Prepare woodwork for painting
Why do you prepare woodwork for painting
The reason you prepare woodwork for painting is to provide adhesion and an excellent finish. The secret to good decorating is to make sure you have excellent preparation in the first place. This is what we do so spend your time doing this right and you won’t go far wrong.
Types of glass paper
Glass papers the main type of sundry that we would use to sand down woodwork with. The reason to use glass paper is to rub out any previously poorly painted brush marks and to provide adhesion for the next coat of paint.
You can also use sanding sponges and these come in a variety of grades.Usually, the higher the grade the finer the glass paper or the sanding sponge. Glasspapers start at 16 grade and go up to about 1000 grade. Sanding sponges are more suited to a previously painted finish that requires a light rubdown and have a professional painted finish before hand. Glasspaper is tougher and therefore is more suited to woodwork finishes that have been poorly painted.
On a standard previously painted finish I would use 120 grade glass paper or sanding sponge. I would go with a lighter grade say 180 if the finish is much more professional and requires less sanding down.
When I was an apprentice we had to prepare woodwork for painting by hand. Nowadays, I do it by using a palm sander. You either make holes in the glass paper where the holes correspond to on the sander backing pad, or you can buy the pads with holes in.
These pads have holes in them which allows the dust to go through and you attach your sander to a dust extractor or trade vacuum cleaner. Using a dust extractor is much healthier, it also requires less cleaning up at the end of the day so they are worth investing in if you’ve got quite a bit of decorating to do.
Most paint finishes are used today are water-based. Adhesion primers allow water-based top coats to stick to previously painted oil-based finishes. You would still need to prepare the woodwork as previously mentioned above by using glass paper to get a good finish. And to make sure the water based topcoat adhere to the previously painted oil based finishes. This is a belt and braces approach and I would recommend it.
My preferred adhesion primer at the moment is Tikkurila Otex Akva. This adhesion primer is water-based, levels out well and dries quickly. There are other adhesion primers like Caparol Haftprimer, which also perform very well. Another adhesion primer I have used is zinsser bullseye 123. Zinsser bullseye 123 is available from most shops. The other adhesion primers (Otex and Haftprimer) I have mentioned are trade primers.
Adhesion primers should be your first coat of paint over oil based surfaces. They provide a tough grip to the existing surface. One way to test this is to do what’s known as the ‘scratch test’. The scratch test is to use your fingernail to scratch the surface once the adhesion primer has been painted on and is dried. If the paint ‘scratches’ off adhesion is not very good. This coat of paint is the most important coat of paint. If the adhesion fails, the top coats fail also
At the danger of repeating myself, prepare your woodwork for painting in the correct manner is the most important part of decorating.
Types of fillers.
There are two types of main fillers I like to use for woodwork. These are wood fillers and fine surface fillers. Wood fillers can be single pack or two pack fillers. Single pack wood fillers are either ready mixed or you have to mix with water. French filler manufacturer Toupret, do a very good single pack, water based wood filler.
Two pack fillers are usually solvent-based that you have to mix with the hardener and these go very hard once mixed. I prefer to use 2-pack wood filler as it dries very quickly and can be shaped. These are ideal for filling structural screw holes and areas where soft filler doesn’t work well.
You can apply 2-pack wood filler either before the adhesion primer, or after you use the adhesion primer. Sometimes, I do both. I usually fill the obvious big holes first. After you use the adhesion primer, more defects show up due to the painting process and sometimes a second fill is required using the two pack.
Fine Surface filler is usually used after the first coat of your preferred top coat is painted. Fine surface filler allows you to fill very small defects that show up after the first coat of top coat of paint has been applied.
The process of preparing with the filler is to stare at the surface, fill, paint, stare again, fill again, paint and to continue in this fashion until you achieve the correct look. Most people never achieve the professional look because they can’t be bothered to go through this process. But again, preparation is everything.
What is caulking? Caulk is a filler that comes in a tube and is placed inside a caulking gun. The filler is squeezed out of the tube by pressing the trigger and is dragged along in straight lines. When I was an apprentice we had to do this process by hand using our finger with powdered filler. This wasn’t ideal as powdered filler is not the best filler to use for this process. It also gave you sore, red raw fingers!
Caulk is applied along the tops of skirtings and down the sides of architraves. It can also be used at the top of walls where it meets the ceiling. Anywhere in fact where timber meets a plastered area or where plastered areas meet each other.
Caulk is flexible in nature and therefore should be used where cracking can easily occur. Caulk can be over painted in an hour although I’ve done it much quicker than this.
Primers, stain blockers and shellac knotting.
New, unpainted timber always require priming prior to any top coats been applied. Most primers today are water-based, acrylic primers. Years ago we always used to use oil based primer or we used to thin out oil based undercoat to use as a primer.
Stain blockers are usually oil-based, although that are some good water based stain blockers out there today. Stain blockers are used sometimes on previously painted woodwork that have got a high level of nicotine or other staining like water stains, that would bleed through the paint work when you apply your finishing coats.
Common stain blockers like Zinsser cover stain or BIN are generally used. Good, old fashioned oil based undercoat is still one of the best stain blockers out there.
The ultimate stain blocker is aluminium primer. This primer is mostly used for highly resinous timber like American redwoods.
Shellac knotting is excrement from the Lac beetle. This is mixed with denatured alcohol (methylated spirits) and is used to block the resin from knots.
This is applied to new timber and generally two coats should be used. It dries very quickly and is a reversible coating.
Reversible coatings are coatings that can come alive again, when used with their solvent. So you can rub denatured alcohol over the dried shellac knotting to liven it up and take it off.
Top coat finishes.
Top coats usually come in 3 types of finishes, eggshell, satin or gloss finish. Eggshell is a semi-matt finish. Satin is a semi-gloss finish. Gloss is obviously is a gloss finish.
All paints manufacturers do all of these finishes. I prefer to use the Tikkurila Helmi range. Although other top quality paint manufacturers like Benjamin Moore, Little Green etc do some very good finishes as well.
Due to health and safety concerns most finishes are water-based. You can still get oil-based finishes, but these are slowly being replaced by water based.
I prefer to spray water based finishes. These finishes dry very quickly and leave a great finish once sprayed. Brushing water-based is more difficult to get a superb finish compared to oil based. Oil based as a finish is much better than water-based with brushing. This is all down to technique in my opinion.
If brushing water-based you need to change the technique from the oil based technique of laying off. You also need to add paint conditioner to the water-based paint to keep the open time longer. The open time is the time it takes for the paint to dry. Water-based paint dries sometimes far too quickly to get a great finish. Paint conditioners sort this problem out.
Also using microfibre rollers sleeves on woodwork can sometimes leave a finished that is almost spray like. When I was an apprentice using rollers on woodwork was a massive no no. How times have changed.
This is how I prepare woodwork for painting. Follow this process and you will not go far wrong.