Plywood Grading - Types of plywood

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When buying plywood from your local Home Depot, Rona, Lowes or other wood supplier, you might have noticed that all the plywood is "graded". The most common plywood grading scheme is from A to D, with A being the highest quality with zero blemishes and great sanding, and D being the worst with the greatest number of blemishes (allowed).

Grading also typically comes in pairs where each grade addresses a different side or “face” of the stock piece, ie one letter will address the quality issues of the front face and the second, the side opposite to the face. So for instance, an A-C plywood sheet would be highly finished on the front face with a relatively poorer finish on the back. Similarly, construction grade C-D (referred to as CDX) plywood, is great for structural use but not for projects requiring a high quality finish.

Bonding Types

Along with the plywood grading system, plywood comes in different bonding where each type is differentiated by the glue used to bind the layers (aka plies) of plywood. We’ll cover each in turn.

Interior Plywood
This type is made for interior use only, from hardwood and softwood species and is generally used in places where exposure to moisture is minimal, e.g. furniture, wall sheathing, cabinetry, etc. Interior plywood is available in most grades and comes in a variety of hardwood species like birch, oak and cherry.

Exterior Plywood
By far, much more sturdier and moisture-resistant than interior plywood, this type can be used outdoors and is easily available from local suppliers. Like its interior counterpart, it also comes in various grades—A-C, B-C and CDX are widely available—and hardwood species.

Marine Plywood
If you’re really looking for highly moisture-resistant plywood, look no further than Marine Plywood, which is both manufactured in top quality and uses the highest adhesives. And though commonly graded A-A for two highly placed faces, hardwood choices for exterior use (where the type would be most useful) are limited.

Structural Plywood
If you’re looking for beauty over brawn, this type is ideal although it is rarely found in a grade higher than C-D and is atypically used in construction sites (as concrete forms). Special resins are used to adhere the layers together and they are designed in such a way that the plies are less likely to separate.

Plywood Sizing
Just like hardwood and softwood sizes, plywood sizes can be just as confusing if not more. Although sheets are usually sold as 4’ wide, they may sometimes be found in 2’ and 5’ widths. Similarly, just as a typical plywood sheet’s length is 8’ they can also be found in 4’ and 12’ sizes as well as metric sizes. The variety can easily confuse the best of us.

And that’s just the beginning; the variation of sizes above will be a walk in the park compared to the thickness dimensions. Common sizes on the US market are ¼”, ½” and ¾”. That said, a ¼” plywood sheet is really 7/32”; ½” a 15/32” and ¾”, a 23/32”.

And though the 1/32” doesn’t seem like much, it can make all the difference when working with plywood. Consider this: a wood craftsman is constructing a bookshelf where a ¾” shelf is inserted into a dado cut into the shelf standards; the 1/32” gap will not only be noticeable, the dado will feel sloppy and unprofessionally handled. To counteract such a situation, the dado will need to be cut at 23/32”, ensuring a snug fit.

Lacquer Finishes

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For centuries, lacquer finishes have been used to give woodworking a long lasting, durable water-resistant finish. Lacquers are available in two styles: spray and brush-on, although they’re both among the fastest drying finishes. That said, brushing on a lacquer finish is more diligent and precise work and takes longer, but is also cleaner than spraying on finish.


What is Lacquer?

Lacquer tends often to be confused with shellac, which arises from shellac coming from the “lac” beetle. Lacquer, on the other hand, is derived from the resin of a varnish tree which is then harvested, distilled and combined with a lacquer thinner to create the common finish. Lacquer is also typically used with a variety of paints to deliver a strong, durable paint finish.

Today’s Lacquer

Lacquer today tends to contain another type of resin, nitrocellulose that combined with other ingredients, allows for a thin coat of lacquer to dissolve within an earlier coat which results in a hard, yet flexible finish. However, one disadvantage to the above is that nitrocellulose lacquer finishes have a high susceptibility to UV light.

Lacquer Application
As mentioned above, lacquer can be applied in one of two ways: sprayed on or brushed on. Spray-on finishes can be bought as aerosol spray cans or can be used with a pneumatic / airless sprayer. Though the former tends to be expensive, quality of finishes is also unbeatable, particularly for small projects. Also ensure that you work in a ventilated environment since solvents used in the lacquer are highly flammable and odours.

Brush-on lacquer finishes tend to dry quickly but not as fast as spray on lacquer. Start by using a bristle brush (preferably with high quality bristles) to apply the finish, but remember to work quickly by first adding a thin layer and not over brushing your work. Additional coats to even out the finish can be added in later.
One last thing: do NOT try to brush a spray-on application or vice versa, since spray-ons tend to dry faster.

Lacquer vs Polyurethane
An advantage to using lacquer finishes over polyurethane is that that for beginner woodworkers, they’re easier to apply, dry a lot faster and don’t need as many brush strokes for a complete finish. And though they may not be as long lasting as poly’s, they are a lot easier to reapply if and when anything happens. Additionally, lacquer finishes can also protect metals.

It is important to note, however that the two finishes don’t work well together; it is very much an either/or scenario.

The 10 Safety Rules Every Woodworker Should Know

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Woodworking is among one of the safest and enjoyable hobbies you can do, provided you adhere to a set of rudimentary and easy to follow safety rules. These woodworking safety rules are designed to be easy to remember and are mostly common sense. That being said, failure to comply with the safety rules can cause serious injury. The work shop is not the place to careless. It is the place to learn and adopt good safety working habits which will in turn make woodworking more fun and enjoyable.

1. Always Wear Safety Equipment
This might seem like a common sense kind of rule, but it’s an important one to remember. During usage of loud power tools like routers and surface planers, wearing ear protection is a noted advantage. Similarly, wear latex gloves while applying finishes. NEVER BE WITHOUT YOUR SAFETY GLASSES. These should be the first thing you reach for when entering the shop.

Sitting Bench Woodworking Plan Video

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" One of the most popular woodworking projects, for hundreds of years is the simple “Sitting Bench”. The bench is easy to make, can be used inside and outside for person or commercial uses and when finished makes an attractive and useful piece of furniture. In homes, in recent years, the sitting bench is seeing revival because it is such a useful item and lends itself to the kitchen, the living room, the bedroom, the entry and almost any other part of the house you can imagine.

The sitting bench we have constructed here is made from something called Cedar of Lebanon or “Cedrus Libani”. This species is native to the Mediterranean but is also introduced in some more temperate areas of North America where it is grown as an ornamental tree because of it's faster growing characteristics.

 

The main feature of our sitting bench is to have been able to “book-match” the top or seat of the bench just at the point where the sapwood and the heartwood meet, creating a beautiful contrast in wood tones. We were also fortunate to obtain some 2” thick wood from the same tree that allowed us to make the legs for the bench without having to laminate thinner woods together.

Our sitting bench design is attractive and useful and will provide years and years of accommodation for relaxing ones wearing bones. The version we have put together here is made without any mechanical fastening devices (no nails, screws, staples or pins). The unit was entirely put together with glue, which will hold it securely, under all normal use for many, many decades to come.

We also wanted to incorporate a bit of “character” into the bench which is why we selected some pieces with knot holes. We also rounded over all the corners on both the top, sides and legs so that even with constant use, there is little chance of anyone bumping themselves on a sharp corner.

Copyright Colin Knecht
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