In repainting a surface that has been painted, varnished, enameled or stained a number of times, it is important to know the character of the surface to be finished, the kind of work that can be satisfactorily done over it, also necessary to know how to properly prepare the surface to receive the finish, as well as to know that certain kinds of work cannot be successfully done over numerous coats.
Flat white and enamel cannot be applied over numerous coats of oil paint, as they will turn yellow and are liable to crack. Grained work cannot be successfully done over an enameled surface, as the surface is so hard and brittle that when oil graining colors are used, it is liable to break loose, chip, crack or check. A surface which has been enameled cannot be successfully refinished except in enamel. The only satisfactory way to remove enamel is with paint remover or to burn the surface.
Painting cannot be done over numerous coats of varnish without danger of checking or cracking, therefore the varnish should be removed before the paint is applied. Where numerous coats of oil paint have been applied and are of a spongy character or have not dried solid, the surface should be burned or the paint taken off with a paint remover. If the surface is cracked or alligatored, it should be cleaned to the wood with a burning lamp or paint remover. If the work is badly cracked and will not permit of burning, it should be painted in flat color. Cracks will not show so badly finished in flat as in gloss.
Where oil paint is to be used over old work sandpaper the old paint to a smooth surface and apply a coat mixed with half turpentine and half oil. If more than one coat is desired, the second coat can be applied of the same paint mixed to a heavier consistency; however, one coat is usually sufficient over old paint. It is not necessary to apply extra coats if the color used is of a similar shade to the old paint. A well covered surface can be made with one coat. Avoid applying more paint than is absolutely necessary to produce a solid finish.
If the work is to be refinished in gloss, clean the surface and sandpaper or rub with steel wool to a smooth surface, then apply one coat of enamel or gloss finish as directed for new work, finishing coat.
If the work has received two or three coats of oil paint which have dried solid without signs of cracking or cheeking, it can be repainted with fair results if first sandpapered smoothly, then covered with a coat of paint mixed flat. When this is hard dry, apply a second coat if necessary; however, if the one coat will produce a satisfactory finish, it is all that should be applied. If an enamel finish is wanted over this same surface, the enamel can be applied over the flat color. The first enamel coat should be reduced with a pint of turpentine to a gallon of enamel. When hard, rub the surface with fine steel wool to cut the gloss and level the surface, then apply a smooth, even coat of enamel, using a full brush and flowing on the enamel. This can be rubbed or left in a gloss finish.
If the work is to be painted or enameled white and the surface has received numerous coats of oil paint and good results are expected, the old paint will have to be removed. Then the surface, if thoroughly cleaned and sandpapered, will be in good condition to receive paint and should be treated in the same manner as new work which has not been sized.
To enamel over a varnished surface, it is very necessary to remove all of the varnish. The ground work for enamel should be built up with a portion of the enamel or a good mixing varnish added to each coat. The paint should be mixed flat, with the enamel or varnish added. The first coat should contain from 1 pint to 1 1/2 pints of enamel to a gallon of paint. Apply the second coat of the same mixture of a heavier consistency. Each coat should be thoroughly sandpapered or rubbed smooth with steel wool before applying another. The third coat can be applied with a good enamel reduced with a pint of turpentine to a gallon of enamel. If a deeper luster is wanted, apply a heavy coat of enamel of the original consistency. This can be rubbed to a flat finish or left in the gloss. If the enamel used is of good quality and the undercoats of varnish are not of a cheap rosin quality, this work will not check nor crack.