Replies

1. 
   Cliff._Johnston | Nov 18, 2001 08:08pm | #1

   *
   John,

   We do decorative concrete resurfacing and have the need to grind down concrete on occasion. I use a diamond cup from Star Diamond on an angle grinder for small areas such as you describe. Star has got quite a line. The designs are good and the diamond lasts longer than anyother product that I have tried to date. As a matter of fact I've started to use quite a few of their products and am in the process of ordering one of their epoxy cup grinders to remove curbside OSHA reg. paint on a job. I prefer diamond products because they are FAST. I'll spend an extra buck or two up front if the job will get done faster and easier, and it is cost effective. To me cost effective doesn't necessarily mean less money. In my experience I've found that spending a buck or two more and finishing up the job faster is well worth it. The customers appreciate it too.

   You can call Robin at Star Diamond at (800) 282-6470 to get a catalog and price list or a quick quote over the phone.

   If cost is a consideration, go to eBay, "diamond blade", and bid on a cheapo for an angle grinder or circular saw. You can then make a series of shallow, parallel cuts where you need to lower the concrete and finish up with a Norton "Gemini", masonry, type 27 grinding disc. In fact if you need to grind down only a 1/16" or so, the Norton Gemini will do the job by itself, although slower. I've been this route with cheapos, and one of them should do this small a job if it is a "one shot deal" for you. As for the grinding discs, I just like the Norton ones. I've tried several different brands, and I find myself going back to the Norton products.

   Well, that's how we do it. If anyone out there has any better ideas I'd like to hear them too. Time is money, and I can always use both.

   Cliff. Johnston
   QUALITY-CRETE RESURFACING & WATERPROOFING
   Stephenville, TX

1. 
   Cliff._Johnston | Nov 18, 2001 08:21pm | #2

   *John,I should add that we tend to go with a diamond blade in an angle grinder as opposed to using a circular saw now. I'm sure that the manufacturers don't recommend it, but we've learned to "free hand" it with a 7" Makita angle grinder and a 7" diamond blade pretty good. It's fast too. We also use a Bosch 4 1/2" angle grinder with a diamond blade to clean out joints, etc.. Again, it's probably not a manufacturer's recommended use for those tools, but it sure does boogey for us.Why do we use the different brands of angle grinders? We use the 7" Makita because it is not only an excellent angle grinder, but it is lighter than most others in this size. Operator fatigue is a major consideration when we need to use the large one. On the other hand we use the Bosch for the smaller one because it is heavier than most 4 1/2" angle grinders and therefore steadier to work with and control. We prefer the Bosch ruggedness and reliability, but the Makita has done a good job for us and the Bosch would be too fatiguing for the larger jobs where we need the 7" size. We're in touch with several other concrete resurfacing contractors, and from what I've heard about their various experiences with other brands of angle grinders, I believe that we have the right combination for our work.Cliff.

1. 
   Gabe_Martel | Nov 18, 2001 10:17pm | #3

   *NO NO NOUse a small chipper/bushhammer and take it down a 1/2 in. Hardly any dust and a lot faster. Then use a concrete epoxy patching compound to make smooth.Gabe

1. 
   Cliff._Johnston | Nov 18, 2001 10:40pm | #4

   *Gabe,We tend to avoid any impact producing tools when we work on concrete, mainly because one never knows how thick the slab is. We've worked on supposed 6" slabs and found only 2 1/2" thickness when we went through unexpectedly in a weak spot. Quite frankly much of the poured concrete around here is of a very poor quality, both design wise and quality wise. I end up telling more people to repour a slab than I end up quoting a figure for on resurfacing.Cliff.

1. 
   John_Lazaro | Nov 18, 2001 11:29pm | #5

   *I'm a firm believer in diamond tools. In fact, the last 14" blade I bought was from PR Diamond out of Las Vegas I believe. Unfortunately, I need to do this job before Tuesday and I need to get whatever tool I need locally. I've got a 14" concrete saw that I could use, but the house is enclosed and this is in a 1/2 bath(5X5 room), so fumes and dust are somewhat of a concern. I know with a grinder I would avoid the fumes, but how much dust? I didn't know if a large shop vac with the hose set on the floor next to the grinding point would work well to keep dust down.Impact tools are a possibility. I know that the floor is 4" plus. I didn't pour it, but I was there. It was a very hot day this summer and the last truck was late on the job and concrete was setting up before it could be properly leveled. They should've done the floor in multiple pours. Live & learn.John

