Thursday, 10 August 2017

How to make a tabled lap joint using a router

Need to create a long board? You have pieces of lumber that are shorter and want to join them to create a longer piece and it is load bearing? You need to create an end to end joint, and also provide enough surface area for gluing. The best way to do this is create an overlap joint. One of the best lap joints is a tabled lap joint. A tabled lap joint combines the strength of interconnecting parts with the large glue surface of a half-lap joint.

Refer this article for more on end to end joints :

The techniques shown in the above link rely mainly on having a table saw and is meant for smaller work pieces. Now, if you do not own a table saw or that the pieces are really long, say 8 feet long and you want to create a piece that is say 14 feet long, it is not practical to use a table saw. The same joint can be accurately created using a router.

First off, measure and mark 1/4" + the width of your work piece on both the pieces by placing them next to each other and marking them simultaneously.

Fit a 16mm slot cutting bit in the router. Measure the offset from the end of the slot cutting bit to the guide on the router bottom plate. Mark the offset on the wood.

Note the "router offset"

Fix a fence on the router offset, so that the router does not cut beyond the joint.

Fence fixed on the router offset

Adjust the depth of the router to 1/3rd the thickness of the work piece. For a 1.5" board, adjust the depth to 1/2". You can use a 1/2" ply as a reference.
Starting at the end of the board, run the router throughout the area that has to be removed.

Sand the surface after routing to get a more even surface for the glue to adhere.

To create the dado, mark half the width of the work piece on the newly formed lap. Set the router depth to 2/3rd the thickness of the work piece. Now for the tricky part, the router does not have a level surface to sit on, the lap is lower than the work piece thickness. So, we use the 1/2" ply that we used to gauge the depth of the router bit to create a level surface and then run the router. This will create the tabled lap on one of the work pieces, repeat the same on the other piece.

Now, align the joint and trim the excess wood we left on originally. Generously apply wood glue on the surface of the lap and strongly secure the the joint.

The Finished Joint

You can buy the tools used in this tutorial @

Sunday, 6 August 2017

Polymers in Construction Chemicals

Construction chemicals are the gift of modern chemistry to the civil construction and waterproofing industry. These chemicals make things that were previously thought impossible, possible. You can waterproof your roofs, construct terrace gardens, design swimming pools on the 10th floor, build retaining walls 100 feet deep, huge underground water tanks, fill gaps without using cement, all because of these chemicals and polymers.

There are a number of brands claiming market leadership in construction chemicals, but the bottom line is they all market various chemicals and additives under different names. The underlying chemicals are the same only varying in degrees of concentration, commercially termed as "solid content". Higher concentration of the active ingredient is indicated as a higher percentage of solid content.

The chemicals largely used are acrylic, latex, epoxy and polyurethane.

Acrylic is used where a UV resistant product is required. Typically acrylic is used in coatings for exterior walls and roofs. Binders used in plaster-crack-fillers are often acrylic polymers. Acrylic polymers bond well to cement and other porous substrates and have good film forming properties. Acrylic binders combined with polyester fibres create an even tougher film that is resistant to cracking with exposure to the elements. The acrylic polymer is also available as a solution that can be used as a binder along with white cement or ordinary Portland cement to create a waterproof coating that is used to coat bathroom floors before laying tiles.

Latex also know as SBR (Styrene Butadiene Rubber) is available as a solution. It has excellent bonding with cement and porous surfaces and is often used as a bonding agent. It is not UV resistant and needs protection, as it quickly deteriorates on exposure to sunlight. The strong point for latex is bonding. Cement with aggregates, water and latex create a superb repair mortar that has universal applications in repairs such as spalled concrete, broken and cracked plaster. Repairs with latex modified mortars, just stick! To create a bond slurry, mix cement with water and latex and bond bore packing to pipes, screed to mother slab concrete, old concrete to new concrete.

Epoxy. Sets like stone. It is what is used in MSeal and other epoxy putties. Epoxy tile grouts seal tile joints permanently. They are acid resistant, water proof and have excellent strength bond strength. Epoxy is also used as a bonding agent to join old and new concrete slabs. Epoxy is the chemical used in adhesives such as Araldite and Loctite Tough.

Polyurethane is another UV resistant polymer and is available as a single and a dual pack product. Polyurethane(PU) is highly elastic and has excellent bonding to most construction substrates. PU is used in sealants to seal construction joints and expansion joints. PU foams are used to fill, seal and insulate. PU foams are used to install door and window frames and as an insulating material in cold climates. PU foams are also used in bore packing, electrical duct insulation and sealing. PU coatings are also used to preserve wood and metal, also as an automotive finish.

