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Member
Country: UK - England
Town: Bristol
Make: Ribcraft
Length: 5m +
Engine: Yamaha
Join Date: May 2006
Posts: 4,299
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With all the Excitement of Peter sat on a upturned Sea rider hull.I found this,, its cut n paste but basic and useful...
Q: What types of resin are there?
A: There are 3 basic types of resin; Polyester, Vinyl ester and Epoxy.
Polyester resins provide good strength at relatively low cost. These resins can provide a wide variety of properties relating to water and chemical resistance, weathering and shrinkage during curing.
Vinyl ester resins are primarily used where improved water and chemical resistance, heat resistance or improved flexibility is required. They have high resistance to acids, alkalis and solvents.
Epoxy resins have a different structure to polyester or vinyl ester resins and are usually sold as a 2 pack system. Epoxy resins do not shrink as much as polyester or vinyl ester resins when they cure. Epoxy resins provide particularly good mechanical strength and adhesion, and have good stiffness, toughness, heat and water resistance.
Q: What is gelcoat?
A: Gelcoat is a specially formulated polyester resin that is applied on the mould face. Designed to give good appearance, colour, water and weather resistance.
Q: What is the difference between flow coat and gelcoat, can either be sprayed to produce a water tight finish?
A: Flow coat is a gelcoat with a wax in styrene additive for use as a top coat. Gelcoat can be sprayed providing that it is “spray gelcoat” not hand lay gelcoat. Both gelcoat and flow coat will give a water tight finish, providing it is used in conjunction with a fiberglass lamination.
Q. Is topcoat the same as flow coat?
A. Yes, topcoat is the same product as flow coat.
Q: Can flow coat be used to enhance the finish to the whole exterior of the hull of my boat 4m long.
A: No, you cannot use gelcoat to enhance the finish on your boat. Gelcoat is very difficult to apply smoothly and burnish up. The best product to use is a 2 pack polyurethane or a 2 pack acrylic.
Q: What type of paint would it be best to use to repaint fibreglass and where can I buy it?
A: I would recommend that you use a 2 pack polyurethane paint or a 2 pack acrylic paint which can be purchased from a good car accessories/paint shop.
Q: My fibreglass glider, painted in 2 pack, has developed small blisters. How can I get rid of them?
A: 2 pack paint blisters are due to the paint being applied over a damp area. Usually blisters appear when the area is in the direct sunlight. You can only sand them back and re-paint the area. If the glider is made of Epoxy resin it must be abraded with wire wool and detergent before painting.
Q: I would like to use gelcoat and I have plenty of time to handwork the finish. Is there a product available for refinishing large areas of gelcoat that I can apply myself? (I have been told that gelcoat will not dry if exposed to air)
A: The product that you need to use is Flow Coat, which is a gelcoat with an additive that allows it to dry completely.
Q: Once flow coat has been used, is it possible to bond to the wax-modified resin if changes or repairs are needed to the structure?
A: Yes it is possible, you need to clean the area thoroughly, preferably using Acetone, then sand back the surface before carrying out the repair.
Q: I am having trouble matching the new gelcoat with the existing gelcoat.
A: Colour matching is very difficult unless you have the manufacturers RAL number.
Q. I would like to add pigment to gelcoat. Do I buy clear gelcoat & add the pigment or white and add the pigment? Will I get the same shade of colour or will one be lighter or darker depending on the gelcoat? Also can I put the pigment in polyester resin for laying up the glass after the gelcoat in the mould?
A. All pigments must be added at 10% to clear gelcoat only. Adding further pigment to a white gel will cause curing problems due to over pigmentation. Any tinting of colour should be done by adding pigment to the base pigment colour, then added at 10% to the gelcoat.
Pigmenting resin is OK following the same mixing ratio, however it is not generally done because clear resins allow you to see any entrapped air bubbles or dry mat you may have missed during layup.
Q: I have been told only spraying gives an acceptable gelcoat finish, but I have also been told application with a paintbrush will give a satisfactory result, but thickness must be controlled. Which is correct? Are there different types of gelcoat for spraying and brushing? How do I know how thick the gel is if I brush it on?
A: Both brushing and spraying the gelcoat give an acceptable finish within a mould, unless you intend to use clear gel coat with a metal or decorative back up. In this case a spray is necessary.
I suggest you coat over twice with gelcoat, allowing the first coat to harden. There are different gelcoat available, depending on whether you are brushing or spraying.
Q. Can I spray gelcoat and resins?
A. Yes. However you must use the correct equipment such as a gelcoat sprayer. You also need to use resins and gelcoats designed for spray use.
