A bag of concrete looks like a commodity and is not. The mixes on our pallet differ in how fast they set, how strong they end up, and what they are willing to forgive — and choosing by price or by whatever was left at the yard is how a fence post ends up wobbling or a slab cracks in its first summer. This guide covers the bagged mixes we stock in Los Angeles, what each one is actually for, and the two decisions — set time and strength — that should drive the order.
Start with the job, then pick set time and strength
Every bagged mix is a trade between two things: how long you have to work it, and what it reaches when it is done. Fast-setting mixes buy speed and cost you working time. High-strength mixes take a normal cure and give you a higher final number. Crack-resistant mixes add fibre to control the shrinkage cracking that shows up on thin, wide pours. Nothing on the pallet does all three.
The second question is volume. Bagged mix makes sense for posts, footings, small pads, equipment bases, curb repairs and anything you can pour before it stiffens. Once a pour crosses into cubic yards, ready-mix delivery is cheaper and more consistent than a crew mixing bags in the sun — and in Los Angeles, the sun is the variable that catches people out. Heat shortens working time on every mix in the table below.
The mixes we stock, side by side
Four families cover almost every bagged pour on a residential or light-commercial job.
| Mix Type |
Best For |
Set Speed |
Watch For |
| Standard 4000 |
Slabs, footings, pads |
Normal |
Needs proper curing |
| Fast-setting |
Posts, repairs |
Very fast |
Short working time |
| High-strength |
Structural, heavy loads |
Normal |
Mix water carefully |
| Crack-resistant |
Thin slabs, walkways |
Normal |
Still needs joints |
Two things the table cannot carry. First, the PSI number on a bag is a 28-day design strength under proper curing, not what you have the next morning — a slab you drive on at day three is nowhere near its rating. Second, all four families are sensitive to how much water goes in. Extra water makes the mix easier to place and quietly costs you strength, and it is the single most common reason a finished pour underperforms the bag it came from.
Standard mixes: the default for slabs and footings
For most footings, pads and small slabs, a standard 4000 PSI mix is the correct answer and the cheapest one. We stock it in two sizes — the PSI-4000 90 lb. bag for crews moving volume, and the PSI-4000 60 lb. bag where the material has to be carried down a hillside driveway or through a house, which in Los Angeles is more often than not.
Bag size is a real decision, not a rounding detail. Fewer, heavier bags mean fewer trips and less handling on an open site; lighter bags mean a single person can still place the pour on a job with no equipment access. Work out total volume first, then choose the bag that suits how the material has to travel.
Where the pour is genuinely structural or carries heavy load, step up. The PSI-5000 mix and the Q-Max Pro PSI-6500 mix cover that range, and the Maximum Spec lightweight PSI-5500 gets high strength into a bag that weighs less to move — useful on upper floors and on the kind of access that makes a standard 90 lb. bag a two-person job.
Fast-setting: posts, repairs and anything that cannot wait
Fast-setting mix exists for one reason: to let a post stand or a repair carry load before the day ends. The fast-setting PSI-4000 mix is the standard choice for fence and mailbox posts, and it is genuinely faster than people expect — plumb the post first, because you will not get a second chance to adjust it. Our guide on avoiding mistakes on fence installation in Los Angeles covers the rest of the post-setting sequence.
When the pour has to carry load quickly rather than just stand up, the very rapid hardening PSI-6000 mix and the 24/6 fast-setting PSI-6000 mix reach usable strength in hours rather than days. That is what you want for equipment bases, bollards and driveway repairs on an occupied property where the client needs to park tonight.
The discipline with all of these is preparation. Have the hole dug, the post braced, the tools wet and the water measured before the bag is opened, and mix only what you can place. A batch that stiffens in the wheelbarrow is a bag thrown away, and on a hot Valley afternoon that happens faster than the bag instructions suggest.