Other chemicals such as polyester also find use in construction to anchor rods in concrete and as body fillers in automotive refinish.

These polymers have revolutionised the construction industry and have lead to more efficient and long lasting structures.

For a range of construction chemicals in India, visit

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Tuesday, 1 August 2017

How to Stain Wood

Wood by itself is a thing of beauty. But in many situations, we need to dress up wood to meet the aesthetic and practical requirements of its design and environment of use. Staining wood is the first step in dressing it up. Make pine look like teak wood or wood look like green bamboo, there are innovative ways to achieve striking results.

There are many schools of practice on how to stain wood. Let us look at some traditional and modern methods each have their own pros n cons.

Traditionally in India, wood is stained using powder pigments. These powder pigments are often chalk powder based and it involves mixing of raw pigments such raw sienna, burnt sienna, burnt umber etc with porbander chalk powder. These are then mixed with dispensing media such as French polish, sanding sealers or solvents such as methylated spirit and applied on the wood using a cotton rag. This method hides most imperfections on the wood and is suitable to any type and colour of wood. Unfortunately, along with hiding the imperfections, it also hides the natural grain of the wood giving it a pasty appearance. This method is suitable only for hand polishing or French polish. The stain thus obtained cannot be coated over by melamine or PU as the solvents used to dispense the pigment are not compatible with these polymer coatings. More over, if coated over, the solvents used to stain the wood begin to evaporate and cause the polymer film to break and eventually peel off.

There is another method to stain wood using powder pigments that does not involve solvents. Pure pigments such as the oxides of iron available in yellow, red and black hues can be mixed with water and applied to stain the wood. The intensity of the stains thus created can be controlled by changing the dilution of the pigment. In such a method, a pre stain coating is recommended as the stain can turn out patchy when applied using a rag or a roller. Application of the water based stain thus created causes the wood grain to get slightly raised lending a rough surface. Pre wetting and sanding of the raised grain is recommended to avoid this problem. This method is compatible with all types of wood coatings. Due to the absence of heavy powder usage, the wood grain appears enhanced and clear. The only drawback to this method is control of the stain intensity. Different batches of the stain may turn out different if the proportions are not the same.

The method recommended by most experienced wood workers is staining using manufactured wood stains. These stains are available off the shelf in a variety of colours. They are available in water

based and solvent based varieties. The solvent based variety carries a fast evaporating solvent which flashes off in about 2-3 hours and is compatible with all types of wood coatings. The water based variety dries off slower but provides a more even finish. The water based stain also needs to be applied after pre wetting and sanding for a smooth finish. Both stains can be applied as is or after dilution with an appropriate solvent. To get an even stain, it is recommended to apply a coat of pre-stain before staining the wood.

Application of Stains

The first step to applying wood stain is applying the pre-stain.

What is pre-stain?
Pre stain is a coating used before staining of wood. It partially closes the grain of the wood and makes it less absorbent. The stain applied after pre stain spreads more evenly.

Is pre-stain available in India?
Pre-stain is not available readily off the shelf in India, but one can easily create a pre-stain using the following method:
Purchase a can of the appropriate sealer - it can be water based or solvent based. Some varieties of sealer are: Water based PU sealer, solvent based PU sealer, Melamine sealer, and for hand polish -
sanding sealer.
Thin it 100% using the appropriate solvent. For water based sealers, use water and for solvent based sealers such as PU Sealers, use PU thinner.
This is your pre-stain.
Apply it along the grains using a cotton rag or a roller.
After the application of the pre-stain, the wood stain can be applied using a clean cotton rag or a roller along the grains. More than one coat of stain can be applied to get a greater colour depth, but remember, more stain means lesser natural wood grain.
This completes the wood stain.

To complete the wood finish, wood sealer must be applied over the stain first. Never sand the wood stain. Sanding must be done only after application of the sealer. The sealer now applied must be applied as a sealer coat and not as a pre-stain i.e. the sealer must now be thicker in consistency and used with the intention of sealing the wood completely. More than one coat of sealer must be applied, sanding with emery grit 180 between coats and with emery grit 320 on the final coat. The wood can then be finished using the top coat.

Hope this helps you stain your wood to perfection.

For a huge range of wood stains and sealers, visit

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