Annie wrote:Sorry, I wasn't very clear.  Normally, when I glue some wood down on top of another piece of wood, there is some spillage, glue 'squodging out' or some type of mess that needs cleaning up before I can put down the next layer.  If I don't clean it up, there will be cured glue that may stop both faces lying smoothly together.  I always clean this up first.

Thank you for the response. I understand now.

I am using the fast hardener and yes the pieces are greasy and oily after it cures. I can see why you like to do it all in 'one shot' with un-thickened epoxy first and then a layer of thickened glue mix while the first layer is still in the 'pot life' time.

Maybe I will try this technique for other parts of my project. Right now the boat is back in storage and I am coating plywood pieces in the garage at home.

I am amazed at how much epoxy this plywood soaks up.

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.

US-based vendors of 6063-T6 products. For example:

https://www.metalsdepot.com/aluminum-products/aluminum-round-tube

https://www.onlinemetals.com/en/product-guide/alloy/6063

The pole vendors used to specify the strength in psi when specifying the alloy (always 6063-T6). These days you've got to do more digging to get the mechanical properties.

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?