Is this grinder powerful enough for my needs?

[sandwich]

My floor has a broom finish that I would like to grind smooth, or at least smoother than it is now in preparation for a 100% solids epoxy.

With that said, the local rental shop carries this grinder, cost is $70/day + $30/day for the diamond plates, they have 16grit and 30grit available. Which would be better for my application?

http://www.nationalequipment.com/pr/5274-Floor-Prep-System/2239/2240/2406

My concern is that this unit runs on 115V and seems a bit weak for the job I need it to do, but the rental shop is assuring me that it will only take 4hours...

 

[thegarageguy]

That grinder looks a little light in the pants, if you have soft slab it might be ok but if it's real dense, it'll skate over the slab and not grind at all. Are there weights to that machine?

 

[sandwich]

The slab is roughly a year old, I really have no idea how hard it is. I don't think the grinder comes with any weights, just a vacuum.

 

[Edger]

You should be OK with that grinder and 30 grit diamonds because all you want to do is smooth the surface which is easy to do, it is when you want to grind below the flat surface that you need power etc.

I advise that you move it along so that it only just grinds the surface because any deeper will leave grinding shoulder marks and expose too many air holes which might leave bubbles in your coating. Do it twice faster rather than once slower.

 

[thegarageguy]

Hate to disagree with you Edger but the whole reason to diamond grind is to not only create a surface profile but also expose the pores of the concrete so you can get good penetration of the primer and get both a chemical and mechanical bond.

 

[sandwich]

Hate to disagree with you Edger but the whole reason to diamond grind is to not only create a surface profile but also expose the pores of the concrete so you can get good penetration of the primer and get both a chemical and mechanical bond.

Well I think I am going to rent it, so I'll let you guys know how it goes. Fingers crossed...

 

[Edger]

Hate to disagree with you Edger but the whole reason to diamond grind is to not only create a surface profile but also expose the pores of the concrete so you can get good penetration of the primer and get both a chemical and mechanical bond.

I do not mind the disagreement, it is good anytime to clarify things, but I know the 30 grit diamonds will give a good scratched surface for the coating to key into regardless of the depth of cut. (If he uses 16 grit which are very coarse the epoxy will not fill in the scratch marks so they will show through.)

As long as the surface has been scratched evenly to remove any shine it is suitable for coating. The high lines of the broom finish will be removed very quickly which is why I think going over it quickly at first is the better way to go. Only actual doing the job will prove me right or wrong because all sorts of things can change the general conditions like concrete hardness and bond hardness of the diamond matrix.

There is no need to completely remove the concrete surface paste. In reality it is harder to achieve what I am suggesting because of high and low spots that cause you to grind deeper into the high spots to be able to scratch up the low spots - depends on how smooth the slab was finished and the size of the segments and how flexibly the segment pads are attached.

 

[thegarageguy]

I started my biz out with a small 16" Mastercraft grinder and 30 grit diamonds (similar to the one pictured)..in some slabs it would just skate the surface, even with 100 lbs of weight. The surface paste is the weakest part of the slab, coating it, regardless of scratching it will still leave you with an inferior surface to bond to, IMO.

Again, scratching the paste will not allow penetration, therefore it will bond to the surface and rely on the surface paste to hold up. Not ideal in a garage.

I guess we'll agree to disagree.

 

[Edger]

Again, scratching the paste will not allow penetration, therefore it will bond to the surface and rely on the surface paste to hold up. Not ideal in a garage.

I guess we'll agree to disagree.

You are referring to a very hard slab there, but his slab might not be very hard. As long as there is no shine left it will be fine. For anyone interested check this article on grinding hard concrete http://www.situp.com.au/Grinding Hard Concrete.html