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wood glue

Guest micgrace

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Havn't had time to digest the report, but I do remember from woodworking magazines that polyurethane glue is poor a sfar as gap filling goes and that is a major consideration. As I fly a wooden plane which I built myself I would be inclined to use a good epoxy and leave resorcino;s for the boat builders. I used resorcinol to build a 28' cold moldd yacht hull, but used epoxy for every other part including the decks.



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Guest pelorus32

Hi Yenn,


your statement about "...a good epoxy..." is an oxymoron 8-) (sorry couldn't resist that)


I hate the stuff! In a good composite layup, vacuum infused and temperature controlled it may be OK. Used as a glue it has more failings than anything I can think of. The ONLY thing it does well is fill gaps.


Epoxy is, among other things, sensitive to heat and will fail at temperatures as low as 50 celsius. This is not hard to achieve in a closed aircraft or wing on a hot summer's day. It is very sensitive to UV radiation and will fail if subjected to it. It is sensitive to temperature whilst curing and may not cure properly or completely.


The real problem with epoxy is that boatbuilders and others from the 60s onwards thought that it was a wonder glue. It is good in the right circumstances (can't really think what they might be...;-)) but a disaster if it is misused which it often is.


Resorcinol is sensitive to temperature during bond formation, it won't tolerate poor alignment and it won't fill gaps. It is however the ultimate torture test glue when used effectively - you can bake it, sit it out in the sun, boil it, keep it wet all the time and subject it to stresses and strains along the way. It will not fail.


I'm a bit passionate about this due to the number of failures I've seen in epoxy joints.


Sorry for the rant.







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Guest micgrace



You may notice, I said resourcinol, traditional The probs with it are high pressure requirement (around 200psi)and poor gap filling and sensitvity to correct mix etc. as pointed outBut, at that time there wasn't really much to pick from. Anyway, you can't really use, what was common at that time, urea/formhaldehyde.


Ihaven't really come across much in the way of epoxiesthat would pass as acceptable.


For me, it'sa bit hard to go past system three, T88 (my opinion) At least it's not that hard to get hold of.


The wood aircraft market probably is far too small for chem companies to come up much in the way of an effective adhesive.


Need something that meets the following requirements. Endures cyclic loads , Peelresistance,Easy to mix, spreads easily, stronger bond than wood (wood fails, not the glue) Stable under all moisture/weather conditions. Doesn't soften at higher temps. Insensitive to excess/shortage of hardner (ideally). Can be painted/varnished, doesn't degrade the timber, easy removal of excess, ready availability


Pretty hard for an adhesive to meet that rather simplistic list . so, at the end of the day that leaves just resourcinol, or T88 (maybe system west, when available) as being readily available that will actually be classed as safe to use.


Of course, if anyone has come across something suitable, let everyone know. (for wood aircraft, that is)


My 2c worth, Micgrace :)


PS I'm not even trying to get into the benefits/drawbacks of any particular type of material for construction, as each has their advantages/disadvantages. micgrace



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