In building or repairing a wooden outside deck, there are a number of things that need to be considered. Some of them are:
-Is there at least a ¼” per foot drop from the side of the building structure to the edge of the deck?
-What kind of wood will be used?
-How will the horizontal to vertical joint be handled next to the structure? Make sure the old or new wood has been screwed down to the deck supports correctly.
-Have the wood plates (usually 4 x 8 sheets of plywood or 3 ½” by ½” tongue and groove) joints been sanded after they were screwed down?
-How are the joints going to be sealed?
-How will the edges of the wood deck be prepared and sealed?
-How is the Durabak 18 applied to the deck plate?
There are of course, other questions, but these seem to be the areas where mistakes are commonly made, so they are important to address ahead of time.
Is there at least a ¼” per foot drop (Slope) from the side of the building structure to the edge of the deck? 65% of all decks that fail, do so because there was improper slope installed when the deck was built. This can be a major or minor issue to correct, but it needs to be addressed before repairs can be made correctly, or in the case of a new deck, do not allow it to be built without proper sloping installed. Without proper slope, water will not run off the deck, it will pond on the deck, or flow up against the building. Before any coating can be installed correctly, develop or install the correct sloping of a deck. Depending on what the issue is about the slope of the deck, there are a number of ways to correct it. Some of the easiest can be just cutting off a few inches of the deck structural support posts. Sometimes polymer concrete can be added on light weight concrete decks. A wood filler can sometimes be used on wood decks. It is sometime possible to install a wooden overlay before applying a new deck.
If there is improper sloping of a deck, and proper sloping cannot be installed, the life of the deck is in question.
Starting with what kind of wood will be used. Sheet plate 4x8 plain CDX or 4x8 tongue and groove, marine grade, or 3 ½” by ½” boards are a few of the most common materials. In all cases the 4x8 sheets need to be screwed down with at least a 1/16”to 1/8” gap all around to ensure enough room for expansion/contraction of the wood and deck. If not enough room is left, the wood plates will develop high lips at all joint lines. It is best to check with your local lumber yard for the correct spacing in your area and exposure to the sun. Where the deck is going to see high sun and high temperature, it is not uncommon to use larger spacing. The larger the spacing, the more attention is required to the joints.
If marine grade plywood is to be used, ask the supplier how the wood was treated, by oil or by powder type of chemical. This is important, because oil is used a lot, and in those cases, it may be necessary to use an oil grade primer before any coating including Durabak 18 non slip can be applied. If a powder was used, the Durabak 18 non slip can go onto the wood after it is cleaned correctly. Remember, all wood is dirty even when it is bought at the suppliers.
Using 3 ½” by ½” tongue and groove has its own issues to deal with and proper gapping is just one of them. Sealing of the wood, both sides and ends has to be done before installation, depending on the sun and area, top coat sealers like Durabak 18 may be necessary for a 20 year deck life. Plastic woods are very expensive, and the life of the deck is shorter than old school installations.
How will the horizontal to vertical joint be handled next to the structure? The best type of joint is a flexible sealing Durabak 18 membrane that will mechanically bond to the structures surface and to the deck substrate surface. Metal joints leak and will not give 20 or 25 year service before wood rot, mildew, and mold set in to destroy the deck structure and most of the time the building structure also.
Make sure the old or new wood has been screwed down to the deck supports correctly. The best way to make repairs or to do a new install is to screw the plates down. Nails and other wood fastener have not proven effective for long term decks. Most nailed down decks fail in 6 to 10 years at best. Using the correct screws for the wood used and putting them down on a 6 inch edge placement and a 12 inch field will be the first step in installing a 20 year deck. The second thing is allowing proper spacing between each piece of wood. The top criteria is sun, amount of sun per day, and how will it hit the deck (meaning part or all of the deck plate). Asking the local lumberyard for insight in the area of the deck is always good information to have, and do not forget the supplier of the wood if it is not a lumberyard. You will find that lumber bought from a lumberyard vs lumber bought from a discount house is not the same in many ways. The gap spacing can be anything from a 1/16” to ¼” depending on the kind and quality of wood. The proper spacing for the application considered will make the difference in the performance of the wood over the deck’s lifetime. Having the wood screwed down correctly leads to high points near the screw lines and the edges of the wood plate.
