[Public-list] Polyester to Polyester bond

[Michael Connolly]

   YAHOO.Shortcuts.hasSensitiveText = true; YAHOO.Shortcuts.doUlt = false; YAHOO.Shortcuts.location = "us"; YAHOO.Shortcuts.lang = "us"; YAHOO.Shortcuts.annotationSet = { lw_1169074613_0: { text: 'sail_505 at hotmail.com', weight: 1, type: ['shortcuts:/us/instance/identifier/email_address']}, lw_1169074613_1: { text: 'public-list at lists.alberg30.org', weight: 1, type: ['shortcuts:/us/instance/identifier/email_address']}, lw_1169074613_2: { text: 'public-list at lists.alberg30.org', weight: 1, type: ['shortcuts:/us/instance/identifier/email_address']}, lw_1169074613_3: { text: 'public-list at lists.alberg30.org', weight: 1, type: ['shortcuts:/us/instance/identifier/email_address']}, lw_1169074613_4: { text: 'public-list at lists.alberg30.org', weight: 1, type: ['shortcuts:/us/instance/identifier/email_address']} };  YAHOO.Shortcuts.overlaySpaceId = "97546169";  YAHOO.Shortcuts.hostSpaceId = "97546168";       Mike,
  Polyester is what is boat is made of.  I assume that like would bond to like.  Clean well with solvent, Acetone works fine and scuff if you can and then clean again with Acetone and I have never had a problem sticking polyester to polyester. 
   
  In fact I was told once that on small more flexible hulls,i.e., on racing dinghys that hull repairs are best when made with the same material as the original hull.  This makes sense to me because Epoxy and polyester have different modulas of elasticity, response to temperature, etc.  So the Alberg 30 was original made of hand laid glass fibres and polyester resin.  If I were repairing a hull damage for instance I would use polyester resin as the resin of choice to effect the repair.  On my 23 Seafarer also a 1966 model I repaired all of the hull defects in the keel,i.e., voids that I discovered in the keel area from the original factory moulding and all the surface blisters using polyester resin.  Usually I thinned the resin with acetone and brushed it on to saturate the cleaned surface.  Once cured this brushed on coat works like a 'primer'  To fill the larger voids I then applied several thin coats of resin either filled with glass fibres or bulked up with micro
 balloons, depending on the size of the void to be filled.  For the final finishing 3M makes a really nice product which is ruddy red in color that is basically polyester resin filled with clay, similar to autobody putty.  The beauty of this is that at this point you don't need structural strength but would like to sand smooth the cured filler.  Then on my bottom I rolled on an expoy primer and then several coats of Interlux 2000 interprotect and then two different colors of bottom paint.
   
  Back to the original problem of repairing hulls using two different resins.  I have seen epoxy repairs cause the surrounding polyester hull to fail.  What happens is that the properties of the two resins are different.  On a hull which flexes a bit, like hulls that are only 1/8" thick then the two resins work against each other where they meet.  One by nature is more flexible than the other.  A 'folding' or stress line forms at the juncture and this causes that line to fracture over time. Even though my Alberg 30 and 23 Seafarer both have hulls that are perhaps 3/8" thick I would use the same resin that was originally used to do any future repairs.
   
  Pooring resin into the bilge isn't the same thing, but why add a different, more expensive material when the polyester resin would accomplish the coating task at hand?
   
  I believe that Epoxies have their place especially when not mixed with other resins.  Such as a new project of making a new hatch cover or making a new laminated tiller.  
   
  Again on surfaces that are likely to flex over time I would like to keep the materials the same.
   
  Michael #133

Mike Lehman <sail_505 at hotmail.com> wrote:
  Would you get the same adhesion with polyester? The area is impossible to 
sand to rough up to improve adhesion, which is why I think epoxy might have 
a better bond. This is actually a question?



Mike Lehman
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