If you just slapped something together and then dashed when you were done, it was slapdash. The paint job was slapdash: it looked like they did it in an hour, without brushes.
The meaning of the word slapdash is clear from its two parts, slap and dash. If you make something in a slapdash way, you slap it together and then dash away — probably so no one would notice. If you want something to look great and last for a long time, then take your time and do it right. If you do it in a slapdash way, you may save time in the short run. But in the long run, you'll lose much more time redoing your shoddy work.