2. 
   Gabe_Martel | Nov 19, 2001 02:27am | #6

   *Cliff,One of our boys can take a 1/2 inch off a 1 inch slab while mixing his batch.Use a 1 inch chisel on a small chipper and starting from the outside of the area to be lowered, walk it on a 45 to 55 degree angle towards the high spot.Grinding will fill the house with dust unless a total wrap is done and the likelyhood of that being airtight is between none and zero.You'al need a little more experience with concrete boys.Gabe

3. 
   Cloud_Hidden | Nov 19, 2001 03:45am | #7

   *Ditto on the dust. It will go everywhere unless you plastic and tape every possible opening and then some. During construction here, I filled three stories with dust just from sawing a 2' long cut in the basement. Rockers on top floor came staggering out gagging. Couldn't see in there for 30 min!Good luck.

4. 
   John_Lazaro | Nov 19, 2001 06:10am | #8

   *Gabe,Sounds like I'll be chipping. What's the best tool for the job? Pneumatic or electric? Would a rental house have it? I favor grinding, but under the circumstances I don't want to deal with the dust.Thanks,John

5. 
   Cliff._Johnston | Nov 19, 2001 06:41am | #9

   *Gabe,We normally don't do indoor work. When we have, we have used the vacuum, plastic & tape and a respirator. It apparently worked for us; however, most of our work is outside - like 99.5%. Actually we go out of our way to avoid indoor jobs.As for the experience - old member of the Bricklayers, Masons, Plasterers and Finishers Union (trained as a finisher back in 1964). You can remove your foot from your mouth anytime that you want to.Cliff.

6. 
   Gabe_Martel | Nov 19, 2001 02:18pm | #10

   *Cliff, Not to worry, foot is not near my mouth, experience with chipping is what is needed and being a good finisher shouldn't mean you have had to chip very often.Gabe

7. 
   Gabe_Martel | Nov 19, 2001 02:22pm | #11

   *John,A small electric should be easy to find. You don't want too big so that it will be easy to control.Rentals normally have dust cleaning fans as well. They look like a cylinder with a fan and filter attached. Sit on the floor and filter the dust as they circulate the air.Good luckGabe

8. 
   Cliff._Johnston | Nov 19, 2001 05:10pm | #12

   *Gabe,Never had to chip one of my pours - that goes back to 1965. We do repair and resurfacing work so we see a lot of botched up jobs.I started out with Morrison-Knudsen on the missile silos in North Dakota. Our work was so good that it hurts to see the trash out there now.Cliff.

9. 
   John_Lazaro | Nov 20, 2001 03:58am | #13

   *Chipped off the hump today. I rented a Bosch hammer and went to town. Pain in the ass as far as I'm concerned. I looked for the finisher so he could fix his flub up and couldn't find him. So I ended up doing the chipping and filling in a couple of other dips. I wish I could have ground the area. It would have gone faster and smoother, but the dust would've been intolerable. Thanks to both of you for your advice and sorry I started an argument.Since I do have the ears of two concrete gurus, the 14" blade on my saw sometimes tends to wander when I'm cutting joints. Is this a problem with the blade because of diameter or what? When cutting, you can actually see the blade distort. This problem doesn't happen all the time, just sometimes. My walk behind saw also has a 14" blade and I've never seen this problem. I believe the walk behind has a Target blade and the hand held (on a cart) has a PR Diamond blade.Thanks,John

10. 
    Gabe_Martel | Nov 20, 2001 04:16am | #14

    *John, There's never an argument between brothers of the trade only different paths. Because we work in concrete the path sets up faster.If you're talking about a quickcut saw with a belt drive, they will wander even when new. They tend to wear at the bearings and wobble more as time goes on. Run the saw along an edge like a strip of 1/2 ply about a foot wide and keep the pressure against the side of the ply for straight lines as you're standing on it.GabePS when the area is open, as in open floors or outside, I prefer the grinder as well. But it's like using a quickcut with a concrete blade in a basement to cut a doorway in a foundation wall. Use saw for 5 seconds and wait 5 minutes for the dust to clear enough to see for another 5 seconds.

