Blockboard: Sizes and Uses

Blockboard, like hardboard, is bonded under high pressure. The glues employed limit its use to inside work.

The most common blockboards are made from rectangular strips of softwood, bonded edge-to-edge to form a core which is sandwiched between single or double veneers of birch.

Blockboard veneered with West African mahogany is available in complete sheets from some timber merchants.

The most common sheet size is 2440 x 1220 mm, but others (1830 x 1220 mm, 2745 x 1220 mm and 1305 x 1220 mm) are available and cut sizes can usually be obtained.

The following sizes are less easily obtainable: 2440 x 1525 mm, 3050 x 1525 mm, 3660 x 1220 mm, 3660 x 1525 mm and 4880 x 1525 mm.

Thicknesses are available at 12, 16, 19, 22, 24 and 32 mm also made, but not easily obtainable in some regions, are sheets 38, 44 and 50 mm thick.

The core material runs the length of the sheet, making it stronger in its length than in its width. The grain of the veneers runs across the width. Single-faced boards have one veneer on each side, double-faced boards two.

Make sure, when using blockboard for table tops and large doors, that the core runs the length of the table top or from top to bottom of the door. The finished job will have less tendency to bow.

Movement

Blockboard can twist, bow, shrink or expand slightly, but careful attention to storage will reduce the risk of movement.

Shrinkage of more than 3 mm in 1200 mm (1/8 in. in 48 in.) is exceptional. Movement in the thickness is slight.

Shrinkage is more noticeable with the birch veneer than with the mahoganies. The birch also tends to ‘check’ into a series of fine lines. This checking is more of a problem with single-veneer boards, where the veneer is thicker, than with double veneers.

Storing

Never lean board against a wall. Lay it flat if you can; if space will not allow this, stand it on its edge as near to the vertical as possible. Do not lean anything against it.

Should the board become bowed or twisted, correct it by applying a load.

Covering

Painting one side of a sheet of blockboard creates surface tensions which pull it into a curve. By painting both sides, the surface tensions are equalised and the board keeps its original shape.

The same principle applies to papering, face veneering and polishing.

Edges

Lip all panels on exposed edges, as they are difficult to clean up to a good finish.

Use softwood lipping for painted work, matching hardwood for boards which have been faced with a decorative veneer.

Decorative veneers

Blockboard can be bought with a decorative face veneer which has been bonded on after the board has been made.

Face veneers are bonded so that the grain runs in the direction of the core: ie. with the length of the sheet.

Unless specially ordered, face-veneered boards will have the selected face veneer on one side only. The reverse will be veneered in a cheaper timber, often one of the cheaper mahoganies. Delivery of teak, oak and mahogany is usually quite prompt, if not from stock. But other veneers may have to be ordered and could take some weeks to arrive.

Laminboard

Laminboard has a core made from strips of softwood narrower than those used in blockboard. Otherwise, the two boards are constructed in the same way.

One of the advantages of laminboard over blockboard is in the surface finish of its face veneers. The core of blockboard often registers its pattern, seen as a regular ripple, through the veneers. This is known as ‘telegraphing’ and is not always visible until a high finish is put on the outer face. Double-veneer blockboards are less likely to telegraph, and the chance of this happening is reduced still further in the smaller core stock of laminboard.

27. June 2011 by admin
Categories: Timber, Woodworking | Tags: | Comments Off on Blockboard: Sizes and Uses

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