The Simpson Strong-Tie CPT88Z concealed post base is a retrofit post base for connecting a nominal 8x8 wood post to concrete while keeping the connection mostly hidden inside the post. This is a post base designed for deck and post-to-footing structural connections. Model Number: CPT88Z. If you want a cleaner-looking post connection without giving up the required separation from concrete, this is the style of connector you use.

What sets the CPT88Z apart is the concealed knife-plate layout. Instead of wrapping the outside of the post with visible steel, the connector uses an internal plate and a standoff base so the finished post looks cleaner once installed. That makes it a solid fit for jobs where appearance matters, especially exposed deck posts, porch posts, and other permanent structures where bulky exposed hardware would stand out.

The 1 inch standoff height is a real-world feature, not just a line in the spec sheet. It lifts the end of the post above the concrete surface to help limit moisture exposure and reduce the chance of decay at the post end. Simpson Strong-Tie specifically calls out this standoff as code-required when supporting permanent structures exposed to weather, water splash, or basement conditions, so it solves both a durability issue and a compliance issue at the same time.

Material and finish matter on connectors like this, and the CPT88Z is built for that environment. The knife plate, washers, and standoff base are made from ZMAX galvanized steel, and the standoff base also gets a textured flat black powder-coat finish for appearance. The supplied 1/2 inch drift dowels are mechanically galvanized. For exterior work and treated lumber applications, that corrosion-resistant finish is one of the reasons this connector gets specified in the first place.

Installation is more involved than a simple saddle-style base, but that is the tradeoff for the concealed look. The post needs drilled 1/2 inch holes and a 3/16 inch slot cut into the end so the knife plate can fit inside properly. The connector is then anchored to concrete with 1/2 inch anchor bolts, and the post is secured with the supplied dowels. Simpson Strong-Tie also notes that anchorage can be cast-in-place or retrofit using adhesive or mechanical anchors, which gives the CPT88Z flexibility for both new work and upgrade jobs.

From a jobsite standpoint, this is a wood-to-concrete retrofit base made for top-supported structural posts, not free-standing posts that need base rotational restraint on their own. Simpson Strong-Tie specifically notes that post bases do not provide adequate resistance to prevent members from rotating about the base and are not recommended for non-top-supported installations such as fences or unbraced carports. That is an important distinction if you are choosing hardware for a structural inspection or a repair scope.

The CPT88Z is a good fit for deck builders, remodelers, framing contractors, and serious DIY users working on permanent exterior structures where the post connection will stay visible. If the goal is maximum simplicity, a standard exposed post base may be faster. If the goal is a cleaner finish, code-required standoff, and a connector sized specifically for nominal 8x8 posts, the Simpson Strong-Tie CPT88Z concealed post base makes a strong case.

Simpson Strong-Tie CPT88Z concealed post base for clean-looking structural posts

If you want an 8x8 post connection that looks a lot better than a standard exposed base and still gives you the standoff you need over concrete, this is the right style of hardware.

• Who it's for: Deck builders, remodelers, and contractors installing top-supported 8x8 structural posts where appearance matters.
• Why it stands out: The concealed knife plate gives you a cleaner finished post, and the 1 inch standoff handles the moisture and code side of the job at the same time.
• Worth knowing: This one takes layout and post prep, so it is not the fastest base to install. Also, like other post bases, it is not intended to solve rotation issues in non-top-supported installations.

• What post size does the CPT88Z fit? It is designed for nominal 8x8 wood posts.
• Can this post base be used for retrofit work? Yes. Simpson Strong-Tie lists the CPTZ series for retrofit post base use and states that anchorage can be cast-in-place or retrofit with adhesive or mechanical anchors.
• Does it keep the post off the concrete? Yes. The connector provides a 1 inch standoff above concrete.
• Is this a good choice for a free-standing fence or unbraced carport post? No. Simpson Strong-Tie notes that post bases do not provide adequate resistance to prevent rotation at the base and are not recommended for non-top-supported installations.