MST MST Hull & Fiberglass Repair 1 — Questions and Answers
Question 1: What is the correct ratio of hardener to resin when mixing standard polyester laminating resin for a fiberglass repair?
- 1–2% MEKP by weight (Correct answer)
- 10% MEKP by weight
- 50/50 by volume
- 5 drops per gallon only
Correct answer: 1–2% MEKP by weight
Standard polyester resin requires 1–2% methyl ethyl ketone peroxide (MEKP) catalyst by weight for proper cure.
Question 2: Before applying a fiberglass patch, the damaged area should be ground to what profile?
- A feathered 12:1 taper (Correct answer)
- A 90-degree straight cut
- A V-shaped groove only
- No preparation is needed
Correct answer: A feathered 12:1 taper
A 12:1 taper grind ensures adequate bonding area and distributes stress across the repaired laminate.
Question 3: Which type of fiberglass cloth is preferred for above-waterline cosmetic repairs due to its smooth surface finish?
- Chopped strand mat
- Woven roving
- Plain weave cloth (Correct answer)
- Biaxial fabric
Correct answer: Plain weave cloth
Plain weave fiberglass cloth sands to a finer, smoother finish and is best suited for cosmetic above-waterline repairs.
Question 4: Osmotic blistering on a fiberglass hull is caused primarily by what process?
- Water migrating through the gel coat into the laminate (Correct answer)
- Electrolysis attacking the hull exterior
- UV degradation of outer gel coat
- Improper antifouling paint application
Correct answer: Water migrating through the gel coat into the laminate
Osmosis occurs when water molecules permeate the gel coat and react with water-soluble compounds in the laminate, forming acidic fluid-filled blisters.
Question 5: When repairing an osmotic blister, what is the first step after opening the blister?
- Allow the hull to dry thoroughly for weeks (Correct answer)
- Immediately apply epoxy barrier coat
- Sand and prime the area
- Refill with polyester putty
Correct answer: Allow the hull to dry thoroughly for weeks
The hull must dry completely — often for 30–90 days — before epoxy barrier coat is applied to prevent moisture from being sealed in.
Question 6: What material is commonly used as a structural core in modern fiberglass boat construction?
- End-grain balsa (Correct answer)
- Solid aluminum
- Carbon steel plate
- Solid mahogany
Correct answer: End-grain balsa
End-grain balsa is widely used as a sandwich core because it is lightweight, rigid, and provides excellent compression strength perpendicular to the grain.
MST MST Hull & Fiberglass Repair 1
What is the correct ratio of hardener to resin when mixing standard polyester laminating resin for a fiberglass repair?