Q. I have chipped gelcoat. What’s best to repair this?
A. You can fill small chips with more gelcoat, then wet sand smooth and polish. For larger chips add a small amount of colloidal silica to thicken, sand smooth and then apply more gel on top to seal surface. Some wax solution should be added to your gel to prevent surface tack.
Note: some chips are too big and must be reinforced.
Q. Can I use polyester on top of epoxy?
A. No. It will not bond properly. You can however use epoxy on top of polyester.
Q. How much catalyst do I use?
A. Thorough mixing of catalyst into resin and gelcoat is very important. Also the correct additions should be observed to maintain good results.
1% is considered a slow mix, 2% is ideal, 3% is a fast mix. Additions outside these bands are not advisable for proper curing, in fact adding more than 4% may result in a failure to cure.
The pot life of these mixes is also determined by temperature. The higher the temperature, the faster the cure. As a general guide 2% addition at 20°C gives 15-20 minutes pot life. The resin will always cure quicker if left in a mass such as the mixing bucket or in castings.
Q: How do I thicken a resin and polyester colour paste?
A: Resin can only be thickened with talc, fillite, A.T.H or any other readily available fillers. Gelcoat is already thickened therefore we would not suggest that you add any more.
Q. How much resin do I use with chopped strand mat (CSM)?
A. CSM requires about 2.5 times its own weight in resin (5kg CSM needs 12.5kg) however some users may use more or less in their fiberglass application.
Q: I have used polyester resin and only part of it has hardened. What’s happened?
A: The problem is caused by not thoroughly mixing the resin and the catalyst.
When mixing make sure you use a rectangular shape stirrer – like a ruler.
Ensure you scrape the sides of the container and mix the solution from the bottom up and back down again.
To ensure a thorough mix, we suggest you also pour the resin from one clean mixing container to another.
Q: Can I fix the problem and how?
A: Yes you can. Remove as much of the uncured resin as possible without disturbing the layers of glass underneath, thoroughly mix up a new batch of resin of sufficient quantity to cover the uncured area and reapply. Thoroughly roll the affected area with a bristle or disc roller.
Q: What resin should be used with carbon fibre?
A: Carbon fibre should only be used with Epoxy or Vinyl ester resin.
Q. What resin is used with Kevlar?
A. You have two choices; polyester resin or epoxy. Epoxy is the more expensive but is much harder and will give a laminate that has a better strength to weight ratio. But in either case with flexing stress the resin will always break around the Kevlar. Kevlar has extreme tensile strength hence its use in bulletproof jackets and other safety equipment.
Q: Are redundant GRP products classified as special waste or can they go to landfill?
A: Redundant GRP products can go to landfill as long as the resin products are fully cured beforehand.
Q: The hull of my boat, below the water line, has “blisters”. Is this osmosis?
A: Yes, this sounds like osmosis. If you break a blister it will taste and smell like vinegar.
Q: Is osmosis a problem with fibreglass?
A: Yes, osmosis is a fibreglass problem: A bad lay-up results in the fibreglass strands performing a capillary action, seeping water through the laminate, the glass fibre gets wet and ends up delaminating.
The only way to tackle this problem is to sand blast the area, pressure wash, then coat with 5 coats of epoxy resin.
Q. My gelcoat is dull and looks chalky?
A. Much of this surface dulling and light scratching can be removed by using a good quality polish. Heavier scratching or deep penetrated weathering may require the use of cutting compound prior to using polish. For large areas a slow speed buffer will speed things up.
Q. I have painted on my gelcoat but it still feels tacky?
A. Gelcoats are air inhibited so they retain some surface tack on all surfaces exposed to air, this is supposed to happen to ensure good adhesion to following layer of GRP. If you wish to use gelcoat as paint you will need to add 2% wax solution or buy pre-mixed topcoat/ flow coat.
Don’t confuse this surface tack with poor curing of gelcoat.
Q. Why isn’t my resin or gel curing?
A. This may be due to adding too little or too much catalyst. Your working environment may be too cold or you may have added too much pigment paste. If the resin or gel has a milky look, it may be contaminated with water.
Q: Why do I have voids – bubble like gaps in my finished product?
A: This is generally caused by poor rollout. Rolling of the laminate is very important to release entrapped air. A bristle or ring roller is generally preferred over the paddle type roller or brush.
Q. How do I get fibreglass to stick to metal?
A. To ensure good bond to metals use a good quality polyurethane adhesive and follow the instructions.
Q: Can I use fibreglass on wood and if so how many layers would I need to put on it to give a strong finish?
