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How To Carry Out a Small Fiberglass Job Using a Mould

  • 4 min read

1. Wash the mould with soap and water and dry thoroughly. Remove any old gelcoat by using apiece of`steel wool or fine (600+ grit) wet and dry sandpaper.

2. Wax the mould using Norski Mould Release wax, as per the instructions on the can. Allow to dry for at least 30 minutes after the last coat.

3. Apply the Norski PVA Release Agent either by wiping it on with a small piece of absorbent sponge or by spraying. Be careful not to leave "runs"in the PVA Release Agent-they will take along time to dry and will come out in the finished product. Do not apply by brush as it will leave "train lines" in the PVA Release Agent coating which will also come out on the finished product. Allow to dry. On a hot, dry day it will take 10 minutes, on a cold wet day it could take two hours or more.

4. Work out the amount of gel coat you will need, based on 5OOgms per square metre. Examples: For 0.5m of mould surface use 250gm of gelcoat, for 1.0muse 500gms, for 1.5m use 750gms, for 2.0m use 1KgOn jobs less than 0.5m allow a bit extra for waste. Pour the gelcoat into a mixing cup (small amount)or ice cream container (large amount).The purchase of one of our ‘Norski Measuring Kits’ is invaluable at this stage.

5. Now work out the amount of catalyst needed. On a dry day allow 1.5%, on a cold day allow 2%.Use a small measure for amounts over 2mls. For amounts less than 2mls count out drops from the catalyst drop bottle (20 drops is 1ml).Example:1.5%-2.0% equals 3040 drops of catalyst per 100ml of Gelcoat Safety: Catalyst is dangerous. Read safety instructions on side of bottle before using.

6.Mix the catalyst into the gelcoat, using a flat stirring stick.

7. Brush the Norski gelcoat onto the mould, using light, even strokes, preferably going in the same direction. Do not push hard on the brush but let it "float" over the surface of the mould, leaving behind a thick coating (about 0.5mm is fine). Go over thin spots and smooth out thick areas until you are satisfied with the job. Work fast as the gelcoat will start to set in about 10 minutes. Wash the brush out straight away with Norski Cleaning Fluid. Allow the gelcoat to "gel" and cure until it is almost touch dry (two hours on a hot day, up to six hours on a cold day).

8. Cut or tear the chopped strand mat to fit the mould, allowing an extra centimetre around the edge. On tight curves tear or cut the mat to fit, adding extra pieces if needed. Put the mat onto a clean surface until ready for use (e.g. newspaper).

9. Work out the amount of resin needed (mix no more than you can use in 30 minutes). Allow 500mls of resin for every square metre of 300gm chopped strand mat.Allow 1Kg of resin for every square metre of 450gm chopped strand mat.Allow 1.5Kg’s of resin for every square metre of 600gm chopped strand mat.

10Now work out the amount of catalyst needed.On a hot day allow 1%, on a cold day allow up to 2%.Example:1.5%-2.0% equals 3040 drops of catalyst per 100ml of resin Use a small measure for amounts over 2mls. For amounts less than 2mls count out drops from the catalyst drop bottle (20drops is1ml)

11. Mix the catalyst into the resin, using a flat stirring stick.

12. Brush a thick coat of resin onto the gelcoat in the mould.

13. Position the glass in the mould on top of the wet resin and then add another coat of resin, taking care not to displace the fibres. It may be necessary to "dab" the brush against the glass fibres rather than brushing to avoid moving them. Make sure that every part of the glass is "wet out' ' thoroughly and that there are no white (dry) spots Wait for two minutes to allow the fibres to fully saturate.

14. Consolidate the laminate by using a metal roller over the entire surface. This removes air bubbles and gives a good quality laminate, free of voids. Don't push the roller too hard or it will clump the glass. If the roller picks up the glass, rinse in cleaning fluid and start again. Set aside and allow to cure for 1-2 hours before attempting another layer.

15.Clean the brush and(mohair)roller in Norski Cleaning Fluid.

16. Add additional layers of glass and resin as needed, noting that the 2nd and subsequent layers can be "laminated" at the same time, as long as each one is rolled properly. Set aside to cure, preferably overnight.

17. Remove "nibs" from the laminate with a sharp knife or abrasive paper (80 grit). (Note: If the laminate has been left for 24 hours or more, it should be sanded all over before flow coating).

18. If you wish to finish the inside layer of your fibre glass project then the correct (sandable) coating to use is ‘Flow coat’. Work out the amount of flow coat you will need, based on 500gms per square metre of mould surface.

19. Now work out the amount of catalyst needed. On a hot day allow 1.5%, on a cold day allow 2%.(Note: This is the same catalyst levels as used with gelcoat).

20.Mix the catalyst into the flow coat and brush onto the job in long even strokes, keeping to one direction if possible. Work fast as the flow coat will "gel" in about 10 to 15 minutes, depending on the temperature. Set aside to dry when finished. Clean the brush in cleaning fluid.21You can sand back the top-coat of flow coat(if desired) with fine ‘wet and dry’ sandpaper(1000/1200 grit) if you require a smoother finish than the flow coat offers with being applied by brush.

22. Your job is effectively complete. All you need to do now is to remove your fibre glass structure from the mould. So, after allowing 24-36 hours for all curing to occur, gently ease your product out of the mould releasing around the edges. 

Here’s what you are going to need...

  • Gelcoat + catalyst (Refer the chart above for volumes)
  • Release Agents (Wax/PVA Release Agent)
  • Brushes for applying everything
  • Measuring Kit (otherwise you will need measuring cups, disposable gloves, stirring sticks,etc)
  • Enough Chopped Strand Matt for your job
  • Enough Resin for the Mat
  • Both Wet and Dry sandpaper and standard 80 grit sandpaper
  • Norski cleaning Fluid orAcetone to clean up any spills
  • Flowcoat and catalyst (Refer the chart above for volumes)SAFETY

PRECAUTIONS: Do not use near fire or flames. Harmful or fatal if swallowed Use disposable gloves to avoid skin contamination. If resin comes into contact with skin, wash uncured resin off with soap and water. Wear safety glasses to avoid eye contamination. Mixed formulation contains Epoxy Resin and Amines. If swallowed do not induce vomiting. Give a glass of water. Contact a Doctor or the Poisons National Information Centre on 0800 764 766(Urgent information only)