FOR SLAB, BEAM, COLUMN AND FOOTING COVER
Keep the cover. Keep the position.
A cover block keeps reinforcement at the distance from the concrete face specified by the structural drawing. CROSSLOCK adds a second job: it engages the crossing of two steel bars so the spacer is better able to stay in position and resist rotation during fixing and concreting.
A drawing sets the cover. The spacer helps maintain it. The correct choice also depends on the steel arrangement and site application.
01 · Start with the drawing
What is concrete cover?
Concrete cover is the distance between reinforcement and the nearest concrete surface. On site, the required value comes from the structural drawing and project specification, rather than from a cover-block packet.
Once the required cover is known, select a spacer that holds the relevant steel at that distance from formwork or the concrete face. Check the cover requirement, steel arrangement and application together.
The cover block does not decide the cover. The drawing decides the required reinforcement position; the spacer helps maintain it during construction.
02 · Why the position matters
Why correct cover matters
Concrete cover helps protect reinforcement and forms part of the intended reinforced-concrete section. Too little local cover can expose steel sooner to moisture, carbonation, chlorides or fire. Moving steel away from its designed position also changes the reinforcement arrangement.
The site check is practical: confirm the drawing, select the right support, and keep reinforcement in position while people work, formwork closes and concrete is placed.
03 · Code context
IS 456 and the project detail
IS 456:2000 addresses the positioning of reinforcement, nominal cover and the use of suitable supports. The project’s adopted code edition, structural drawings and engineer’s specification control the actual cover and support arrangement.
Use the specified nominal cover, confirm that the chosen spacer suits the steel and formwork, and ask the project engineer when a detail is unclear. This page does not replace a design or approval document.
Read the CROSSLOCK IS 456 cover and spacer guide for further context; confirm code clauses against the adopted edition before using them for project approval.
04 · The spacer’s real job
A good cover block must do more than give height
A spacer can have the correct nominal height and still miss its purpose if it moves, rotates, breaks or deforms enough to alter steel position. Reinforcement adjustment, formwork, foot traffic, concrete placement and vibration all affect supports.
Assess dimension, retention, stability and the space available for concrete around the permanent spacer. Confirm bar compatibility on the current product page or with CROSSLOCK before installation.
- Provide the required distance to the concrete face.
- Stay at the intended support point and orientation.
- Suit the actual reinforcement arrangement.
- Allow concrete to occupy the space around the spacer.
05 · The CROSSLOCK idea
How CROSSLOCK locks
The defining feature of the CROSSLOCK cover-block family is how it engages reinforcement. Instead of relying only on contact with one bar, the spacer is designed to locate at a crossing of two bars.
The two steel directions help control orientation when the correct bars are fully engaged in the correct slots. This helps the spacer remain associated with the reinforcement it supports during normal site handling. The official product photograph shows the actual geometry; choose fit from the current product information.
Self-locking does not replace reinforcement tying. Tie and fix the cage or mesh to the structural detail; the CROSSLOCK engagement concerns the spacer’s position.
06 · Fixity and rotation
Why staying oriented matters
If a cover block moves from its support point or turns into a different orientation, local cover can change even though the product’s nominal height is correct.
A well-designed single-bar spacer can also retain its position. CROSSLOCK uses the bar crossing to provide an additional positional reference. For either method, check actual fit and retention in the project arrangement.
| Support approach | What holds its orientation | Site check |
|---|---|---|
| Loose block | Contact and weight | Check displacement or tilting during work. |
| Single-bar engagement | Clip on one bar | Check bar fit and retention. |
| CROSSLOCK crossing engagement | Two reinforcement directions | Check correct model and full engagement. |
07 · Inside the concrete
Concrete should pass around the spacer
The cover block remains within the finished concrete. Its open body leaves space for fresh concrete to occupy the area within and around the spacer. Placement and compaction still need to follow the project method.
The official product photographs show the openings and contact surfaces. A specific void-area percentage or performance comparison should be used only with an approved product drawing or test record.
08 · Performance
Strength alone is not enough
A spacer’s site performance depends on its dimensions, ability to stay fixed, stability under use and whether it retains the intended cover after loading. A single load figure does not establish suitability for every member or chair application.
Where formal approval is required, ask for the applicable product test record and check it against the project specification. The British Standard reference below identifies the performance standard; it is not a product certification claim.
09 · Product selection
Choose by application, cover and steel
Start with the structural drawing, then match its required cover to the steel arrangement. A slab mesh, beam cage, column cage and footing mat do not use identical support geometry.
These four cards route to the current WooCommerce product records. Product pages remain the source for available specifications, packet quantities and current prices.
