Thread: Fibreglass guard repair

I have done a fair bit of fiber glassing over the years and always guessed it and never had a problem. As long as you close you will be right.

Dave

Just to add without reading your other thread, I would tap a piece of ice cream lid with a thin bit of ply behind it while you do the first layer, them remove it. This will give you the bridge needed to get started.

Dave

This looks a bit tricky. I've had a geek on Google for repairs to fibreglass. It seems I'll have to enlarge the damaged area because the fibreglass has to be feathered back on the inside.

I was also thinking of packing some plaster of paris on the non damaged side, (over Glad wrap) then reversing it and using that as a mould for the damaged side.

I'm assuming that the rads are the same.

Ken

You will need to clean the sides back about 25mm, just take the angle grinder to either side and clean it up. If you put it on too thick thats fine, just grind it back. Then use some car body filler over the lot and sand it to blend it in. The inside wont need finishing as it's not seen.
Don't forget to wear a mask when grinding it and sanding it.

Dave

Thanks Dave, sounds like you have some experience, I have absolutely none.

I have the resin, a catalyst, and some fibreglass matting. Do I also need some gel coat, or will I just get away with the resin and some body filler, if necessary?

The other option is to buy a second hand guard from Mal at Australian Metalworking Hobbist.

Ken

Hi Ken,
I have done a fair bit on both surfboards, surf ski's and car fiber glass panels etc, it's pretty much all the same.
Just think of it as wood once it's set, then sand it down to shape. If you sand to much, just add a bit more.
If you use the ice cream lid backing when it's almost dry just bend it away and take it off. You can then add more resin and matting on both sides to fill it up. Just do a few layers at the time to build it up and let it cure for 1/2 hour to 1 hour, then re apply until you have built up to the top or just over. You can just use resin for your last coat, then grind or sand it down.
I find it easier to just finish up with car filler and jobs that are going to be painted.

Dave

Gel coat is the thin coloured layer that is sprayed into a mould when making sonething like your guard up initially. It is more UV resistant, opaque, accepts tint for a surface finish etc, but primarily it is a barrier layer to prevent glass fibre from the layup from being visible on the surface and able to soak up moisture.

Since you are not making a part in a mould you do not need it.

Resin pack should give a reasonable start point for the mixture of resin to hardener, but with polyester it can be varied from half to double depending on working temperature and required setting time. Higher temp and more hardener both shorten working time, add more hardener for cool weather to maintain working time, less for hot weather.

Epoxy resins much more fussy about mix, to much of either part and it just stays gooey/sticky, can't be finished properly etc.

I did a fibreglassing course some years ago when I was rebuilding my Bolwell and I have done a lot of repairs just like yours.

Originally Posted by neksmerj

Question. How do you measure out the quantities of filler and hardener? From memory it's 50 parts filler to 1 part hardener by weight.

No more than 2% catalyst max. In hot weather like we have now you would probably be down to about 1/2 -3/4%. maybe even less

For the small amounts you would need to do your small repair, you can weigh the resin using kitchen scales and measure the catalyst with a small syringe. Good idea to put the scales in a clear plastic bag before using them. For some reason the Kitchen bosses usually doesn't like resin on their scales.
I have a chart of catalyst to resin ratios which I know I have scanned but I have just spent the last 20 minutes looking for it but can't find it.
If you want to slow the reaction down to give you a bit more working time, keep the resin in a fridge until you catalyse it. Be warned that once you use a fridge for storing resin it will smell of resin forever.

Originally Posted by neksmerj

What happens if you underdo or overdo the hardener?

Ken

Over doing it - Worst case - the catalysed resin can catch fire in the container.
Not so bad - it cures before you have fully wet out you glass and the job is ruined.
Under doing it. the resin just doesn't cure. (it will actually cure eventually but it can take a while. When I was working on the car, in winter, I had to use a fan heater to get the reaction to happen)

With your guard, I'd be giving it a really good clean, with acetone, inside in the area you are repairing. You need to get rid of any oil or grease. You should also give it a wipe with liquid Styrene to reactivate the old resin just before applying the new resin.
Most fibreglass material supply places have handout sheets on how to do repairs etc. Also a good book to have a read of is called "how to repair fibreglass bodied cars" (or something like that) by Miles Wilkins published by Osprey publications.


Remember safety. The Catalyst is dangerous stuff. If you get it in your eyes you will more than likely loose your sight in that eye, so safety glasses while ever you are working with resin. Also wear gloves. The Ansell disposable latex that you buy in a box of 100 or so are pretty good. The resin doesn't effect them but prolonged exposure to acetone will.

hope this helps
regards
bollie7

Thought I'd try making a mould using plaster of paris laid over cling wrap. I'm making a mould of the undamaged side of the guard in the hope that when reversed, it will serve as a mould for the damaged side.

