Instead of giving the link I can summarize the article in this email. =
SMC is actually polyester based but the way GM incorporated the mold releas=
e agent during manufacturing makes polyester resin a poor choice for repair=
. Here is the article that I wrote for the GMCMI newsletter issue 96, Sum=
mer 2006, that might be of some interest to you. The earliest 1973 ve=
hicles have =E2=80=9Chand laid=E2=80=9D =EF=AC=81berglass, at least for the=
front body assembly. Somewhere between serial number 24 and 50 this proce=
ss became SMC (sheet molded compound). This was a new composite material fo=
r use in the automotive, industrial, and personal watercraft markets that p=
resents unique repair problems. Parts made with SMC are produced in compre=
ssion molds, so they are smooth on both the inside and outside. SMC parts =
do not have an outer gel coat, but they are usually painted or color molded=
. When the paint is sanded off, the underlying surface has a marble appear=
ance. When damaged SMC is sanded, short coarse =EF=AC=81bers are exposed a=
nd a dryer powdery dust is produced compared to conventional
materials.SMC =
is a polyester-based material, but it cannot be repaired with polyester res=
in. This is due to the mold release agent that is present throughout the en=
tire SMC part. Unlike conventionally molded parts where release agents are =
applied to the mold surface, SMC is compounded with them in the resin mix f=
or quicker processing. This means that as the damage is sanded to prepare a=
good bonding surface, fresh mold release agent is exposed. Polyester resin=
products are not strong enough to adhere to this surface. SMC SHOULD ONLY =
BE REPAIRED USING EPOXY-BASED RESINS, FILLERS AND ADHESIVES. For good adhe=
sion, when painting, use only catalyzed type paint systems -- at least for =
the
primer.When a part is broken or crushed, it is dif=EF=AC=81cult to real=
ign the pieces with each other because the frayed =EF=AC=81bers tend to =
=E2=80=9Chang up=E2=80=9D on one another. Use a saw blade to cut the length=
of cracks or tears. This relieves the stress on solid laminates which ofte=
n return to their original shape with little force. A router is excellent =
for removing damaged core material without disturbing intact face skins. Tr=
y to remove as little material as possible so the repair does not grow too =
large. However, solid laminate must be exposed for a good
repair.Next, supp=
ort the part so nothing gets distorted during the repair process. This can =
be as simple as strips of 2 inch wide masking tape or as elaborate as a cus=
tom-made clamping =EF=AC=81xture. With the part supported, proceed to prep=
aring the bonding surface by grinding a taper or steps around the damage. T=
his is the critical step for functional repairs but it is also the most ove=
rlooked and abused. If a taper is to be used, measure the depth of the val=
ley and calculate how far the sanding must extend to achieve the desired ra=
tio. Mark the outer edge of the taper using a marker and begin sanding inw=
ard toward the valley. Be sure to remove material slowly so the taper progr=
esses evenly. Wet the entire bonding area with resin, then begin saturatin=
g each ply of reinforcement before it is placed. Work on a sheet of plasti=
c so the fabric can be easily lifted from the table once it is ready. A =
=EF=AC=82exible rubber squeegee is the best tool for spreading the resin ev=
enly through the fabric and removing excess which may be present. Place the=
reinforcement into its spot on the repair, ensuring the proper orientation=
. Stop every few layers to compact the patch as much as possible. A squeege=
e or grooved roller works well for this. Continue stacking the repair plies=
at right angles until all the material that was removed has been replaced.=
A =EF=AC=81nal cover layer is then added over the entire area. Sand befor=
e painting. Emery Stora > On Sep 21, 2016, at 12:14 PM, Espen =
Heitmann wrote: > > Emery please give me the link as=
I need to read up a bit on SMC, I have the 3M 8115 that I will use to glue=
a couple of panels back on bu I bought a > can of U-pol SMC filler for o=
ther repairs ( >
http://www.ebay.com/itm/U-pol-SMC-1-1Ltr-Black-High-Adhe=
sion-Easy-Sand-Plastic-Bumper-Filler-BEST-Price-/221792843460?hash item33=
a3e236c4:g:GOsAAOxyJypTk57S > )but that is of course polyester based.. =
> -- > 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Mean Gree=
n Machine, > And just sold my 1973 26'-2 # 581 White Canyon lands under t=
he name Dobbelt tr=C3=B8bbel > in Norway > > > __________________=
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