I did not use mat, but rather woven fabric. What I bought off ebay was 6.4 oz. 59 inc wide X 30' long. Here is a link :
Brand New *fiberglass Cloth Plain Weave 6 48oz 59"Wide in 30ft Long | eBay
Here is the link to the epoxy I used:
Epoxy Resin Boat Building Marine Grade Laminating for Fiberglass and Wood 2 Gal | eBay
This resin mixed 1:1 to make mixing it easier. There may easily be better resin, but I think it is more than adequate for our use.
As to how many plies you should use depends on how much resin is in the layup and the weight
of the fabric. I would plan on 4 -5 ply to build up the thickness. You can judge by paying attention the the buildup across the scarf. If you layup across the scarf (which you wull have to grind flat after the cure) the build up here is the same thickness as the panel you are building up.
You want to work the resin through the fabric and make sure it s fully wetted out, but no excess to add weight
, but little strength.
Here is a Utube for layup off the unit, but the techniques are similar.
Here is a good write up that looks pretty good:
Fiberglass Repair by Don Casey - BoatTECH - BoatUS
I scarfed in scrap pieces left over from the internal fiberglass pieces removed to be replaced with new cabinets etc. I did not make new panels from fiberglass layup, but listed is what I could find to help.