Rottenstone And Pumicestone

[la Huerta]

how long should i wait till rubbing out after finishing a project with poly?

[LuckyDuck]

La huerta: I don't know, I have usually waited only a couple of days, rarely longer if the weather has been humid and the finish still feels tacky. Do others with more experience have any comments?

[soundman]

It is probably worth checking out EEE ultrashine for this purpose most people use it on the lathe but I know several people are having good sucess with it in flat work hand rubbed or with a machine.

check the u beaut link at the bottom of the page.

cheers

[la Huerta]

when rubbing out with very fine wet'n'dry is it supposed to dull the surface (been practicing on a small piece), i found in my experiements that the surface would not come to a high sheen with the sandpaper, i used water and tried a few different polishes too, but the dullness from the sanding could still be seen in certain light.....got to get it right before i move onto the table...

the EEE looks good but this has to be finished this weekend for the delivery guy to pick up Mon. so just using what i have at hand...

[kiwigeo]

Like Lucky I now use abrasive papers, and finish up with automotive polishing compounds if a mirror finish is required.

Check there's no silicone in the automotive polish youre using....

[durwood]

My background is in automotive refinishing so maybe I should clear up a few misconseptions.

The use of abrasive paper is to level the finish as the flatter it is the better gloss it is possible to get. What a spray painter does is:

*build up the primer/filler coats to as flat and imperfection free surface as possible. depending on the repair/new panel he needs to apply paints which will fill all lumps and bumps.

* He then rubs back using wet/dry or just dry paper with the aid of a guide coat. This is a light coat of a contrasting colour to the primer. Grey primer/ black guide coatred primer /white etc. Usually the paper grade depends on how rough the surface is, the smoother he applys it the finer the paper he can rub down with.

If you were preparing wood you need to work from coarse to fine the same way.

There is no point in rubbing with really fine paper if your next step is to apply something else which ends up rough again. There is no point in applying clear if the grain of the wood is so open it needs heaps of material to fill the grain (hense wood filler)

*what abrasive paper is doing is filing back the surface, you are putting into the paint/varnish etc scratches. Coarse paper removes the material quickly, following with fine reduces the depth of the scratch. You keep working to the finest paper so that when you switch to a compound /polish or wax you have very fine scratches to remove or fill.

On timber you have to have enough finish so that you can rub any low spots out without breaking through to the wood. Thats why a painter would not apply colour/clear until the scratches in the surface were so fine they would be filled easily by the material. You need to have rubbed the primer finally with 600 or above so that the colour could fill the scratches and build up finish on top. From there on you always rub with finer paper again 800 up to 1500 maybe 2000.

If you want to get a mirror finish on a flat surface this needs to be done with a backing block not your hands as the idea is to take off the high spots (like planeing). The block and paper also shows where you have touched the surface as it dulls any gloss. Once the whole surface is dull you only need to compound the scratches out left by the fine paper.

The finer the grade the smaller the scratches the less material you need to shave off to get to the scratch free finish. Compounding also wears away the coating so if you have deep scratches and you try to buff or rub them out you can still rub through to the wood if they are deep enough.

Automotive compounds come in two types. Silicon is not in these materials or any others that a painter would use. Compound only rubs the surface to a gloss finish, it leaves no material on the surface once you wipe it off you can paint again if you want, thouhg to be safe it would be wshes with a solvent. Polish/wax on the other hand is meant to apply a coating over the finish filling any marks /scratches and protecting the paint from dirt/moisture etc.

Compunds for lacquers (they have tripoli and pumice type grits in them). It is just a paste - grit, oil to glue it together, a cleaning agent, a chemical to allow the oil to mix with water as thats how its thinned down if needed.

Compounds for polyurethane type finishes are another matter they have in them fine grit the same as abrasive paper (aluminium oxide and others) and other chemicals which allow the compound to produce a gloss. polys are too hard for normal compounds which don't give a shine as good as the correct ones.

* Spray painters usually compound after 24 hours or less if the paint was baked. You can compound before final drying but it will loose some of its shine. After a week some paints are so hard it can be extremely difficult to get even the finest scratches out, its neally as hard as glass. If there was a mark it would be rubbed with fine paper until it was gone and then compounded again. No problem as long as there is enough material.

For Poly I would leave it 24 hours or more (don't forget if its cool allow more time) Usually the abrasive paper is rubbed wet not only does it stop the dust but the dust is toxic. Don't rub it dry unless you have a mask and the right dust extraction on your sander or near you when you hand rub.


You need to be careful on timber that you don't generate too much heat as the wood can not soak it up and you can blister the paint. You can even do this on metal which does draw away the heat if you don't know what you arte doing. Paint not completely is easier to burn.

Don't forget a coat of paint is not very thick sprayed material needs several coats to leave enough to work on. For lacquers its about 5 coats (that equals about the thickness of a piece of paper.) enamel/polys need at least 2 coats to get the same thickness.

This is only a rough guide:
A 150 grade paper scratch would be neally right through the coating with one pass
2000 would put a scratch about 5% into the surface.

You can get 20,000 grit paper which is so fine it works as well as the compound in producing a gloss

[Billylad]

Durwood that waas very informing.Thanks for your effort