As part of an LAA required Mod scheme, to reinforce the seat belt/harness attachment points in my project, I need to use epoxy to install some small wood blocks and ply gussets.
I have some West clear epoxy and "slow" hardener. Normally, I use Aerodux, but the surfaces have previously been sealed with epoxy varnish and although I have sanded down as far as I dare, to what looks like bare wood, I think an epoxy would be my best option in this case.
It appears that I have to add an appropriate amount of a suitable filler to use my epoxy resin as a "wood glue". The joints are all very close fitting and the materials involved are spruce, mahogany & birch ply and some ash blocks.
I have searched the web and West's own helpful guide, but can't establish which of the many available fillers would be best for my own particular purpose.
It looks like a choice between "Colloidal Silica" and West's "403" microfibre, with appropriate pre-coating of the surfaces with unfilled mix.
I also need to laminate some 0.8mm Birch ply to a small area of extruded polystyrene foam. From what I read years ago, I understand that after pre-coating both foam and ply with unfilled epoxy, I need to use a "slurry" mix of epoxy and microballons, to help fill the rough surface of the foam. Is this a good method?
Ian Law
West epoxy for wood joints & use of fillers.
-
Steve Brown
- Posts: 257
- Joined: Wed Jan 02, 2008 11:00 am
Hi
You have identified the right materials & method.
The addition of the 403 fibres to the already mixed epoxy produces a somewhat heavy but structural filler that will not run out of joints and will act a good glue and enable a thin fillet to exist between the joining materials.
The use of microballons - I have always used the white hollow glass bubbles not the reddish phenolic balloons - makes a filler material that is not structural but is lightweight - good for small fillets under structural glass tapes in corners (only) to avoid air bubbles and for light weight fillers. You would never use micro between glass layups for instance.
I have not used colloidal silica other than as a small addition to mixed microballoons to stiffen it and preventing slumping. I think it is quite expensive and microfibres (flocked cotton + epoxy = flox) are fine in most structural applications.
Since the ply is to be laminated to the foam which is itself weak and is not acting as structure other than anti-buckling support, the use of a microballoon slurry like double cream is fine for filling the foam pores and hence improving the bond/key but without using neat mixed epoxy which is heavy. A very thin wipe of epoxy on the ply ensures good adhesion.
Avoid high humidity days & keep the temperature at above or around 21 deg C for the first 24 - 48 hrs to ensure the hardener kicks off and gets full strength.
Regards
Steve
You have identified the right materials & method.
The addition of the 403 fibres to the already mixed epoxy produces a somewhat heavy but structural filler that will not run out of joints and will act a good glue and enable a thin fillet to exist between the joining materials.
The use of microballons - I have always used the white hollow glass bubbles not the reddish phenolic balloons - makes a filler material that is not structural but is lightweight - good for small fillets under structural glass tapes in corners (only) to avoid air bubbles and for light weight fillers. You would never use micro between glass layups for instance.
I have not used colloidal silica other than as a small addition to mixed microballoons to stiffen it and preventing slumping. I think it is quite expensive and microfibres (flocked cotton + epoxy = flox) are fine in most structural applications.
Since the ply is to be laminated to the foam which is itself weak and is not acting as structure other than anti-buckling support, the use of a microballoon slurry like double cream is fine for filling the foam pores and hence improving the bond/key but without using neat mixed epoxy which is heavy. A very thin wipe of epoxy on the ply ensures good adhesion.
Avoid high humidity days & keep the temperature at above or around 21 deg C for the first 24 - 48 hrs to ensure the hardener kicks off and gets full strength.
Regards
Steve