Crack-resistant and specialty mixes
Shrinkage cracking is a surface-area problem, which is why it shows up on walkways, thin pads and patio slabs rather than on deep footings. The crack-resistant PSI-4000 mix carries fibre reinforcement that holds the paste together while it shrinks, and it is worth the upgrade on anything wide, thin and visible.
It is not a substitute for detailing. Control joints still have to be cut or tooled so the slab cracks where you decided rather than where it wants to, and reinforcement still belongs in anything structural — our guide to rebar and accessories covers the steel and the chairs that keep it at the right depth.
Three specialty bags cover the jobs that are not really slabs. Anchoring cement expands slightly as it sets, which is what makes it the right material for setting railing posts and bolts into existing concrete rather than patching around them. Non-shrink precision grout is for bedding base plates and machinery where a gap under the plate would defeat the whole connection. And the commercial-grade countertop mix is formulated for cast work where the finish matters as much as the strength.
Concrete, mortar and mason mix are not interchangeable
The same pallet usually carries mortar and mason mix, and they get grabbed by mistake. Concrete contains coarse aggregate and is meant to be placed in a form and carry load. Mortar is fine-graded and meant to bond masonry units together, which is a different job with a different failure mode — the pre-blended Type S mortar and the Type N mortar mix sit next to the concrete and do not substitute for it. Our mortar types guide explains which is which and why Type S is the LA default.
Two more that live on the same shelf and confuse people: Type S mason mix is mortar sold for block work at scale, and high-strength structural repair mortar is a patching material for damaged concrete rather than a pour material. If the bag says mortar, it is not going in a footing.
Ordering and placing in Los Angeles conditions
Calculate volume from the actual hole or form, not from a plan dimension, and add for over-excavation and for the bag that splits. Bagged yields are printed per bag; multiply and round up rather than making a second trip mid-pour. For round footings and piers, the forms in our Sonotube concrete forms guide set the volume for you, and the wider concrete forms collection covers boards, stakes and release agents.
Heat is the local variable. A mix placed at two in the afternoon in the Valley has less working time and loses water to evaporation faster than the same mix at eight in the morning, which affects both finish and final strength. Pour early where you can, keep the material shaded before it goes in, and keep the surface damp while it cures rather than letting the sun pull the water out.
Store bags off the ground and covered. Cement is hygroscopic, and a pallet that sat through one wet night will contain lumps that never fully break down. Browse the full range in our concrete mix collection and the wider mortars and aggregates collection — we deliver bagged material and aggregate across Los Angeles County, and a pallet delivered to the job beats forty trips to a counter.
Frequently asked questions
What PSI concrete do I need for a footing?
For typical residential footings a standard 4000 PSI mix is the usual specification, but the number that matters is the one on your approved drawings or in the local code requirement for the work. Structural and heavily loaded pours step up to 5000 PSI or higher.
Can I use fast-setting concrete for a slab?
Generally no. Fast-setting mixes are formulated for posts and small repairs where you need the pour to stand quickly, and their short working time makes it very difficult to place, screed and finish a slab properly. Use a standard or crack-resistant mix and give it a normal cure.
Do I need to mix fast-setting concrete for a fence post?
Many fast-setting products are designed to be placed dry in the hole with water added afterwards, and others are mixed conventionally — follow the bag, because the two methods are not interchangeable. Either way, brace the post plumb before the concrete goes in.
What is the difference between concrete mix and mortar mix?
Concrete contains coarse aggregate and is designed to be formed and to carry load. Mortar is fine-graded and designed to bond masonry units to each other. Mortar in a footing will not develop the strength a footing needs, and concrete in a mortar joint will not bond or tool properly.
How many bags of concrete do I need?
Work out the volume of the hole or form in cubic feet, then divide by the yield printed on the bag. Add a margin for over-excavation and spillage, and round up — a short pour finished the next day has a cold joint through it.
Does adding more water make concrete easier to work with?
It does, and it costs you strength. Extra water above what the mix design calls for increases the water-to-cement ratio, which lowers final strength and increases shrinkage cracking. Measure the water rather than judging it by eye.
