Always undertake any base repairs prior to base tuning. If the damage will affect the smooth action of the side edge guide sliding down the base then the repair will need to be made prior to edge tuning.
Skis to be repaired should be dry & not cold, say at room temperature.
Clean the affected area with base cleaner to ensure proper adhesion of the repair.
Score/rough up the inside of the hole for good adhesion. A Stanley knife or razor blade is good for this.
For deep repairs, ‘undercut' the edges of the hole so that the molten p-tex flows underneath. This also ensures good adhesion.
Use masking tape to protect the base around the repair site & place a metal scraper flat on the base next to the repair site.
If possible, warm/heat the damaged area of the base to minimise the temperature difference between the molten repair candle & the base to obtain better adhesion. A hair dryer is good for this.
Light the p-tex candle* & hold over the metal scraper & allow to drip on the scraper until the flame is blue (no carbon) & the p-tex is running.
Move the candle over the repair site & drip in the p-tex. It's best to keep slowly rotating the candle in your figures to minimise carbon deposits & hold the candle about 6/7mm above the base for ensure accurate placement of the drips. Slightly overfill the hole in width & height to leave a slight dome & leave to fully cool. Deep holes may require 2 or 3 layers, leaving the previous layer to cool.
Use a metal scraper to scrape off the excess p-tex. If you're carefull you could use a chisel, hand surform, base rasp or craft knife/razor blade to remove excess p-tex from the repair. Start from the middle of the repair & work out to minimise the risk of pulling out the repair. A useful tip when using the metal scraper is the more vertical you hold the scraper the less it will cut. The metal scraper acts as a true bar or a straight edge across the metal edges of the ski to ensure that the repair is level with the surrounding base material.
If the repaired area is significant in size then use a steel brush or structure tool to impart structure to the repaired area, although a gentle rub with some medium/fine sand paper works well. Then tune the base as described under the Base Tuning section.
* P-tex candles are only readily available in either clear or black which is a problem if your skis have coloured bases. Some skis have what appears to be a coloured base but it is infact a clear base over coloured/patterned sheet. Your skis are tools to be used so don't get too hung up about having bases that look like a patch work quilt after a few repairs - just think of them as battle scars!
Another thing to remember is that whilst a DIY base repair can be as strong & functional as a store repair it probably won't be as good cosmetically as a store will usually belt grind the skis after undertaking the base repairs to smooth them off. Whilst this gives a great finish it's just removed half a mm off your bases!
Advanced Base Repairs
For better adhesion, ‘weld' in a flat p-tex repair stick using a ‘Base Doc' tool (it looks like a soldering iron) or a repair pistol (like the RP105 or RP360 Skimender repair pistols) preheating the surrounding p-tex first until ot softens before applying the filler. Deeper holes can be filled in one go when welding.
Major Base Repairs
For major damage that penetrates the p-tex through to the core of the ski (know as ‘core shots') or is close to the edge it's necessary to weld in a ‘foundation' layer prior to applying the p-tex. For this you use a product called Metal Grip which is available on a roll or in cut lengths. Metal Grip is a co-polymer wire of resin & polythene. It will bond to most materials at a lower temperature than p-tex. It's the ideal 'foundation' material for repairing major damage to bases where in the past only a patch might have been successful. Metal Grip has to be installed using either a Base Doc tool or using the hot tip/plate of the repair pistol. DO NOT put Metal Grip wire in a base repair pistol as if it was a p-tex rod, just use the hot tip of the pistol to apply it.
Thoroughly clean the base in the affected area with wax remover. Rough-up the inside of the gouge & undercut the edges if possible. Use the hot tip of the Base Doc/pistol to melt/spread/weld a thin layer of Metal Grip over the exposed area. Let the area cool completely - 10 minutes will do it. Complete the repair with a top coat of p-tex. Finish the repair in the normal way.