CL-20
Slab bottom steel
A crossing-lock cover block for slab bottom reinforcement. Confirm required cover and bar fit against the current listing.
CLB-25
Beam reinforcement
The bottom slot accommodates a ring or stirrup up to 10 mm diameter. Check the beam cage arrangement, specified cover and main-bar fit before use.
CLB-40
Column and beam side
A crossing-lock option for column or beam-side cover. Verify ring and main-bar compatibility before specifying it.
CL-50
Footing and foundation
A cover-block option for footing reinforcement mats. Check the drawing, actual bar arrangement and support need.
10 · Installation
Install at the correct crossing
Check the drawing and choose a product suitable for the required cover and steel. Place the spacer where the two bars cross, engage the intended slots fully, then check that it seats on the formwork or supporting face as designed.
Continue tying the reinforcement normally. Recheck support positions after reinforcement adjustment and before concrete placement. Replace any damaged, loose or wrongly fitted spacer.
- Confirm required cover and the reinforcement arrangement.
- Check the product’s current fit guidance for the actual bars.
- Engage at the correct crossing and verify stable orientation.
- Inspect supports again before concreting.
11 · Quantity planning
Use enough spacers to hold the steel level
There is no universal spacing for every reinforced-concrete member. The needed number depends on bar size, steel stiffness, arrangement, local loading and the project’s fixing method. Support must be sufficient to prevent sagging or displacement.
Use the existing requirement calculator for an initial product and quantity plan, then confirm it against the drawing and site conditions. Add support where concentrated loads or unusual details require it.
12 · Compare support methods
Compare cover-block options fairly
Manufactured cementitious spacers can be suitable when their dimensions, strength, quality and fixing meet project requirements. Inconsistent or weak site-made pieces may create problems in the cover zone.
Plastic spacers can provide controlled dimensions and quick installation, but their effectiveness still depends on geometry, retention and compatibility. CROSSLOCK’s distinguishing approach is engagement at a two-bar crossing.
| Approach | Potential benefit | Check before use |
|---|---|---|
| Site-made mortar block | Locally available | Size, strength, consistency and fixing. |
| Manufactured cementitious spacer | Controlled manufacture | Quality evidence, dimensions and fixing. |
| Single-bar plastic spacer | Quick fitting | Clip retention and bar fit. |
| CROSSLOCK crossing-lock spacer | Two-bar positional reference | Correct model, full engagement and project fit. |
Continue with the established PVC cover block guide, or compare the different role of a plastic rebar chair.
13 · References
Codes and technical reading
Use the project-adopted code and product evidence for design approval. These resources explain the relevant topics; they do not certify any CROSSLOCK product on this page.
- IS 456:2000 — Plain and Reinforced Concrete — Code of Practice. Confirm the applicable edition and clauses from the project’s approved copy.
- BS 7973-1:2001 — Product performance requirements for spacers and chairs (BSI).
- Spacers and chairs (The Concrete Society).
- MPLAST INDUSTRIES — current CROSSLOCK product drawings and relevant test records, requested for project review.
14 · Next steps
From cover requirement to site use
If the drawing and reinforcement arrangement are clear, choose the matching product and plan quantity. If the detail is unusual, share the drawing with the technical team before selecting a spacer.
15 · Common questions
Frequently asked questions
Why is it called CROSSLOCK?
The family is named for its engagement at a crossing of two reinforcement bars. Those two directions help locate and orient the spacer.
Is CROSSLOCK simply another PVC cover block?
PVC describes a material. CROSSLOCK describes the crossing-lock design used by this product family. Material alone does not establish fit or retention.
Does self-locking mean the steel does not need tying?
No. Reinforcement tying and fixing remain necessary. Self-locking describes the spacer’s engagement with the steel, not the fixing of the whole cage or mesh.
Why does rotation of a cover block matter?
If a spacer turns into another orientation, the effective distance from steel to formwork can change. Check fixity as well as nominal height.
Can I choose the cover from the product list?
No. Check the structural drawing or project specification first. The product list helps select a spacer after the required cover is known.
Are cementitious cover blocks always wrong?
No. Properly manufactured cementitious spacers can be suitable. Their quality, dimensions, strength and fixing must meet the project requirement.
Is a plastic rebar chair a cover block?
Both support reinforcement, but a cover block maintains cover to a concrete face, while a chair primarily supports upper reinforcement at its required level. See the separate rebar-chair guide.
Does a spacer load classification apply to plastic rebar chairs too?
Do not transfer a cover-block load classification to a chair. Assess each product using its own applicable test evidence and the project requirement.
Need help?
Ask CROSSLOCK about your site
Share the member, specified cover, reinforcement arrangement and a drawing or site photograph if available. CROSSLOCK can help identify a suitable product and quantity-planning route.