What is the secret of applying super thin body filler to selective areas of a GRP panel? Due to overenthusiastic power sanding I have created some areas that are locally scored and/or depressed relative to the intended surface. I am talking less than half mil here. I always end up with too much body filler , say 2mm thick, and create more problems sanding it down than I started with! Is there a tool/technique to use or a method of thinning the filler so it 'flows' better and leaves a nice feathered edge?

The only real answer is, practise. Small dents are harder than big ones. I've been doing it for 25 years and still get it wrong once in a while

I think I seem to remember being told years ago that if you put acetone on the spreader the filler will not stick to it and you can spread it thin.

could try spray filler, long time since i used it. presume its still available

Go to your local factor and ask for Dolphin Glaze, self levelling filler

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Originally posted by Mark Allanson
Go to your local factor and ask for Dolphin Glaze, self levelling filler

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Originally posted by deltron63

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Originally posted by Mark Allanson
Go to your local factor and ask for Dolphin Glaze, self levelling filler

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I wouldn't use it on fiberglass, too hard to rub down

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Upol high build primer is ideal for small scratches

Yo can buy stopper which is ideal for light scratches this can be sanded down with fine wet and dry and gives excellent results. Use a high build primer then acrylic stopper job done

2nd vote for stopper, it goes on great and is very easy to sand down, ive used it over the years for very minor stuff that shows through the first primer coat, once this is on and sanded, any tiny deviations dissapear.

Yup - use stopper.

Are stopper and filler the same? I can't find a difference explained on the 'net anywhere but I thought stopper was much finer?

Stopper is usually a very fine cellulose putty which air dries.
Don't use it on large defects as it can shrink when it dries (and large applications would take a long time to dry).

On spreading filler thin, even if not for this application...

Apply many times, a little at a time, avoid big lumps of it which may create a low spot around the filler without due care.

if you do have a hump, use a hard flat board to rip it back without touching the local substrate before moving onto to anything flexible (and a much finer grade)

in the latter stages having it all one colour really helps, followed by guide coats.

Went to my local branch of Brown bros today and was recommended/sold some 3M Acryl-Red glazing putty 05098 for the job. I questioned the title but the instructions seem to define the job I need to do. Comes with mega health warning. If I never post again you know why!

I've put abit of fiberglass resin in the mix in the past,makes it much more spreadable.someones bound to be along shortly to say you shouldn't but i've never had any problems doing it!

Many thanks to those that pointed me in the right direction. Just thought I would post that the stuff recommended by Brown Bros in my previous post is brilliant. Highly recommended.

I have used an acrylic stopper (lechler??) probablyy similar to the 3M stuff. Waaay better than the cellulose stuff, goes nice and hard, sticks better, doesn't sink. In fact better in every way I can think of Reckon it is the best tip for anybody doing bodywork.