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Stripping Techniques

DEVELOPING SOME SKILLS

This section deals with the basic skills we need to develop in order to undertake a varnishing project. The rest of the book will make repeated reference to this section so read it well. Much of the success of your project lies in the following pages of this chapter.

1. STRIPPING TECHNIQUES

The start of a project often includes the need to return the timber to its natural colour, generally because the existing finish is patchy. Perhaps there are areas of break down where it is thin or bare in spots and discoloured, or perhaps the grain is dark (or light) from a poorly executed job before. There are numerous reasons why we would choose to remove what’s there and start again.

a) Using A Scraper

The different types of scrapers have been listed in Chap 2, but it is pertinent at this stage to offer some tips on how to use them. My preferred scraper for stripping is a Skarsten 35 as it is small and light, fits easily in the palm of my hand and can be used one-handed, with the other hand holding the heat gun. All the long handled scrapers generally need both hands to control the scrape which is not convenient when using a heat gun as one has to continually put it down and pick it up, which slows progress a lot. If there is no convenient place to put it down while it is running it will have to be turned off and on constantly, which is also not good for the thermostat in the heat gun and means you need to wait for it to come back to full heat before it is usable again. More time consumed. Nevertheless, a long handled scraper is a more powerful tool and it certainly has application with chemical strippers and when ‘dry’ scraping is appropriate.

The scraper handle must be held firmly with the blade vertical to the surface, the direction of pull is with the grain, and the pull force should be as light as is possible. The harder you pull, the greater the opportunity to lose control of the blade, which will result in it skewing off at an angle and creating a scour mark.

Much of the skill in stripping therefore is in the timing – knowing when there has been sufficient heat for the varnish to lift easily, or with chemicals, judging accurately how well they are working so that the removal is easy.

If you are using a long handled scraper hold the handle firmly in one hand and put the other on the shaft. The second hand controls the downward pressure ie. depth of cut and also keeps the blade firmly to the surface preventing skews. The first hand controls the intensity, direction and length of the pull. It is important to understand though, that a lot of damage can be done very quickly with a scraper that is not properly controlled, so don’t rush at it.

b) Stripping With A Heat Gun

Stripping tools include your heat gun and extension cord, choice of scraper and possibly files for sharpening it, masking tape for the edges of the job, particle mask and your undivided attention.

Tape the edges of the area you are working in. Tape small areas at a time, and when completed the section, move on. If the edge of the tape is damaged remove it before moving on and you may consider applying a double tape, one over the other to also help preserve the adjacent surfaces.

With the heat gun turned on to its high setting play it over the surface. Don’t hold it in the same spot for any length of time – rather, move slowly over an area a few inches square and note how much time and heat is required for blisters to start to form under the coating. The perfect point at which to put the scraper to the job is just before the blisters start to form. At this temperature the heat has softened the coating sufficiently, so that with a firm hand and moderate downward pressure, pulling the scraper towards you with the grain, will remove the varnish, generally right down to the timber. Play the heat again to any bits that did not come off, scrape these and then move on to the next area.

I like a combination of high heat applied to a small area as being the quickest and most efficient method, as it allows the whole heated area to be removed before the surface cools, often requiring a single pass with the scraper and a single heating of the area before moving on. When blisters form it does tell you that the coating has popped away from the substrate, but it is a very short moment thereafter to a point where the heat will burn the timber, marking it. This is undesirable because the depth of the marking will need to be sanded out creating a low spot as well as more time and effort in sorting it out.

If the object that is being stripped has any radii, eg. like a cap rail which is flat on top but with rounded edges, be very careful to take a small bite with the scraper on the radius. At no point do we really want to remove timber, but on a radius it is very easy to do so, creating a series of narrow flat spots, all of which need to be faired later. You need a firm hold on the scraper when working a radius and it is wise to both shorten the length of the stroke and the width of the bite, as it is very easy to ‘run off’ the edge putting a deep score mark across the edge grain. To avoid this, the scraper must be at right angle to the surface and the pull stroke is at right angle to the scraper, so as you proceed around the radius, the scraper will move from horizontal to the vertical. If you do score the surface, it is best to remedy the situation immediately in case you miss it at a later stage and it remains forever in your face. Sharpen the scraper and pare away at the timber until the score has been removed. You now have a dish in the surface. Pare away at the outer extremities of the dish, flattening it out somewhat, then move on, with heightened awareness. When coating up you should remember to apply extra coats in this area and it may fill over time. Alternatively if the mark is very deep it can be filled with a UV stabilised wood filler then grained with stains. Either way, it is not a good look.

Scraping is always with the grain. An exception is around a fitting as it is often difficult to remove the final millimetre or two that is immediately adjacent to the fitting. Heat the area well and putting the end of the scraper to the edge of the fitting, work around the fitting using a soft touch with the scraper so there is no impression or mark left on the timber. Any scratch marks across the grain will be difficult to sand away. Be aware of the adjacent surfaces too, particularly if they are painted, as too much heat on the edge tape will penetrate quickly and blister the paint underneath.

A heat gun does not work well on multipack coatings in my experience. They are by nature far more resilient to temperature and even the concentrated heat supplied by the heat gun will often fail to get them to ‘pop’ at the substrate. This leads to a situation where one is tempted to linger longer in a single spot, in the hope that it will ‘pop’, but the only effect will be that the timber will be marked, literally burned. Some multipacks will soften somewhat, but their enormous adhesion characteristics often causes splinters of wood to come off with the scraper which is most undesirable for the flat surface we hope to eventually achieve. This softening will permit some progress and repeated heating and scraping to the same place will bring one eventually back to the sealer coat, but it is a long process. Once arrived at the sealer coat, heat has no further use, as the timber itself which has been penetrated by the sealer coat has to be physically removed. Doing this ‘dry’ with a scraper can have disastrous results, (particularly on timber with a confused grain,) which include pulling up splinters of wood from the surface. Doing it ‘wet’ has the best results I have found, and this method is explained in the following section – Stripping with Chemicals.

c) The Hot Sand

I acknowledge my good friend and fellow varnisher Tim Mitchell who showed me this many years ago. It is not Bondi Beach on a 40oC day. Unfortunately.

At the end of the stripping process there will be some residue of varnish left, particularly in the grain. One could remove timber with the scraper until that too is gone but this is wasteful and hard work.

Using the heat gun on high, apply heat to a small area, then with 80 grit silicon carbide sandpaper, either by hand or on a soft block, sand the surface with the grain. The softened varnish will roll out of the grain leaving the surface clean and ready for preparation.

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