Scratch Repair

[newkitman]

Getting ready to install the wiring on the TD body. While cleaning everything up I noticed  serious scratch on the left front fender of my TD kit. Something must have shifted in storage and gave it a deep scratch.           I can try buffing it out but I’m thinking I’ll have to sand it out and then apply jel coat and final buff. Never have applied jel coat. What are the things I should watch oput for? Do I have to mix the jel coat with anything? Any help is greatly appreciated.

Allen Caron
VW based 53MGTD - "MoneyPenny"
"If one thing matters, everything matters" - from the book The Shack

[Paul Mossberg]

Did the scratch penetrate the gel coat?

Paul Mossberg
Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
2005 Intermeccanica Roadster

If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)

[newkitman]

I think so. The bottom of the scratch is white.

Allen Caron
VW based 53MGTD - "MoneyPenny"
"If one thing matters, everything matters" - from the book The Shack

[Richard Wobby]

One afternoon as I was sharing a green bottle with Hulmet he shared with me hgis secrets to good fiberglass repair. Remember this was over a few green bottles and I’ve got this blackout thing going on ever since I started really working on my drinking problem. I think this is pretty much what he said. I even conjured up a few mental images to share with you all in those places he stressed detail.

Surface scratches can be buffed out of gelcoat with polishing compound, but deep scratches must be filled. When the gelcoat surrounding a scratch is in good condition, the filler of choice is gelcoat paste, which provides both filler and finish in a single application-but not a single step. Because the surface of the cured paste will be uneven, sanding and polishing are required to smooth the repair and blend it with the rest of the hull. Except for color matching, gelcoat repairs are easy and straightforward.

Gelcoat Choices
You will find gelcoat available as both a resin and in a thicker putty form called paste. For scratch repair you want paste. Repair kits comprised of a small amount of gelcoat paste and hardener, a selection of pigments, mixing sticks, and sealing film can be purchased for less than $20. Buy a flexible plastic spreader if you don’t already have one. You will also need sheets of 150-, 220-, 400-, and 600-grit wet-or-dry sandpaper. A single sheet of each will be more than ample to fair all the paste in a repair kit.

If you are repairing several scratches, add a small bottle of styrene to your list of supplies. Wiping each scratch with styrene just prior to filling it partially reactivates the old gelcoat, resulting in some chemical bonding between the old gelcoat and the new. Otherwise the bond between old and new is strictly mechanical-like a coat of paint. A mechanical bond is normally adequate, but the more extensive your repair, the more certainty you want.

Color Matching
The hardest part of a repair to the surface of a replicar is matching the color. Professionals who do gelcoat repairs daily still have difficulty getting a perfect match. Even “factory” colors don’t match exactly after a replicar has been in the sun for a few years.

White has the significant advantage of being fairly easy to match, and once a small repair is buffed out to a gloss, shading differences will be unnoticeable. Matching colors is somewhat more challenging.

A color-sample card from your local paint store that matches your car can provide valuable help. Ask the store clerk the formula; they custom-mix the color by adding tints to a white base. The formula may call for a half-dozen different tints, but the important ones are those specified in the largest quantities. You can use the tints in your repair kit to approximate the formula.

Always color gelcoat paste before you add the catalyst. Put exactly one ounce of paste into a mixing cup and add the tints a drop at a time. Keep track of the number of drops of each tint. When the color looks close in the cup, touch a drop of the mix onto the hull. Make needed adjustments until you are satisfied with the match-don’t expect perfection-then write down the formula so you can duplicate it for the rest of the paste.

Preparing the Scratch Never try to repair a scratch by simply painting over it with gelcoat. Gelcoat resin is too thin to fill a scratch and gelcoat paste is too thick. Instead of penetrating scratches, gelcoat paste will bridge them, leaving a void in the repair. To get a permanent repair, draw the corner of a scraper or screwdriver down the scratch to open it into a wide vee.

This is the time to wipe the open scratch with styrene to reactivate the old gelcoat.

Catalyzing
The hardener for gelcoat is the same as for any polyester resin-methyl ethyl ketone peroxide, or MEKP. Gelcoat resin usually requires 1 to 2 percent of hardener by volume (follow the manufacturer’s instructions). As a general rule, four drops of hardener will catalyze 1 ounce of resin at 1 percent. The mix shouldn’t kick (start to harden) in less than 30 minutes. Hardening in about two hours is probably ideal. Always err on the side of too little hardener. Also be certain to stir in the hardener thoroughly; if you fail to catalyze every bit of the resin, parts of the repair will be undercured.

Spreading Gelcoat Paste
Work the gelcoat paste into the scratch with a flexible plastic spreader. Let the putty bulge a little behind the spreader; polyester resin shrinks slightly as it cures, and you’re going to sand the patch anyway. Just don’t let it bulge too much or you’ll make extra work for yourself.

Scrape up any excess paste beyond the patch area.

Covering the Repair
Gelcoat will not fully cure in air. To seal the surface of a scratch repair, cover it with a sheet of plastic film. The kit may include sealing film. Otherwise a section of kitchen “zipper” bag works especially well because it tends to remain smooth and the gelcoat will not adhere to it. Tape one edge of the plastic to the surface just beyond the repair, then smooth the plastic onto the gelcoat and tape down the remaining sides.

Sanding and Polishing
After 24 hours, peel away the plastic. The amount of sanding required will depend on how smoothly you applied the gelcoat.

A 5 1/2-inch length of 1 x 2 makes a convenient sanding block for a scratch repair. Wrap the block with a quarter sheet of 150-grit paper, and use the edge of the block to confine your sanding to the new gelcoat. Use short strokes, taking care that the paper is sanding only the patch and not the surrounding surface. Never do this initial sanding without a block backing the paper.

When the new gelcoat is flush, put 220-grit wet-or-dry paper on your block and wet sand the repair, this time with your block flat. Use a circular motion and keep a trickle of water running on the sanding area. Feather the repair into the old gelcoat until your fingertips cannot detect a ridge. If the fender is curved, take care not to sand the repair flat.

Abandon the block and switch to 400-grit wet-or-dry paper. Wet sand the surface until the repair area has a uniform appearance. Follow this with 600-grit wet-or dry. Wear cloth garden gloves-the kind with the hard dots-to save the tips of your fingers.

Dry the area and use rubbing compound to give the gelcoat a high gloss. Swirl a soft, folded cloth over the surface of the compound to load the cloth, then rub the compound onto the repair area. Buff it with a circular motion, using heavy pressure initially, then progressively reduce the pressure until the surface becomes glassy. If the gelcoat shows swirl marks, buff them out with a very fine finishing compound.

Finish the job by giving the repair area a fresh coat of wax. If your color match is reasonably good, the repair will be virtually undetectable.

[newkitman]

Richard you are da man! Thanks for the highly detailed description that an old Geezer like me can understand. Its invaluable infor for the rest of the members as well. Maybe Paul can add this to some technical area in our forum so we don’t lose it!

Allen Caron
VW based 53MGTD - "MoneyPenny"
"If one thing matters, everything matters" - from the book The Shack

[Paul Mossberg]

Nicely done Wobby!

this one is a keeper!

Paul Mossberg
Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
2005 Intermeccanica Roadster

If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)

[Paul Mossberg]

Great idea Allen.

I created a PDF out of Wobby’s article into a PDf and will send it along to our host to add to the download manuals section

Paul Mossberg
Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
2005 Intermeccanica Roadster

If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)

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