The cutting, bonding and trimming of high pressure laminates
Brent Plastics Cutting Service
When Brent Plastics Ltd provide High Pressure Laminates cut to the client’s cutting list we will always add at least 3mm to the required sizes to allow for trimming of the edges once the laminate has been bonded to a suitable substrate.
CUTTING BY THE CUTOMER USING HAND TOOLS
If a tungsten carbide tipped circular saw is not available for use High Pressure Laminates can be cut using hand tools.
A/. Hand Saw
Laminates should be cut with a sharp, fine toothed tenon or dovetail saw held at a low angle, the sheet should be supported on both sides of the cut as close as possible and over the entire length. If the saw is not sharp excessive pressure will have to be applied to make a cut and this could result in the sheet splitting. Scribing round pipes, mouldings, etc should be done with a coping saw.
B/. Scoring Tools
Alternatively, a tungsten carbide tipped Brent Plastics Laminate cutting knife can be used. The sheet should be laid flat on a firm base, decorative side up. It should then be scored with the Laminate cutting knife blade held against a thin straight edge using firm pressure and taking care not to accidentally scratch the decorative surface, this operation is repeated until the decorative surface is cut through revealing the dark brown core, the sheet should then be broken upwards against the edge of the rigid straight edge.
LAMINATING A SUITABLE SUBSTRATE
The best material to laminate onto is Medium Density Fibreboard (MDF).
B/. Plywood & Blockboard
Because of the un-evenness of the surface we do not recommend using either plywood or blockboard as a suitable substrate for laminating.
LAMINATING YOUR PANEL:
A/. Applying your edging.
Cut your edge strips 3mm wider than the core and apply with contact adhesive. When the adhesive is fully cured flush the edge strip to the surface of the substrate taking care not to angle the edge, this can be done with a router, plane or hand file.
B/. Applying the face laminate:
When laying the surface laminate make sure that there is sufficient overhang all round (3mm – 10mm is normal). After coating the substrate and back of the laminate with contact adhesive wait for the adhesive to become touch dry. At this stage the adhesive will only stick to itself (hence the name contact adhesive)
Place dowel rods or pieces of clean timber on the surface of the substrate and then positiion the laminate on top of the rods but not touching the surface of the substrate. Ensure that the laminate is positioned with an overhang all around and then withdraw the first rod pressing across the surface firmly, in a backward and forward movement, with a cork sanding block wrapped in a soft clean cloth.
Continue this movement gradually withdrawing the rods one by one, this will mean that no trapped air will be left between the laminate and substrate which is the most common cause of bubbling under the surface. When all the rods have been withdrawn continue with even heavy pressure across the surface of the whole board to ensure a good even bond.
Once the bond has achieved its full strength the overhang of the face laminate then needs to be trimmed back flush to the edge, this can be done by using a router, hand plane or file. to finish the edge a furniture scraper can then be used.
BONDING LAMINATES USING CONTACT ADHESIVES:
Contact adhesives are not the best form of adhesive system to use when bonding laminates, however in many cases there is no alternative than to use contact adhesives, if one is aware of the pitfalls, uses the correct substrate and carries out the correct procedures then a long lasting and good bond can be achieved.
It is important that when bonding with contact adhesives certain procedures are carried out correctly to obtain the best results, these procedures are as follows:
> The best substrate is Medium Density Fibreboard (MDF).
>Always spread the adhesive onto the substrate and the back of the laminate
>Only bring the two surfaces together when the correct tack – level has been achieved. A simple method of checking the tack – level is to touch the surface with the tip of your finger. The surface should feel tacky to the touch but there should be no stringing of the adhesive to the tips of the fingers, do not let the surfaces get completely dry .
>Always ensure that the adhesive is spread onto the substrate in one direction and onto the back of the laminate in the other direction , for example along the length of the substrate and across the width of the laminate, this will give a cross linking effect when the two surfaces are joined together.
>Too much adhesive will give a weak bond, the spread should be even and not too thick but must cover the whole surface of the substrate and the laminate.
>It is always a good idea to give the substrate a priming coat first. This should be a 50/50 mix of the adhesive and solvent which will give a watery mix that can be brush applied, this will seal the surface. Leave for a minimum of 12 hours to allow the mix to be completely absorbed into the surface of the substrate. This is particulary important when using MDF which can be very absorbent.
>Serrated spreaders of the correct tooth size should always be used. For a professional application we strongly recommend the use of the Brent Plastics KG150 Contact Adhesive Glue Spreader.
>After bringing the two surfaces together in the manner previously described firm pressure should be applied to the surface. We strongly recommend the use of the Brent Plastics hand held laminating roller. The use of the hand held laminating roller will apply pressure to the surface equal to the PSI pressure obtained in most cold presses.
ADHESIVE BOND FAILURES:
The two most common adhesive bond failures are bubbling and stress cracking.
Adhesive bond failure, commonly known as bubbling, may occur in conditions of high humidity or wetting if there are weak areas of adhesive bond (usually associated with hand applied contact adhesives). High instances of bubbling also occur when plywood or blockboard are used as a substrate.
If the Laminate has been bonded in normal warm/dry conditions using contact adhesive and the panel is subsequently subjected to high levels of humidity, the laminate will expand. The amount of creep will depend on the panel dimensions (the larger the panel the greater the movement), and if there is a weakness in the bond the laminate will lift from the substrate. This will be seen as bubbling, to reduce the risk of bond failure (bubbling) the following measures should be taken.
1 – If possible avoid the use of contact adhesives if the panels are to be installed in wet areas or areas of high humidity
2 – If there is no alternative to using contact adhesive the panel widths should not exceed 600mm
3 – To minimise dimensional movement, the longest dimension of the panel should be cut in the length direction of the laminate sheet, i.e. parallel with the sanding lines. (Laminate movement is approcimately twice as great across the sheet width as it is along the length).
4 – The Laminate should be pre-conditioned in temperature/humidity conditions similar to those of the final installation, for at least three days prior to bonding.
5 – It is inadvisable to use contact adhesive when plywood or blockboard are used as the substrate. Contact adhesive has no filler and therefore is not a gap filling adhesive. The surfaces of plywood and blockboard are sanded with drum sanders, this leaves minute highs and lows on the surface which contact adhesive is unable to fill, as a consequence small pockets of air become trapped under the laminate surface. As this air warms up it has no where to go and the pressure breaks the bond and forces a bubble onto the surface.
B/. Stress Cracking.
Laminate is a paper based material and therefore expands when wet and shrinks when dry. Consequently, in conditions of low humidity caused by central heating, localised heat sources or hot air vents, shrinkage may occur which can result in cracks at sharp internal corners.
Stress cracking is the result of tension stresses set up when dimensional movements of the laminate and of the substrate to which it is bonded are different in either rate or direction. Stress cracking most often occurs when contact adhesive is used.
To prevent stress cracking the following measures should be taken.
1 – Internal corners of apertures and cut outs must always be smoothly radiused to as large a radius as possible, with 5mm radius minimum. This radius should be increased as the side lengths of the apertures are increased.
2 – When screwing through panels oversized holes must be used with screw caps to ensure that the fixing screw does not impinge on the laminate.