Brush marks are usually due to lack of skill on the part of the operative,
but there are occasions when the paint itself is to blame.
The brush employed may also be partly responsible. It is well known that most brushes need" breaking-in" before they are at their best, and every painter should know how to prepare a new brush for use as well as how to take care of it during its active life.
Brushes which are neglected and are not properly cleaned after use, or are allowed to rest on their bristles instead of being kept properly suspended in a brush-keeper, are not only the cause of" nibs" or "bittiness," but lose the elasticity which is one of the signs of a good-quality tool.
One of the essentials of good painting, therefore, is a high-grade brush, maintained in first-class condition, and much of the poorly finished paintwork which one sees can be traced to the use of a cheap, coarse-bristled brush, the purchase and use of which represent the falsest form of economy for the decorator.
Different types of finish necessitate differences in technique so far as application is concerned, and it is rare to find a painter who is equally proficient with them all Broadly speaking, finishes may be divided into two main types: " flowing" and "non-flowing"; the average enamel being typical of the first and the ordinary oil paint of the second. Before brushing on any finish, it is highly necessary to determine to which class it belongs, for on this fact depends the manner in which the brush should be manipulated. "Flowing" paints find their own level and must not be worked or worried too much; "non-flowing" paints need just the opposite treatment.
Brush Marks in Oil Paint.- The rule in the application of oil paint is to put on as little as is necessary to cover the surface, and to brush it out thoroughly, as if it were worth its weight in gold. It must be crossed and finally laid off, and the final result should be a beautifully smooth surface with no evidence of brush marks. If any appear, they are probably due to one or more of the following causes: (a) too much paint applied and insufficient brushing out; (b) brush too coarse in bristle or not sufficiently flexible; (c) brush too fully charged with paint when laying off; the completion of the process should be done with as light a touch and as dry a brush as possible.
Brush Marks in Enamel.- The principle in the application of enamel is to spread the material as evenly as possible and to allow it to flow out to its own level. Paints which flow out of their own accord usually set more rapidly than the non-flowing variety, and it is essential to find out how long they remain" open." Brush marks are probably the result of: (a) the use of a coarse-bristled brush which separates the paint too firmly for the ridges that it forms to flow together again; (b) failure to keep the edges " alive," with the result that the join shows up; (c) attempting to layoff after the finish has begun to set.
Brush Marks in Distemper or Water Paint.-The quality of the brush is exceedingly important if a good, smooth finish is to be obtained, and the cheap variety, which usually contain fibre, should be avoided. Distemper should be put on with a fully-charged brush and any marks which may be left can be attributed to one or more of the following causes: (a) distemper insufficiently thinned and consequently over-pigmented, so that the pigment portion" piles-up" under the brush; (b) surface too porous or " hot," so that the distemper sinks in too rapidly to allow time for proper laying off; (c) failure to keep the edges" alive" and wet.
Brush Marks in Flat Wall Paints.-Modern flat wall paints have a high pigment content, bound in a medium which helps to promote flow after application. If the surface is properly prepared and the flat wall paint put on with ordinary care, no marks should be left, but should they occur, they can be put down to (a) too absorbent a ground, or (b) over-brushing. If the porosity of the surface has not been sufficiently satisfied, the liquid portion of the paint will be absorbed before the latter flows together and levels out the marks. Too much brushing, moreover, brings the liquid to the surface and tends to leave a gloss spot.
If the finish in which they appear is allowed to dry and harden, there is no remedy for brush marks, other than rubbing down and repainting, and it may be observed that the rubbing down should be very thorough, since, if any traces of the marks are allowed to remain, they will occur, also, in the new finish.
The most practical manner of eliminating brush marks while the finish is still wet is by means of a stippler.