How to make 25mm holes in block walls?

[phil090207]

I'm drilling several 25mm holes in concrete block walls for plastic water pipes. Total wall thickness is about 300mm including cavity. I have a 1500W SDS Plus drill. I've never done this before.

I bought a 28x300mm diamond core drill bit and used it in hammer mode as instructed by the man in the shop. I got through five blocks successfully before the cutting segments completely disappeared. I've now read that this type of bit should be used in rotary mode only. Actually I tried that, and it seemed to make no impression on the block at all. At least hammer mode makes a hole - though it takes several minutes to get through a block.

Before I go and buy another one, is this the best tool for the job? I notice TCT core bits are also available. Which is better, TCT or diamond?

And how can I avoid rapidly destroying the bit?

Thanks Phil.

 

[JohnD]

if you have a good big drill, an ordinary tct masonry bit (not a core drill) will last much longer. It will be slow in dense concrete, but quick in light blocks.

You can get extension sleeves for larger drills (look out for a threaded shoulder and smaller spigot at the end of the shaft) which works out cheaper than buying several long drills. (this may not be right for SDS+ drils)

 

[^woody^]

You don't use a diamond or TCT hole saws on hammer - they are saws not drill bits. Thats why you have no diamonds left on it

A good diamond cutter should easily cope with any common concrete block.

A TCT one will too, only it will wear down quicker.

An SDS bit will last the longest, and should do this job a bit faster - no longer than a minute - and you can use hammer

 

[phil090207]

Thanks JohnD and Woody,

So you both think an ordinary SDS masonry hammer bit is the best bet. I didn't realise you could buy these as big as 25mm, but I see screwfix have them about the same price as the core bits. I will get one of these and give it a go!

Phil.

 

[^woody^]

The only issue with an SDS bit is that it will blow a bigger bit of the wall off when it exits. Drill from out to in if it is possible as the plaster can be made good easier than the brickwork.

It may not help you now, but Aldi and Lidl do good offers regularly with 25mm SDS bits as part of a set. Worth getting them when they come up

 

[Paul Barker]

Never listen to people who stand behind a counter. Every time I am in B and Q I overhear a person in orange giving completely wrong advise to someone.

The people behind counters are on minimum wage, if they were any good they would be on a better wage.

You were given rubbish advice.

I would use a diamond core drill if you have a lot to do.

 

[cornishman]

I'd prefer to use a diamond core drill or pre drill with a smaller size to prevent breakout, and drill from outside in if possible.

 

[Softus]

At 28mm I'd use SDS+ masonry - on hammer this ought to be a breeze.

I wouldn't use a core drill, at that small diameter, because I'd expect to be forever clearing out the core.

 

[Doctor Drivel]

Never listen to people who stand behind a counter. Every time I am in B and Q I overhear a person in orange giving completely wrong advise to someone.

The people behind counters are on minimum wage, if they were any good they would be on a better wage.

Many are old and can't get, or want, better paid jobs. In one local B&Q the plumber "expert" was spot on. He was freshly retired from the design side and took a job because he was bored.

 

[seaangler]

Never listen to people who stand behind a counter. Every time I am in B and Q I overhear a person in orange giving completely wrong advise to someone.

.

dont tar everyone with the same brush , a lot of people behind a counter know what they are talking about - If you go to a "proper" shop or builders merchants

anyone who shops in places like B&Q deserves to get told crap
(that should get some comments )

 

[^woody^]

Going a bit OT, but I tend to never listen to anyone in a shop nowadays, as whatever the shop, or age of the person, no-one seems to know anything about the stuff they are actually selling, but are merely there to stock the shelves and take your money at the till.

If I'm a bit bored I may ask one for advice, and listen to the crap, before then asking some really difficult questions

Some of the builders merchants are OK if you know the guys have been working there for a long time, and I am surprised that a hire shop person does not know about his gear.