Shot Blasting

[repomannwp]

In deciding to epoxy my garage floor I read everything I could find on preparation and loved the idea of shot blasting but was concerned about some of the warnings I read. First, from my investigation, it appears that shot blasting is the best overall method for prepping a concrete surface to receive epoxy. The warnings seemed to focus on the possibilities of damaging your surface if not used properly and that it may be a bit much for a DIY'er.

Well, I'm here to say that shot blasting worked great for me, and was SUPER easy to do. In fact, I think you have to be completely careless to have a chance at any damage to your slab.

My garage floor is 17 years old, had been sealed once, had normal paint, oil and liquids all over it in the course of time, but otherwise was in good shape. The slab had control joints center cut in each direction. I filled in the joints with SikaFlex and then got to work shot blasting.

First pic is what I started with, second shows the right half shot blasted, left half not yet prepped but with some dust on it, and the third gives you a sense of the shot size being used, its pretty tiny. The process is very clean when used with a large vacuum unit, very little cleanup. The shot blasting didn't effect the Sikaflex at all, that stuff is great. 550sq.ft. took me about 4 hours total, rental cost was about $300 for the blaster, vacuum, magnetic broom and shot.. pricey, but worth it IMHO.

 

[Edger]

That is great. I found shot blasting to be the best prep as long as the concrete was not too soft. Some concretes are soft and you get deeper lines dug into the surface where the shot blaster overlaps. Usually leaves about 10 sq.ft. in each corner unprepped too.
I take my hat off to you for using the machine correctly.

 

[Jaguar Fan]

Super. Where did you rent? And post more pictures!

 

[theoldwizard1]

I would love to see pictures of the rig you used, especially the vacuum. Is the shot then recycled ?

 

[repomannwp]

A few more pics. The rig I used was rented from BJ's Rentals in San Diego, it was a Blastrac 1-8DEZ unit. I bought one bag of shot which was about 40 lbs worth, since it was $80 a bag, I was motivated to make 1 bag last. The magnetic broom is a must. The way the unit works is you feed the shot in the hopper from above, close and attach the vacuum hose. You then set the unit height so the skirt at the bottom is close to the ground, fire up vacuum, fire up Blastrac and then you walk behind as you go. A good amount of shot escapes the skirt at the bottom so you need the broom to gather it up, and then reload it back in the hopper from time to time. I'd do about 4 to 5 rows of blasting, then I'd reload the shot, clean the vacuum, and repeat. The vacuum unit (sorry, don't have any specs on it, it just came with the blastrac) dumps the dust into a bin at the bottom of the unit, and you just pull out the tray and empty it -- pretty simple. Overall, the vacuum captured 95%+ of the dust.

The hopper on this unit is pretty small, so it only took about 1-2 lbs of shot at a time and since you reload it, the shot goes a long way. I used at most 3/4 of my bag for my 550sq ft. You can get about 2" from the edges of the flooring, so you still have some hand grinding to do. In my case, my concrete flooring is a tension slab with a very hard surface. I had to walk this unit VERY SLOWLY in order to get that 80grit type surface look, which was good because there was no danger of damaging the floor even if I stopped forward motion briefly. But this also meant it took me about 4 hours to finish the whole thing. Better safe than sorry. I've already returned the unit, so this is about it for pictures of the shot blast prep.

 

[LegacyIndustrial]

Excellent job, like a pro.

 

[tncatadjuster]

I bought mine in 1988, and it has been a great machine, still running strong.

 

[Irondrive]

Fantastic!