A sanding sealer is simply a thinned version of a lacquer- or varnish-based finish that has been modified with zinc stearate or a resin (usually vinyl). These additives make the finish easier to sand and give it better “holdout,” which is the ability to make subsequent coats lay out smooth.
Sanding sealer is lacquer or another basic coating that contains zinc stearate. As a soft, fluffy soap, stearate gives the lacquer loft, allowing it to build up faster and fill in pores more efficiently. As well as softening the lacquer, it acts as a lubricant, so that its powders come off easily.
In fact, it's actually better NOT to use a sealer. The sealer is used only because it's easier to sand. Zinc stearate, the material with which the sealer is loaded so that it is easier to sand, softens the film and decreases the water resistance of the lacquer topcoats.
It is used before finishing with either gloss or flat lacquer. It requires less sanding and has good sealing and hold- out properties. PRINCIPAL USES: It is ideal for interior sealed wood such as furniture, store fixtures, cabinets, doors, and panels.
Sanding Sealer is not recommended as a final finish because it is not as durable as a topcoat. Seal Sanding Sealer with any General Finishes water-based topcoat, EXCEPT General Finishes Enduro- Var, for improved water and chemical resistance.
Ingestion May cause nausea, headache, dizziness and intoxication. Skin contact This product is rapidly absorbed through the skin and may cause symptoms similar to those of ingestion. Repeated exposure may cause skin dryness or cracking. Eye contact Causes serious eye damage.
“As for a sanding sealer, I usually just use shellac. Typically a 1 lb cut. There are two ways to do this. I either buy pre-mixed shellac (Bullseye SealCoat), and dilute it from 2lb cut to 1lb cut.
Regular readers will know that we do not recommend over-thinning the Cellulose Sanding Sealer; it's a common myth that it needs to be thinned 50/50 to work better, but as a general rule this is incorrect.
But polyurethane doesn't bond so well over finishes marketed as sealers, especially over sanding sealer. This sealer is good for use under non-polyurethane varnishes because regular alkyd varnishes gum up sandpaper. So to speed production, a sanding sealer can be used for the first coat.
Whether you're painting floors, tabletops, or bar tops, achieving a good lacquer finish is really important. Not only will it protect your surfaces for years to come, but it can also greatly improve the look of the finished product too.
We recommend no more than 1-2 coats, then finish with 1-2 coats of topcoat.
When to Use Sanding Sealer. Sanding sealer should be used after the wood has been sanded down to a bare finish but before the topcoat (such as paint) has been applied. Applying sanding sealer to a stained surface is generally not recommended, as the sanding step will scuff away the stain.
At least three lacquer coatings will work best if you want your wood piece to be protected and last for a long time. Sand with a very cautiously and precisely fine-textured sandpaper. You must wait between each layer of lacquer you put on your wood object.
How to Sand Lacquer. If you're hand sanding lacquer, start by wetting the surface lightly and using 320- to 400-grit sandpaper to smooth the surface until you see your desired sheen and finish.
The thin viscosity makes it easy to spread and allows it to penetrate into porous woods. To start apply 1 thin coat and allow it to dry. Lightly scuff sand to remove any raised grain fibers, then apply an additional 1 to 2 coats to seal wood and provide an excellent surface that will be ready to topcoat.
Expert Tips For an Extra Smooth Finish:
A sanding sealer is not the same as a wood conditioner. Whereas a wood conditioner is a pre-stain treatment that reduces blotchiness when staining, a sanding sealer is applied only to bare wood that is not going to be stained.
A sanding sealer must be applied after the stain but before the finish coat because otherwise it would prevent the stain from penetrating.
To give the subsequent poly layers something to bond to, sand lightly between coats with 320-grit sandpaper wrapped around a hard block.
Allow the second coat to dry 1 hour before sanding lightly and applying a finish coat. Brush Application – For best results, use a natural bristle brush. Apply the sealer to the surface using long and even strokes, brushing back into the wet material to maintain a wet edge.
The main difference between an undercoat, sealer, and primer is that primers are applied to new surfaces, while sealers are applied before a primer or as a substitute for a primer. An undercoat is typically used on a surface that was previously painted.
Interior Oil-Based Sanding Sealer will dry to touch in 2 to 3 hours and can be sanded after 3 hours or when sanding sealer is thoroughly dry. Using a cleaning solvent, such as paint thinner or mineral spirits, is recommended for cleanup.
Types of Sealers
Sealers, from left, include oil-based fast-dry sanding sealers, shellac sealer in clear and pigmented forms, primer for paint, lacquer-based vinyl and stearated sanding sealer, glue size, and water-based sealer.