Will have to wait for the plaster to set to see if I was successful. It's about 10mm thick.

Ken

Ken
Have you tried some resin on the cling wrap to see if the resin affects it?
What you are doing with the plaster will work ok provided the resin doesn't eat the cling wrap away. Even then you would be able to sand the resin down a bit to get rid of the plaster.
You could also have used a bit of waxed sheet gal or zincalume (not black steel or aluminium as the resin sticks to this a lot easier than gal or zincalume) as a support and just clamp it to the guard.

The really important thing is to make sure the metal ( or what ever else you are using as a support, except for cling wrap as I think that might be a bit hard to wax up. lol) is well waxed with ceara wax or a similar release agent for polyester resin. At least 6 or 7 coats of wax and followed with a coat of PVA (thats PVA for resin NOT PVA wood glue - different things) I have heard of car wax or floor wax being used with varying degrees of success. With a small job like yours it might be worth trying floor wax if you have some as at the end of the day if it is a failure you only have to cut it out and start again.

For an effective, lasting, repair it is essential that you grind the damaged edges back until you get past the damage and delamination and then grind the edges down to a feather edge. From what I can see in your pic, with the thickness in the guard, I'd be grinding back about 20 -25mm from the edge. Prepare your new matt so that each layer is slightly larger than the one before it. For that repair I'd only be using 225gsm split strand as its a bit more flexible than anything heavier and so will go around the corner a bit easier for you. Don't forget the wipe with liquid styrene just before you start to layup.

Bit of advice - don't grind it in your shed as the dust goes everywhere and sticks to everything. it also absorbs moisture really well and any exposed steel starts to go rusty quite fast. Don't ask me how I know this.
Even though it might sound like overkill for a small job like this make sure you cover yourself all over before grinding. paper overalls are the best. If you just use work clothes then use old ones that you can bin when you are finished as you will never get all the glass particles out of them. What ever you do don't try and wash them in the household washing machine. SHMBO will take a very dim view of this. lol
Use a good face mask suitable for grinding fibreglass.

Ive attached a couple of pics showing some of the stuff I did on my car some time back now.

No 076.jpg

no 078.jpg

regards
bollie7

Bollie7,

Thanks for all your advice. Sounds like I should be giving this task to an expert, and let them worry about the health issues.

Is there anyway I can get away without feathering, and still end up with an even thickness?

1. It's nigh impossible to get a grinder inside the guard, it's only 3" wide.
2. The thickness of the existing fibreglass is only 2.5mm to 3mm thick.

Ken

Ken.
Its not that hard provided you take the right precautions in respect to your safety. No different in concept to machining really.
It was a bit hard to judge the thickness from the pic but at 2.5 -3mm thick I'd go back about 10- 12mm.
As far as getting in there, do you have a rotary burr and something to drive it? A conical burr in a real coarse tooth pitch would be ideal but you can make do with finer ones. In a pinch you could even file it back with a coarse file or emery/sand paper. It doesn't have to be perfect, just reasonably uniform. The idea is it gives you a larger surface area for the new resin to bond with the old.
In your case, as its a guard, I doubt if it would have a lot of load on it, though I wonder what caused the damage in the first place. I'd assume its been hit by something rather than a failure of the guard itself.
Thinking about it further, you could probably do a good repair in this instance by epoxying some thin sheet metal to the inside and just using auto body filler to bring the surface up to the required height. Sanding smooth and painting.
You would still have to make sure there was no grease and/or oil on the surface where you wanted to epoxy. Just give it a good rough up with sand paper and a good wash with acetone or possibly thinners. This is all assuming there is enough clearance between the guard and the pulley/belt to allow for the extra thickness at the repair.

hope this helps
regards
bollie7

Just a tad too hot yesterday to do anything. 40 degrees in the shade.

The plaster mould came off easily, and when turned over and offered up to the damaged side, looks like a perfect fit.

There's a bit of touching up on the inside where the folds in the cling wrap left their impression.

I've ordered a right angle drive for my Dremel so I can get inside the guard for feathering.

Another ruff pic.

Ken

The plaster of paris mould I made, has warped out of shape in the heat, and no longer fits the shape of the guard on the damaged side, so it's back to the drawing board.

I'm now in possession of a Dremel right angle drive, $35 and well built, so I can get inside the guard to feather back the edges with a grinding disk.

I'm now faced with clamping the guard down onto a flat board, and using that as a former. Where the guard turns 90 degrees, I'll use some modelling clay on the outside radius.

What medium can I use to prevent the fibreglass from sticking to the board? There was some suggestion that cling wrap may dissolve when used as a release backing. Baking paper perhaps?

Any advice is appreciated,

Ken