11. 
    John_Lazaro | Nov 20, 2001 06:52am | #15

    *Since we're on the subject of basements, I've got another question. This year, I started cutting joints in my basement floors. Everyone around here just pours them and lets them crack as they may. Anyway I got tired of hearing customers complain and started cutting joints. I read an article in the last month or so where some guys are starting to cut joints in basement walls. What's your opinion on this?John

12. 
    Gabe_Martel | Nov 20, 2001 02:13pm | #16

    *John,IMHO cutting joints in walls of a typical home would be foolish.Gabe

13. 
    Cliff._Johnston | Nov 20, 2001 06:12pm | #17

    *John,Yeah, I figured that you'd reach the same conclusion that I did on chipping vs. grinding. Yeah, grinding does kick up some dust. A shop vac helps some. Once we even built a small, quick, stick frame covered with plastic to avoid chipping. Tough to see what we were doing all of the time, but it still beat chipping. We've even taken the filter out of a shop vac and extended the exhaust hose outside to vent the dust - messy for the outdoors, but on a new construction site out in the boonies, it worked.Some engineers and builders have been recommending and cutting joints in house slabs down here in the South for over a decade. Most builders that I am in contact with don't do it. Some do and swear by it. There were some references to it on the Concrete Network website. I've found some good synopses of lengthy articles there on occassion. I have zero experience with basement walls - only seen 6 basements down here in 30 years, and my experience up north with them was zero.Every finisher has his own preferences. It depends on what his priorities are in achieving the finished product. What works for me may not work for Gabe. It doesn't mean that either of us is right or wrong, even though according to Gabe's priorities I may be wrong or according to my priorities Gabe may be wrong. The end result(s), the satisfaction of the contractor with the job and the satisfaction of the customer are the true measurements of success of the project - not to mention profitability for the contractor.Cliff.

14. 
    John_Lazaro | Nov 21, 2001 05:01am | #18

    *I never cut joints in basement slabs before because nobody else did. I went through another builders house this Spring and saw sawn joints in the floor. From that point on, I've been sawing joints in mine. For years, all basement customers always call and are worried about the cracks in their basement floors. And I have to go throught the whole spiel about no control joints and concrete will crack, blah, blah, blah, blah.....I've cut joints in about six basements this year and only one cracked outside a joint. I'm a believer.I wasn't sure about the wall joints. I read the article lately and always on long basement walls we get cracks. I really don't want to joint a wall. I was just fishing for opinions.Thanks,John

15. 
    Gabe_Martel | Nov 21, 2001 05:20am | #19

    *Even in long commercial walls, sawcutting a joint wouldn't be an option.We will make a break in the pour at specific locations, install a waterbar and start the next wall section and so forth but a sawcut would be a waste of time.Even if you had a residential wall 200 feet long and you wanted to sawcut into 1/4s you have no way of knowing where the pressure points would be and thats where the crack would occur. A slab is easy to layout. A wall is nearly impossible.Gabe

16. 
    Cliff._Johnston | Nov 21, 2001 05:49am | #20

    *John,We see a lot of retaining walls down here. Joints are not cut; however, the recommendation is usually to have a control joint every 20' - not that everyone, or even 20% of the contractors do it. For what it's worth, about 85% of the retaining walls that we see have failed in one way or another. The good ones are poured with a keyway to interlock the sections together. Don't know if that would be recommended for a basement though.Gabe, any thoughts?Cliff.

17. 
    Gabe_Martel | Nov 21, 2001 02:15pm | #21

    *Cliff,I would venture to guess that most of the failures can be attributed to 2 things. 1. improper preparation of the base.2. insufficient wall for the load.Here in Canada and all northern States, frost heaving would go with the first.Gabe

18. 
    John_Lazaro | Nov 22, 2001 04:30am | #22

    *I see a lot of retaining wall failures around here. Usually it's either drainage problems ( no stone behind the wall and drains) or trying to get the wall vertical with not enough lean to it.John

19. 
    John_Lazaro | Nov 22, 2001 04:34am | #23

    *If you're talking concrete retaining walls....failures always revolve around improper design and installation as Gabe's points illustrate. My dad poured some retaining walls about 48" high that've been standing for almost 40 years and are in great shape.John

2. 
   John_Lazaro | Nov 22, 2001 04:34am | #24

   *
   I've got to grind a 36" X 36" area in an enclosed basement that has a visible hump (1/4" - 1/2") in the concrete. Any ideas as to the best method or tools? I plan to use a respirator and shop vac next to area to control dust. Basement is not yet finished, but don't like working in a dust cloud. Adding floor leveler to the area is not an option.
   John