Pore filing with sanding sealer

[Dave Bagwill]

From a longer article here: http://www.hoodfinishing.com/Literature ... illing.doc

I've not tried this so would appreciate your comments.

The excerpt:
When grain filling with a sanding sealer over open grain woods, apply a heavy double-pass coat with and against the grain. A double-pass coat constitutes first spraying with the grain, waiting 30 seconds or so then spraying against the grain or, in perpendicular direction from the initial coat. It does not matter whether the initial pass coat is with or against the grain, so long as the two pass coats are perpendicular to each other and closely as close equal in thickness. The purpose of spraying with and against the grain is to have the two 90 degree films flow into each other, providing better film characteristic and filling properties, particularly on porous woods. Allow the double pass coat dry at least two hours before applying the second double-pass coat. Do not sand the first double-pass coat. Apply a second double-pass coat in similar manner to the first double-pass coat. Let the second double-pass coat dry overnight - the longer the better. The extended drying time for both double-pass coats allows the latent solvents (tail solvents) to evaporate from the four films applied hence, providing better sanding properties and firm packing of the grain.

After the extended drying time, sand both coats down as far as possible without disturbing the stain. If filling natural mahogany, for example, sand the sealer coats all the way down to the wood grain. Use a 220 grit no-load sandpaper. This will pack the grain nicely and yield very good results. Machine sanding will pack the grain best, but riskier to burn through to the stain, if such exists. Unless you are filling oak or ash, two double pass coats of a heavy-bodied, high-solids sanding sealer will generally suffice to give you good grain filling results. On cherry, a single double-pass coat should suffice; two double-pass coats, however, would yield far better results.

If filling oak or ash, a third double pass coat may be necessary after the aforementioned sanding then sanded back down to the grain or as far as possible without disturbing the stain. Use 220 grit no-load paper or finer for this sanding. Giving this third coat at least two hours drying time prior to sanding will allow for some shrinkage and make sanding easier and pack the grain more effectively. Letting it dry overnight prior to sanding will yield even better results because of shrinkage and drop down.

Topcoat as normal with the finish and sheen of choice. It is not necessary to sand between the first two coats of the topcoat. However, sanding after the second coat is a must to remove imperfections, which will telegraph as added coats are applied.

Building a finish with sanding sealer rather than leaving its residue in the grain only must be avoided. First, to make them sand easier sanding sealers are soft by design, which will leave a soft base to the overall finish thus, susceptible to press marks and inferior mar resistance. Second, have lousy water, heat and alcohol resistance. Equally important, unless you are looking for that aged look in your grained filled finish, cracking of the finish within a year could also result. To achieve a crackled finish multiple coats of a soft sanding sealer is used (without sanding between coats) as an undercoat over an extremely hard topcoat. Moreover, that currently nicely filled finish will look much less attractive in about thirty days due to film shrinkage and dropping of the built up sealer.

When pore filling with a sanding sealer under pre-cat or post-cat lacquers or conversion varnishes, seal the sanded sealer with one to two coats (single pass) of a non-stearated vinyl sealer without sanding between the coats and after. Vinyl sealers are hard to sand but, more important, are highly flexible and offer excellent resistance to heat and moisture. Used under non-self-sealing pre-cat and post-cat finishes, nearly guarantees these high performance topcoats from cracking and chipping. As such, two coats are recommended and, be left in tact and not sanded. Any added staining or stain repair due to burn through should be done prior to applying the vinyl sealer coat(s).

[John Parchem]

"If filling natural mahogany, for example, sand the sealer coats all the way down to the wood grain. Use a 220 grit no-load sandpaper. This will pack the grain nicely and yield very good results. "

Am I reading it correctly that one ends up packing the pores with the residue from sanding the sealer back? It might just be poorly written where the "This" in "This will pack the grain ..." is referring to the spray process rather than the sanding process. I could not tell.

[Tim Benware]

"If filling natural mahogany, for example, sand the sealer coats all the way down to the wood grain. Use a 220 grit no-load sandpaper. This will pack the grain nicely and yield very good results. "

Am I reading it correctly that one ends up packing the pores with the residue from sanding the sealer back? It might just be poorly written where the "This" in "This will pack the grain ..." is referring to the spray process rather than the sanding process. I could not tell.

I had the same question but thought it meant the latter (spray process).

[John Link]

The problem with sanding sealer or any material that dries by evaporation is that it shrinks ... and shrinks ... and shrinks some more, 10 years down the road, even. Not really the ideal filler.

[ken cierp]

Ditto John Link, srinkage is the concern -- That is why Pore o Pac is such a good choice, the pores are being filled with tinted silica, the holes are leveled, gone! But is a PITA to use -- so bravo to the chem techs, Pacer Zpoxy offers the best of both worlds, does not srink over time, is clear (amber -- to the point that regular epoxies turn an awful yellow green) and best of all its has proven compatibility for use under most top coat chemicals.

[Dave Bagwill]

Easy to use? Non-toxic?