Polyurethane varnish touchup

When a polyurethaned floor (for example) has a small mark that needs touching up, what's the recommended procedure? I've sanded the spot with 1000 grit wet&dry, and tried applying a dab of poly with a small brush. The flaw in that approach was immediately obvious, since the newly applied poly surface was raised and clearly not going to blend in. I wiped it off with turps, back to the drawing board. It seems that it might be necessary to thin the poly in order to be able to feather the edges. If so, in what proportion, and if not, what else?
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Gib Bogle wrote:

Apply the varnish with a rag or sponge?
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Stuart Noble wrote:

Yes, I replied with this approach about repairing some emulsion paint to a wall some time ago. I would recommend a scrap piece of foam. Not too much varnish on it and work out from the centre in a circular pattern, dabbing until the foam runs out of varnish. Hence, only use a tiny amount to load the foam each time and increase the area you are dabbing by a small amount each time by adding a very little more varnish each time. Do not try to use the foam as a paint pad, but just dab it against the wood.
Be very careful that you do not try to spread the varnish out too far, as you may end up with a mat or cloudy finish. Try it on a scrap piece of wood that has been brushed with the varnish and allowed to dry first.
Let us know how you got on please. As I have never tried this with varnish, only with paint of all types.
Dave
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Dave wrote:

Thanks. Since it seemed I wasn't getting any replies, I went ahead and tested with a piece of wood. I put two coats, sanded a small patch with 1000 grit, then applied a 50-50 mix of poly and turps. I used a brush, not having thought of the foam idea. The result is semi-satisfactory. I do get a surface with a different (lower) reflectivity. This could be partly because I do not have the identical polyurethane. The floor was done by someone else, with a final satin coat. I thought the semi-gloss poly I have would be roughly equivalent to the one that was used, but for whatever reason the result is not perfect. I may have to find some of the same poly.
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Dave wrote:

Thanks. Since it seemed I wasn't getting any replies, I went ahead and tested with a piece of wood. I put two coats, sanded a small patch with 1000 grit, then applied a 50-50 mix of poly and turps. I used a brush, not having thought of the foam idea. It looked OK, so I then tried it on the actual sanded patch on the floor. The result is semi-satisfactory. I do get a surface with a different (lower) reflectivity. This could be partly because I do not have the identical polyurethane. The floor was done by someone else, with a final satin coat. I thought the semi-gloss poly I have would be roughly equivalent to the one that was used, but for whatever reason the result is not perfect. I may have to find some of the same poly.
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Stuart Noble wrote:

No. Apply big blob and sand back with wet and dry once dry.. Go up to 1200 grit and T-cut.
Didnt you guys EVER touuch up cars you were selling?
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The Natural Philosopher wrote:

I think any final step that involves sanding will produce a surface that is noticeably different from the surrounding surface. Even a light touch with 1000 grit is clearly visible. I haven't tried a cutting paste (I guess that's what T-cut is.)
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