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Old 03-12-2008, 01:46 AM   #12 (permalink)
trebuchet03
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Join Date: Dec 2007
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The Miata - '01 Mazda MX-5 Miata
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Quote:
Originally Posted by MetroMPG View Post
So to clarify... Joint compound is the same as wall mud, correct?

And you abandoned it in favour of bondo for smoothing out the plug because of the bubbles?

EDIT: I can see the attraction of using wall mud - it would be really easy to sand & shape, compared to bondo.
Yes, wall mud=joint compound -- I interchange those terms at will (sorry)

We didn't abandon it so much as we used it as a primer/conversion coat. Wall mud cures by drying (which is why it can't get wet). Bondo chemically cures and contains styrene. Because it contains styrene, it will melt polystyrene foam (and won't actually stick). So the mud is used as the initial build up/primer and acts as a compatible layer between the foam and Bondo.

If we wanted to use bondo from the start (no mud), we would need to apply a layer of glass and epoxy resin to serve as a boundary (this is what was done last year).

And yes, wall mud is SO MUCH easier to sand and shape. But it has long cure times. Bondo is much much harder, much smoother when sanded and cures quickly (sets within minutes - or seconds if too much hardener is used )



I think this will be the method used in the future - unless something better comes along
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