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

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

Thursday, 27 July 2017

Melamine vs PU

Two of the moat popular transparent/natural wood finishes are melamine and PU(Polyurethane). Melamine and PU are both synthetic hydrocarbon polymers which form a film over the wood surface that is coated, thus laminating it. The purpose of lamination is to preserve the wood by not allowing the moisture of the wood to escape, preventing it from damage from the elements and protecting it from wear and tear from use. Both finishes enhance the aesthetics of the wood by allowing light to refract inside the transparent layer formed by them. Both the finishes have a similar application procedure by spray. So, what is the difference between the two?

The main difference is in the life of the coatings and its resistance to the elements.
PU Finished Door

Melamine was a great improvement over wood polish as a transparent wood finish when it was introduced in the Indian market in the late 80s and the 90s and is popular to date due to its economy. But melamine has its limitations. The film formed by melamine is only moderately resistant to water. It deteriorates when exposed to sunlight. The film easily yellows and looses lustre. The film begins to crack at the wood joints over time.

With the advent of polyurethane (PU) in the late 90s, most of the shortcomings of melamine were covered. PU forms a tougher film than melamine. It is more scratch resistant. It is flexible and does not crack with the movement of the wood joints. It is UV resistant and can be used on woods that are used in exteriors, such as entrance doors and windows. It does not yellow easily and gives a high lustre. The lustre is also retained longer due to its UV resistance.

PU gives clear advantages over melamine as the application procedure remains the same for both and there is no new skill required to apply PU. Thus the work involved takes the same time and effort on part of the applicator.

Consider wood finishing as a one time investment as reworking of wood finishes takes up lot of resources, skill, time and money. Go for the best coating for your expensive teak or other exotic woods as it will not only preserve the wood but also enhance its aesthetics.

Some things to note when applying Melamine or PU

Melamine/melamatt polish as it is popularly known among the painting contractors is usually sprayed over French/hand polished surfaces, which is not the intended procedure of application.

A study of melamine shows that for all intents and purposes, as in PU, was not originally developed as a wood coating. It is a product of innovation and adaptation that these products are used as coatings. The adaptation requires a specific application procedure for the product to perform as a wood coating. These application procedures are grossly ignored by applicators and contractors.
A damaged French Polished door

Applicators apply generous coats of French polish and NC Based Sanding sealers as a preparation for the final coating by melamine or PU. They do this as their skill set for colour matching of wood is based on French polish techniques.

The melamine and PU films often fail as the solvents in the French polish and NC sealers are not compatible with solvents used in PU and melamine coatings. Also, the solvents in the French polish applied under transparent coatings are exposed to light and begin to evaporate and cause blisters in the polymer film formed over it.

It is thus highly recommended for all intents and purposes that application of French polish be avoided when any such coatings are applied. Wood coated by French polish has its own charm and should not be over coated by polymer coatings.

There are much simpler and compatible colour matching techniques for melamine and PU using wood stains, which we shall discuss in another post.

For a huge range of wood finishes visit

Wednesday, 12 July 2017

Why it is worth investing in quality paint for mild steel

Mild steel fabrications such as entrance gates, safety grills, rolling shutters, collapsible gates, sliding doors etc are known and used for their strength amd durability. They take a short time to be fabricated and can be quickly installed.
They however have a high initial cost and are meant to last a lifetime.

Mild steel has an achilles heel though and it is rust and corrosion. Expose to water, sunlight, dust and pollution cause the structure to corrode and loose its strength and its lifespan quickly shortens. The high initial cost comes to no avail.

It is wise thus to preserve the mild steel structure using anti corrosive paints and coatings.

Normal enamels and metal primers available in the market such as redoxide and zinc chromate primers are prepared using alkyd based binders. These binders typically have a lifespan of 1-2 years on exposure to the elements. The binder being the main film forming and barrier forming medium in the paint heavily influences the life of the paint. Due to the  inferior quality binder, the regular enamels begin flaking and chip off in a short span of time, leaving a small area of mild steel exposed. Smaller areas of exposed mild steel corrode much faster and begin to rust. Rust being more voluminous than mild steel causes the paint in the area around the corroded spot to chip off, causing even more rust, snowballing into a much more serious problem.

To save your invested time and money, it is hence worth investing in a good quality coating for your metal structure. It is also worth following best practices while applying the coating.

To coat any mild steel structure, the following is the best coating procedure.

Start off by removing any corrosion or rust using a rust remover and if necessary use a wire brush. Pay special attention to weld joints and corners as these are the most stressed and are prone to rust. Apply a coat of epoxy based metal primer generously over the surface. Zinc phosphate based epoxy primers are the best ones as the zinc phosphate acts as an active rust inhibitor. Allow the primer to fully cure. Fill dents, crevasses and holes using a polyester based putty, commonly known as a body filler. Give ample time for the putty to set. Apply another coat of the zinc phosphate primer. Allow to cure. To finish the coating aesthetically and to build resistance to deterioration of the coating from exposure to UV, apply a polyurethane based enamel as the final coat. Apply 2 coats of the PU coating, typically using spray equipment.

The above treatment will provide an extremely durable finish and a long life to the mild steel structure.

