Rebedding hardware: why thickened epoxy?

[unbusted67]

Don Casey, and a few other people offering instructions online for bedding deck hardware, suggest wetting out the hole in the deck, then sucking out the un thickened epoxy and then squirting in thickened epoxy. Why is this? Why not just use un thickened epoxy? Is there something structurally wrong with un thickened epoxy? Does adding colloidal silica make the epoxy tougher? More flexible?

[beetle]

epoxy resin is a brittle binder, silica is a solid that is good at transmitting energy without fracturing. the analogy is rebar and cement; cement is brittle, rebar is good at transmitting forces. if you build only in cement you will have many cracks in short order, the rebar prevents that.

if you use pure epoxy resin as a filler in the hole in the deck, then apply force by compressing it with a bolt and nut the epoxy will fracture faster than if you mix silica (or any other thickener that can transfer load through the resin matrix) into the epoxy.

there is a detail here as regards bedding hardware in a cored deck that Don is speaking to. the plain resin is injected first to wet out the core, then removed, leaving behind wet core that tends to prevent water transfer to the core. adding thickened epoxy, allowing it to dry, then redrilling the hole and then adding the bolt under compression sllows the thickened cured epoxy to absorb the compression loads.

- rob/beetle

[unbusted67]

Okay got it. Thanks for the enlightenment. And thanks to me for stopping the job and asking a question instead of plowing blindly through the project.

[mike d.]

What is not mentioned is that you need to dig out the core around the perimter of the hole between the inner and outer layers of glass tape up the bottom of the hole fill with unthickened epoxy, let set a little while, but not long enough to let epoxy start hardening, then pull off tape let epoxy drain out,retape hole then fill with thickened epoxy and let harden.!

[roverhi]

I put in straight epoxy resin and then suck it out. Figure this thoroughly wets out all the surfaces so they are water tight. Then mix non compressible filler (West Systems #4) to fill the hole. That is all done after routing out the core using a Dremel 199 bit. If you are installing new hardware, don't drill all the way through the inner skin so the epoxy will be retained in the puka. If the hole is already all the way through or you couldn't stop yourself from going all the way, use heavy duty duct tape to seal the hole on the underside. Masking tape will not hold.

[capngeo]

Originally Posted by roverhi

I put in straight epoxy resin and then suck it out. Figure this thoroughly wets out all the surfaces so they are water tight. Then mix non compressible filler (West Systems #4) to fill the hole. That is all done after routing out the core using a Dremel 199 bit. If you are installing new hardware, don't drill all the way through the inner skin so the epoxy will be retained in the puka. If the hole is already all the way through or you couldn't stop yourself from going all the way, use heavy duty duct tape to seal the hole on the underside. Masking tape will not hold.

My favorite…..

[minaret]

I just use thickened without the straight resin stage. You don't need to worry about the bond to the core here, it is not the primary concern and thickened will bond to it just fine without the resin coat. What you are trying to do is bond the two skins together, which us why thorough decoring to bare glass is so important. This is to prevent the core crushing under the compression load of the fitting being fastened and deforming. Each fastener will have a tube of epoxy/silica around it when done properly. The prevention of compression is as least as important as the extra sealing off of the core. Mix your goo not too thick and you can do it in one step with no messy syringes and still sleep soundly. Like mayo, not like peanut butter.

[thinwater]

Originally Posted by minaret

I just use thickened without the straight resin stage. You don't need to worry about the bond to the core here, it is not the primary concern and thickened will bond to it just fine without the resin coat. What you are trying to do is bond the two skins together, which us why thorough decoring to bare glass is so important. This is to prevent the core crushing under the compression load of the fitting being fastened and deforming. Each fastener will have a tube of epoxy/silica around it when done properly. The prevention of compression is as least as important as the extra sealing off of the core. Mix your goo not too thick and you can do it in one step with no messy syringes and still sleep soundly. Like mayo, not like peanut butter.

Exactly. Leave it a little resin rich and it is one step. I find that if I go too thick, packing in the thickened epoxy is too likely to capture bubbles, no matter how careful I am to go bottom up.

[minaret]

Originally Posted by thinwater

Exactly. Leave it a little resin rich and it is one step. I find that if I go too thick, packing in the thickened epoxy is too likely to capture bubbles, no matter how careful I am to go bottom up.

It's less brittle mixed like that as well.

[ericgfx]

How does the six10 compare to the West System #4 (I assume 404? aka high density WEST SYSTEM | Products | Product Selection Chart) as far as compression and fracturing?

Thanks for all the wisdom, love the rebar analogy.