The Brew Cabin

On the paving pages you say to use a roller not a whacker plate for compacting sub-base.
Interseted as to why? looking at HSS catalogue - whacker plate I'm thinking of using has a compaction force is 25kN on a 700 x 320 plate.
Yet a large roller only has 18.7kN ........... surely the higher compaction force the better.

I know you can get lightweight wharker plates but I would not use one of them for sub-base.

I'd use the roller as the whacker plate is blOOdy heavy to lift off the truck!

It's a bit more complicated than that, Rick. Centrifugal force alone does not determine how effective is a piece of kit at compacting a given material. Comparing vibratory rollers with vibrating plate compactors (known, in the vernacular, as a Wacker Plate - no 'h'; it's the name of a German company that manufactures all sorts of compaction equipment) is not a direct comparison ,as they achieve their effect in slightly different ways. A Vib Plate relies mainly on vibration at a specific frequency and amplitude, while a Vib Roller brings extra weight (dead-weight) to the equation, and very, very generally speaking, achieves a greater depth of compaction than a Vib Plate.

Further, comparing the very limited range of kit on offer from a Hire shop doesn't give the full picture. Many Vib Rollers achieve a centrifugal force equal to or greater than a Vib Plate, but we're straying into the realm of geo-mechanics and civil engineering, when what this website is mostly concerned about is compacting a 100-225mm thick sub-base for pavement usage.

I'm not sure that I say, anywhere on the site, that a roller should be used in preference to a Vib Plate. I would agree with that statement for larger jobs, but for the vast majority of residential patios and driveways, a Vib Plate is usually more than fine, and, with the exception of the farty little Vib Plates capable of being lifted in one hand and carried in the front basket of a Kiddie's bike, most of the Vib Plates available from Hire Shops are eminently suitable to the task in hand. For contractors, I would recommend using a suitable roller when conditions allow, but for the typical DIYer or smaller job, then there's nowt wrong with relying on a Plate Compactor.

using has a compaction force is 25kN on a 700 x 320 plate.
Yet a large roller only has 18.7kN ........... surely the

Ooops - post error try again -
I have a 2 fold task for compaction.

1. I have a 60m run around house where I have dug out 1.3m wide x 150mm deep and barrowed in 25tonne of DTp1 ..this will be compacted down ready to take a paving slab with a soldier paviour either side of it.
Thought a wacker plate better for this.

2. I have a drive of around 250m2 this is currently 150mm below finished level, and a mixture of as scrapped to and Dtp1. I thought of compacting that down now - (it had services trenches, drains etc. laid about a year ago) ... then filling up with DTp1 and finish compacting later in the year to final level, for a 50mm sharp sand & clay paviour finish.

What would be the best tool for the job - the 25kN compaction force wacker plate or the 18.7kN compaction force roller?

I had sort of discounted the roller due to difficulties getting into corners of path base.


Or perhaps I need to hire both ? luckily I have a 20% discount card for HSS - need it at their prices.

Rick

I reckon you're right, Rick - normally, a plate compactor for the path, and a roller for the driveway would be the right prescription, but, seeing that there's a significant time lag between doing the compacting and doing the laying, and that the driveway is going to be paved with clays, then you could just rely on a plate compactor and not bother with a roller. If you were laying blacktop to the drive, then a roller would be a better option, but it's just complicating the issue and doubling the hire fees you're paying to "Hire Summat 'Spensive" ;)

I'm surprised someone on the Self-build group hasn't bought their own Vib Plate and sold it on to a newbie once they've completed their own build. You can pick up a reasonable second hand plate for around 250 quid, which is what? around a couple of months hire? And then, when you've finished, you can sell it on for 250 quid, and you've only paid for the fuel and oil! :)

BTW - were you at the H&R show at the NEC last month? I thought I saw someone in the so-called 'Restaurant' wearing a badge with your name, but I wasn't sure and by the time I'd turned around, I lost sight of them. Was it you?

Thanks for comments - no it wasn't me at the show.

I would happily buy a wacker plate - maybe I ought to star looking in the Free Ads etc.

Rick