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PART THREE - The Gel Crack The first thing to realise is that every GRP car will have a gel crack on it somewhere. Even brand new cars will or, after a professional respray a crack will appear from just knocking it in the garage or by fixing new items of trim, badges etc. so don't get paranoid about gel cracks. They may look unsightly and annoying but, unlike rust on metal cars, they are not going to affect the structure in any way. I have just supplied a brand new Esprit Turbo hot off the transporter with two gel cracks on it due to over zealous trim fitting but fortunately they didn't show! Gel crack from stone under arch The worst thing to do is to eliminate just one crack and make more of a mess doing so; it is far better to save up and do the whole car in one go, culminating in a superb respray. the second thing to understand is that it TAKES TIME, a great deal of time, to carry out repairs correctlyand, as described in the opening article of this series, the technique is the same for ANY GRP car. The cost of professionally repairing a Reliant or Ferrari is equal and only the final painting and finish will give the price differential. Crazing due to window movement With the simple crack then, wash the car first. It is amazing how many people grind away , sweeping all the muck into the freshly ground area and then splodging over the mess with filler. Dry it thoroughly and dewax the area if required with white spirit or 2 star fuel. Now comes the moment of truth. Get your grinderette and remove the guard so you can obtain the correct FLAT angle of attack and gently grind the crack area, overlapping the end of each crack line by at least an inch. The crack shows up as a dark yellow line so you know when it stops. DO NOT grind away at such an angle that you go straight through the lot but use a gentle angle i.e. 15 degrees to the horizontal. Correct grinder angle DO NOT (as, incredibly, many manuals tell you) ROUT OUT each line of the crack and fill it with filler, rather like doing lino-cuts at school (do they still do lino-cuts?) because each 'line' will show as soon as it is painted. Grind enough away to just enter the mat layer i.e. go through the paint and gel coat layer. The mat layer will show up white and 'rough hairy' to the touch. Use an 80 grade paper disc on the grinderette. Next feather the paint/grind edge with 80 production paper at 90 degrees to the grind mark to remove the marks and to give a gentle slope to the repair. Another myth - there is no such thing as re-gelling. You do not put gel coat resin over the area because gel resin is sticky on the top surface and you cannot rub it down but, more to the point, any resin on its own is brittle and the crack will work through again. In the same vein filler on its own will have the same effect but 90% of the so called repair specialists will just grind away and slop filler over it and in about four to six weeks the marks will show through the paint again. The next stage is the only correct way and that is to paint resin over the ground area and 'lay up' the piece of tissue which has been pre cut to shape. Just jiggle the resin up to the paint boundary and when it is FULLY set i.e. dry to the hand (don't forget there will still be a slight stickiness, but your hand will not stick to it), mix up your filler and spread it evenly over the tissue/resin and over the paint boundary. When it is set use 80/220 paper on a file or a block to contour it; a second application of filler may be needed. Finally finish off with 220 grade paper because all spray fillers and hi-build primers are designed to take out the 220 marks. the main pot3ntial faults are firstly creating 'flats' on curved surfaces such as wings where when using a file it will work at a tangent to the curve instead of following it, and secondly causing hollows in large flat panels i.e. doors, bonnets, boot lids, where the panel will flex every time you rub and consequently you rub (dig) harder thus causing a hollow in the middle of the repair. Thirdly not spending enough time i.e. the resin is not fully set before applying the filler and, finally, the filler not mixed thoroughly; some areas gone off, some still soft and leaving grinding or score marks everywhere. all these defects will show up immediately when the repair is painted. Remember, just one simple gel crack on, say, a bonnet will take from start to finish 45 minutes to one hour. Now, how many gel cracks have you found?marks will show through the paint again. The next stage is the only correct way and that is to paint resin over the ground area and 'lay up' the piece of tissue which has been pre cut to shape. Just jiggle the resin up to the paint boundary and when it is FULLY set i.e. dry to the hand (don't forget there will still be a slight stickiness, but your hand will not stick to it), mix up your filler and spread it evenly over the tissue/resin and over the paint boundary. When it is set use 80/220 paper on a file or a block to contour it; a second application of filler may be needed. Finally finish off with 220 grade paper because all spray fillers and hi-build primers are designed to take out the 220 marks. the main pot3ntial faults are firstly creating 'flats' on curved surfaces such as wings where when using a file it will work at a tangent to the curve instead of following it, and secondly causing hollows in large flat panels i.e. doors, bonnets, boot lids, where the panel will flex every time you rub and consequently you rub (dig) harder thus causing a hollow in the middle of the repair. Thirdly not spending enough time i.e. the resin is not fully set before applying the filler and, finally, the filler not mixed thoroughly; some areas gone off, some still soft and leaving grinding or score marks everywhere. all these defects will show up immediately when the repair is painted. Remember, just one simple gel crack on, say, a bonnet will take from start to finish 45 minutes to one hour. Now, how many gel cracks have you found?   page created with Webpage Designer (NS)