Measure the stairs before buying a carpet runner. Take measurement tape and mark the size of tread from inside and outside. Carpet runner also covers riser, so add the size of riser too. Once you are finished measuring the stairway, buy the carpet by increasing two or three inches more in the actual size you measured. You can use pieces of old carpet for padding, carpet pads will not get attached on the riser so you do not need more carpet for fulfilling this purpose.
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You will need to fix tackless strips at the edges of tread and riser in order to give your carpet perfect grip on stairs. Cut the strips a few inches smaller than tread and then hammer nails on the strips. Fix the carpet pads that should be one-fourth inch smaller than the actual size of tread and cover down the riser for two to three more inches. Get the padding stapled with electric stapler.
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Start installing the carpet runner from the top of the staircase, use carpet glue to stick it first on the treads. You have to staple the carpet at bottom of each riser every three inches away. Now try fixing the runner into the edges of riser and tread, for doing this appropriately you will need a kicker, you can get it on rent from the carpet shop. Kicker will help you in fixing the carpet on the staircase from every corner.
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