Upon opening the mailbag and scouring its contents this month, I discovered that more and more of you out there are asking questions on specific installation procedures for a variety of projects. Good. The best installers are those who continuously stretch the learning curve, and paying attention to detail is one of the best ways I know to go about doing just that. Question: What are the proper fasteners for securing ¼-inch underlayment? Answer: The Engineered Wood Association (formerly the APA) indicates the proper fastener to be a 3d ring- or screw-shank nail, minimum 12 1/2 gauge (0.099 inch) shank diameter for underlayment ¼- to ½-inch thick. Question: How close should the nails or staples be from the edges of the underlayment panels? Answer: The distance from the edges of the underlayment joints should generally not be more than 3/8-inches back from the joint. This stops any peaking of the underlayment panel that would show through the finished floor Question: How far should the underlayment joints be offset from the subfloor joints? Answer: The general consensus is 6-8 inches. The further the joints are offset, the less chance of movement being deflected from the subfloor joint to the underlayment joint. This should apply to both the side and end joints. Question: Should the underlayment fasteners extend down into the floor joists? Answer: No. The subfloor should be fastened to the joist system, but the underlayment should be fastened to the subfloor. Question: Should the underlayment joints be butted tight, light, or spaced? Answer: It depends upon the manufacturer of the underlayment. Most manufactures recommend the joint to be butted lightly, while others recommend the joints to be spaced. No underlayment manufacturers recommend the underlayment joints to be butted tight. Most manufacturers warn against fastening any fullness into the panels. Question: What are the best patching techniques for underlayment joints? Answer: You always want to keep the compressive strength of the patching compound as high as possible. To achieve this, you must follow the patch manufacturer’s water-to-powder recommendations to the letter. You will note that the patching compound will be a little thick, and is limited in its coverage. To aid in the spreading of the patch, dampen the joints to lessen the absorbency of the underlayment joints, making the patch easier to spread. Do not add more water to the patch. Question: How important is acclimation to underlayment panels? Answer: Underlayment panels should be protected from moisture prior to their installation. Many installers of underlayment believe that underlayment stored in a dry warehouse is adequate for acclimation. Not true. In order to acclimate underlayment, the panels should be removed from the skid and stored on edge in the room(s) where they are to be installed for several days prior to installation. Underlayment panels left in skids take longer to acclimate. Question: What is the main cause of squeaks in a wood floor system? Answer: There are two main causes of squeaks in wood floors, and both are related to movement. The first is when the edges of two pieces of wood rub against each other; the second is the result of a piece of wood moving on the shank of a fastener. Some squeaks are installation related, but most are the result of the wood drying, and the resulting shrinkage. Question: What causes tunneling of a sheet vinyl directly over an underlayment joint? Answer: Tunneling is a de-bonding of the sheet vinyl and/or patching compound directly over the underlayment joint caused by an excessive movement of the underlayment at the joint. There are several causes for the movement: moisture; improper fastening; over-watering of the patching compound; low compressive-strength patching compound; and improper fastening of the underlayment joints. Question: What causes nail heads to show through the surface of the sheet vinyl? Answer: Occasionally, fasteners may “pop” or “back out.” In these cases, fastener heads sometime rise above the underlayment surface and “telegraph” as bumps through resilient floor covering. The best way to prevent nail popping is to use the proper fasteners. Ring- and screw-shank nails have a higher withdrawal resistance. Make sure to use a fastener length approximately equal to the total thickness of the underlayment and subfloor. Always remember to make sure the subfloor is dry. Installing underlayment over a damp subfloor allows the fastener to back out when the wood dries and shrinks.