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How low can you go? Polyester

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I'm adding a fitting with a backing plate. I want to mix up some polyester and microballoon goo as filler between the undersurface of the deck and the backing plate... 

only thing is... it's 40° (4°C)... can i put a wee heater inside to keep it a bit warmer? Will it set up anyway? Do I have to wait for spring?

Thanks!

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Yes, you can heat the space. I've done lots of polyester and epoxy work in the middle of Vancouver's winter (similar temps). The epoxy would take 5 days to get really hard.

I don't know how polyester works with cold frankly, so heating is the simple way to do it. Just don't burn the boat down. With polyester an hour will do it.

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This Sunday should give you a decent window of opportunity - supposed to get up to 11C.

Otherwise a heater is highly advisable if it can get you close to 10C.  Crank up the MEKP ratio to close to 3%.  

There are limits to how much you crank up the MEKP.  If it doesn't start to gel after about 40 minutes, scrap it.

It may still harden but greatly reduced mechanical properties IIRC

Without a heater and you are facing 4C, I wouldn't even bother trying it.

Edit - a heat gun or halogen lamp will also heat things up.  Something to kick start the reaction, which should generate some heat of it's own to help things along, if it is not too thin a layup .

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The most important variable in this discussion is the temperature of the resin. Warm up the resin before adding the hardener. Do not add extra hardener thinking its going to make it cure faster. It messes up the final product if you exceed 3%. It shouldn't matter if the substrate is cold. 

We do this all the time with epoxy resin. Its also a nice trick to make it runny in normal weather.

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^ +1. Warm the resin and backing plate. Small heater will suffice. I used 1000 watt ceramic car heater. If you can set the heater under the work the column of rising air will keep it just about right for an overnight cure

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I much prefer lamps to heaters. 

We like the 125 watt brooder lamps as they don’t ever heat enough to burn. 

My Shop has about a dozen of those clamp on lights with the  big silver “mixing bowl” reflector. I have found places like Tractor Supply in the US or Canadian Tire in Canada tend to have clamp and on lights with the nicest clamps. 

As the heating is radiant they will warm the surface in a small area even when there is a light breeze. 

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40 minutes ago, cameron said:

I've done similar work using System Three's Cold Cure epoxy.  No heaters or lamps.  All good.

Everything comes at a price.  Probably an ideal resin system for this particular application though.

However the tensile strength of Cold Cure is about 20% less than most other epoxy formulation.  Also, viscosity is listed as 1,660 cps, which is about double that of S3 Silvertip laminating resin and WEST 105/206.  Again, fine for the OPs purpose, but I wouldn't try laminating with Cold Cure.  

 

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I was replacing some rotten deck core from the interior of the boat.  Used it to bed the new core and stick the old skin back on.  Worked fine in this application.  Might not be the best for many other projects though.

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I have used kerosene lamps on a beach after dark to get glass work to kick

cardboard plywood or plastic sheets help to contain the heat

but why not use 5200 or other flexible filler ?

on both inside and out !!

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I feel like if I'm trying to spread the load of the backing plate over a wide section of deck that flexible filler wouldn't be as good. I'm imagining that the flat backing plate would still point load the irregularities in the underside of the deck if i used something flexible.

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