Annie wrote:

[...] My own method would be to clear up epoxy on the top layer down to a smooth base, and then coat the bare wood of both faces before mixing up the glue mix.  [...]

Annie,

I am not able to understand your method. You say to 'clear up the epoxy on the top layer' and then also to 'coat the bare wood of both faces'.

If both faces are bare wood then where is the top layer that needs epoxy cleared up?

Thank you to everyone for the help and advice. I think I have a good plan now. I will be sure to seal up the edges of the ply very well. It looks like I will need to buy much more epoxy than I expected.

I also wanted to invite Arne and Robert to discuss my excel sheet here so that we avoid taking over Janine's Kittiwake topic.

Robert,

You said here that 'your target group of US-based aluminum flagpole or lightpole buyers the commercial vendors still specify metal strengths, bending moments, etc. in English units of pounds-per-square-inch, foot-pounds'

I have not been able to find any specifications regarding strength from any of the vendors. The datasheets specify the material but not the material properties. I attached a screenshot as an example.

I have been using sites like this to get the 'Tensile Yield Strength' in MPa and then following Arne's equations. I think this is valid. Please tell me if I got something wrong.

Scott.

Scott wrote:

I will be using small paper cups and never putting more than two pumps in at a time (using West System 300 mini pumps). As Annie says it is not so bad to run out of epoxy in the pot and need to mix more. It is much worse to have the whole thing become a hot and urgent situation.

I am not sure how thick I need to make these sealing coats of epoxy on the mast step layers. Do I need to have it thick enough that the piece looks like it is encased in smooth glass? Or is it OK to end up with a thin coat that is still a little rough?

I believe the purpose of this sealing coat is to prevent starving the joint when I bond the mast step layers to the hull and layers below. Is a thin, rough, sealing coat enough to ensure that the wood will not soak up too much epoxy when I glue it into the boat?

I tend to use containers with a wide base - I have an everlasting supply of yoghurt pots from which the set glue breaks out easily - because the smaller the cup, the more likely the epoxy is to warm up while you are mixing it.

I wouldn't put a sealing coat between each layer and let it partially cure.  My own method would be to clear up epoxy on the top layer down to a smooth base, and then coat the bare wood of both faces before mixing up the glue mix.  That way you don't need to worry about amine bloom, sanding or how far the epoxy has cured.  My rule of thumb is never, never to put the glue mix directly onto the wood unless it's a really runny mix; and then I make sure there are plenty of microfibres to wick the epoxy to dry places.

I rarely have a problem with amine bloom from slow - 206 - hardener.  It's the 205 that causes the problems and sometimes the coating is positively slimy.  I try to avoid using fast hardener.  But washing with fresh water with a drop of ammonia in it sorts the problem.

Scott D wrote:

Well, at least your cup didn't melt.  I've done that a few times.  

The epoxy wasn't wasted.  It was the basic overhead cost of learning.  

The worst part is that I am re-learning this. The last time I did any epoxy work was around 2015. I used a red plastic solo cup to mix up some epoxy. First I almost burned my hand, then the cup started melting and separating before the whole thing suddenly kicked into a solid block of plastic.

I will be using small paper cups and never putting more than two pumps in at a time (using West System 300 mini pumps). As Annie says it is not so bad to run out of epoxy in the pot and need to mix more. It is much worse to have the whole thing become a hot and urgent situation.

I am not sure how thick I need to make these sealing coats of epoxy on the mast step layers. Do I need to have it thick enough that the piece looks like it is encased in smooth glass? Or is it OK to end up with a thin coat that is still a little rough?

I believe the purpose of this sealing coat is to prevent starving the joint when I bond the mast step layers to the hull and layers below. Is a thin, rough, sealing coat enough to ensure that the wood will not soak up too much epoxy when I glue it into the boat?

The only time I would ever dream of mixing up a batch of epoxy that big is when I'm coating or laying down fibreglass.  Why would you?  It takes about 15 seconds to pump the epoxy and one minute to mix it.  I cannot see the point of 'saving time' when it means that you are putting yourself under pressure to get the mix out of the container and on to the wood.  If you run out of glue half way through the job, it's vaguely irritating to have to go and mix up some more; if the epoxy starts going off it's a recipe for disaster. As you pointed out, the first thing that goes through your mind is the cost of wasting it, so you are inclined to use it anyway, even though the pot is getting hot and the mix thickening while you use it.  The cost of this pot of epoxy (which is actually, a lot cheaper in real terms than it was 40 years ago) is nothing compared with your peace of mind after the event (did you achieve a decent glue joint?) and, in the worst case, the piece of wood that has to be removed as there are big gaps in the joint because the epoxy had gone hard before it squeezed out.

I am not renowned for throwing money around, but even I will ditch half a pot of epoxy rather than risk a sub-standard joint.  However, the secret of success is, when in doubt, mix less.  Frankly, I think it's easier to mix another batch than to faff around with iced water, which I would undoubtedly tip all over the wood I'm about to glue!

Anonymous wrote:mistakes with epoxy. With the temperature back to a more reasonable dry 68 Deg F yesterday I thought it would be OK to mix up four 'pumps' of West System epoxy at once. I was wrong! About half of it 'went off' in the cup and turned rock hard while I was spreading epoxy. I am trying not to think about how many dollars worth of epoxy I used to make this cup-shaped yellow disk. I will make smaller batches and spread them thin as soon as I can in the future.

An icecream bucket of ice to put your mix bucket inside may help. Also, using a more bowl shaped mix container helps (to keep the epoxy spread out thin to stay cool). I have used a take out salad dish for a lot of stuff like this. I have also seen people put the epoxy into paint trays (there are cheap paint tray liners that can be tossed when there is too much hard epoxy in them to be used any more) to keep things cooler.