"Tissue" fiberglass repair for stress cracks?

[JackW]

A friend of mine who is restoring a vintage 1960's Lotus Elan was describing a technique that seems to be all the rage for Lotus Owners who are trying to eliminate the tendency for stress cracks to propagate through their shiny new paint jobs.

He says that after sanding down through the gel coat you overlay a very thin layer of fiberglass mat to fill in pits and minor stress cracks before applying the paint. Here's a short description:

It's been reported that some quality restoration shops cover the body skin with a fine fiberglass matt, sometimes referred to as tissue. I like the idea of this method as it helps tie the surface together, especially after repairs, with a uniform surface and that may inhibit the return of minor stress cracks that go undetected. It also suggests the possibility of effectively dealing with pin holes and other defects uncovered by extensive grinding, that one may not want to use filler on. I also don't want to change the thickness of the glass body or ruin character lines that I've worked hard to establish, hence it must be pretty thin and able to conform to compound curves.

In the US, matt is identified by its weight per square yard where 1.0 oz matt literally weights about 1.0 oz per square yard. In Europe I believe they refer to it in gms per meter but I could be wrong.

At home I have 0.3, 0.5, and 1.0 oz weights. I've noticed that the really light weight tissue is relatively stiff for its weight, presumably to enable handling with out falling apart. I found this stiffness can cause issues when trying to make it conform to compound curves.

What weight matt is used to tissue a body?

The consensus is to use the 1.0 oz cloth in what I've seen. Just was wondering if any buggy drivers have tried this.

[surfnc]

Jack
I had not seen this done before but have used it recently to repair a badly damaged Manx. I used 2 layers of 4oz cloth since the gel coat was fairly thick on this body.

Here is the one of the damaged areas ground down to the fiberglass. You can see the underlying cracks.



Here is the repair laid up with the 2 layers of 4oz cloth. (Do not worry about the cloth in the undamaged area, it will be sanded off.)



Here is the area sanded fair with 120grit.



I used a high build primer (Duratec Base Primer) to cover the weave and pin holes.



I sanded that fair with 220grit. Then sprayed surface primer. (Duratec Surface Primer)



I will sand this fair with 400 grit and top coat.

The 1oz cloth will have less weave to cover but will need more layers to build up. The high build primer filled the 4oz weave without a problem.

Vince
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