Have the wood plates (usually 4 x 8 sheets of plywood or 3 ½” by ½” tongue and grove) joints been sanded after they were screwed down? Now look to see if the edges and screw holes have been sanded. If not that is the next thing to do on a repair or new install. Take a 4 inch belt sander and quickly go over all of the edges and field plate screw holes. Doing this will make a huge difference in the amount of deck coating needed at the end of the deck project. Just take the edges and screw holes down to the level plain of the new wood.
How are the joints going to be sealed?
The size of the gaps will determine what comes next. If a 1/16” gap is all that is needed, cut the tip of a tube of SIKA Flex A to fit the groove and apply just enough caulk to seal the gap. Now this does not mean having any caulk on the edge of any of the wood. Filling a 1/16” gap requires time and is harder to fill than a ¼” gap. Give this small gap the time it needs to do a good job. In all cases 1/16” or ¼” gap, the caulk should never be above the level plain of the wood deck installed. When the caulk is above the level plain of the wood it will be seen every time the sun shines on the deck. In the cases where the sun is going to hit the deck at different times, at different amounts, and different length of time, the best way to seal the deck is to use a Durabak 18 fleece. This fleece is a 120 lb. fiberglass and cotton fleece. This membrane fleece is installed quickly and easily. Just practice a little to get a feel of how much Durabak 18 smooth material needs to be under the fleece so that when the fleece is laid into the smooth Durabak 18 material the whole fleece gets wet from the bottom up. Next back roll the fleece and make sure that just a little material comes out from under the fleece. It is important that there is enough Durabak 18 under the fleece to make it wet from underneath, and enough to make a good bond to the wood at the same time. Too much material under the fleece will cause pockets of material that when it starts to dry, bubbles will appear under the fleece, and it will not be flat. Now if a bubble appears under the fleece when drying, just take a sharp knife and cut the center of the pocket, and push out the extra material. If the pocket is already dry, take a knife, cut the pocket, sometimes remove the center 1/8” of the fleece over the bubble and push just enough Durabak 18 under the fleece to make a new bond under the fleece while keeping the surface flat.
How will the edges of the wood deck be prepared and sealed? The best way to seal the edges is to use the 4 inch fleece and Durabak 18 smooth and do a joint membrane around the edge of the wood plate. The wood plate should have been installed at least an inch past the last support that the plate was screwed down to. If it has been done this way, apply Durabak 18 to the underside of the wood plate, the edge of the plate and about 3 inches out from the edge of the plate. Now apply the 4 inch fleece to the bottom of the wood plate, pulling it up around the edge of the plate and onto the top of the wood plate. Now back roll as above and seal the edges.
How is the Durabak 18 applied to the deck plate? With the fleece now applied to the edges and all plate joints needing the fleece membrane, take smooth Durabak 18 and roll all of the plate with the first coat of Durabak 18 smooth at 15 wet mils, but stay at least ½” away from all fleece membrane. When the first coat of smooth is dry, a second coat of Durabak 18 non slip needs to be applied at 15 wet mils. Now if the fleece has been installed correctly, the second coat should be applied to the deck plate, and all of the joint fleece membranes should disappear. If they do not, too much material has been left under the fleece membrane, and a second coat of Durabak 18 smooth needs to be applied to only the areas where the fleece membrane is too high to be covered over by the second coat of the Durabak 18 non slip. Very seldom will all of a deck need to be coated with a second coat of smooth Durabak 18 to hide the seals. But once in a while an area of a deck will need 2 coats of smooth.