I don't look at just the margin on labor. I look at the overall job structure. Then I mark up accordingly.
Here's one I just bid (rough numbers)
This will be a design/assist job so design time is incl
Misc Mat $20,083
Quoted Mat $124,000
Subs $23,535
DJC $1902
Equip $4300
Direct Labor 1777.13hrs @19.50 x 1.35 = $46,782
Indirect Labor
PM 120hrs @ $39.00 x 1.20 = $5616.00
Supt 80 hrs @ $27.00 x 1.35 = $2916.00
Design fee 16 hr @ 35 x 1.35 = $756.00
Total COST = $230,245.00
15% OH = $ 34,537.00
0% Profit
Bid Price = $264,782.00
Now, since this is a high Mat/Subs to labor ratio job (3.58 to 1), I can bid this at 0% profit and still make $19.43 margin $/MH ($34,537/1777hrs).
It's an OK job, but good in today's market.
Let's suppose the owner was furnishing the fixtures (worth $103,500)
That brings my margin $/MH down to $10.70. I would then add a profit markup of say, 10% to get the margin $/MH to 18.90
I know that's confusing, but it's all about risk on labor. The more material $'s are there, the safer we are.
And this really doesn't apply to the original situation, where he had $3500 in mat and $12000 in labor, but if this was my ratio and the owner was buying 20-25K of fixtures, it would apply.