Special care must also be taken to protect parts that are sunken in the ground. 2-3 coats of the epoxy zinc phosphate primer must be applied before installation. The primer coat must not be damaged during the installation.

Thickness of the coatings on parts that are exposed to hand and foot traffic must be built up using an intermediate hi-build coating to resist wear and tear.

Saturday, 29 April 2017

Cement Based Powder Tile Grouts Vs Epoxy Tile Grouts

Tile joint fillers also known as grout are traditionally white cement based powders that are used to fill gaps between tiles and other gaps in bathrooms and flooring. It is common practice even today to use white cement dyed with mineral based powder pigments (known commonly as oxide powders) to fill tile joints in bathrooms, flooring and terraces. While this fills the joints, it is not very long lasting. Being a cement based compound, it is not waterproof. It is absorbent and as a result carries moisture, leading to fungal/algal growth. This is what gives that ugly black/green stain to the tile joints. Also being a lime based product, it is not resistant to common cleaning agents such as acids and bathroom cleaners. This leads to erosion of the grout and ultimately water leakages through the joints.

To cover some shortcomings such as quick discolouration and uniform colour matching, many powder based cement grouts are available. These powder based cement grouts don't do much more that the above. They have no great resistance to cleaning agents and also are not waterproof. Some powder grouts do have additives to enable wide-tile-joint filling where normal grouts tend to crack. SBR based additives are also available to enhance the waterproofing capabilities of powder grouts, but they do nothing to enhance the resistance to cleaning agents.

Epoxy grouts cover all the above shortcomings. They work well as waterproof and chemical resistant tile joint fillers. They also work well on wide tile joints. They have a smooth glossy finish and never loose colour.

Epoxy grouts are supplied as 2 part or 3 part packs. They consist mainly of a resin and a hardner. 2 pack epoxies usually have a coloured resin and 3 part epoxies have clear resins and hardners and a third pigmented powder component used as an opaque filler. 2 part epoxies are easier to use in that they are easier to mix and apply. 3 part epoxies are cumbersome to mix and cause some amount of wastage.

Unlike powder grouts which have to be mixed with water to get a paste like consistency to apply. Epoxy grouts are ready to use once all its components are mixed. The mixed epoxy has a pot life of 25-45 minutes. It is prudent to be cautious while deciding on the quantity of material to be mixed. Mix only so much that can be used within its pot life. The immediate tack free time is about 10-15 minutes after application. The excess grout must be cleaned up before about 20 minutes from application. The only drawback for epoxy grouts is that it can leave behind a mess if not cleaned up properly in time. Epoxy grouts are usually applied using spacers between tiles so as to provide larger surface area for the grout to bond to the substrate. Spacers of 3mm minimum are recommended. Epoxy grout needs a dust and moisture free substrate.

Most bathroom leakages can be arrested using epoxy grouts. Epoxy grouts applied in a contrasting colour to the tiles form a beautiful grid pattern that is both modern and minimalist in design.

Epoxy grouts, as discussed above, out-perform on most criteria and are the future in tile laying.

For Commercially available Epoxy Grouts refer to "Bathroom leakage repairs - Waterproofing Tile Joints using Epoxy Grouts".

Wednesday, 12 April 2017

What is the Difference Between Duco NC Lacquer and PU?

Duco is a brand owned by Akzo Nobel (formerly ICI) and represents a Nitro Cellulose (NC) Based lacquer available in transparent and opaques. NC lacquers were widely used in the automobile industry to finish vehicle bodies to get a tough weather resistant, glossy film with performance far superior to the then prevalent enamels. But there were a few drawbacks to NC. NC Lacquers are highly viscous and take large amounts of thinner to thin to a sprayable consistency. Nitrocellulose on exposure to sunlight deteriorates, looses gloss and turns yellow. It is also notorious to apply on edges and often begin to peel off at the edges. The NC paints needed to be periodically buffed to remove the yellowed top layer. This leads to reduction of the paint film thickness. NC lacquers are also sensitive to ambient temperature and humidity during application. The temperature and humidity are known to adversely affect the gloss of the finish.

With the advent of Polyurethane coatings, NC began loosing popularity as the preferred choice for vehicle body painting. PU as polyurethane is popularly known, has far better technical specifications to NC. PU is colour fast in sunlight and does not deteriorate even on prolonged exposure. PU forms a tougher film than NC due to extensive cross-linking introduced in the polymer. PU does not chip or peel off like NC. No buffing is required to maintain colour and gloss. PU can also be applied in a wide range of atmospheric conditions as compared to NC. PU is also easier to tint and match than NC due to the clarity of its binder and lower viscosity. PU can also be tinted to metallic shades. PU is also available in matt finishes.

Both NC and PU are used to coat wood and metal. These materials are also in wide use in home decor. PU is now the leading coating in the automotive industry and is fast gaining popularity in the decorative segment as well.

With green standards fast becoming the norm, PU is also available in water based variants that can be used to coat wood. They have a comparable performance to Solvent based PUs and are much easier to apply. They don't require elaborate spray equipment and also do not pose a health hazard as they can be brushed on.