cold Cure but in these times I would just work with 105 (the normal West epoxy) or any of its common copies. Heat the resin in the container if you want to accelerate cure. Epoxy is all about heat and never about ratio or additives - unless of course you change the hardener.

Polyester uses a catalyst and the ratio can be changed but epoxy is like lego. You need a specific number of hardener molecules for specific numbers of resin molecules. I have built four boats with epoxy and we use heat all the time to get it to work properly.

The specific heat capacity of lead is pretty low - about 1/30 that of water. So given that lead is 11 times more dense than water it should be about 3 times easier to heat up a kilo of lead than a kilo of water.

Conductivity will be a problem with heating a metal but if you shine the lights at the area you want to warm I am pretty sure it will cause a change. Halogens certainly do well in my shed at heating resins when required. So put the halogens on as soon as you can when the job starts - don't use a heater as the warm air may not get directed at the keel, whereas the light can be aimed more easily. Keep them on with the epoxy but you may need to move them away - check often with your hands to keep the temp below scalding.

I once post cured an epoxy 38 ft trimaran. We heated the whole boat structure 38 ft long by 30ft wide in a huge plastic tent with two massive tall LPG bottles and two rented jet like space heaters. We also rented two industrial fans and ran them to circulate the air inside. The boat had thermocouples on it and we watched the whole thing get up to 65 degrees for 6 hours. We would hold our breaths and run in to adjust the fans, we were scared of carbon monoxide poisoning. If we can heat a whole boat, you can heat a keel - if you need more equipment - rent a heater and turn it on. But be careful, these things are monsters.

www.kennards.com.au/heater-space-125000-btu-lpg.html

Remember that epoxy loves sticking to many things but often does not like sticking to metal. When trying to stick it to aluminium I put on clear epoxy resin and then, with gloves on, get out some 80 grit sandpaper and sand the resin and the metal. This makes a resin and metal slurry that gets the resin deep into the metal and also stops any quick oxide production. Then I add whatever I need on top of the resin - in your case the filler. Lead does not oxidise as quickly as Aluminium but personally, I would do this anyway as it helps increase adhesion. Epoxy will fall off certain substances, but a good sand beforehand with 80 grit and keeping the paper new, don't use old and contaminant covered paper, then the slurry, would give you the best chance of it sticking well.

www.epoxyworks.com/index.php/auto-body-repairs-with-west-system-epoxy/?hilite=%27sticking%27%2C%27metal%27

Some at Cruiser forum had your problem - look at the thread

www.cruisersforum.com/forums/f55/lead-keel-what-sticks-well-85490.html

cheers

Phil