A: Yes you can use fibreglass on wood. 2 layers of 450g CSM would be okay in most low load applications. The wood will offer a certain amount of strength in the first place.
Q. I plan to make a mould from foam. Can you please advise which is the correct foam to use?
A. To make things easier you should consider a polyester mould, however to go this route make sure to use polyurethane foam as polystyrene foam is attacked by resins.
Q. If I make a timber/MDF mould do I need to varnish it first and then use a release agent after?
A. Yes, you will need to seal the mould before applying release agent.
Q. I intend making a medium sized mould using 450g CSM. Can you please tell how many layers of glass I will need? Also will woven roving be needed?
A. You must bear in mind weight versus strength. To build a lasting mould you would be looking at 5 layers of CSM. I would recommend a skin with 300g followed by 3 layers 450g then some 25mm foam ribs to help with rigidity followed by at least 1 more layer 450g over everything.
Woven isn’t usually required on small mouldings but a layer between the second and third 450g CSM can help improve flexural strength. Don’t forget to brace your pattern well inside as this will be supporting a fair bit of weight.
Q: Why does the resin drain from the sides of my mould and pool in the bottom?
A: There are a number of causes:
1. You may have applied too much resin and it is slumping to the bottom of the mould.
2. You may have over agitated the resin. Agitation reduces gel and increases flow causing the resin to drain to the lower level of the mould.
3. You may have purchased an inferior quality resin to do the job.
Q: Why use surface tissue when laying up fibreglass?
A: Surface tissue has very high resin pick up and is normally used behind the gelcoat layer to provide additional strength by getting fibers close to the surface in complex areas of the mould. Tissue is also used as an aid in preventing “read through” of the internal structure of the fibreglass.
Q: Why does the glass pick up on my roller?
A: There are several factors that can cause this problem.
1. The resin is nearing gel time. To give a more efficient lay-up time, reduce the area the resin is applied.
2. Styrene has evaporated from the resin. Use fresh catalysed resin.
3. Rolling too fast.
4. Too high a percentage of glass, apply more resin.
5. Dirty rollers. Clean in fresh solvent.
Q: Why does the tooling gelcoat pull away from my plug?
A: Catalysation of tooling gelcoat is critical. Do not use more than 2.4% in the tooling gelcoat as more can cause excessive shrinkage. Do NOT allow tooling gelcoat to cure completely as it can shrink and pull away. This means you should never leave tooling gelcoat over night or over a weekend without laminating first.
Never reduce tooling gelcoat with anything.
Q: My resin is taking a long time to go off, why?
A: There are several factors that can cause this problem.
1: You may have used too little catalyst. This will create a slow cure, but a strong laminate.
2: Your catalyst may be old. Time affects the ability and stability of the catalyst. Use a new supply of Catalyst.
3: Resin uses a product called “Cobalt” to promote the resin. The more cobalt, the faster the reaction time to the catalyst.
You may have purchased resin that was created for use in the summer months and you are using it in the cooler Autumn / Winter months. Use a resin promoted for the time of the year.
4: Your product may be below the manufacturers recommended usage temperature. The product should never be used if its temperature is 15°C or below.
The ambient air temperature will also affect the cure time. Increase the amount of catalyst used, but do not work greater than 2%
5: The resin or the glass reinforcing may be contaminated.
Q: I have hot spots over my finished lay-up. Why?
A: This can be caused by a poor resin / catalyst mixing technique. Ensure you mix your product thoroughly.
Resin pooling or resin rich areas can also cause this problem. Reduce your resin usage over the area.
Q: My resin is going off very rapidly. Why?
A: There are several factors that can cause this problem.
1: You may have used too much catalyst. This will create a rapid cure, produce a vast amount of exothermic heat and create a weak laminate.
2: Resin uses a product called “Cobalt” to promote the resin. The more cobalt, the faster the reaction time to the catalyst.
You may have purchased resin that was created for use in the cooler Autumn / Winter months and you are using it in the summer months. Use a resin promoted for the time of the year.
3: The ambient air temperature will also affect the cure time. Keep the product and the project you are working on out of direct sunlight.
4: The polymerisation or hardening reaction of resin gives off heat. It is important that this reaction be controlled. This is done by keeping the concentration of catalyst to a minimum. It is important not to laminate too many layers at one time. Allow the lower layers to cool to room temperature before continuing with additional layers.
5: The resin or the glass reinforcing may be contaminated.
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