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Old 08-04-2011, 09:00 AM
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help me understand fiberglass/smc repair and products

Hey all, I did a basic search and got some answers but not all. I just need someone to explain the difference between epoxy resin SMC resin and polester resin and when to use the three and why. I have done some fiberglass repair in the past but am wondering how correct I was. Also the difference between mat and cloth would be appreciated. Thank you
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Old 08-04-2011, 01:32 PM
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SMC vs polyester

SMC is made from a mix of glass, heat activated catalyst and resins. Usually containing epoxy. This is compounded together, then sent to a molder. the molder puts this in a high pressure male/female mold and presses it. The heat from this cures the part. Can take as little as a few seconds to large parts taking a minute or 2. Repairing this type of part needs to be done with epoxy resins.

Polyester resins are liquid of various formulas. It is sold as liquid and applied either by hand or gun along with chopped glass, glass cloth, mat cloth. This can be repaired with polyester resins.

Chopped glass is not unlike twine. It comes in 50 lb rolls and is feed into a chopper motor on top of a gun which cuts and sprays it into the resin catalyst and in the mold. Cloth is woven materal in various weights. 1/4 oz to say 4 oz. It is woven like cloth with stands going vertical to each other. Chopped strand mat is mat that looks like the same matieral that comes out of a chopper gun, short (2-4 inch long strands in a random pattern) but is in mat form - normally in 60" wide rolls.

Hope this helps you.
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Old 08-04-2011, 02:51 PM
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ok so the smc has to be repaird with an epoxy resin only i presume? what would happen if a polyester resin would be used?
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Old 08-04-2011, 04:29 PM
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Very well may have adhesion problems. There are several SMC resins so you might get away with on one but not another.
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Old 08-04-2011, 07:12 PM
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You can use smc repair on fiberglass but not fiberglass repair on smc. The smc repair actually works better on fiberglass .
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Old 08-04-2011, 08:22 PM
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Quote:
Originally Posted by swvalcon
You can use smc repair on fiberglass but not fiberglass repair on smc. The smc repair actually works better on fiberglass .
It works better on fiberglass then the smc itself? Now is smc resin in a class of its own or pretty much the same as epoxy resin? So when it comes to regular fiberglass repair the polyester resin and cloth is the way to go?
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Old 08-06-2011, 11:30 AM
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I always use the matt myself I don't care for the cloth. Never had a real problem with strength.
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Old 08-08-2011, 12:24 AM
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I fix alot of semi hoods and most of that stuff is smc. The repair procedure is the same just have different resins. All the stuff we use is from Evercoat and they use a cream hardner just like what you would use with body filler. The cost is $100 a gallon compared to the polyster stuff at $50. The fiberglass mat works much better than the cloth.
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Old 08-08-2011, 08:18 AM
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The problem with the cloth is it can leave patterns that come thru to the paint, even when buried under primer. The Mat has no patterns and is more like the glass sprayed into a mould that most stuff is made from.

Brian
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Old 08-08-2011, 09:53 AM
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any repairs to a corvette should be done with epoxy resin even the older ones. i use matt and i also use cloth. i prefer the cloth for many things . cloth is suppose to be covered with vail cloth for hiding.
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Old 08-08-2011, 10:20 AM
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Quote:
Originally Posted by shine
any repairs to a corvette should be done with epoxy resin even the older ones. i use matt and i also use cloth. i prefer the cloth for many things . cloth is suppose to be covered with vail cloth for hiding.
When do you decide when you should use cloth or matt?
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